1 ECOLOGY OF Sagittaria kurziana AND DISTRIBUTION OF PERIPHYTON IN THE SPRING FED RAINBOW RIVER By PETER A LEXANDER SLESZYNSKI A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2009
2 2009 Peter A. Sleszynski
3 To my parents and grandparents
4 ACKNOWLEDGMENTS I would like to thank my supervisory committee chair (Dr. Edward Phlips) fo r his advice and guidance, and Dr. Michael Kane for advice on micropropagation techniques, use of his laboratory facilities and his guidance. I would also like to extend my appreciation to Dr. Charles Cichra, Dr. Thomas Crisman, and Dr. Patrick Inglett fo r their assistance and invaluable input while serving on my committee, Dr. Mary Cristman for her help with statistical analysis, Nancy Philman for her assistance and advice with the micropropagation work and Bret Whiteley for aid with map creation
5 TA BLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................................... 4 LIST OF TABLES ................................................................................................................................ 8 LIST OF FIGURES .............................................................................................................................. 9 ABSTRACT ........................................................................................................................................ 12 CHAPTER 1 INTRODUCTION ....................................................................................................................... 14 Study Site ..................................................................................................................................... 16 Research Objectives .................................................................................................................... 19 2 ECOLOGY OF Sagittaria kurziana (Gluck) IN THE RAINBOW RIVER ........................... 24 Methods ....................................................................................................................................... 25 Study Site ............................................................................................................................. 25 Spatial Variability in the Morphology of Sagittaria kurziana .......................................... 26 Determination of In Situ Growth of Sagittaria kurziana .................................................. 27 Tissue Nutrient Content of Sagittaria kurziana ................................................................. 29 Ph otosynthesis Light Flux Relationships for Sagittaria kurziana .................................... 29 Growth of Introduced Sagittaria kurziana ......................................................................... 32 Growth Response of Sagittaria kurziana Exposed to Flowing Water ............................. 35 Statistical Analyses .............................................................................................................. 35 Results .......................................................................................................................................... 36 Spatial Variability in the Morphology of Sagittaria kurziana .......................................... 36 Determination of In Situ Growth of Sagittaria kurziana .................................................. 36 Tissue Nutrient Content of Sagittaria kurziana ................................................................. 37 Photosynthesis Light Flux Relationships for Sagittaria kurziana .................................... 37 Growth of Introduced Sagittaria kurziana ......................................................................... 38 Growth Response of Sagittaria kurziana Exposed to Flowing Water ............................. 39 Discussion .................................................................................................................................... 39 Spatial Patterns ..................................................................................................................... 39 Elemental Composition of Plants ....................................................................................... 42 Photosynthesis versus Light Relationships ........................................................................ 43 3 IN VITRO PROPAGATION OF THE SUBMERSED SPECIES Sagittaria kurziana .......... 58 Introduction ................................................................................................................................. 58 Methods ....................................................................................................................................... 59 Culture Establishment ......................................................................................................... 59 Effects of Benzyladenine (BA) on i n Vitro Regeneration of Sagittaria kurziana ........... 60
6 Comparative Effects of Different Cytokinins on in Vitro Regeneration of Sagittaria kurziana ............................................................................................................................ 60 In Vitro Propagation in 500 m L Erlenmeyer Flasks ......................................................... 61 Establishment of ex Vitro Plants (Microcuttings) .............................................................. 61 Results .......................................................................................................................................... 62 Effects of Benzyladenine (BA) on in Vitro Regeneration of Sagittaria kurziana ........... 62 Comparative Effects of Different Cytokinins on in Vitro Regeneration of Sagittaria kurziana ............................................................................................................................ 62 In Vitro Propagation in 500 m L Erlenmeyer Flasks ......................................................... 62 Establishment of ex Vitro P lants (Microcuttings) .............................................................. 63 Discussion .................................................................................................................................... 63 4 EFFECTS OF NITROGEN ON IN VITRO GROWTH OF Sagittaria kurziana (Gluck) ...... 73 Introduction ................................................................................................................................. 73 Methods ....................................................................................................................................... 76 Stock Plant Cultures ............................................................................................................ 76 Effects of Nitrogen Form and Concentration on In Vitro Growth .................................... 77 Sagittaria kurziana Tissue Nutrient Concentrations ......................................................... 77 Statistical Analyses .............................................................................................................. 79 Results .......................................................................................................................................... 79 Effects of Nitrate on Growth ............................................................................................... 79 Interactive Effects of Nitrate and Ammonium on Growth ................................................ 80 Carbon and Nitrogen Tissue Concentrations ..................................................................... 81 Discussion .................................................................................................................................... 82 5 SPATIAL DISTRIBUTION OF EPIPHYTIC AND BENTHIC ALGAE IN THE RAINBOW RIVER, FLORIDA .............................................................................................. 102 Introduction ............................................................................................................................... 102 Methods ..................................................................................................................................... 104 Study Site ........................................................................................................................... 104 Spatial Distribution of Epiphytic and Ben thic Algae ...................................................... 105 Epiphytic Biomass ............................................................................................................. 107 Statistical Analyses ............................................................................................................ 108 Re sults ........................................................................................................................................ 110 Spatial Distribution of Epiphytic and Benthic Algae ...................................................... 110 Environmental Conditions and Relationships to Algal Distribution .............................. 111 Epiphyte Biomass .............................................................................................................. 113 Discussion .................................................................................................................................. 113 Epiphyte Distribution ........................................................................................................ 113 Benthic Algal Distribution ................................................................................................ 117 6 SUMMARY ............................................................................................................................... 133 APPENDIX A DDITIONAL DATA ........................................................................................... 141
7 LIST OF REFERENCES ................................................................................................................. 143 BIOGRAPHICAL SKETCH ........................................................................................................... 154
8 LIST OF TABLES Table page 2 1 Differences in site conditions at four treatment locations, for sediment controlled 12week Sagittaria kurziana growth experiment. .............................................................. 53 2 2 Characteristics of Sagittaria kurziana sampled August 2002 at five sites along the Rainbow River, Florida. ...................................................................................................... 54 2 3 Mean growth of Sagittaria kurziana after 1 0 days and mean epiphyte cover at four sites on the Rainbow River, Florida in May 2004. .................................................... 55 2 4 Mean percent composition of carbon, nitrogen, and phosphorus in new growth tissue collected at four sites on the Rainbow River, Florida in May 2004. ................................ 56 2 5 Photosynthesis measurements made on Sagittaria kurziana tissue collected at four locations along the Rainbow River Florida in March 2003. ............................................ 57 3 1 Leaf dimensions of Sagittaria kurziana grown in vitro and ex vitro acclimated in a mist house for eight weeks. ................................................................................................... 72 4 1 Results of statistical analyses on the effects of NO3 on growth response of Sagittaria kurziana in vitro. .................................................................................................................. 99 4 2 Results of statistical analyses on the effects of NH4 +, NO3 and their interaction (NH4 + NO3 -) on growth response of Sagittaria kurziana in vitro. ............................... 100 4 3 Mean percent carbon and nitrogen content within tissue of Sagittaria kurziana samples collected in the Rainbow River and at different in vitro media NH4 + / NO3 concentrations. ................................................................................................................... 101 5 1 Results of logistic regression analysis between percent coverage of algae and measured e nvironmental variables. ................................................................................... 131 5 2 Biomass of epiphytic materials and Sagittaria kurziana plants at five sites adjacent to respective transects, on the Rainbow River, Florida in July 2002. ................................. 132 A 1 Chemical analysis of river sediments collected in the Rainbow River upstream of K.P. Hole and approximately 3 km from the headsprings in 2001. ............................. 141 A 2 Mean dry weights for materials accumulated from the water column of the upper Rainbow River over 4 hours on September 23 and October 2, 2002. ............................ 142
9 LIST OF FIGURES Figure page 1 1 Sagittaria kurziana in the headsprings of the Rainbow River, Florida in 2002, with undisturbed areas in the foreground and areas disturbed by recreational activities in the background. ...................................................................................................................... 21 1 2 Sagittaria kurziana in areas of reduced flow, with epiphytic and benthic algal coverage, near K.P. Hole County Park in the Rainbow River, Florida in 2002. ................ 22 1 3 Rainbow River in north central Florida and southwestern Marion County. ...................... 23 2 1 Sampling locations for spatial variability in the morphology of Sagittaria kur ziana in situ in Rainbow River, Florida in August 2002. .................................................................. 45 2 2 Sampling locations for in situ growth of Sagittaria kurziana, and tissue nutrient content of Sagittaria kurziana in Rainbow River Florida in May 2004, and sections of the river, near K.P. Hole County Park where light attenuation and light attenuation by epiphyte were measured in February 2008. ..................................................................... 46 2 3 Photosynthetic rat e, measured as oxygen evolution, from Sagittaria kurziana tissue 2/s light. ...................... 47 2 4 Percentage of photosynthetically active radiat ion (PAR) transmitted through epiphyte samples collected in Rainbow River, Florida in March 2008. ........................... 49 2 5 Growth of Sagittaria kurziana after 12 weeks at five locations in the headsprings are a of Rainbow Springs, Florida. ....................................................................................... 50 2 6 Growth of Sagittaria kurziana after 12 weeks at five locations in the headsprings area of Rainbow Springs, Florida. ....................................................................................... 51 2 7 Growth of Sagittaria kurziana after 8 weeks at a site exposed to river flow and an adjacent site protected by polycarbonate tubing. ............................................................... 52 3 1 In vitro propa gation of Sagittaria kurziana. ....................................................................... 67 3 2 Effects of benzyladenine (BA) concentration on the growth of Sagittaria kurziana after 3 weeks in vitro culture. ............................................................................................. 68 3 3 Effects of four cytokinins (2 Mol/L) on the growth of Sagittaria kurziana after 3 weeks in vitro culture. .......................................................................................................... 69 3 4 In vitro growth of Sagittaria kurziana in 500 m L Erlenmeyer flasks with 250 m L of strength MS media. ........................................................................................................ 70
10 3 5 E x vitro growth of micropropagated Sagittaria kurziana microcuttings in a mist house. ............................................................................................................................ 71 4 1 Effect of nitrate concentrations on biomass and leaf production of Sagittaria kurziana in vitro. .............................................................................................................. 88 4 2 Effect of nitrate conce ntrations on root and shoot production of Sagittaria kurziana in vitro. .................................................................................................................................. 89 4 3 Effect of NH4 + and NO3 concentrations on dry weight of Sagittaria kurziana in vitro. .................................................................................................................................. 90 4 4 Effect of NH4 + and NO3 concentrations on number of leaves of Sagittaria kurziana in vitro. ................................................................................................................................. 91 4 5 Ef fect of NH4 + and NO3 concentrations on average leaf length of Sagittaria kurziana in vitro. ................................................................................................................................. 92 4 6 Effect of NH4 + and NO3 concentrations on root production of Sagittaria kurziana in vitro. ................................................................................................................................. 93 4 7 Effect of NH4 + and NO3 concentrations on average root length of Sagittaria kurziana in vitro. ................................................................................................................................. 94 4 8 Sagittaria kurziana after 3 week in vitro culture in the presence of different NH4 + and NO3 levels. ................................................................................................................... 95 4 9 Effect of NH4 + and NO3 concentrations on number of shoots production of Sagittaria kurziana in vitro. .................................................................................................................. 96 4 10 Effect of NH4 + and NO3 concentrations on number of shoot leaves of Sagittaria kurziana in vitro. ................................................................................................................ 97 4 11 Relationship between tissue nitrogen content and growth response of Sagittaria kurziana grown in vitro at different medium nitrogen concentrations. ............................ 98 5 1 Portion of the Rainbow River, Florida, in which 20 transects were sampled for distribution of epiphytic and benthic algae in 2000 and 2001. ......................................... 121 5 2 Distribution of filamentous epiphytic algae along 20 cross -channel transects in the Rainbow River, Florida during September 2000. ........................................................... 122 5 3 Distribution of benthic algal mats at 20 cross channel transects in the Rainbow River, Fl orida during September 2000. ........................................................................................ 123 5 4 Distribution of filamentous epiphytic algae on the upper portion of SAV relative to water depth and SAV canopy height, measured at 5 transects along the Rainbow River, Florida. ............................................................................................................... 124
11 5 5 Relationship of mean percent cover of filamentous algae on the upper half of Sagittaria kurziana blades to A) plant canopy height and B) water depth. ................... 126 5 6 Relationship of mean percent coverage of non-filamentous algae (bar) on the upper half of Sagittaria kurziana blades to A) SAV canopy height and B) water depth. ...... 127 5 7 Relationship of mean A) percent cover and B) thickness of benthic algal mats to mean water depth (m) along 5 cross channel transects in the Rainbow River, Florida .. 128 5 8 Distribution of benthic algal mats relative to water depth and SAV canopy height, measured at 5 transects along the Rainbow River, Florida sampled monthly from February to May 2001. ....................................................................................................... 129
12 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy ECOLOGY OF S agittaria kurziana AND DISTRIBUTION OF PERIPHYTON, IN THE S PRING -FED RAINBOW RIVER By Peter A. Sleszynski May 2009 Chair: Edward Phlips Major: Fisheries and Aquatic Sciences Florida springs are characterized by constant year round water temperature, high water clarity, and consistent water quality. The goal of this work was to study a spring-fed river ecosystem in the context of the general question of whether it is a homogeneous system in terms of the distribution of Sagittaria kurziana and algae (i.e., epiphytic and benthic algae) or a heterogeneous system re quiring greater emphasis on spatially intensive research Results suggest that the Rainbow River is in some respects a structurally heterogeneous ecosystem influenced by channel dynamics similar to other lotic systems. Sagittaria kurziana, the dominant a quatic macrophyte in many Florida spring runs, exhibited spatial differences in structure and growth on small spatial scales in the headsprings and river channel Low flow, shallow areas represented a different habitat than the higher flow main channel. D istribution s of epiphytic and benthic algae along cross -channel transects were heterogene ous on different spatial scales Logistic regression analyses indicated that characteristics such as structure of SAV beds and profiles of the river channel associat ed with differences in water velocities were correlated to the distribution of epiphytes. Shading effects of epiphytes on Sagittaria kurziana were studied Epiphytic colonization on leaves had a significant effect on light transmission. However, photosynthetic response of leaf tissue to light gradients, suggests that Sagittaria kurziana is tolerant to low light
13 levels. Potential impacts of epiphytic shading are therefore dependent on their specific heterogeneous distribution along the river. An in vitr o protocol, developed to propagate and conduct research on Sagittaria kurziana, was used to study the effects of nitrate and ammonium on its growth because of cultural eutrophication. No significant detrimental effects were observed on growth of Sagittari a kurziana, with the exception of root elongation at nitrate concentrations above current ambient concentration in the Rainbow River. Effects of ammonium levels had a greater effect on root growth and therefore may have greater longterm implications on t his ecosystem. It was concluded that the growth and distribution of the primary producers in the spring run environment are spatially heterogeneous and need to be studied at a spatially intensive scale.
14 CHAPTER 1 INTRODUCTION Lotic systems are often ch aracterized by their ecological heterogeneity and complexity (Hynes 1970), and can be viewed as a mosaic of geomorphic features such as channels and bars (Ward 1998). Spatial heterogeneity is effected by interactions between surface water, subsurface wate r and floodplain areas (Ward and Tockner 2001), creating a diversity of aquatic and riparian habitats (Ward 1998). These hydraulic forces influence the colonization and distribution of heterotrophs and autotrophs (Hynes 1970, Stevenson 1983). In many rivers the distribution and abundance of algae and plants is also subject to temporal variability, as it relates to seasonal, inter annual and event -driven changes in environmental conditions such as floods and droughts. Not all rivers are subject to the sam e degree of spatial or temporal heterogeneity. For example, rivers dominated by groundwater spring inflows have historically been viewed as exceptionally stable and homogeneous (Odum 1957). The aquatic environments of Floridas largest springs are consi dered to have low spatial and temporal variability because of the large groundwater basin they originate from adding stability to the quantity and quality of water discharged. Two of the largest springs of Florida, Silver and Rainbow Springs, each average over 20 m3/s (Roseneu et al 1977), and form rivers greater than 5 km in length. The water column environment has a constant year round water temperature, high water clarity, relatively consistent year round water quality (Holland and Cichra 1994) and di scharge rates (Scott et al 2004), which differs from most lotic systems. It was these reliable water column conditions caused by the fresh flow of groundwater that led Odum (1957a) to hypothesize that these ecosystems represent a rare set of homeostatic environmental conditions.
15 Water temperature and availability of light and nutrients are factors critical to the growth and distribution of SAV. When these factors limit growth, distribution of SAV can be affected. In Florida springs the high water clar ity, shallow depth, stable year round temperature and constant supply of groundwater decrease potential factors limiting growth, reflected in high cover of SAV in these ecosystems. Many of the large spring-fed rivers in Florida, such as the Silver and Rai nbow rivers are characterized by a high coverage of SAV predominantly Sagittaria kurziana (Odum 1957, Holland and Cichra 1994, Quinlan et al 2008). It may be for this reason that the effects of environmental change or heterogeneity on the growth and dist ribution of SAV in these ecosystems have not been extensively studied. At a system -wide scale, m any spring dominated systems appear not to conform to the principles of the River Continuum Concept, which describes a continual change in the structure and fun ction of rivers, from a dominance of allocthonous carbon inputs in headwaters, toward an increasing importance of autochthonous carbon inputs downstream (Vannote et al 1980). With further downstream progression rivers often become more turbid which can i nfluence light availability, leading to a decrease in the abundance of submersed aquatic vegetation (SAV) (Barko and Smart 1981, Havens 2003). Spring dominated rivers clearly diverge from this model, and due to great water clarity and significant nutrient availability spring -dominated rivers often contain high levels of benthic primary production, even in the headwaters. Despite this well documented distinction, much remains to be learned about the spatial and temporal heterogeneity of primary producers i n such systems, as well as the factors that control this heterogeneity in these apparently stable systems. This dissertation research focused on variability in populations of the dominant macrophyte Sagittaria kurziana and the distribution of epiphytic an d benthic algae and how they relate to characteristics of the spring -fed river ecosystem
16 Study Site Springs are important to lotic systems, creating unique thermally stable aquatic environments for biota in areas globally, including Florida (Scott et al. 2004), Texas, ( Mitchell et al 2000), Slovenia ( Mori and Brancelj 2006), and Australia ( Taylor et al 2004). Florida, with 700 springs, has more springs than any other state or country (Scott et al. 2004). These springs are fed from an aquifer made up of a series of layers of carbonate sediments, limestone, and dolostone of variable permeability, with thicknesses of over 1200 m (Scott et al. 2004). Florida springs are diverse and have been categorized by chemical characteristics such as chloride, calciu m, sulfate and saline concentrations (Whitford 1956, Odum 1957) and spring discharge. Discharge rates range from large 1st magnitude springs, with rates greater than 2.83 m3/s, to 3rd magnitude springs, with discharge (flow) rates between 0.028 and 0.28 m3/s (Scott et al 2004, Rosenau et al 1977). Individual springs however are known for their homeostasis in year round water column conditions (Scott et al. 2004). The Rainbow River is a clear water, spring run located in southwestern Marion County in n orth central Florida (Figure 1 3). It is approximately 9 km long and is fed by a large number of artesian springs and seeps along the first two kilometers. The spring run is approximately 45 to 60 m wide and averages less than 3 m in depth with isolated deeper areas (Chapter 5). The spring run flows south toward Dunnellon, where it joins the dark tannic water of the Withlacoochee River, which flows west for several k ilometers before entering the Gulf of Mexico. Water in the Rainbow River comes predominant ly from the geologic stratum known as the Ocala Limestone, which is part of the Floridan aquifer. The karst topography of the Rainbow Rivers recharge basin is mainly unconfined at the surface, allowing percolation of rainfall (Knowles 1994), and as a res ult, discharge from the Rainbow Springs system is influenced by local rainfall patterns. The recharge basin or local karst area that affects the spring discharge is
17 approximately 2400 km2, encompassing portions of western Marion, southeastern Levy, and so uthern Alachua counties (Knowles 1994). Groundwater discharge of Rainbow Springs is characterized by optically clear water, consistent chemistry (Holland and Cichra 1994) and temperatures near 22 C throughout the year (Rosenau et al 1977). The light ex tinction coefficient ( ) at Rainbow Springs has been estimated to be less than 0.065/m (Duarte and Canfield 1990b). Comparatively, values for clear natural lakes average around 0.2/m, while in turbid lakes can exceed 4/m (Wetzel 1983). Fluctuations in discharge of the spring fed Rainbow River is much less than nearby surface water rivers like the Withlacoochee with historical records ranging from 13.8 m3/s on 3 October, 1932 to 34.8 m3/s on 12 October, 1964 (Rosenau et al 1977, Scott et al. 2004) for t he former and between 1.6 to 63.1 m3/s from 2004 and 2007 for the later One of the dominant characteristics of the Rainbow River ecosystem is the presence of the macrophyte, Sagittaria kurziana (Sleszynski 2000). Sagittaria is one of 13 genera that compr ise the Alismataceae or water plantain family (Sutton 1989). Plants of this monocotolydenous family are distributed worldwide but they are more prevalent in temperate and tropical regions of the northern hemisphere including southeastern Canada and the eastern half of the United States (Sutton 1989). Of the ninety species in this family, the genus Sagittaria contains forty species, eight of which are indigenous to Florida and are typically found growing as submersed or amphibious plants (Sutton 1989). Plants of this genus, commonly called arrowhead plants, are characterized by their distinct but highly variable leaf shape (Adams and Godfrey 1961). Sagittaria kurziana, commonly called spring -tape, inhabits spring runs in Florida (Figure 1 1) It was first described by Gluck (1927) as the largest Sagittaria in the whole world. This species produces phyllodial strap -like or ribbonlike leaves up to 2.5 m long
18 (Godfrey and Wooten 1979). The Rainbow River was described as a Sagittaria run in 1942 (Mar chand 1942) and was documented as the dominant macrophyte in 1996 and 2000 present over more than 50 % of the river bottom (Sleszynski 2000). Epiphytic and benthic algae are also common elements of the primary producer community in Florida spring runs incl uding Rainbow and Silver rivers. SAV provides surface area for recruitment of epiphytic algae ( Madden and Kemp 1996). Whitford (1956) described a complex algae communit y growing on leaf blades of macrophytes in Florida spring runs that included diatoms, filamentous green algae and cyanobacteria. T axa of diatoms included Cocconeus Synedra, Achnanthes Melosira Terpeinoe Eunotia Navicula and Fragilaria Historically, benthic mats of algae and cyanobacteria were also an important component of the Sil ver River submersed aquatic community (Odum 1957). Large mat communities of the filamentous cyanobacteria Lyngbya wollei have also been observed recently on the sediment surfaces in both the Silver (Quinlan et al 2008) and the Rainbow r iver s (Figure 1 2 ). SAV communities in Florida spring runs are currently impacted by anthropogenic activities Recreational pressures on the Ichetucknee River (DuToit 1979) and Rainbow River (Holland and Cichra 1994, Mumma 1996, Mumma et al. 1996) disturb and uproot macr ophyte communities particularly in shallow water. The effects of disturbance can be exacerbated by growth of exotic plant species like Hydrilla verticillata which have been introduced to many spring runs. These environmental changes have the potential t o alter the structure and function of spring ecosystems. This has already been observed at Wakulla and Wacissa Springs (Scott et al 2004). Recent management efforts in Florida springs have focused on increasing nitrate concentrations from cultural eutrophication (Florida Springs Task Force 2000). Nitrate concentrations of 1.3 mg/L at Rainbow Springs (Scott et al. 2004) greater than 0.1 mg/L have
19 been measured at undeveloped areas of the spring recharge basin (Jones et al. 1996). The recent Florida Depar tment of Environmental Protections Springs Initiative emphasized that increasing nitrates may lead to increased epiphytic and benthic algae and may negatively impact the SAV community of springs (Florida Springs Task Force 2000). The effects of these cha nges are not widely understood because of a lack of investigation of the spatial variability of the SAV and periphyton community in Floridas spring fed rivers. Primary producers have been studied in Florida springs (Odum 1957, Notestein and Frazer 2006), although less attention has been given to the unique conditions of spring -fed rivers (Quinl a n et al 2008 ). Research Objectives Research in Florida springs has included groundwater hydrology, water chemistry, and proliferation of algae (Florida Springs Task Force 2000, Stevenson et al. 2004, Notestein and Frazer 2006). However, many gaps remain in understanding the relationships between the structure of spring run environments and the ecology of dominant macrophyte species, such as S kurziana. Such species are critical components of the structure and function of spring ecosystems both in terms o f primary production (Odum 1957) and as habitat for invertebrates and other fauna (Epifanio et al. 2003, Steigerwalt 2005, Sammons et al 2006). The focus of this work was to: Investigate the ecophysiology of S kurziana community in the Rainbow River within the context of heterogeneity of the benthic community Little data exists on the structure and dynamics of this keystone species. In this study d ata were collected on variability in plant morphology, growth rate, and responses to varying light level s, to fill gaps in knowledge of S kurziana. Develop in vitro propagation methods to facilitate research on S kurziana. In vitro propagation is an effective t echnique for conducting research on aquatic and amphibious plants (Bird and Jewett -Smith 1994, Kane et al 1999) and for producing large quantities of plants without need for collection of plants from natural systems. Development of an effective method to propagate S kurziana can be applied to habitat restoration work and research on environmental heterogeneity.
20 Use in vitro techniques to investigate the effects of NH4 + and NO3 on growth of S kurziana and the species ability to assimilate each compound N itrate concentrations have increased in many Florida springs (Jones et al 1996), and concerns have been raised about the effect of these changes on the ecology of spring ecosystems (Florida Springs Task Force 2000). The effect of differing NO3 and NH4 + concentrations on the growth of S kurziana was investigated under controlled conditions to give insight to the potential of heterogeneity within the environment Investigate potential patterns in the spatial distribution of epiphytic and benthic algae in the Rainbow River and how they are related to environmental characteristics of the system, such as channel morphology, and macrophyte structure and abundance. The distribution of epiphytic and benthic algae along spring runs was investigated to improve our understand ing of sources of variability and help place changes in algal coverage within the context of spatial and temporal heterogeneity Historically, complex epiphytic and benthic algal communities have been observed in Florida springs (Whit ford 1 956, Odum 1957). Recent increases in nitrate levels in Florida springs have raised concerns about potential increased growth of algae in springs (Stevenson et al. 2004). L imited historical data, and spatial heterogeneity in algal distribution, make compa risons between recent and past algal coverage and biomass difficult. Recent studies in the Rainbow River suggest that there is considerable heterogeneity in the distribution of SAV (Sleszynski 2000). Limited success of restoration efforts in impacted ar eas along the Rainbow River and their failure to reestablish in specific locations also suggest s spatial variability in the environmental conditions affecting growth of Sagittaria kurziana. The overall goal of this work was to explore the ecology of Sagi ttaria kurziana and distribution of algae (i.e., epiphytic and benthic algae) in a spring run ecosystem The Rainbow River was used as a case study to investigate the ecology of Florida spring runs within the context of the overall question of ecosystem homogeneity and lotic system theory R esults of this study should improve understanding of the ecology of spring run ecosystems such as the Rainbow and Silver rivers, and assist efforts to ensure their future integrity
21 Fig ure 1 1. Sagittaria kurziana in the headsprings of the Rainbow River, Florida in 2002, with undisturbed areas in the foreground and areas disturbed by recreational activities in the background.
22 Figure 1 2. Sagittaria kurziana in areas of reduced flow, with epiphytic and benthic algal coverage, near K.P. Hole County Park in the Rainbow River, Florida in 2002.
23 Figure 1 3. Rainbow River in north central Florida and southwestern Marion County.
24 CHAPTER 2 ECOLOGY OF Sagittar ia kurziana (GLUCK) IN THE RAINB OW RIVER Sagittaria kurziana (Gluck), commonly called SpringTape, is a submersed aquatic species that inhabits many spring runs in Florida (Godfrey and Wooten 1979). This species produces phyllodial strap like or ribbon-like leaves up to 2.5 m in length and was first described by Gluck (1927) as the largest Sagittaria in the whole world Submersed macrophytes provide important habitat for invertebrates and other fauna (Epifanio et al 2003, Steigerwalt 2005, Sammons et a l 2006). Studies in the 1980s and 1990s documented S. kurziana as the dominant, submersed species (Duarte and Canfield 1990a, Water and Air Research Inc. 1991, Holland and Cichra 1994). As recently as 2000, Sagittaria kurziana was determined to be the cover over 50% of the river bottom (Sleszynski 2000). Similar results have been reported for Silver Springs (Quinlan et al 2008). Therefore, it plays an important role in the structure and primary productivity of this ecosystem. Recent concerns over possible adverse effects of cultural eutrophication in Florida spring runs on aquatic plant populations has heightened the need to better understand their ecology. An important part of this understanding involves defining patterns of plant distribution in relation to spatial heterogeneity of environmental conditions. Given the relative stability and homogeneity of many physical and chemical characteristics of spring runs, spatial and temporal heterogeneity of S. kurziana distribution has been largely overl ooked in previous research efforts. Previous research on the S. kurziana community has included quantifying spatial heterogeneity due to recreational impacts (Holland and Cichra 1994, Mumma 1996, Mumma et al 1996). Mapping of submersed species in the Ra inbow River in 1996 and 2000 (Sleszynski 2000) indicated changes in distribution of individual species along the river, measured at spatial scales down to 5 m over the 4 year period, suggesting heterogeneity in the structure and growth of S kurziana
25 commu nities. The goal of this study was to further investigate spatial heterogeneity of S. kurziana distribution in spring runs using the Rainbow River as a case study including a number of hypothetical considerations related to possible driving factors. Hypot hesis 1 Size and morphology of Sagittaria kurziana are homogeneous along the upper the Rainbow River. Water temperature, chemistry, clarity, depth, and velocity are important to growth of SAV. Due to the homogeneity in these conditions along the spring run, the size of Sagittaria kurziana were expected to be consistent. Hypothesis 2 Relative growth rates of S agittaria kurziana at in -channel locations with high er water velocities and out -of -channel locations with low er water velocities are the same. Water velocities influence rate of movement of dissolved nutrients and metabolites between the water column and plant surfaces, which can influence the physiology and growth of submersed plants. Hypothesis 3 Tissue content of carbon, nitrogen, and phosphorus from S agittaria kurziana at in -channel locations with high water velocities and out of -channel locations with low water velocities are the same. Tissue concentrations of nitrogen and phosphorus relative to carbon can indicate nutrient limitations within the environment affecting growth. Hypothesis 4 Light availability, is above levels needed to maximize photosynthetic rate of Sagittaria kurziana. The photosynthetic response of leaf tissue to different PAR levels, and attenuation levels by epiphyt es was used to examine the potential for light limitations of plant production Hypothesis 5 Growth response of S agittaria kurziana introduced at locations within the headsprings of the Rainbow River, are the same. Plants grown in identical sediments we re exposed to regions with different light levels and water velocities to help define factors influencing variability in growth rates. Hypothesis 6 Growth response of S agittaria kurziana exposed to high water velocities and isolated from those conditions using artificial polycarbonate tubing, are the same. Methods Study Site The Rainbow River originates at Rainbow Springs (lat. 290608 N., long. 822616W.), which is located in Marion County in north central Florida. The river flows south for approxim ately 9 km, with channel depth averaging between 1.5 to 2.5 m. Historical records indicate a range of discharge from 13.8 m3/s on 3 October 1932 to 34.8 m3/s on 12 October 1964
26 (Rosenau et al 1977, Scott et al 2004). Water temperatures average 22 C th roughout the year, and the springs that form the river are characterized by great optical clarity (Scott et al. 2004). Light extinction coefficients ( ) at the headwaters of the Rainbow River have been estimated to be less than 0.065/m ( Duarte and Canfiel d 1990b). Spatial Variability in the Morphology of Sagittaria kurziana Plant size and morphology were measured at five sites located at one kilometer intervals along the Rainbow River ( Figure 2 1 ). Site 1 was the farthest upriver and was located 1 km downstream from the headsprings. Sagittaria kurziana was present in the headspring area, but this portion of the river was excluded from sampling due to large areas of sandy, disturbed river bottom, large patches of the native plants Potemogeton illinoens is Ludwigia repens and Utricularia sp. not found in other parts of the river, and Hydrilla verticillata Sampling did not occur along the lower 4 km of the river because the character was distinctly different due to extensive presence of Hydrilla vertic illata and changes in hydrology from downstream impoundment on the Withlacoochee River. Sampling occurred during late summer (August 2002) when plants we re expected to be actively growing. Width of the river at the five sampling locations ranged from 28 to 44 m. Water depths ranged from 1.27 to 2.14 m. Large portions of the shoreline along the Rainbow River were developed with residential housing and associated docks and bulkheads. To avoid sampling in areas disturbed by humans, or the potential shadi ng effect of shoreline trees, plants were collected from mid -channel locations. Ten plant specimens were collected at each site. Plants were selected randomly by throwing ten weighted pieces of flagging tape into the river at each site. Plants closest t o individual flags were removed using snorkeling gear and uprooted from the sediments without damage to the roots. Water depth was recorded to the nearest cm at the location of each plant, using a graduated staff pole. At each
27 site, mean flow rate (m/s) was recorded over a 60 -second period using a FP -201 Global Flow Probe. Plants were returned to the lab for analyses. At the lab epiphytic algae were removed from the individual leaves of the plants using forceps and by rinsing leaves with small amounts of water. Data collected from individual plants included number of leaves, length of longest lea f fresh weight of above ground biomass, number of roots, mean length of roots, fresh weight of below -ground biomass, number of dead leaves, shoots, and inflore scence stalks. Prior to weighing above and below ground biomass, excess water was removed by shaking leaves and blotting with paper towels Plant samples were weighed using an Ohaus Company Ranger scale to 0.1 g. Epiphyte samples were dried at 70 C for 48 hrs and weighed. Determination of I n S itu G rowth of Sagittaria kurziana A 1 km section of the Rainbow River, characterized by a meandering channel, was selected to study the growth of Sagittaria kurziana under different flow regimes because b ends in the river provided a set of heterogeneous conditions where comparisons could be made in lieu of long-term hydrologic changes in spring discharge. Growth of Sagittaria kurziana was measured at two locations with in -channel and out -of -channel plots. Plots in the deeper main channel (in -channel) had higher flow rates measured at 0.27 and 0.33 m/s. Plots in shallower areas beyond the main channel (out -of -channel) had flow rates below the meter sensitivity of 0.1 m/s. Mean depths of all plots were similar ra nging from 0.81 and 1.62 m resulting in high light availability at the river bottom. Site A (in -channel) and Site B (out -of -channel) were approximately 0.5 km upstream of t he second two plots Site C (in -channel) and Site D (out of channel Figure 2 2). The two i n channel plots ( sites A and C) were characterized as having less epiphyte cover on leaves than sites B and D (out -of -channel).
28 Growth measurements were made in May 2004, when diurnal photoperiods were long and possibility of plant senescence wa s low. In addition, sampling occurred before the peak period of recreational use, which begins Memorial Day weekend, to minimize disturbance by swimmers and boaters. Ten plants were tagged and measured at each site. Sagittaria kurziana grows in a rosett e with new growth at a central apical meristem. New leaves are formed at the center, and elongation occurs at the base of the leaves near the sediments (Odum 1957). Growth of individual plants was measured by piercing each leave with a needle 2 cm from t he base of the plant just above the sediments, to create small leaf scars ( Tomasko et al. 2001). These scars were persistent and could be identified at the end of the growth period of the study. Epiphytes were not removed from leaf surfaces. Plants were selected randomly by throwing ten weighted pieces of flagging tape into the river at each site. Plants, at each site, were selected within 5 m of each other. Plants were marked with field flagging tape so they could be located 10 days later. Water dept h was recorded to the nearest cm at the location of each plant, using a graduated staff pole. Mean flow rates (m/s) were recorded over a 60 -second period at each plot using a FP 201 Global Flow Probe. Plants were collected after 10 days, placed in separ ate plastic containers and returned to the lab. In the lab, epiphytic algae were removed from the individual leaves of the plants using forceps and by rinsing leaves with small amounts of water. Leaves were inspected for the tagging scar. New growth tis sue was excised from the initial plant tissue. New plant tissue and initial plant tissue from individual plants were dried at 70 C for 24 hrs and weighed to 0.001 g using a TR 203 Denver Instrument scale. Epiphytic materials was dried at 70 C for 24 ho urs and weighed to 0.001 g and constant weight.
29 Tissue Nutrient Content of Sagittaria kurziana Tissue nutrient content in plants reflect the availability of nutrients within their environment. Relative concentrations of carbon, nitrogen, an d phosphorus can indicate limitations in nutrients which can affect plant growth. Sagittaria kurziana tissue was analyzed for carbon, nitrogen and phosphorus content to determine relative availability at different locations. New growth tissue from the aforementioned plant growth tests was analyzed after samples were dried and weighed. Samples from three plants at each of the four sites were selected randomly, ground with a mortar and pestle, and stored in sealed glass scintillation vials. Percent carbon and nitrogen of tissues were determined using a Carlo Erba NA1500 CNS Elemental Analyzer. Percent phosphorus of tissues was determined using persulfate digestion (Schelske et al. 1986). Photosynthesis Light Flux Relationships for Sagittaria kurziana Photosynthetic response of Sagittaria kurziana leaf samples to a range of light intensities was tested under controlled laboratory conditions. Photosynthetic rates were measured as the evolution of oxygen with an YSI Model 5300 Biological Oxygen Monitor. Using a collim ated condensed quartz light source and a system of neutral light filters, excised plant samples were 2/s of light. The highest intensity tested, 2/s, is approximately 60% of the maximum ins tantaneous light flux expected at mid summer in Florida (Edward Phlips, pers. comm.), significantly higher than expected saturation levels for submersed aquatic plant species. Plant specimens were collected from four locations i n the Rainbow River (Figure 2 2) Specimens from Sites A and B were collected and analyzed on 4 March 2003. Specimens from sites C and D were collected and analyz ed on 8 March 2003. Three plants were collected from each site and returned to the lab for immediate analysis.
30 An YSI Model 5301 monitoring chamber was used to analyze oxygen produced from leaf tissue samples. This monitoring chamber is comprised of a sample chamber a cylindrical glass chamber opened on one end. The plant sample is placed inside and the opened end is sealed with an oxygen probe during analyses The sample chamber is surrounded by a reservoir of water to keep the sample chamber at a predetermined temperature. This reservoir was connected to a Fisher Scientific Isotemp Refrigerated Circulator Model 900 set at 22 C, the approximate temperature in the Rainbow River, to maintain the water and tissue at this temperature for the duration of the analyses. A magnetic stirrer was used to ensure complete mixing in the reservoir In the lab, 20 -mm sections were cut from the upper portion of leaves. Samples with epiphytic materials on the leaves were placed int o scintillation vials with 20 mL of distilled water and shaken until epiphytes were dislodged. All epiphytes were removed from leaf samples before phot osynthetic analysis. The sample chamber was filled with 20 m L distilled water to which 2 mL of a 200-mMol/L sodium bicarbonate solution were added as a sour ce of carbon. Pressurized nitrogen gas was bubbled through the solution for several seconds, to de crease partial pressure of oxygen to near 50% of saturation before analysis of each sample. Individual tissue samples were then placed into the sample chamber on a wire mount and the open end of the chamber was sealed without any traces of gas bubbles w ith the oxygen probe. Measurements of oxygen production were recorded on a Cole Parmer Linear 1200 plotter. Each sample analysis began under dark conditions. Output was recorded for 5 minutes until output on the plotter was linear and stable Light in tensity was then increased to 50 2/s of light and the leaf sample was exposed to that light level until a consistent, linear output rate of oxygen evolution was observed on the plotter. Light levels were successively increased through the range defined above with light intensit y remaining the same until a stable,
31 linear output rate of oxygen was observed for 5 minutes. After analyses, the width of the leaf was measured to calculate its surface area. As a separate experiment, the effect of relative shading by shoreline tree canopies, were measured in February 2008 using a Licor quantum sensor. Measurements taken in the mid channel of Rainbow River were compared to measurements taken directly under an oak tree canopy the branches of which were approximately 2 m above the water surface. The mid channel location was in direct sunlight away from the shading effects of the canopy. At each location, measurements were taken at the surface and depths of 0.5, 1, and 1.5 m to determine the compounding effect of light attenuation through the water column. In February, the diurnal cycle is approximately 11 hr light/13 hr dark. Light attenuation measurements were taken 3.5 hrs after sunrise and again at 5.5 hrs after sunrise (mid day) to approximate the relative effects of shading. Measur ements were repeated three times on the same day, at both times of the day. To investigate the potential shading effects of epiph ytes on leaf surfaces in low epiphytes coverage areas in main channel locations and high epiphyte coverage at low water veloc ity locations outside of the main channel, leaf samples were collected from both environments. Light attenuation by epiphytes was measured in February 2008 by collecting leaf samples of Sagittaria kurziana with epiphytes from eight locations along a 1 km section of the Rainbow River characterized by a meandering channel (Figure 2 2). Four locations were out of the main channel and had epiphyte coverage greater than 50%. Four locations were within the deeper main channel and had epiphyte coverage less tha n 50%. Two leaf samples were collected from each location. In the lab, a 400 mm2 leaf section was excised from the distal portion of each leaf sample. The sample size was determined by measuring the leaf width and cutting an appropriate length.
32 Epiphyte s were carefully removed from one side of the leaf tissue using a scalpel blade, and placed on a delineated 20 x 20 mm (400 mm2) area in the center of a Petri dish. The sample was suspended in a thin film of deionized water so the epiphyte sample could be distributed within the 20 x 20 mm area. Light attenuation measurements were taken out doors, on a sunny day, using a LiCor quantum sensor. For each sample, an ambient light reading was taken through a Petri dish with a thin film of deionized water but n o algal sample. The LiCor sensor was placed directly under the delineated sample area with the water so the sunlight could pass through the Petri dish and water to the probe. An algae sample was then placed in the 20 x 20 mm area on the Petri dish and the light probe was placed under the sample so the sunlight would pass directly through the sample to the probe. Light measurements were take n with the light probe at five different locations under each algae sample, and means were calculated After light m easurements each epiphyte samples were removed from the plates, dried at 70 C for 24 hours and weighed to 0.001 grams using a TR 203 Denver Instrument scale. The epiphyte sample from the opposite side of the leaf tissue sample was removed as described ab ove and the procedure repeated for each leaf sample. Percent transmission was calculated as the fraction of incident light passing through the periphyton matrix. Growth of I ntroduced Sagittaria kurziana Growth of Sagittaria kurziana was compared among locations in the headsprings of the Rainbow River to explore potential heterogeneity in growth response to variability in light level and water velocities. Questions of heterogeneity in growth conditions were raised by observed patchiness in cover of Sagi ttaria kurziana in the headsprings and failed attempts at revegetation by transplanting plants from other portions of the river. To avoid variability in plants viability caused by exposure to pathogenic or microbial interactions, plants were propagated us ing in vitro
33 techniques (see Chapter 3) To control for potential sediment effects, all plants were grown in the same substrate. Sagittaria kurziana plants grown in vitro in 500-mL Erlenmeyer flasks were harvested after eight weeks (see Chapter 3). Indiv idual plants were separated and rinsed. Plants were transferred into 60 -cell (3.8 cm wide x 6.0 cm deep cells), polystyrene plug trays containing coarse vermiculite supplemented with 16 8 12 nitrogen-phosphorus -potassium slow release Osmocote fertilizer at a rate of 26 g/0.28 m3. An individual plant was placed into each of the 60 cells. Trays were placed under intermittent mist (10 sec/ 15 min) in a shaded greenhouse with 350mol m2/s PAR and a 27/24 C day/night temperature range. After eight weeks, plants were acclimated to aquatic conditions by transferring the trays into a circular 950 -L tank approximately 55cm in depth and 150 cm in diameter. The tank was kept full, and water was continuously added at a rate of approximately 500 m L /minute to ci rculate water and maintain a stable temperature and avoid stagnation. After two weeks, individual plants were removed from plug trays and transferred to sand in plastic containers with solid bottoms to avoid loss of sediment. Sediment was obtained from a local sand quarry and was free of organic material or other supplements. The containers were 85 mm top diameter, 58 mm bottom diameter and 70 mm depth and were appreciably larger than anticipated root growth. Plants were allowed to acclimate and root in the tank for six weeks Just prior to initiation of the field study, plants were trimmed of dead leaves and remnant aerial leaves using a scalpel to obtain plants of similar leaf number and size. Each container with one plant served as the experimental unit. Ten replicate plants were used at each of the four growth experiment sites. Ten plants were transferred to each of four field sites in the headsprings area of Rainbow Springs on 20 August, 2002 (Figure 2 1, Table 2 1). This experiment also tested for changes in
34 growth rates during the fall months. Sites I and II with higher light levels (1550 2/s ) and sites III and IV with lower light levels (less than 500 2/s ) were compared. Light measurements were taken at the surface of the water at mid day at the beginning of the experiment using an Apogee Basic Quantum Meter model QMSW SS. Site I, and II had no tree canopy and maximum PAR light flux of 1550 2/s. Site I was characterized by a sandy bottom, depth of 1.5 m and water velocity of 0.45 m/s measured using a FP201 Global Flow Probe. Site II was in a bed of S. kurziana plants approximately 0.5 m tall at a water depth of 1.5 m and mean water velocity of < 0.1 m/s. Sites III and IV were characterized by heavy oak canopies and lower light levels. Site III was characterized by a sandy bottom, PAR measured at the surface at 100 mol/m2/s, depth of 1.0 m, water velocity of < 0.1 m/s, but good circulation from spring vents. Site IV was characterized by a rocky bottom with a high level of organic silt, PAR surface light fluxes of 350 2/s, depth of 1 m, and water velocities of < 0.1 m/s with poor circulation. During the growth experiment, the following parameters were determined for each plant: mean length of leaf, length of longest leaf, and number of entire leaves, damaged or fragmented leaves, shoots, leaves on shoots, and dead leaves. Leaf lengths were measured from the base to the tip of each individual leave, using a 150-mm vinyl ruler. Dead leaves were removed every two w eeks, and the total number of dead leaves, collected over the 12 weeks, was used to estimate leaf turnover. After 12 weeks, plants were returned to the lab. Epiphytic algae were removed from the plants, and the plants were dried at 70 C for 24 hours. A bove and below ground plant biomass w ere measured on a Fisher Scale Series 7000 Model 7303D, to 0.001 g.
35 Growth Response of Sagittaria kurziana Exposed to Flowing Water Growth of Sagittaria kurziana was compared between locations with high water velociti es (0.45 m/s) and those isolated from the flowing water by clear poly -carbonate tubes. This experiment was conducted to eliminate interacting effects of sediments and epiphyte colonization present in the in situ growth experiments conducted downstream. Tubes were 15 cm long and 7 cm in diameter and were placed vertically around the plants with open ends facing down onto the sediment surface and up into the water column. Tubes eliminated direct flow over the plants but allowed for water exchange at the e nds of the tubes. The location of the experiment was near the source of spring discharge, lacked suspended solids, and avoided accumulation of sediments inside the tubes which could affect sediment fertility. Methods used to propagate plants were describ ed above. Plants were transferred to the two sites in the headsprings area of Rainbow Springs on 20 August, 2002 (Figure 2 1). Measurements on individual plants were determined at week 0 and week 8 and included: mean length of leaf, length of longest le af, and number of entire leaves, damaged or fragmented leaves, shoots, leaves on shoots, and dead leaves. Dead leaves were removed every two weeks to quantify leaf turnover. Total numbers of dead leaves over the 8 -week period were calculated. After week 8, the experiment was terminated because plants had grown to the top of the tubes. Statistical Analyses Statistical differences among mean values of plant size, in situ growth rates, tissue nutrient content and photosynthetic rates at different location s were analyzed using one way ANOVA (SAS 2000). Pair -wise comparisons between specific sets of means were made using Tukeys Multiple Range tests at p < 0.05 significance level. Comparisons between ratios of values such as dry weight of epiphytes to dry w eight of plant samples, relative growth rate (dry weight of new tissue to dry weight of initial plant tissue), and carbon to nitrogen tissue content
36 were made by calculati ng ratios for individual samples before statistical analyses were performed. Differe nces between light attenuation measurements and dry weights of epiphyte samples on the upper and lower portion of leaf samples were compared using paired t tests. Results Spatial Variability in the Morphology of Sagittaria kurziana For the nine measure s of plant morphology mean values for five of the variables root length, below -ground biomass, and number of dead leaves, shoots, and inflorescence stalks were not statistically different among the five sites (Table 2 2). Mean values of leaf number were h igher at sites 2, 3, and 4, than at site 5. Mean values at site 1 were not statistically different from the other four sites. Mean values for the length of the longest leaf were statistically longer at sites 1, 2, and 3 than at site 5, and site 4 statist ically had the shortest leaf length. Above ground biomass was not statistically different for sites 1, 2, 3, and 4, but these sites had statistically greater means than the mean for site 5. Mean number of roots were not statistically different for sites 1, 2, 4, and 5, with the mean for site 3 being statistically less than the remaining sites. All five sites were along the deepest main portion of the channel characterized by higher flow rates. Mean water depths at the five sites ranged from 1.27 to 2. 14 m, and mean flow rates at sites 1 through 5 were 0. 19, 0.28, 0.32, 0.24, and 0.22 m/s respectively. Determination of In S itu G rowth of Sagittaria kurziana Significant differences among sites were observed for mean values of initial plant dry weight initial plant below ground biomass, relative growth rate, epiphyte dry weight, and epiphyte dry weight per unit of plant dry weight (Table 2 3). Mean dry weight of new plant biomass production over ten days was not statistically different at the four sa mpling sites, however mean initial plant dry weights were greater at the two shallower, lower -flow sites (out -
37 of -channel), than the two deeper, higher -flow sites (in -channel). Calculated mean relative growth rates (new growth dry weight/initial plant dry weight/day) ranged from 9.8 mg/g/d at site C (in channel) to 2.1 mg/g/d at site B (out -of -channel). Mean dry weight of epiphytic material on plants and the ratio of epiphyte dry weight to Sagittaria dry weight were significantly higher at out -of -channel than in channel sites (Table 2 3). Higher relative growth rates occurred at sites with higher water velocity greater water depth, and lower abundance of epiphytes. Tissue Nutrient Content of Sagittaria kurziana Mean percent tissue content of carbon, nitrogen and ratio of carbon:nitrogen (C:N) of new growth tissue at all four sites were not statistically different (Table 2 4). Mean percent nitrogen ranged from 2.9 to 3.2 %, and C:N ranged from 12.0 to 13.1. Mean percent tissue content of phosphorus w as greater at upstream in channel and out of channel (3.5 and 4.4 mg/g) sites than the two downstream sites (2.8 and 3.0 mg/g). N:P ratios ranged from 0.7 to 1:1. Photosynthesis Light Flux Relationships for Sagittaria kurziana Rate of oxygen production (P ) per p lant tissue surface area of Sagittaria kurziana, collected at four locations on the Rainbow River gradually increased with increasing PAR until becoming saturated (Isat) at PAR levels between 258 and 3 68 mol/m2/s (Table 2 5) (Figure 2 3) Mean val ues for the four sites were not statistically different. Mean light intensity at half maximum photosynthetic rate (I1/2sat), ranged from 63 to 155 mol/m2/s (Table 2 5). Mean value of light intensity at half the maximum saturation level w as statistical ly higher at site A than at the other three sites. Photosynthetic efficiency, or rate of photosynthesis per unit biomass per unit of incident irradiance (Kirk 1994), ranged from 115 to 233 mol/m2/s. Light transmission through epiphyte samples ranged from 2 % for high levels of epiphyte coverage to 71 % for low epiphyte cover (Figure 2 4). Light transmission through epiphyte ranged from 2 to 71 % for samples collected at shallow, low water velocity sites
38 (Figure 2 4B) compared to 32 to 73 % for samp les collected at deeper, in channel sites, with higher water velocity (Figure 2 4C). Distribution of epiphytes on leaves w as patchy i n most samples with areas of heavy and light coverage. No statistical d ifferences were o bserved between epiphyte coverage on the upper and lower surface of leaf tissue. Microscopic inspection of samples revealed that epiphytic material was a combination of pennate diatoms, filamentous green algae, filamentous cyanobacteria, and particulate material. Growth of Introduced Sag ittaria kurziana Plants placed at four sites in the headsprings showed substantial growth over twelve weeks in terms of final plant size and shoot production. Sites I and II had PAR le vels at 1550 2/s and flow rates of 0.45 and < 0.1 m/s respectively. Sites III and IV had light levels of 2/s respectively and both with flow rates < 0.1 m/s. The size of plants characterized by the mean leaf length and longest le af length, increased most at site III (Figure 2 5 A) which was characterized by low light and low flow rates (Table 2 1) Mean values of plants at sites I and II2/s, were not statistically different after 12weeks and lower than at site III Mean leaf length and longest leaf length were significantly lower at S ite I V 2/s PAR), and decreased over the 12-week study period The increase in numbers of entire or undamaged leaves per plant was significantly high er at S ites III than Sites I, II, and IV (Figure 2 5 B). The number of damaged leaves per plant was highest at Site I and lowest at Site III (Figure 2 5 B). Asexual reproduction in Sagittaria kurziana occurs through formation of rhizomes. Leafy shoots alo ng rhizomes produce secondary branching and additional leafy shoots. Mean shoot production per plant and total shoot leaves per plant were greatest at site I (Figure 2 6 A) which was the only site exposed to high flow rates (0.45 m/s) Mean shoot producti on w as also significantly greater at site I V than at sites II and III. Mean above -ground and below -ground
39 d ry -weight biomass was significantly greater at site I than the remaining three sites (Figure 2 6 B). Growth Response of Sagittaria kurziana Exposed to Flowing Water The change in mean leaf length and longest leaf length over eight weeks was greater for plants isolated from flowing water (Figure 2 7A). Mean numbers of shoots produced and mean total lea ves produc ed on shoots w ere greater for plants ex posed to flowing water (Figure 2 7B). Although structures influence flowing water and patterns of sedimentation, n o accumulation of epiphytic material or suspended solids was observed on either the plants or sediment, in either experimental set Discussio n The Rainbow River was described as a Sagittaria run in 1942 (Marchand 1942) Sixty seven years later little is know n about the ecology of this system This lack of data is important because of the species central place in the structure of these Florid a ecosystems. The distribution of Sagittaria kurziana is limited to these lotic systems and the species response to environmental changes has implications on the ecosystems. The results of this study suggest that growth and structure of Sagittaria kurziana are affected by spatial heterogeneity in the physical features of the spring run, as in other lotic systems (Mackay et al. 2003, Renofalt et al. 2005). This conclusion is supported by spatial patterns in the distribution, growth, and photosynthetic rat es of S kurziana. Spatial Patterns Sagittaria kurziana, collected along a 4 km stretch of the main high -flow channel of the Rainbow River, supported the idea of homogeneity, with equal below -ground biomass at five sites and similar aboveground biomass at four of the five sites. Mean water velocities at these sites ranged from 0.19 m/s to 0.32 m/s. However S kurziana measured in shallower side -
40 channel areas, with low flow rates (<0.1 m/s), had significantly higher above -ground biomass, below -ground biomass, and accumulated dead leaf tissue than plants in the main channel areas Conversely, relative growth rate (RGR) of S kurziana in the side channel regions was lower than the deeper main channel. These observations suggest that shallow areas, with low water velocity, represent a different habitat than the main channel relative to the growth of S. kurziana. One potential explanation for this heterogeneity in growth rate and plant size may be differences in availability of light due to shading, and nutrients in the water column influenced by water velocity Leaf production and standing crop of SAV at the individual plant scale is a balance between growth responses to resource availability, and losses from grazing and other factors (Madsen 1991). S ize and morphology of plants (Spence et al 1973, Chambers 1987) includi ng the genus Sagittaria (Richards and Ivey 2004), change in response to resource availability. Differences in spatial distribution and growth rates of SAV at small, in -channel scales have been observed elsewhere (Renofalt et al 2005). Differences in growth in lotic systems can be due to nutrient and light availability, flow rate and substrate composition (McCreary 1991, Martinez Daranas et al 2005). For example, Vallisneria ameri cana, grown in varying levels of light, increased biomass product 2/s PAR to approximately 20 2/s PAR (Blanch et al. 1998) Relative growth rate of Elodea canadensis grown under varying sediment fertility and carbon availability, ranged from less than 10 mg/g/day t o over 40 mg/g/d (Pagano and Titus 2004). The results of the aforementioned comparison of main and side channel locations revealed growth rates of S kurziana (2.1 to 9.8 mg/g/d) lower than other reported literature values for other SAV species (Blanch et al 1998,
41 Pagano and Titus 2004). A positive relationship between RGR and water velocity and negative relationship between epiphytic cover and RGR prompt ed further investigation. To explore the level of spatial heterogeneity in plant growth further, four different micro habitats in the headsprings of the Rainbow River were selected for study. The goal was to examine the growth of plant propagules established in pots of equal substrate. Potted propagules placed at four locations within 50 m of each oth er in the headsprings, differed in growth responses among plants. Locations were selected for differences in light levels and flow rates. Personal observations, of this area over several years, revealed low coverage of S kurziana. P atchy distribution i n the area and failed attempts at reestablishing S. kurziana, collected from donor sites along the river, supported the notion that growth conditions within this limited area might be heterogeneous. The results revealed four trends. First, no significant differences were noted in root formation among sites with the exception of site I. Consistency in root response might be expected due to the use of the same sediments for the introduced plants. Second, dry weight and shoot production were greatest at si te I. These plants grown in the presence of PAR levels of 1550 mol/m2/s and flow rates of 0.45 m/s showed a marked decrease in leaf length and significantly higher shoot and biomass production. L ight level s were consistent at sites I and II, but site I w as exposed to higher water velocities. One explanation for th e difference in growth is that aquatic plants will assimilate nutrients from the water column in lieu of the sediments (Rattray et al. 1991) and that flowing water improves nutrient availabi lity to SAV and eliminates metabolites ( e.g O2) by the continuous replacement of water surrounding leaves (Losee and Wetzel 1993). Madsen (1991) also observed larger plants in streams than in still water Third, leaf length was longest at site IV. Mea n PAR at site IV (100 mol m2 s1) was the only one of the four sites below saturation levels measured for this species. Elongation of shoots
42 is an adaptation to lower light (Barko and Smart 1981, Barko et al. 1982, Imamoto et al. 2007). Leaf shape, siz e and surface area are influenced by light level (Spence et al. 1973). Fourth, mean plant size decreased at site IV. Although the reason for this decline is not clear, they may have been impacted by unidentified pathogens or herbivores (Titus and Hoover 1991). These differences suggest a potential for heterogeneity in growth of S kurziana at a small spatial scale. No human activities were permitted in these areas during this study, making disturbance an unlikely source of variability. Elemental Comp osition of Plants Concentrations of carbon and nitrogen in plant tissues collected from the aforementioned in situ growth study were not distinctly different between the main and side channel environments. Carbon, nitrogen and C:N tissue content of S kur ziana were the same at all four sampling sites. Mean tissue carbon content for S kurzian a ranged from 3 7.7 to 38.4%, similar to the 32 to 34% reported for other species of SAV (Gerloff and Krombholz 1966, Touchette et al. 2003). M ean tissue nitrogen con tent of S kurzian a were also similar to that reported by Touchette et al. (2003) for several other species of SAV Tissue phosphorus levels of Sagittari a kurzian a collected in the Rainbow River were different among sites and between levels found for two other species of SAV, Myriophyllum triphyllum and Lagarosiphon major growing under oligotrophic conditions (1.0 mg/g) and eutrophic conditions (5.0 mg/g) (Rattray et al 1991). Low nutrient availability can limit plant growth (Pagano and Titus 2004) and can be reflected in tissue concentrations (Feijoo et al. 1996, Valentine and Heck 2001). Although variability in phosphorus levels in situ did not reflect differences in measured relative growth rate, differences between upstream versus downstream sites suggests potential heterogeneity in phosphorus availability. Limited nutrient analyses of sediments from the spring run also revealed a potential for heterogeneity of nutrients within the sediments (Appendix Table A 1) This small scale
43 heterogeneity may suggest that the distribution of sediments along the spring run are influenced by disturbance events from both fish and wildlife and human activities, and the processes of resuspension and sedimentation as in other lotic systems. Photosynthesis versus Ligh t Relationships Quantity and quality of light are important to the growth rate and form of SAV Little data exist on photosynthetic potentials of Sagittaria kurziana. The photosynthetic response of S kurziana to varying levels of light indicated that ma ximum rates of oxygen production can occur at instantaneous PAR light fluxes as low as 150 to 350 2/s. Maximum instantaneous PAR light flux in summer at latitude 29 N (north central Florida) can reach over 2/s (Edward Phlips, per sonal communication). Light levels recorded for saturation of photosynthesis are between 6 % to 15 % of peak light levels at mid summer and less than 10 % of full summer sunlight for half saturation of photosynthesis. By comparison, the submersed genera Hydrilla Myriophyllum and Ceratophyllum maximize photosynthesis at 28 to 33 % full sunlight flux (Van et al. 1976), and other species continue to grow at light levels between 2 and 10 % of available surface light (Meyer et al. 1943, Sheldon and Boylen 1977, Salvucci and Bowes 1982,). Estimates of light attenuation by epiphytes and tree canopies indicated a strong influence on light availability to SAV. Light availability has been central to the study of the community structure of SAV (Chambers 1987, Ko rschgen et al. 1997, Pilon and Santamaria 2002). Exceptionally high w ater clarity in the Rainbow River with l ight attenuation coefficients ( ) of 0.606/m 5 km downstream of the headsprings, in combination with shallow water depths, generally result in hi gh light availability at the river bottom. Tree canopies limit light availability and affect plant distribution along other Florida streams ( Canfield and Hoyer 1988,
44 Duarte and Canfield 1990a, Fletcher et al 2000). Shoreline tree canopies extending over the Rainbow River are found in limited areas. In those areas the potential effect is high, with measured PAR levels reduced to below 20 % of ambient levels. Equally, estimated light attenuation by epiphytes samples in this study indicated a strong poten tial reduction of light as high as 90 %. No distinct differences were seen between light attenuation by epiphytic cover at shallow, low -flow areas (Figure 2 4B) and deeper, high -flow areas (Figure 2 4 C), but a continual rate of exponential light decay wi th increasing epiphyte density was observed, similar to that observed by Frankovich and Zieman (2005) for marine seagrass in Florida Bay. Epiphytes negatively affect SAV by decreasing the amount of incident light reaching leaves (Sand Jensen 1977), and if light levels are reduced enough, plant production decreases (SandJensen and Borum 1991). The potential impact on SAV in the Rainbow River is dependent on ambient light levels, heterogeneity of the distribution of epiphytes, and the photosynthetic respon se of S kurzina to varying PAR levels. Given the limited amount of data available on light -photosynthesis relationships in this study, it is premature to draw broader conclusions about the role of epiphyte cover in dictating system -wide production of Sagittaria kurziana in the Rainbow River. However results suggest that differences in light availability and water velocities have the potential to influence the distribution of S. kurziana.
45 Figure 2 1. Sampling locations for spatial variability in t he morphology of Sagittaria kurziana in situ in Rainbow River, Florida in August 2002.
46 Figure 2 2. Sampling locations for in situ growth of Sagittaria kurziana, and tissue nutrient content of Sagittaria kurziana in Rainbow River, Florida in May 2004, and sections of the river, near K.P. Hole County Park where light attenuation and light attenuation by epiphyte were measured in February 2008.
47 Light intensity (umol/m 2 /s) 0 200 400 600 800 1000 1200 1400 Photosynthesic rate (mg O 2 /min/mm 2 ) 0 5 10 15 20 Site A Light intensity (umol/m 2 /s) 0 200 400 600 800 1000 1200 1400 Photosynthetic rate (mg O 2/ min/mm 2 ) 0 5 10 15 20 Site B Figure 2 3 Photosynthetic rate, measured as o xygen evolution from Sagittaria kurziana tissue samples exposed to 0, 50, 152, 275, 625, 775, and 2/s light Readings were taken on three replicate plant samples. Analyses were conducted from plants collected in Rainbow River, Florida at four locations in March 2003. Plants at two locations had no epiphytic cover (A and C) and plants at two other locations had 75 100 % epiphyte cover (B and D).
48 Light intensity (umol/m 2 /s) 0 200 400 600 800 1000 1200 1400 Photosynthetic rate (mg O 2 /min/mm 2 ) 0 5 10 15 20 Site C Light intensity (umol/m 2 /s) 0 200 400 600 800 1000 1200 1400 Photosynthetic rate (mg O 2 /min/mm 2 ) 0 5 10 15 20 Site D Figure 2 3. Continued
49 y = -15.043Ln(x) + 41.662 R2 = 0.659 0 20 40 60 80 100 0 2 4 6 8 PAR transmision (%) A y = -7.7267x + 49.109 R2 = 0.4793 0 20 40 60 80 100 0 2 4 6 8 PAR transmision (%) B y = -21.557x + 68.043 R2 = 0.5556 0 20 40 60 80 100 0 2 4 6 8 Periphyton biomass (mg dry wt/cm2) PAR transmision (%) C Figure 2 4. Percentage of photosynthetically active radiation (PAR) transmitted thr ough epiphyte samples collected in Rainbow River, Florida in March 2008. A) Results from all eight locations (N=32). B) Results from four locations outside of main channel with higher epiphyte coverage. C) Results from four locations within the deeper m ain channel with lower epiphyte coverage.
50 -100 0 100 200 300 average longest Sites Leaf elongation (mm) I II III IV A A B B C B B C A 0 5 10 entire damaged Sites Leaf production I II III IV A B B B B A BC C AB Figure 2 5. Growth of Sagittaria kurziana after 12 weeks at five locations in the headsprings area of Rainbow Springs, Florida. Study conducted from August to October 2002. Mean change from time zero to wee k 12 in A) average leaf length/maximum leaf length, and B) number of entire/damaged leaves on individual plants (mean + SD). Tukeys Multiple Range Test was used to compare mean values. Means with different letters are significantly different.
51 0 10 20 30 shoot number total shoot leaves Sites Shoot production I II III IV A A A C C B B C C 0 0.5 1 above ground biomass below ground biomass Sites Dry weight (g) I II III VI A B B B B B BC C A Figu re 2 6. Growth of Sagittaria kurziana after 12 weeks at five locations in the headsprings area of Rainbow Springs Florida. Study conducted from August to October 2002. Mean change from time zero to week 12 in A) number of shoots and total shoot leaves per plant, and B) mean above -ground and below -ground dry weight biomass per plant (mean + SD). Tukeys Multiple Range Test was used to compare mean values. Means with different letters are significantly different.
52 0 50 100 150 average maximum Leaf length (mm) flow no flow A A B B A 0 5 10 15 shoots total shoot leaves Number flow no flow B B A A B Figure 2 7. Growth of Sagittaria kurziana after 8 weeks at a site exposed to river flow and an adjacent site protected by polycarbonate tubing. Study conducted from August to September 2002. Both locations were at the headsprings area of Rainbow Springs, Florida. Mean change from time zero to week 8 in A) average leaf length/maximum leaf length and B) mean number of shoots and total shoot leaves per plant (mean + SD). Tukeys Multiple Range Test was used to compare mean values. Means with different letters are significantly different
53 Table 2 1. Differences in site conditions at four treatment locations, for sediment controlled 12 week Sagittaria kurziana growth experiment. All four sites were located in the headspring area of Rainbow River, Florida. Measurements were taken in Aug ust 2002. Treatment Locations Site I Site II Site III Site I V Flow ( m/s ) 0.45 <0.1 <0.1 < 0.1 Surface light 2/s) 1550 1550 100 350 Depth (m) 1.5 0.5 1.0 1. 0
54 Table 2 2. Characteristics of Sagittaria kurziana sampled August 2002 at five sites along the Rainbow River, Florida. Tukeys Multiple Range Test was used to compare mean values. Means with different letters are significantly different (p<0.05) Standard deviations given in parentheses Site 1 Site 2 Site 3 Site 4 Site 5 Leaves (#) 16.6 19.1 16.7 18.4 11.1 (6.1) (3.9) (3.2) (3.5) (3.9) AB A A A B Length of 0.73 0.71 0.81 0.40 0.53 longest leaf (m) (0.24) (0.11) (0.05) (0.07) (0.14) A A A C B Fresh weight 40.9 37.8 36.5 27.1 22.4 abo ve ground (21.6) (10.7) (10.6) (7.4) (15.5) biomass (g) A A A A B Roots (#) 35.2 39.6 22.9 35.6 27.9 (17.0) (10.0) (13.3) (6.9) (10.6) A A B A A Root 45.0 73.2 72.3 66.1 47.0 length (mm) (17.7) (23.6) (44.4) (20.0) (22.0) A A A A A Freshweight 4.1 4.0 2.4 3.5 2.5 below -ground (3.5) (1.6) (2.2) (1.4) (2.1) biomass (g) A A A A A Dead 2.1 2.4 2.6 2.5 1.0 leaves (#) (2.0) (1.6) (2 .0) (1.6) (1.4) A A A A A Shoots (#) 0.4 1.3 1.1 0.5 0.9 (0.7) (1.7) (1.0) (1.3) (0.9) A A A A A Inflorescence 0.0 0.2 0.2 0.0 0.2 stalk (#) (0.0) (0.4) (0.4) (0.0) (0.4) A A A A A Epiphyte dry 0.256 0.212 0.057 0.702 0.256 weight (g) (0.132) (0.211) (0.045) (0.360) (0.235) B B B A B Depth (m) 1.40 1.41 2.14 1.27 1.59 0.05 0.09 0.08 0.10 0.12 C C A D B
55 Table 2 3. M ean growth of Sagittaria kurziana after 10 days and mean epiphyte cover at four sites on the Rainbow River, Florida in May 2004. Tukeys Multiple Range Test was used to compare mean values (n=3). Means with different letters are significantly different ( p<0.05) Standard deviations given in parentheses. Mean water velocities (m/s) were recorded over a 60 -second period at each location using a FP 201 Global Flow Probe. Site A Site B Site C Site D In channel Out of channel In channel Out of channel Dry weight of new 0.12 0.09 0.13 0.16 growth tissue (g) (0.06) (0.07) (0.04) (0.08) A A A A Dry weight of 1.87 4.57 2.03 6. 27 initial plant tissue (g) (0.85) (1.46) (1.35) (6. 54) B AB B A Initial above 1.56 4.03 1.88 5.16 ground dry (0.80) (1.27) (1.28) (5.38) weight (g) A A A A Dead leaf 0.00 0.39 0.02 0.31 dry weight (g) (0.00) (0.26) (0.00) (0.72) A A A A Initial below 0.31 0.54 0.15 1.12 ground dry (0.15) (0.23) (0.09) (1.20) weight (g) B AB B A Relative growth 7.6 2. 1 9.8 4 7 rate (mg/g/d) (4 3 ) (1 .5 ) (7 5 ) (3 9 ) A B A A Epiphyte dry 0.12 2.12 0.03 1.38 weight (g) (0.04) (1.36) (0.04) (1.42) B A B A Epiphyte/plant 0.07 0.43 0.01 0.25 Dry weight (0.02) (0.14) (0.01) (0.20) C A C B Water velocity (m/s) 0.33 < 0.1 0.27 <0.1 Depth (m) 1.40 0.98 1.62 0.81
56 Table 2 4. Mean percent composition of carbon, nitrogen, and phosphorus in new growth tissue collected at four sites on the Rainbow River, Florida in May 2004. Tuke ys Multiple Range Test was used to compare mean values (n=3). Means with different lett ers are significantly different (p<0.05) Standard deviations given in parentheses. Nutrient ratios calculated from mean values for individual sites. Site A Site B Site C Site D In channel Out of channel In channel Out of channel Percent Carbon 38.3 37.7 38.4 38.1 (% dry weight) (0.5) (0.2) (0.1) (0.1) A A A A Percent Nitrogen 3.2 3.1 3.0 2.9 (% dry weight) (0.5) (0.3) (0.6) (0.5) A A A A Phosphorus 3.5 4.4 2.8 3.0 (mg/g dry wgt.) (0.5) (0.5) (0.3) (0.3) A A B B Carbon:Nitrogen 12.0 12.2 12.8 13.1 Nitrogen:Phosphorus 0.9 0.7 1.1 1.0
57 Table 2 5 Photosynthesis measurements made on Sagittaria kurziana tissue collected at four locations along the Rainbow River, Florida in March 2003. Samples from sites A and B were collected and analyzed on 4 March. Plants at site A had no epiphytes on leaves. Plants collected a t site B had over 50% epiphytes on leaves. Plants from sites C and D were collected and analyzed on 8 March. Plants at site C had no epiphytes. Plants at site D had greater than 50% epiphyte cover. All epiphytes were remo ved before analyses. Tukeys Multiple Range Test was used to compare mean values (n=3). Means with different letters are significantly different (p<0.05) Standard deviations given in parentheses. Site A Site B Site C Site D Light intensity at 357 368 258 332 saturation (42) (98) (108) (41) (mol/m2/s) A A A A Light intensity at 155 83 67 63 saturation (mol/m2/s) (23) (35) (25) (21) A B B B Ik 233 125 115 123 (83) (35) (38) (35) A A A A Macrophyte 140 165 108 140 s urface area (mm2)
58 58 CHAPTER 3 IN VITRO PROPAGATION OF THE S UBMERSED SPECIES Sagittaria kurziana Introduction In vitro propagation is a technique that a llows for the culture and growth of plants under controlled conditions of light, temperature, and nutrient availability. The culture media usually include a defined inorganic salt mixture and organic components including carbohydrates, vitamins, and growt h regulators to promote propagation (Owen and Miller 1992, Barcelo -Munoz et al. 1999, Niedz and Evens 2007) Since culture is typically under aseptic conditions, this environment eliminates pathogens and microbial interactions. In vitro propagation is an effective technique for producing large quantities of plants without collection and removal of plants from natural systems. These techniques have also been applied to research on aquatic (Ailstock et al 1991, Bird and Jewett Smith 1994, Kane et al 1999 ) and wetland plants (Kane et al 1989, Rogers 2003). The genus Sagittaria (Alismataceae) contains aquatic and amphibious, monocotyledonous species with emergent, floating, and submersed leaf forms (Godfrey and Wooten 1979). Sagittaria kurziana Gluck, c ommonly called Spring Tape, inhabits spring runs in Florida (Godfrey and Wooten 1979). This species produces phyllodial strap like or ribbon like leaves up to 2.5 m in length and was first described by Gluck (1927) as the largest Sagittaria in the whole world. It is the dominant native species in many Florida spring runs such as Ichetucknee, Silver, and Rainbow River and therefore plays an important role in the primary productivity, structure, and ecology of these systems. Florida spring run ecosystem s are affected by changes caused by anthropogenic actions. D isturbance to the plant community from recreation and human development was documented on the Rainbow River as early as the 1940s (Marchand 1942) and more recently in studies of the
59 Ichetucknee River and Rainbow Ri ver (DuToit 1979, Holland and Cichra 1994, Mumma 1996). Populations of native, submersed aquatic vegetation (SAV) in springs are under threat from competition and have been replaced by the exotic and invasive submersed aquatic plant s pecies Hydrilla verticillata (Scott et al. 2004) Increased nitrate levels in spring discharge also pose potential threats of competition for resources from increased algae biomass (Stevenson et al 2004). These disturbances and changes create the potent ial for increased spatial and temporal heterogeneity in spring runs. Research in needed to increase our understanding of the response of Sagittaria kurziana to its environment to give us insight into these potential changes. The objective of this study w as to develop a micropropagation protocol that may be useful for research on this species (see Chapter 4) the ecology of Florida spring runs (see Chapter 2), and restoration efforts. Methods Culture Establishment Specimens of Sagittaria kurziana were co llected from the Rainbow River, placed in plastic bags and returned to the lab. Excised shoot tips were rinsed for 15 minutes in tap water. Surfaces of plant tissue were sterilized by immersion in 1.2% sodium hypochlorate solution containin g 1 drop Tween 20 per 100 mL for 10 minutes, followed by three successive five minute rinses in sterile, distilled, deionized water. Surface sterilized shoot tips were then further trimmed to approximately 2 mm in length and transferred singly into 150 x 25 m m cultur e tubes containing 12 mL basal medium (BM) consisting of strength Murashige and Skoog (1962) mineral salts (PhytoTechnology Labs, Shawnee Mission, KS), 0.56 mMol/L myoinositol, 1.2 Mol/L thiamine HCL, and 87.6 mMol/L sucrose, and supplemented with 0.25 mg/L benzyladenine (BA). All media were adjusted to pH 5.7 with 0.1 N KOH prior to autoclaving at 1.2 kg/cm2 and 121 C for 20 minutes. Cultures were maintained at 25 C under a 16-hour
60 photoperiod provided by cool -white fluorescent lamps (Sylvania F96T 12\ CW \ SS) at 45 2/s measured at culture level. Cultures were indexed for cultivable contaminants using procedures described by Knauss (1976). Stocks and cultures were subdivided every three weeks. Effects of Benzyladenine (BA) on i n Vitro Regenerat ion of Sagittaria kurziana Based on previous work with Sagittaria latifolia ( Kane et al 2000), the effectiveness of BA to propagate shoots was tested. Single shoots were excised from three week old, stabilized indexed stock cultures and transferred to 60 m L glass culture vessels containing 30 m L basal medium (BM) consisting of strength Murashige Skoog mineral salts (PhytoTechnology Labs, Shawnee Mission, KS) supplemented with 0.56 mMol/L myoinositol, 1.2 Mol/L thiamine HCL, and 87.6 mMol/L sucrose. Culture media were supplemented with benzyladenine (BA) at served as the experimental unit ( Figure 3 1A). Ten replicate vessels were innoculated for each treatment using a completely randomized design. Cultures were maintained for three weeks at 25 C under conditions described above. Treatment effects on leaf length, shoot number, and corm number were recorded after 3 weeks of culture. Main treatment ef fects were evaluated using the general linear model (GLM) procedure one way design developed by Statistical Analysis System (SAS 2000). The experiment was performed twice. Comparative Effects of Different Cytokinins on in Vitro Regeneration of Sagittaria kurziana Using an experimental design similar to the one on the effects of benzyladenine above, ten replicate culture vessels were inoculated for each of the following treatments: 2 isopentenyl adenine (2ip), Kinetin or Meta topolin. Ten add itional culture vessels containing BM and inoculated with single shoots served as controls. Cultures were maintained for three weeks as previously described. The same variables were measured after 3 week culture and.
61 evaluated using the general linear m odel (GLM) procedure one way design (SAS 2000). The experiment was performed twice. In V itro Propagation in 500 mL Erlenmeyer Flasks Sagittaria kurziana was cultured in vitro in 500 m L Erlenmeyer flasks (Figure 3 1B) up to 10 weeks to determine the optim a l culture interval for shoot production. Single shoots were excised from stabilized, indexed stock shoot cultures and transferred to 500 m L glass Erlenmeyer flasks containing 250 m L BM. No cytokinins were added to the medi um A culture flask inoculated with a single shoot served as the experimental unit. Thirty -five flasks were inoculated with single shoots to initiate the experiment. Seven additional shoot explant s were measured at the start of the experiment to obtain To data. Cultures were maintain ed as previously described. Every two weeks, seven flasks were randomly selected and the shoot cultures harvested. Data collected included leaf production, leaf length, shoot and shoot leaf number, inflorescence number, and total dry weight. Main treatm ent effects were evaluated using the general linear model (GLM) procedure one way design (SAS 2000). Establishment of ex V itro Plants (Microcuttings) Establishment of plants ex vitro from in vitro shoot microcuttings (Figure 3-1 A) was evaluated over an eight week period in 60-cell (3.8 cm wide x 6.0 cm deep cells) polystyrene plug trays containing course vermiculite. The vermiculite was supplemented with 16 8 12 nitrogen -phosphorus -potassium slow -release Osmocote fertilizer (Scotts -Sierra Horticultural Product Company) at a rate of 26 g/ 0.28 m3. One plant was placed into each of the 60 cells. Trays were placed under intermittent mist (10 sec/15 min) in a shaded greenhouse from late August through early October 2001, with 350 mol/m2/s natural sunlight and a controlled 27/24 C day/night temperature range. Every two weeks, the following data were collected for each cell: number of leaves, leaf length, shoot number and total number of leaves on all shoots.
62 After eight weeks, percent survival for the 60 cells was determined. This acclimatization experiment was repeated from April through May 2002. Results Effects of Benzyladenine (BA) on in Vitro Regeneration of Sagittaria kurziana Shoot regeneration was by rhizome production (Figure 3 1C). A disti nction was made between shoot and corm production. The former had well developed leaves (Figure 3 1A) and the la t ter were swollen leafless structures or corms ( Figure 3 1D) Shoot production (Figure 3 1E) in BM (0 Mol/L BA) was significantly less than in BM supplemented with 2.0 Mol/L and 4.5 Mol/L BA (Figure 3 2A). Shoot production was not statistically different among the other BA concentrations. Corm production was equal regardless of BA treatment (0.5 to 4.5 Mol/L), but significantly less than for BM alone (Figure 3 2B). Leaf elongation was enhanced in the presence of BA (Figure 3 2C). Comparative Effects of Different Cytokinins on in Vitro Regeneration of Sagittaria kurziana Shoot and corm formation also occurred in BM supplemented with the f our cytokinins. No significant difference in shoot or corm production was observed in the presence of the four cytokinins or the control (Figure 33A and Figure 3 3B). Mean leaf elongation was significantly greater for plants cultured in BM alone and in BM with kinetin and 2ip, than in BM with BA or meta topolin (Figure 3 3C). In V itro Propagation in 500 m L Erlenmeyer Flasks Number of leaves and maximum plant length increased significantly between week 0 and 4, increasing from a mean of 4 to 13 leaves and 70 to 127 mm, respectively (Figure 3 4A). No statistical differences were observed among weeks 4 through 10. Asexual reproduction in Sagittaria kurziana occurs through the formation of shoots along branching rhizomes (Figure 3 1C). Leafy shoots along t he rhizomes produce secondary branching an d additional leafy shoots
63 Contrary to the size of the original plant placed into the flask, number of shoots, number of leaves on shoots, and total dry weight of plants and shoots did not change between weeks 0 a nd week 4, but increased significantly over weeks 4, 6, 8, and 10 (Figure 34B and Figure 3 4C). In vitro i nflorescence production w as observed by week 6 Establishment of ex V itro Plants (Microcuttings) Ex vitro survival of planted in vitro microcutting s by the end of the 8 -week acclimatization period was 98 and 100 % for the two trials. Ex vitro plants possessed well developed leaves and roots with new shoot production (Figure 3 1F). Leaf production on the planted microcuttings during that period incr eased from 3.7 to 8.7 (Figure 3 5A). After 8 weeks, leaf length was highly variable ranging from 5 to 115 mm (Figure 3 5B). In addition to the growth of planted microcuttings, shoot formation was also observed with a significant increase in production at weeks 4, 6 and 8 (Figure 3 5C). Shape of leaves in situ in spring runs are ribbon like. Leaves on aerial ex vitro plants were narrow at the base and flared at the tip and represented a terrestrial growth form (Figure 3 1G) This was distinctly different from the linear leaf shape of the submersed in vitro propagules (Table 3 1 )(Figure 3 1G) Discussion These results demonstrate that Sagittaria kurziana can be propagated in vitro in liquid media for research (see Chapter 4) and restoration purposes (see Chapter 2) Establishment of in vitro culture indexed as free of cultivable contaminants was possible using apical meristem tissue from field collected donor plants E fforts were made to improve both the effectiveness of the basal media on growth and propagation of this species through the addition of growth regulators Previous studies have shown a positive effect of BA on growth of aquatic plants in vitro Maximum shoot production in vitro of the amphibious species Cryptocoryne wendtii occurred in media supplemented with 20 Mol/L BA (Kane et al. 1999). Shoot formation in
64 Myriophyllum spicatum and Potamogeton crispus was stimulated by addition of 2.0 mg/L BA (Zhou et al. 2006). In vitro propagation of Sagittaria latifolia was maximized using media supplemented with 1.1 Mol/L BA (Kane et al 2000). R esults for Sagittaria kurziana indicate similar mean plant size, shoot production, and corm production in the presence of different BA concentrations. This may be due to the fact that the species is s ensitive to low concentrations and that all treatments showed a similar effect, or alternatively that BA concentrations tested were too low to affect plant growth. Similarly, the separate addition of three other cytokinins at 2 Mol/L did not promote sign ificantly increased shoot or corm production, consequently, no clear advantage was observed by supplementing basal media with cytokinins for propagation of Sagittaria kurziana. Propagation of large numbers of plants requires shoot development in vitro an d acclimatization to ex vitro conditions. Significant shoot production of Sagittaria kurziana occurred in culture vessels containing 250 m L of strength MS media without supplementation with BA or any of the other cytokinins. Shoot production increased significantly every two weeks after week 4 but yellowing of plants and shoots became apparent by week 8. Production of plants for research and preservation efforts in situ also requires acclimatization of in vitro propagules to ex vitro conditions. Ex v itro plants with well developed roots and new shoot s were effectively acclimated from in vitro propagules, with a 99 % survival rate after 8 weeks Plants propagated in this manner were also used for in situ growth studies in the Rainbow River lasting sev eral weeks (see Chapter 2). These results demonstrate an effective method of propagating in vitro and ex vitro propagules of Sagittaria kurziana. During acclimatization of in vitro propagated plants to ex vitro conditions, it was noted that Sagittaria kur ziana developed an aerial form distinct from its typical submersed leaf
65 morphology. M orphological variability of leaf shape in the genus Sagittaria is well documented (Adams and Godfrey 1961). This change in morphology, from linear to ovate, is likely du e to environmental differences During an extended drought along the Silver River, this author observed a similar form. Leaves of submersed plants were ribbon shaped but leaves of plants growing on exposed areas of the shoreline had shortened leaves whic h were spoon shaped with narrow bases and wide distal ends. This was a temporary amphibious form. Godfrey and Wooten (1979) also observed that, during periods of extended low water levels, emergent plants produce relatively short phyllodes, which may be dilated at their tips. Plants, acclimated in a greenhouse as part of this work showed this same form, as a persistent terrestrial form. This represents the first report of a terrestrial, aerial form for this species The first observation of in vitro an d ex vitro corm formation for Sagittaria kurziana was also observed during this study. Corm formation has previously been documented in other species of Sagittaria in vitro (Campbell 1998) and in situ (Godfrey and Wooten 1979) suggesting the potential in this species Corm formation in vitro is influenced by the genetic potential of the plant, the growth environment, and components of the culture media (Ascough et al. 2008). Development of this micropropagation technique for Sagittaria kurziana presents clear advantages. Due to the pressures being placed on the spring run ecosystems collection of large numbers of plants in situ for habitat restoration may be detrimental to that ecosystem This technique will decrease reliance on collection from natural populations. The application of micropropagation techniques to restoration work in spring runs should be well suited due to the asexual reproduction of submersed aquatic plants and the potential for low genetic diversity. However due to the isolated nat ure of individual spring runs the potential exists for genotypic differences between different springs. Investigation of this genetic diversity may itself give
66 some insight as to the evolution of this species. Development of t his protocol will also be ad vantageous for future experimentation on the physiology of this species (see Chapter 4) because it allows for producti on of large numbers of pathogen-free plants. This micropropagation technique should be an effective tool for future research and restorat ion efforts.
67 Figure 3 1 In vitro propagation of Sagittaria kurziana. A) Single shoot explant used for culture inoculation, B) Erlenmeyer flask and glass baby food jar culture containers, C) rhizomatous branching a fter three week culture D) corm formation, E) generation of multiple rhizomes from single shoot explant after three -week culture F) a cclimatized eight -week old plantlet and G ) leaf morphology of aerial ex vitro linear ex vitro and linear in vitro grow th. A B A C D E F G 1 cm 1 cm 1 cm 1 cm 1 cm 1 cm
6 8 0 2 4 6 0 0.5 1 1.5 2 2.5 4.5 Benzyladenine (Mol/L) # Shoots A B AB AB AB AB A A 0 2 4 6 8 0 0.5 1 1.5 2 2.5 4.5 Benzyladenine (Mol/L) # Corms B A B B B B B B 0 40 80 120 0 0.5 1 1.5 2 2.5 4.5 Benzyladenine (Mol/L) Leaf length (mm) C B A A A AB AB AB Figure 3 2. Effects of benzyladenine (BA) concentration on the growth of Sagittaria kurziana after 3 weeks in vitro culture. A) shoot production, B) corm production, and C) leaf elongation Results represent mean responses of ten repli cate cultures from two replicate experiments (mean + SE). Tukeys Multiple Range Test results indicated as letters on top of bars, with different letters represent significant differences (p<0.05).
69 0 2 4 6 Control BA Kinetin Metatopalin 2ip Growth regulator (2Mol/L) # Shoots A A A A A A 0 2 4 6 8 Control BA Kinetin Metatopalin 2ip Growth regulator (2Mol/L) # Corms A A A A A B 0 40 80 120 Control BA Kinetin Metatopalin 2ip Growth regulator (2Mol/L) Leaf length (mm) C A A A B B Figure 3 3. Effects of four cytokinins (2 Mol/L) on the growth of Sagittaria kurziana after 3 weeks in vitro culture. A) shoot production, B) corm production, and C) leaf elongation Results represent mean responses of ten replicate cultures from two replicate experiments (mean + SD). Tukeys Multiple Range Test results indicated as letters on top of bars, with different letters represent significant differences (p<0.05).
70 0 50 100 150 200 250 300 0 2 4 6 8 10 Weeks Leaves leaf number maximum leaf length (mm) A C AB A A A BC C BC AB A A A 0 100 200 300 400 0 2 4 6 8 10 Weeks # Shoots shoot number shoot leaves B D D D C B A D D D C B A 0 1 2 3 4 5 0 2 4 6 8 10 Weeks Dry weight (g) C C D D D B A Figure 3 4. In vitro growth of Sagittaria kurziana in 500 m L Erlenmeyer flasks with 250 m L of strength MS media Se ven flasks were sampled at 2 week intervals for A) number of leaves and maximum leaf length, B) shoot and shoot leaf production, and C) plant total dry weight (mean + SD). Tukeys Multiple Range Test results indicated as letters on top of bars, with differ ent letters represent significant differences (p<0.05). C A B A
71 0 5 10 15 0 2 4 6 8 Weeks # Leaves explant shoots A D C B A C C BC B A D 0 5 10 15 1-9 10-19 20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-99 100-109 110-119 Length of microcutting leaves (mm) Plant number B 0 0.5 1 1.5 2 0 2 4 6 8 Weeks # Shoots BC C C C B A Figure 3 5. E x vitro growth of micropropagated Sagittaria kurziana microcuttings in a mist house. A) Mean number of leaves, B) size frequency distribution of leaves on microcuttings, and C) mean shoot number. (mean + SD). Tukeys Multiple Range Test results indicated as letters on top of bars, with different letters represent significant differences (p<0.05). B A C
72 Table 3 1. Leaf dimensions of Sagittaria kurziana grown in vitro and ex vitro acclimated in a mist house for eight weeks. Leaf Proximal Medial Distal Length of Length length width width width flared area (mm) (mm) (mm) (mm) (mm) In vitro 65.2 3.2 3.2 3.0 NA Aerial 59.9 3.1 2.9 7.7 22.6
73 CHAPTER 4 EFFECTS OF NITROGEN ON IN VITRO GROWTH OF Sagittaria kurziana (GLUCK) Introduction The effects of increased nutrients, or eutrophication, on aquatic ecosystems are well documented (Neundorfer and Kemp 1993). Increased nutrient availability can lead to increased plant growth if nutrient levels were previously limiting. Nitrogen specifically is critical for formation of amino acids, proteins, and other compounds (Dewanji 1993). In the aquatic environment, the two most common forms of nitrogen a re nitrate and ammonium (Wetzel 1983). Ammonium is typically found in sediments that are often anaerobic, while nitrate is often the dominant form in water. Both forms can be assimilated by aquatic plants, however, ammonium uptake is energetically more e fficient because of the requirement for nitrate to first be reduced, and therefore is typically preferentially used (Short and McRoy 1984, Raven 1985). Concerns have been raised regarding the possible negative effects of increased nitrogen levels in Flor ida springs (Florida Springs Task Force 2000). In the 1990s, many of these springs had nitrate concentrations above 1 mg/L (Jones et al. 1996), which represents an increase from historical levels of 0.04 mg/L at Silver Springs in 1907 and 0.34 mg/L at Ra inbow Springs in 1927 (Roseneau et al 1977, Scott et al 2004). Growth rates of submersed aquatic plants can be limited by low nitrate and ammonium concentrations. Conversely high levels can negatively affect growth of certain aquatic plants that are ad apted to low nitrogen levels (Borum et al 1989), with nitrate enrichment of water causing decreased shoot production (Burkholder et al 1994, Katwijk et al 1997). Sagittaria kurziana Gluck, commonly called SpringTape, inhabits spring runs in Florida (Godfrey and Wooten 1979). This species produces phyllodial straplike or ribbon like leaves up to 2.5 m in length and was first described by Gluck (1927) as the largest Sagittaria in the whole
74 world. This species is common in Florida springs and spring runs (Godfrey and Wooten 1979). These eco systems are unique to Florida and represent one of the most productive ecosystems in the world (Odum 1957). Sagittaria kurziana is the dominant native macrophyte in many spring runs in Florida (Duarte and Canfiel d 1990a) such as the Rainbow River (Holland and Cichra 1994) and is present over more than 50 % of the river bottom ( Sleszynski 2000) making it an important component of the river ecosystem. Therefore, the potential effect of higher nitrate concentrations on this plant could have significant implications on the ecology of the Rainbow River and similar spring runs. However, l ittle is known regarding the effects of changing nitrogen concentrations on growth of S agittaria kurziana. In addition, recent incre ases in nitrate levels in Florida springs have raised concerns about potential effects on growth of epiphytic and benthic algae ( Stevenson et al. 2004). Changes in productivity, growth rates, and form could change competitive advantages with other macrophytes or algae resulting in changes in community structure. Increased productivity may also lead to increased accumulation of biomass, organic materials in sediments and changes in nitrogen cycling between sediments and the water column. This may ultimately lead to spatial heterogeneity in sediment composition and fertility and may be a factor influencing the distribution and growth rate of Sagittaria kurziana. In vitro propagation is a technique which allows for the uniform growth of plants without norma l environmental variability from factors such as exposure to pathogens and other microbial/plant interactions, growing aseptically on a defined medium under controlled conditions of light, temperature, and nutrient availability. Thus, in vitro culture all ows for evaluation of plant growth responses to various factors under highly defined and controlled conditions. Applications of in vitro culture have, for example, been used to screen effects of
75 growth regulators and herbicides in aquatic plants (Kane and Gilman 1991, Christopher and Bird 1992) The in vitro culture environment is artificial, with highly controlled environmental conditions and inclusion of organic carbon sources (sucrose) in the medium as an energy source (Desjardins et al 1995). Direc t comparisons between growth in vitro and in situ should consider these controlled conditions and lack of interactions between micro and macro flora and fauna. Concentration of tissue nutrients has been used as an indicator of nutrient availability to, an d assimilation by, a plant (Gerloff and Krombholz 1966, Feijoo et al 1996). Therefore, the relative tissue concentration of nitrogen can be used as a method of comparing nitrate assimilation rates between plants growing in vitro and in a spring run such as the Rainbow River. Increased nitrate concentrations in groundwater of Florida springs are apparent (Jones et al 1996). Nitrate levels measured at ten locations along the 9 km Rainbow River from November 2002 through November 2004 were approximately 1.0 mg/L (0.016 mMol/L) (Southwest Florida Water Management District unpublished data). Comparatively, water quality data from wells within the recharge basin ranged from < 0.1 mg/L in undeveloped areas of the recharge basin to 5.2 mg/L suggesting the pot ential for increased concentrations in the springs in the future (Jones et al. 1996) and spatial and temporal heterogeneity in nitrogen concentrations. Data on ammonium concentrations in sediments of springs are limited, but Stevensen et al (2004) observed levels as high as 20 mg/L (0.32 mMol/L) in Manatee Springs. The objective of this study was to determine how changes in nitrate and ammonium concentrations may influence growth of one of the dominant macrophytes in Florida springs, Sagittaria kurziana, within the context of three research objectives: 1) Nitrate concentrations in spring discharge are increasing due to cultural eutrophication. Does growth of Sagittaria
76 kurziana increase or decrease with increasing nitrate concentrations when tested in vitro ? Because of flow rates in the river, nitrate availability was expected to be higher than ambient concentrations therefore concentrations tested were above those measured in the river. 2) Accumulation of organics within river sediments may lead to increased availability of ammonium due t o development of potentially anoxic sediments. Therefore potential effects of increased nitrate concentrations must be investigated in the context of interactive e ffects of increased ammonium availability. Does in creased ammonium concentration relative to nitrate levels, have a negative or positive effect on growth of Sagittaria kurziana when tested in vitro ? 3) Is the growth of Sagittaria kurziana negatively affected at tissue nitrogen concentrations above those found in plants growing in situ in the Rainbow River? Methods Stock Plant Cultures Aseptic shoot cultures of Sagittaria kurziana were established in vitro as previously described in Chapter 3 using surface sterilized lateral shoot meristems cultured in 150 m L glass baby food jars containing 40 m L of liquid medium consisting of strength Murashige and Skoog (1962) mineral salts (PhytoTechnology Labs, Shawnee Mission, KS), 0.56 mMol/L myoinositol, 1.2 Mol/L thiamine HCL, and 87.6 mMol/L sucrose. All m edia were adjusted to pH 5.7 with 0.1 N KOH prior to autoclaving at 1.2 kg/cm2 and 121 C for 20 minutes. Stock shoot cultures were increased by dividing the rhizomes produced and subculturing them at 21-day interval s All stock cultures and experiments were maintained at 21 23 C in a 16 h light/8 h dark photoperiod provided by cool -white fluorescent lamps (Sylvania F96T12\ CW \ SS) at 25 35 2/s as measured at culture level.
77 Effects of Nitrogen Form and Concentration on In Vitro Growth A factorial design was used t o test the effects of various combinations of nitrate and ammonium concentrations on the in vitro growth of Sagittaria kurziana. The basal medium (BM) consisted of strength Murashige Skoog mineral salts (PhytoTechnology Labs, Shawnee M ission, KS) without nitrogen supplemented with 0.56 mMol/L myoinositol, 1.2 Mol/L thiamine HCL, and 87.6 mMol/L sucrose. The nitrogen component of Murashige and Skoog basal salt is supplied by KNO3 and NH4NO3 (Murashige and Skoog 1962). Nitrogen addit ions to the BM were made using these two nitrogen sources. Nitrate concentrations tested were 0, 1, 5, 10, 20, and 40 mMol/L. Ammonium concentrations tested were 0, 1, 5, 10, and 20 mMol/L. Nitrate and ammonium concentrations in full strength Murashige and Skoog medium with nitrogen are 40 and 20 mMol/L nitrate and ammonium, respectively (Murashige and Skoog 1962). Since NH4NO3 was a source of nitrogen addition, treatment concentrations with less nitrate than ammonium were not possible. Rhizome segment s, 30 50 mm long with three leaves, were harvested from 3 -week old stock cultures that served as the explant source for each experiment. A single explant cultured in a 150 m L glass baby food jar (5.5 cm wide and 8.5 cm tall) containing 40 m L medium was th e experimental unit, with five replicate vessels per treatment. The experiment was performed twice. After three weeks, culture dry weights, leaf and root numbers, leaf and root length, and number of rhizomatous shoots were scored. Lengths of the two long est leaves and roots and all rhizomatous shoots were measured to the nearest millimeter. Sagittaria kurziana Tissue Nutrient Concentrations The Rainbow River is a spring -fed r iver located in southwestern Marion County in north central Florida. As part of a separate study, n ew growth of plants in situ was monitored at four locations approximately 2 2.5 km downstream from the headsprings area, near the K.P. Hole
78 County Park (see Chapter 2, Figure 2 2). A 1 km section of the Rainbow River, characterized by a meandering channel, was selected to study the growth of Sagittaria kurziana under different flow regimes. B ends in the river provided a set of heterogeneous conditions where comparisons could be made in lieu of longterm hydrologic changes in spring dis charge. Sites A and C were in the deeper portion of the river channel where flow rates were approximately 0.3 m/s, and sites B and D were in shallower areas where flow rates were < 0.1 m/s. Measurements were taken after a ten -day period in May 2004, when light availability was high and potential for plant senescence was low These plants were removed from the river and tissue from small newly developed leaves at the center of the plant rosette was collected for tissue nutrient analysis. Three plant sa mples were analyzed from each of the four sites. To compare nitrogen content in plants, collected from the Rainbow River and those grown under in vitro conditions, samples were collected from plants grown in the presence of three different concentrations o f nitrogen, the control (0 mMol/L NH4 +/0 mMol/L NO3 -) full strength MS media (20 mMol/L NH4 +/40 mMol/L NO3 -), and 1 mMol/L NH4 +/10 mMol/L NO3 (that was determined to produce the greatest leaf elongation and shoot production, from the results of the in vitro factorial experiment ) Samples from three culture containers were analyzed for each of the three experimental concentrations. All samples were dried at 70 C for 24 hours (Gerloff and Krombholz 1966), and a 0.1 to 0.2 g dry weight sample was collected per plant. Samples were ground using a mortar and pestle, stored in glass scintillation vials, and refrigerated until analyzed. Percent carbon and nitrogen of tissues were determined using a Carlo Erba NA1500 CNS Elemental Analyzer. Carbon levels were analyzed to verify that carbon sources were not limiting growth and nitrogen assimilation
79 Statistical Analyses Main and interaction effects of ammonium and nitrate concentrations on growth were examined using SAS version 8.01 (2000). Due to the categor ical nature of the treatment concentrations, Proc GLM two -way test was used to test sources of variability from nitrate and ammonium concentrations, and the interactions. Tissue concentrations of carbon and nitrogen were analyzed using the same procedure. Pair -wise comparisons among means were made using Tukey s Multiple Range tests at the p < 0.05 significance level Results Effects of Nitrate on Growth Nitrate concentration had a significant effect on growth of Sagittaria kurziana in vitro for six of seven variables measured (Table 4 1), with dry weight s being equal for all nitrate levels (Figure 4 1A) M ean leaf length was highest in the presence of 10 mMol/L nitrate more than 80 mm greater than the control. Mean leaf lengths were less in the pres ence of 40 than 10 mMol/L nitrate but the difference was only 21.6 mm (Figure 4 1B). Mean l eaf number was statistically greater in the presence of 5, 10, 20, and 40 mMol/L nitrate than the control (Figure 4 1C). Mean root length in the presence of 20 and 40 mMol/L nitrate was statistically less than in the presence of 0, 1, 5, and 10 mMol/L (Figure 4 2A). Mean r oot number ranged from 14.9 in the presence of 0 mMol/L to a maximum of 21.9 in the presence of 10 mMol/L. Mean r oot numbers in the presence o f 0 mMol/L and 40 mMol/L were statistically similar and less than in the presence of 5 and 10 mMol/L nitrate (Figure 4 2 B). Mean s hoot number increased from 1.3 shoots (0 mMol/L) to a maximum of 3.3 shoots in the presence of 40 mMol/L nitrate (Figure 4 2 C). There were no statistical differences among mean shoot number in the presence of 1, 5, 10, and 20 mMol/L nitrate. Asexual reproduction in Sagittaria kurziana occurs through the formation of rhizomes. Leafy shoots along the rhizomes produce secondary branching and additional leafy
80 shoots. Mean t otal shoot leaf formation increased from 2.4 (0 mMol/L) to 7.8 in the presence of 20 mMol/L nitrate. No statistical differences were observed among mean total shoot leaves for 1, 5, 10, 20, and 40 mMol/L nitr ate Interactive Effects of Nitrate and Ammonium on Growth Statistical differences among nitrogen treatments were found for all measu red variables of growth (Table 4 2 ). Measurements of mean dry weight (dw) biomass ranged from 0.110 to 0.246 g Maximum mean dry weight of 0.246 g was in the presence of 1 mMol/L NH4 +/5 mMol/L NO3 and decreased with increasing concentrations of nitrate and ammonium (Figure 4 3 ). Mean l eaf number ranged from 6.3 to a maximum of 11.0 in the presence of 0 mMol/L NH4 +/0 mMo l/L NO3 and 10 mMol/L NH4 +/10 mMol/L NO3 -, respectively (Figure 4 4) Mean leaf lengths ranged from a minimum of 5 7 in the presence of 0 mMol/L NH4 +/0 mMol/L NO3 to a maximum of 149 mm in the presence of 1 mMol/L NH4 +/10 mMol/L NO3 (Figure 4 5 ). Mean leaf length decreased with increasing nitrate and ammonium concentrations. Overall, leaf growth decreased at higher nitrate and ammonium concentrations. Mean root number increased from 14.9 (0 mMol/L NH4 +/0 mMol NO3 -) to a maximum of 23.9 in the presence of 1 mMol/L NH4 +/10 mMol/L NO3 (Figure 4 6). Mean root length increased from 34 to a maximum of 61 mm in the presence of 0 mMol/L NH4 +/0 mMol/L NO3 and 1 mMol/L NH4 +/5 mMol/L NO3 -, respectively, and decreased with increasing ammonium and nitrate concen trations (Figure 4 7). The shortest mean root length was 9 mm in the presence of 20 mMol/L NH4 +/20 mMol/L NO3 -, which was significantly less than for the control. A qualitative change was also observed in the presence of the highest concentrations of 20 mMol/L NH4 +/20 mMol/L NO3 and 20 mMol/L NH4 +/40 mMol/L NO3 where leafless corms were formed (Figure 4 8).
81 Mean s hoot production increased from a low of 1.3 shoots to a maximum of 4.7 shoots in the presence of 0 mMol/L NH4 +/0 mMol/L NO3 and 1 mMol/L NH4 +/10 mMol/L NO3 respectively (Figure 4 9) Mean s hoot leaf formation increased from 2.4 (0 mMol/L NH4 +/0 mMol/L NO3 -) to 16.7 in the presence of 1 mMol/L NH4 +/20 mMol/L NO3 and decreased with increasing nitrate concentrations (Figure 4 10) Carbon and N itrogen Tissue Concentrations To compare tissue nitrogen levels between in vitro cultures and plants growing in situ in the Rainbow River, tissue concentrations of carbon and nitrogen were measured. Plant tissue, collected from the in situ sites, contained statistically similar total carbon concentrations, ranging from 37.7 to 38.4 % (Table 4 3). Carbon levels for all three in vitro treatments were statistically equal (39.6 to 40.1 %), but statistically greater than for in situ sites. Plant tissues coll ected from the four river sites contained statistically similar total nitrogen content, ranging from 2.9 to 3.2 % (Table 4 2). Tissue nitrogen concentrations in in vitro plants grown in the presence of 0 mMol/L NH4 +/0 mMol/L NO3 and 1 mMol/L NH4 +/10 mMo l/L NO3 -, were statistically less than in situ collected plant tissue. Tissue nitrogen concentrations of plants grown in the presence of 20 mMol/L NH4 +/40 mMol/L NO3 were statistically greater than in situ collected plant tissues. Mean dry weights, leaf length, and root length were statistically greater in the presence of 1 mMol/L NH4 +/10 mMol/L NO3 than in the presence of 0 mMol/L NH4 +/0 mMol/L NO3 and 20 mMol/L NH4 +/40 mMol/L NO3 (Figure 4 11). Mean shoot production in the presence of 1 mMol/L NH4 +/10 mMol/L NO3 and 20 mMol/L NH4 +/40 mMol/L NO3 were statistically similar and greater than the control.
82 Discussion The results of the in vitro experiments show a mixed response of Sagittaria kurziana to different levels of nitrate and ammonium. No nega tive effect was observed on total dry weight and leaf growth of Sagittaria kurziana at nitrate levels up to 40 mMol/L, with increases between the lowest tested levels (0 and 1 mMol/L), and no significant differences among tested concentrations of 5 to 40 m Mol/L nitrate By contrast there was a marked decrease in root growth at the highest nitrate concentrations. A s ignificant decrease in mean root length was observed in the presence of 20 mMol/L and 40 mMol/L nitrate, and mean root number decreased at 40 mMol/L nitrate. Neg ative growth effects from increased nitrate availability have been observed in other SAV species, in particular marine, seagrass communities linked to cultural eutrophication. Harlin and Thorne Miller (1981) noted that increased nitra te in the water column -ground biomass of Zostera marina In another study of Zostera marina leaf production, root production, and plant survival Mol/L (Touchette et al. 2003) Thursby (1984) observed no increase in leaf elongation of Ruppia maritime at nitrate concentrations above 0.1 shoot growth in Zoster a marina (Harlin and Thorne Miller 1981). Results from these seagrass studies showed negative effects at concentrations lower than those tested on Sagittaria kurziana. Ammonium a second source of available nitrogen to plants, is a reduced form common in anaerobic sediments. Although water column concentrations of ammonium in the Rainbow River range from 0.010 to 0.099 mg/L (Southwest Florida Water Management District, unpublished data), p ore water levels up to 20 mg/L (0.32mMol/L) have been measured in s ediments of Manatee Springs (Stevenson et al 2004). In this study, ammonium had a significant effect on six of the seven measured growth variables for Sagittaria kurziana (Table 4 -
83 1). Maximum d ry weight leaf length, and root length were observed at 1 m Mol/L NH4 +. At higher ammonium concentrations growth decreased, which is consistent with results of other studies. For example, g rowth of Vallisneria natans peaked at water column ammonium concentrations up to 0.3 mMol/L, but decreased above this level (Cao et al. 2007). In another study of marine seagrasses, Wilson and Bennett (2008) found that root length decreased in the presence of ammonium concentrations above 10 mMol/L. In terrestrial plants, a mmonium assimilation occurs in the roots where it is used to synthesize compounds such as amino acids and proteins (Guo et al 2006). The capacity of the roots to convert ammonium into amino acids and proteins can be exceeded, leading to accumulation of ammonium in the roots and transport to the shoots. Am monium is toxic to plants at higher concentrations (Britto and Kronzucker 2002), but by assimilating NH4 + into nitrogen rich organic compounds the toxic effects are eliminated (Cao et al 2007). It has been hypothesized that this carbon consumption in roo ts to avoid toxic effects, can compete with synthesis of long chain carbo n molecules needed for growth thus inhibiting plant growth (Guo et al 2006). This process may explain decreased growth of Zostera marina observed at elevated ammonium levels (Katwi jk et al 1997). Corms were also formed at the highest levels of NH4 + tested in this study. Possible f actors effecting corm induction in vitro are genetic potential, growth conditions, and chemicals added to culture media or subsequent endogenous compounds (Ascough et al. 2008). Corms are swollen modified stems where plants store carbohydrates and have been noted in several species of Sagittaria in situ (Godfrey and Wooten 1979) in vitro (Campbell 1998) and recently in S. kurziana (see Chapter 3) Th is work demonstrates the species ability to form corms, and since in vitro culture conditions are controlled, the formation of swollen structures on stems in Sagittaria
84 kurziana are the result of endogenous compounds. Although it cannot be concluded from this study these compounds may be by product of ammonium metabolism Sagittaria kurziana T issue N utrient C oncentrations Tissue nutrient concentrations have been used to reflect nutrient availability in submersed aquatic plants (Feijoo et al. 1996, Valent ine and Heck 2001). In this study, tissues were analyzed for nitrogen content t o both compare the effects of nitrogen availability on growth of plants in vitro and to compare tissue nitrogen concentrations to plants collected from different locations in the Rainbow River. T issue nitrogen levels of plants grown in vitro ranged from 0.7% in plants cultured in nitrogen -free medium to 5.2% in plants grown in the presence of 20 mMol/L NH4 + /40 mMol/L NO3 -. This range extended beyond the range of 1.98 and 4.43 % reported for Vallisneria americana, Ceratophyllum demersum, Heteranthera sp. Myriophyllum sp Potemogeton spp, growing in situ in lakes (Gerloff and Krombholz 1966, Touchette et al 2003) Nitrogen levels in plants collected from the Rainbow River ranged from 2.9 to 3. 2 % well within the range for other SAV species. The fact that nitrogen content of the in situ plants significantly exceeded values observed for plants grown in vitro at 1 mMol/L NH4 + /10 mMol/L NO3 (2.2 %) suggests that nitrogen ava ilability to Sagittaria kurziana in situ is greater than the concentration of 0.02 mMol/L observed in the water column of the spring run (Southwest Florida Water Management District, unpublished data), likely due to sediment sources and the effects of flow ing water. Flowing water increases nutrient availability to plants (Hynes 1970) by decreasing the boundary layer around leaves (Harlin and Thorne Miller 1981) and reducing limiting effects of diffusion gradients. Flow rates greater than 0.3 m/s are commo n along the Rainbow River as described in Chapter 2.
85 The ratio of carbon to nitrogen (C:N) has also been used as an indicator of nitrogen deficiencies because n itrogen assimilation is dependent on sufficient availability of carbon for growth (Touchette and Burkholder 2000) Carbon availability in vitro can be a mixed reliance on heterotrophic absorption of sucrose added to the media and autotrophic CO2 fixation, and growth is not considered limited by carbon under such laboratory conditions (Desjardins et al 1995). In this study, C:N in plant tissues grown in the presence of 1 mMol/L NH4 + /10 mMol/L NO3 was 18 which is co nsistent with 18.3 noted in plant tissue of seagrass species (Atkinson and Smith 1983). The C:N in Thalassia testudinum varied from 18 to 26 in a nitrogen enrichment experiment (Valentine and Heck 2001) which was more than twice the 7.8 in in vitro plants grown in the presence of 20 mMol/L NH4 + /40 mMol/L NO3 suggesting that Sagittaria kurziana is tolerant of higher tissue nitrogen. The tissue nitrogen levels in vitro of 5.2 % were also higher than the 3.48 % recorded for Vallisneria natans grown under hypereutrophic conditions (Cao et al 2007). Although this study focused on short term effects, long term survival of Sagittaria ku rziana is demonstrated by growth of stock cultures at -strength MS media of 10 mMol/L NH4 + /2 0 mMol/L NO3 for more than a year. This study demonstrated in vitro experimentation as a tool to investigate the physiological effects of varying nutrients con centrations on aquatic vegetation. In situ growth experiments are complicated by interactions with microbial populations and environmental variability which are minimized in vitro Nitrate concentrations in local groundwater near Rainbow Springs has bee n measured at two to three times that of current discharge levels at Rainbow Springs suggesting the potential for future increases in nitrate concentrations in the spring runs (Jones et al 1996). Thus it is important to understand the effects of increase d nitrogen availability on the dominant native submersed species Sagittaria kurziana. In situ tissue
86 nitrogen levels in SAV are the result of assimilation through both the leaves and roots ( Rattray et al 1991). Sediment fertility has been considered to have a greater impact on nitrogen allocation for plants than water column nutrients (Xie et al 2005) C onversely, Nichols and Keeney (1976) found that Myriophyllum spicatum, when grown in the presence of ammonium concentrations greater than 5 mMol/L had rates of ammonium uptake by leaves several times greater than by roots Results of this study suggest that Sagittaria kurziana is more sensitive to NH4 + than NO3 in terms of negative effects on growth, and that the effects may be greater on roots which w ere consistent with results for Vallisneria natans (Cao et al. 2007). In a previous study on the edaphic conditions of Sagittaria species, S kurziana was found growing in sediments of 0.1 % organic matter (Wooten 1986), which does not appear consistent w ith layers of fine organic particulates greater than 0.5 m in the Rainbow River Sediments measured at five locations near K.P.Hole County Park on the Rainbow River had highly variable soil (Appendix Table A 1 and Biesboer, 1987). Fertility of flooded sediments is important to nitrogen cycling because it influences the redox potential and relative con centrations of reduced and oxidized forms of nitrogen compounds. Soluble compounds leach into the sediments from decaying dead plant and animal tissue, therefore decomposition of plant detritus in sediments can lead to increased NH4 + by mineralization of nitrogenous organic compounds. Therefore productivity rates, leaf turnover, and biomass accumulation can influence NH4 + reserves in the sediments. In areas of high water velocities or frequent disturbance these sediments can be exported downstream, but i n areas with low water velocity they can accumulate leading to heterogeneity of sediment fertility leading to spatial heterogeneity in nutrient availability From an ecological perspective it is
87 possible to hypothesize that future increases in nutrients in springs may ultimately result in elevated pore water concentrations of ammonium in sediments. This potential increase in ammonium availability could lead to changes in growth rates of Sagittaria kurziana, potential changes in competiti on with other SAV or algal species and increased spatial and temporal heterogeneity Decreased rate of leaf production and elongation could lead to increased shading from accumulation of epiphytes. Reduced growth rates of roots may have implications on the ability of plants to remain anchored in sediments. Rooted aquatic plants can be impacted by uprooting from loosely consolidate d sediments by high water velocities (Chambers et al. 1991) or dislodged by physical disturbance, as observed for Vallisneria americana rosett es (Titus and Hoover 1991) and S. kurziana on the Rainbow (Mumma et al 1996) and Silver rivers (personal observations) Due to the importance that this dominant macrophyte plays in primary productivity, structure and ecology of these systems, further wor k in situ is required to clarify potential effects of these interactions.
88 0 0.1 0.2 0.3 0 1 5 10 20 40 Dry weights (g) A A A A A A A 0 50 100 150 200 0 1 5 10 20 40 Leaf length (mm) A B D CD ABC BC AB 0 5 10 15 0 1 5 10 20 40 Nitrate concentrations (mMol/L) Leaf number B C A A A A AB Figure 4 1. Effect of nitrate concentrations on biomass and leaf production of Sagittaria kurziana in vitro. Results represent mean response of pooled data from two replicat e experiments in liquid medium with five replicate cultures per experiment (mean + S E ). Values represent final A) dry weight, B) leaf length, and C) leaf number after 3 week culture period. Tukeys Multiple Range Test results indicated as letters on top of bars, with different letters represent ing significant differences (p<0.05).
89 0 25 50 75 0 1 5 10 20 40 Root length (mm) AB A C BC A A AB 0 10 20 30 0 1 5 10 20 40 Root number ABC B C BC AB A A 0 1 2 3 4 5 0 1 5 10 20 40 Nitrate concentration (mMol/L) Shoot number A C C B AB AB AB Figure 4 2. Effect of nitrate concentrations on root and shoot production of Sagittaria kurziana in vitro. Results represent mean response of pooled data from two repl icate experiments in MS liquid medium with five replicate cultures per experiment (mean + SD). Values represent final A) root length, B) root number, and C) shoot number after 3 week in vitro culture. Tukeys Multiple Range Test results indicated as let ters on top of bars, with different letters represent ing significant differences (p<0.05).
90 Nitrate Concentration 0 mmol/L 1 mmol/L 5 mmol/L 10 mmol/L 20 mmol/L 40 mmol/L Dry weight (mg) 0.0 0.1 0.2 0.3 0.4 0 mmol/L 1 mmol/L 5 mmol/L 10 mmol/L 20 mmol/L Ammonium Concentration B B AB B A AB AB A AB AB B A AB AB B B B B B B Figure 4 3. Effect of NH4 + and NO3 concentration s on dry weight of Sagittaria kurziana in vitro. Values represent final dr y weight after 3 week in vitro culture. Results represent mean response of pooled data from two replicate experiments in liquid MS medium with five replicate cultures per experiment (mean + S E ). Tukeys Multiple Range Test results indicated as letters o n top of bars, with different letters represent ing significant differences (p<0.05).
91 Nitrate Concentration 0 mmol/L 1 mmol/L 5 mmol/L 10 mmol/L 20 mmol/L 40 mmol/L Number of leaves 0 2 4 6 8 10 12 14 0 mmol/L 1 mmol/L 5 mmol/L 10 mmol/L 20 mmol/L Ammonium Concentration DE BCD BCD ABC ABC CDE BCDE ABC A BCD ABCD ABCD ABC AB CDE BCD ABCD E BCDE CDE Figure 4 4. Effect of NH4 + and NO3 concentration s on number of leaves of Sagittaria kurziana in vitro. Values represent number of leaves after 3 week in vitro culture. Results represent mean response of pooled data from two replicate experiments in liquid MS medium, with five replicate cultures per experiment (mean + S E ). Tukeys Multiple Range Test results indicated as letter s on top of bars, with different letters represent ing significant differences (p<0.05).
92 Nitrate Concentration 0 mmol/L 1 mmol/L 5 mmol/L 10 mmol/L 20 mmol/L 40 mmol/L Average leaf length (mm) 0 50 100 150 200 0 mmol/L 1 mmol/L 5 mmol/L 10 mmol/L 20 mmol/L Ammonium ConcentrationF CDEF BCDEF ABCDE ABCDE AB ABCD A BCDEF AB ABC ABCD ABCD DEF ABCDEF DEF EF ABCDEF DEF ABCD Figure 4 5. Effect of NH4 + and NO3 concentration s on average leaf length of Sagittaria kurziana in vitro. Values represent av erage leaf length after 3 week in vitro culture. Results represent mean response of pooled data from two replicate experiments in liquid medium with five replicate cultures per experiment (mean + S E ). Tukeys Multiple Range Test results indicated as let ters on top of bars, with different letters represent ing significant differences (p<0.05).
93 Nitrate Concentration 0 mmol/L 1 mmol/L 5 mmol/L 10 mmol/L 20 mmol/L 40 mmol/L Number of roots 0 5 10 15 20 25 30 0 mmol/L 1 mmol/L 5 mmol/L 10 mmol/L 20 mmol/L Ammonium Concentration ABC A ABC B AB ABC ABC A A ABC ABC AB A ABC ABC B BC C ABC B C ABC C Figure 4 6. Effect of NH4 + and NO3 concentration s on root production of Sagittaria kurziana in vitro. Values represent num ber of roots after 3 week in vitro culture. Results represent mean response of pooled data from two replicate experiments in liquid MS medium with five replicate cultures per experiment (mean + S E ). Tukeys Multiple Range Test results indicated as lette rs on top of bars, with different letters represent ing significant differences (p<0.05).
94 Nitrate Concentration 0 mmol/L 1 mmol/L 5 mmol/L 10 mmol/L 20 mmol/L 40 mmol/L Average root length (mm) 0 20 40 60 80 100 0 mmol/L 1 mmol/L 5 mmol/L 10 mmol/L 20 mmol/L Ammonium ConcentrationCDEFGH BCDEF CDEFGH ABCDE DEFGH ABCD FGH AB DEFGH A ABC CDEFGH CDEFGH H FGH EFGH FGH FGH GH CDEFGH Figure 4 7. Effect of NH4 + and NO3 concentration s on average root length of Sagittaria kurziana in vitro. Values represent final ro ot lengths after 3 week in vitro culture. Results represent mean response of pooled data from two replicate experiments in liquid MS medium with five replicate cultures per experiment (mean + S E ). Tukeys Multiple Range Test results indicated as letters on top of bars, with different letters represent ing significant differences (p<0.05).
95 Figure 4 8. Sagittaria kurziana after 3 week in vitro culture in the presen ce of different NH4 + and NO3 levels. Results represent plants grown in the presence of A ) 0 mMol/L NH4 + concentrations, and from left to right, 0, 1 and 5 mMol/L NO3 -, B ) 1 mMol/L NH4 +, and from left to right, 1, 5, and 10 mMol/L NO3 -, and C ) 20 mMol/L N H4 +, and from left to right, 20 and 40 mMol/L NO3 -. C A B 1 cm 1 cm 1 cm
96 Nitrate Concentration 0 mmol/L 1 mmol/L 5 mmol/L 10 mmol/L 20 mmol/L 40 mmol/L Number of shoots 0 2 4 6 8 0 mmol/L 1 mmol/L 5 mmol/L 10 mmol/L 20 mmol/L Ammonium Concentration CD CD BCD ABC BCD ABCD A ABC ABCD ABCD AB AB ABC CD ABCD ABC AB B D AB ABC Figure 4 9. Effect of NH4+ and NO3 concentrations on number of shoots production of Sagittaria kurziana in vitro. Values represent number of shoots after 3 we ek in vitro culture. Results represent mean response of pooled data from two replicate experiments in liquid MS medium, with five replicate cultures per experiment (mean + SE). Tukeys Multiple Range Test results indicated as letters on top of bars, with different letters representing significant differences (p<0.05).
97 Nitrate Concentration 0 mmol/L 1 mmol/L 5 mmol/L 10 mmol/L 20 mmol/L 40 mmol/L # Shoot leaves 0 5 10 15 20 25 0 mmol/L 1 mmol/L 5 mmol/L 10 mmol/L 20 mmol/L Ammonium ConcentrationC BC BC BC BC BC ABC AB ABC ABC A AB AB ABC BC ABC ABC BC BC BC Figure 4 10. Effect of NH4 + and NO3 concentration s on number of shoot leaves of Sagittaria kurziana in vitro. Values represent total number of le aves on shoots after 3 week in vitro culture. Results represent mean response of pooled data from two replicate experiments in liquid MS medium with five replicate cultures per experiment (mean + S E ). Tukeys Multiple Range Test results indicated as let ters on top of bars, with different letters represent ing significant differences (p<0.05).
98 0 0.2 0.4 0.6 0.7 2.2 5.2 Dry weight (g) A B A B 0 100 200 300 0.7 2.2 5.2 Leaf length (mm) B C A B 0 50 100 150 0.7 2.2 5.2 Root length (mm) C B A C 0 4 8 0.7 2.2 5.2 Tissue nitrogen content (%) Shoot number D B A A Figure 4 11. Relationship between tissue nitrogen content and growth response of Sagittaria kurziana grown in vitro at different medi um nitrogen concentra tions. Concentrations left to right: 0 mMol/L NH4 +/0 mMol/L NO3 -, 1 mMol/L NH4 +/10 mMol/L NO3 -, and 20 mMol/L NH4 +/ 4 0 mMol/L NO3 -. Values represent final A) dry weight, B) leaf length, C) root length, and D) shoot production after 3 weeks of in vitro cu lture (mean + SD) (N=3). Tukeys Multiple Range Test results indicated as letters on top of bars, with different letters represent ing significant differences (p<0.05).
99 Table 4 1. Results of statistical analyses on the effects of NO3 on growth response of Sagittaria kurziana in vitro. Results represent mean response of pooled data from two replicated experiments, with five replicate cultures per experiment. Treatment concentrations ranged from 1 to 40 mMol/L NO3 -. Source DF Type III SS M S F Value Pr > F Dry weight NO3 5 0. 024 0.005 2.28 0 .0 593 Leaf number NO3 5 41.3 8.3 4.91 0.0009 Leaf length NO3 5 41614.3 8322.9 12.52 <0.0001 R oot number NO3 5 486.8 97.4 5.61 0.0003 Root length NO3 5 5198.4 1039.7 6.90 <0.0001 Shoot number NO3 5 26.5 5.3 6.45 <0.0001 Shoot leaf number NO 3 5 239.9 48.0 635.00 0.0001
100 Table 4 2. Results of statistical analyses on the ef fects of NH4 +, NO3 and their interaction ( NH4 + NO3 -) on growth response of Sagittaria kurziana in vitro. Results represent mean response of pooled data from two replicated experiments, with five replicate cultures per experiment. Treatment concentrati ons ranged from 1 to 40 mMol/L NO3 and 1 to 20 mMol/L NH4 +. Source DF Type III SS MS F Value Pr > F Dry weight NH4 + 4 0.068 0.017 4.82 < 0.000 1 NO3 5 0.108 0.022 6.09 < 0 .0001 NH4 + N O3 10 0.071 0.007 2.01 0.0344 Leaf number NH4 + 4 66.860 16.715 8.98 <0.0001 NO3 5 68.620 13.724 7.37 <0.0001 NH4 + NO3 10 33.411 3.341 1.80 0.0642 Leaf length NH4 + 4 18352.292 4588.073 5.18 0.0006 NO3 5 74756.709 14951.342 16.89 <0.0001 NH4 + NO3 10 25319.094 2531.909 2.86 0.0025 R oot number NH4 + 4 171.052 42.763 2.20 0.0707 NO3 5 896.205 179.241 9.22 <0 .0001 NH4 + NO3 10 554.500 55.450 2.85 0.0025 Root length NH4 + 4 17814.026 4453.506 20.94 <0.0001 NO3 5 9652.554 1930.511 9.08 <0.0001 NH4 + NO3 10 10409.306 1040.931 4.90 <0.0001 Shoot number NH4 + 4 19.144 4.786 3.26 0.0130 NO3 5 59.561 11.912 8.12 <0.0001 NH4+ NO3 10 64.0472 6.405 4.37 <0.0001 Shoot leaf number NH4 + 4 269.665 67.416 2.50 0.0445 NO3 5 874.029 174.806 6.47 <0.0001 NH 4 + NO 3 10 441.601 44.160 1.63 0.1000
101 Table 4 3. Mean percent carbon and nitrogen content within tissue of Sagittaria kurziana samples collected in the Rainbow River and at different in vitro media NH4 + / NO3 c oncentrations. Standard deviation included in parentheses. Tukeys Multiple Range Test results of carbon and nitrogen levels indicated as letters below values (n=3). Different letters represent significant differences between sites and in vitro treatmen ts (p<0.05). Carbon Nitrogen C:N (% of tissue (% of tissue Molar ratio Rainbow River in situ sites Site A 38.4 3.0 13.0 (0.6) (0.1) (0.4) B B C Site B 37.7 3.1 12.3 (0.3) (0.2) (0.7) B B C Site C 38.1 2.9 13.2 (0.5) (0.1) (0.4) B B C Site D 38.3 3.2 12.2 (0.5) (0.4) (1.9) B B C In vitro Treatments 0 mMol/L NH4 + / 39.6 0.7 54.2 0 mMol/L NO3 (0.2) (0.1) (3.6) A D A 1 mMol/L NH4 + / 39.7 2.2 18.0 1 0 mMol/L NO3 (0.3) (0.1) (0.6) A C B 20 mMol/L NH4 + / 40.1 5.2 7.8 4 0 mMol/L NO3 (0.3) (0.3) (0.4) A A D
102 CHAPTER 5 SPATIAL DISTRIBUTION OF EPIPHYTIC AND BEN THIC ALGAE IN THE RA INBOW RIVER, FLORIDA Introduction Submersed aquatic vegetation (SAV), epiphytic algae and benthic algae are important components of the structure and function of many aquatic ecosystems, both in terms of primary production (Odum 1957) and as habitat for invertebrates and other fauna (Epifanio et al. 2003, Steigerwalt 2005, Sammons et al 2006) SAV influences the distribution of epiphytes by providing surface area for recruitment ( Madden and Kemp 1996). C onversely, high levels of epiphytes can influence the productivity and distribution of SAV by limiting light availability (Tilley et al. 1985, Sand Jensen and Borum 1991, Zimba 1995). Spatial and te mporal variability in the distribution of epiphyt ic and benthic algae ha ve been documented in many aquatic systems ( Krejci and Lowe 1987, Kahlert et al. 2002) Distribution has been related to factors such as light and nutrient availability (Biggs 2000) a nd physical dynamics such as waves and currents (Biggs and Stokseth 1996). Over the past century, research on the distribution of epiphytic and benthic algae in SAV -dominated ecosystems has focused on light and nutrient availability as it relates to produ ctivity ( Chetelat et al. 1999, Dodds and Welch 2000, Notestein and Frazer 2006). Previous work on community succession and resource constraints showed that high light levels encourage both increased algal biomass and development of filamentous green and blue -green algal communities (Mosisch et al. 2001). In lotic ecosystems, water velocities decrease in and around SAV beds (Losee and Wetzel 1993), which can result in accumulation of biological metabolites and decreased nutrient availability (Titus and Ada ms 1979, Schulz et al. 2003). Odum (1957a) observed that flow rates and light levels declined with depth in Sagittaria kurziana beds in Silver Springs, Florida.
103 The clear water of spring -fed rivers provides light and flow conditions conducive for growth of epiphytic and benthic algae. Among the numerous spring -fed rivers in Florida, many contain extensive algae communities (Stevenson et al 2004). For example, in Floridas largest first order spring system, Silver Springs, Whitford (1956) described a complex epiphytic community that included filamentous algae and diatoms. Historically, a lgal mats of filamentous cyanobacteri a have been observed in many Florida springs (Odum 1957). Recent increased nitrate levels in Florida springs have raised concerns a bout potential effects on growth of epiphytic and benthic algae ( Stevenson et al 2004). Some research ers ha ve suggested that biomass has increased in recent years due to cultural eutrophication (Stevenson et al. 2004, Notestein and Frazer 2006). However limited historical data and spatial heterogeneity of algal distribution s in spring runs makes comparisons between recent and historical algal levels difficult. Rainbow River in north central Florida provides an excellent opportunity to examine the distr ibutional patterns of epiphytes and benthic algal mats because of its high water clarity, stable temperature, and extensive SAV. The river supports a substantial epiphytic and benthic algal community year around. Spatial heterogenetiy in the environment, both in terms of growth conditions (i.e., light, and nutrients) and rates of immigration and emigration at a site can result in differences in algal biomass. The objective of this study was to determine whether patterns exist in the spatial distribution of epiphytic and benthic algae on the Rainbow River and how they relate to environmental characteristics of the system such as channel morphology and macrophyte structure and abundance. This research objective was pursued within the conte xt of three hypot heses: 1) E piphytic abundance on the upper and lower portions of the Sagittaria canopy is different, 2) Epiphyt ic abundance is correlated to channel morphology and SAV
104 structure within the channel, and 3) Benthic alga l mat percent cover and thickness are correlated to channel morphology and SAV structure. Knowledge of the sources of variability and patterns of distribution of epiphytic and benthic algae is important to understanding the dynamics of these populations. Methods Study Site The Rainbow River begins at Rainbow Springs (lat. 290608 N., long. 822616W.) located in Marion County in north central Florida. The river flows south for approximately 9 km, where it merges with the Withlacoochee River. Historical records indicate a range of river discharge from 13.8 m3/s on 3 October 1932 to 34.8 m3/s on 12 October 1964 (Rosenau et al 1977, Scott et al 2004). The springs that feed the river are characterized by high optical clarity. Light extinction coefficients ( ) at the headwaters of the Rai nbow River have been estimated to be less than 0.065/m ( Duarte and Canfield 1990b). Total suspended solids (TSS) range from 0.12 mg/L at the upstream extent of the river to 1.38 mg/L nine km downstream (Holland and Cichra 1994). Chlorophyll a concentrati ons increase from 0.25 mg/L at the river source to 2.98 mg/L nine km downstream (Holland and Cichra 1994). The submersed plant community of the river forms a dense cover dominated by the native species Sagittaria kurziana (Holland and Cichra 1994), which has ribbon -like leaves of up to 1 m in length (see Chapter 2). Holland and Cichra (1994) estimated the abundance of eight additional species of SAV along 20 transects but o nly Sagittari a kurziana and Hydrilla verticillata were widespread along the river These findings were consistent with GIS mapping conducted in 1996 and 2000 (Sleszynski 2000). Mapping results indicated over 80 % of the river bottom was vegetated of which > 50 % was Sagittaria kurziana.
105 Spatial Distribution of Epiphytic and Benthic A lgae The spatial distribution of epiphytic and benthic algae was estimated along twenty transects located at approximately 250 m intervals along the length of the Rainbow River ( Figure 5 1). The headspring area was excluded from sampling due to large area s of sandy, disturbed river bottom and areas of Potemogeton illinoensis Sampling also did not occur along the lower 3 km of the river due to extensive Hydrilla verticillata and altered hydrology from the impoundment of the Withlacoochee River just downst ream of its confluence with the Rainbow River. The first transect was located approximately 0.5 km downstream of the headspring area. Each transect began on the western shoreline and ran perpendicular to the river to the east bank of the river. Along ea ch transect estimates of percent coverage of epiphytic and benthic algae were made every 5 meters using a 0.5m x 0.5m quadrat. Areas disturbed by human activities were common along the western shoreline near bulkheads and docks, where adjacent upland prop erties were developed with residential housing. To avoid bias, data collection began 10 m from the western shoreline. Tree canop ies were present along portions of the western and eastern shoreline s To avoid bias due to the effects of shading, measureme nts along transects were terminated on the eastern shoreline where the Sagittaria community ended. All measurements were taken via snorkeling. Due to differences in the width of the river, the number of quadrats varied from 8 to 16 per transect. Transec ts did not continue into emergent grass beds if present, usually along shallow sides of the river. Sampling occurred in Se ptember 2000, when algae growth is not expected to be limited by light levels or photoperiod. The Rainbow River is a popular site f or recreation. SAV and associated epiphytes in shallow areas of the river less than 1.5 m can be disturbed by boaters, swimmers, and tubers (Mumma et al 1996). T o avoid potentially high levels of disturbance
106 during the peak summer recreational season, w hich might bias results, sampling occurred after Labor Day (4 September ) from 13 21 September 2000. For epiphyte determinations, separate estimates were made for the upper and lower half of the Sagittaria kurziana, and Vallisneria americana. A categor ical method was used for measuring percent cover of filamentous algae that followed guidelines of Braun Blauquet (1932). Percent cover was recorded in the following categories : 0 to 9 10 to 19, 20 to 29, 30 to 39, 40 to 49, 50 to 59, 60 to 69, 70 to 79, 80 to 89, 90 to 99, and 100 %. Length of filamentous algae attached to plants was determined using a 150 -mm vinyl ruler. Within each quadrat, three replicate length measurements were taken on the upper portions and three on the lower portions of plants. Percent cover of benthic algal mats was also estimated within each quadrat using the categories described above. Three measurements of benthic mat thickness were made within each quadrat using a 150 -mm vinyl ruler. A second survey of epiphytic and benthic algae was conducted in spring and early summer 2001 before the peak summer recreational season, that started on Memorial Day (28 May) a time when anthropogenic disturbance would be expected to be low. Five of the 20 transects (3, 7, 12, 16, and 20) use d for the September surveys were also used in this survey (Figure 5 1). These transects were approximately 1 km apart. Each was sampled once monthly during February, March, April, and May 2001. Along each transect, estimates of percent coverage of epiph ytic and benthic algae were made every 2 m using a 0.5m x 0.5m quadrat. Due to disturbance of vegetation by landowners along the western shoreline where Sagittaria sp. or Vallisne r ia sp. were not present, the first measurement along each transects was mad e 2 to 4 m from the river bank depending on conditions. Separate estimates of percent cover of both epiphytic filamentous and epiphytic encrusted/non -filamentous algae were made on both the
107 upper and lower portion of the plants. Percent cover categories used were 0 to 5, >5 to 25, >25 to 50, >50 to 75, and >75 to 100 %. Length of filamentous algae and the percent cover and thickness of benthic algal mats were measured using the same technique as for the September 2000 survey. During the percent cover est imations of algae in February, March, April, and May 2001, other measurements of physical and biological structure were made at each quadrat location. Water depth, height of SAV canopy, and mean SAV leaf length (extended) were measured using a staff pole with 1 -cm increments. Percent cover of SAV was determined, within the 0.5 m x 0.5 m quadrat using the cover categories 0 to 5, >5 to 25, >25 to 50, >50 to 75, and >75 to 100 %. Water velocity can influence epiphytic populations (Biggs and Thomsen 1995) therefore, a method was developed to approximate the degree to which leaves were influenced by water movement within the water column. Aerenchymous leaf tissue in Sagittari a kurziana causes leaves to orient vertically when undisturbed by water movement ( Sleszynski, personal observation). Water movement forces leaves to bend in the direction of the current decreasing the canopy height of SAV A ratio of one for canopy height to absolute leaf length, represent ed a vertical position with no leaf displace me nt. No shoreline tree canopy was present above sampling locations. Epiphytic Biomass Epiphytic dry weight biomass on Sagittaria kurziana was estimated at five sites immediately downstream of Transects 3, 7, 12, 16, and 20 ( Figure 5 1 ) to avoid disturbanc e to the transects. No Vallisneria americana was present in these plots. The width of the river at these locations ranged from 28 to 44 m. To avoid variability caused by the effects of disturbance due to recreational activities in shallow, shoreline areas, sampling occurred in the deeper, middle portions of the river. Epiphytic algal biomass samples were collected in July 2002 to determine
108 distribution along the river during mid summer compared with early and late summer for previous transect surveys Epiphyt ic algal biomass samples were collected at the individual plant scale. Plants were selected randomly at each site by throwing a weighted piece of vinyl flagging into the water and allowing it to sink to the bottom. The plant at the location of the submersed flagging was collected by snorkeling. The plant was carefully uprooted, and while underwater, placed into a plastic bag. Soft sediments facilitated removal of both leaves and roots of the plants. Ten replicate plants were collected at each s ite. Water depth was recorded at the location of each collected plant using a graduated pole. Mean water velocity was measured at the center of the river at each sampling site, 0.5 m above the Sagittari a kurziana bed, using a FP 201 Global Flow Probe ove r a 60 -second interval. In the lab, each collected plant was processed by stripping epiphytic algae off of the individual leaves. Epiphytic material w as dried at 70 C for 48 hours, placed in a desiccator to cool, and weighed on a Denver Instrument Mode l precision balance to 0.0001 g. Prior to weighing fresh weight biomass of plants, excess water was shaken off leaves and blotted dry with paper towels Statistical Analyses Analys e s of differences in mean percent cover and filament length of epiphytic alga e between the upper portion and lower portion of plants among the 20 transects (September 2000) were conducted using the paired t test procedure. Mean percent cover of filamentous, epiphytic algae for individual transects w as calculated using the medi an value of each percent cover category for each quadrat measurement (e.g ., 62.5 for the category 50 to 75) Individual tests were run for each transect (SAS 2000).
109 A one way ANOVA was used to test for significant differences in mean values of percent c over and filament length among the 20 transects (SAS 2000) U nequal sampling sizes occurred among transects because of differences in river width and transect length. Pair -wise comparisons of means for specific treatments were made using Tukeys Multiple Range tests at p < 0.05 significance level. Abundance of epiphytic and benthic algae at the 5 transects (February, March, April, and May 2001) was analyzed using stepwise logistic regression due to the categorical nature of the data (SAS 2000). Th is tech nique allow for regression of categorical data by predicting a particular outcome. They use a transformation (called a logit) to predict values between 0 and 1. The equation then predicts the natural log of the odds of a particular category. A stepwise logistic model was applied when variables were added, then removed from the model by the Wald statistic criterion if the significance level was greater than or equal to p = 0.05. Independent variables of downstream extent (transect number), water depth, percent cover of SAV canopy height of SAV, actual plant height, and the ratio of plant canopy height to actual plant height (estimation of leaf displacement ) were tested as components of a predictive model for percent cover of epiphytic and benthic algae. Data for each of the four months were analyzed separately. Analyses for differences among mean epiphyte biomass at the five sampling locations was conduct ed using 1 one way ANOVA (SAS 2000). To normalize data for differences in plant size, epiphyte dry weight w as divided by Sagittaria kurziana fresh weight for individual samples before statistical analyses. Pair -wise comparisons of means between sites for epiphytic dry weight, Sagittaria kurziana fresh weight, and ratio of epiphyte dry weight to Sagitt aria fresh weight were made using Tukeys Multiple Range tests at the p < 0.05 significance level.
110 Results Spatial Distribution of Epiphytic and Benthic Algae The periphyt ic community in SAV beds of Rainbow River was comprised of an epiphyte community o f diatoms, the filamentous cyanobacterium Lyngbya sp. and filamentous green algae (M. Cichra and C. Cichra, unpublished data), and benthic mats of predominantly Lyngbya sp. (Cowell and Botts 1994, Sleszynski pers. obs.). Mean value o f the upper portion of the SAV was significantly less than on the lower portion of the plants at 18 of 20 transects, with the exception of Transects 3 and 6 (Figure 5 2A). Mean percent cover ranged from 0 to 31 % on the upper portion of plants and 28 to 78 % on the lower porti on. Mean percent cover of epiphytes on the upper portion of plants w as not statistically different among transects, with the exception of the value at Transect 11 being statistically less than at Transect 16. Mean percent cover of epiphytes on the lower portion of plants was not statistically different among the twenty transects. Mean length of filamentous algae attached on the upper versus lower portion of SAV, was statistically similar at 15 of 20 transects Mean algal lengths at Transects 4, 7, 9, 11, and 12 were the exception, with lengths shorter on the upper than on the lower portion of plants (Figure 5 2B). Mean length of algae, on the upper portion of plants at individual transects ranged from 0 to 5.1 mm. Those on the lower portion of the pl ants at individual transects ranged from 1.0 to 3.9 mm. Comparison of means among individual transects indicate d that mean filament lengths on the upper portion of the plants were s ignificantly longer at Transects 16 than Transects 1 through 7, and 9 thr ough 12. Filament lengths were longer at Transect 17 than Transects 4 through 6, 11, and 12, and filament lengths were longer at Transect 20 than Transects 1 through 7, 9, 11, and 12
111 (Figure 5 2B). On the lower portion of the plants, mean filament length was longest at Transect 16, which was significantly greater than mean lengths for Transects 1, 5 and 6. Mean lengths for the remaining transects were not significantly different from one other. Benthic algal mats were found a t all transects except Tra nsect 5. Mean percent cover of benthic mats at the remaining 19 transects ranged from 4 to 98 % (Figure 5 -3A) Means at Transects 2, 8, and 17 were significantly greater than those at Transects 1, 4, 5, and 20. Mean percent coverage at Transects 10, 13, and 18 were greater than at Transects 4 and 5. M ean thickness of the mats ranged from 0. 2 to 10.0 mm (Figure 5 3B). The highest mean was at Transect 8, which was significantly greater than those at T ransects 1, 3 through 6, and 20. Mean percent cover and mat thickness showed similar spatial patterns Environmental Conditions and Relationships to Algal Distribution Logistic regression analyses were conducted on data collected from the five transects surveyed in February, March, April, and May 2001 to e xplore relationships between algal distribution and environmental conditions. The analyses for percent coverage of filamentous algae on the upper portion of the plants identified three significant independent variables that contributed to the models: wat er depth, SAV canopy height, and ratio of canopy height to plant length of SAV (Table 5 1). Water depth was significant in February and April. Along Transects 3, 7, and 12, where a clearly defined deeper portion of the channel was observed, percent cove r of filamentous epiphytic algae was higher in shallow areas near both banks of the river (Figure 5 4). Along Transect 7, percent cover was low on the west side of the river which was the edge of an emergent grass bed with water depths of approximately 1 .5 m greater than at the shoreline. At Transects 3 and 12, higher cover was observed within a narrow area in mid channel. The river bottom along most transects was covered with Sagittari a kurziana or isolated areas of Vallisneria americana, but in both c ases, SAV cover was sparse and bottom type was
112 predominantly sand (Transect 3) or rock (Transect 12). Along Transects 16 and 20, where a distinct channel was not present, epiphytic coverage was more consistent across the width of the river (Figure 5 4). Canopy height of SAV contributed to the model in March. A n in verse trend was observed between percent cover of filamentous algae on the upper portion of plants and canopy height (Figure 55 A). Higher percent cover of epiphytes was observed at water depths of 1.0 to 1.5 meter than at depths greater than 1.5 m (Figure 5 5 B). The ratio of canopy height to plant length of SAV also contributed to the predictive model in February and April. Analyses for percent coverage of non -filamentous algae on the upper portion of the plants identified two significant independent variables that contributed to the model: SAV canopy height and water depth (Table 5 1). The former had the greatest influence on the model, contributing in all four months. Percent cover of non-filamentous algae increased with increasing canopy height (Figure 5 6A). Maximum mean percent cover was observed at water depths greater than 0.5 to 1.0 m (Figure 5 6B). Variables contributing to the model results for percent cover of filamentous and non filamentous epiphytes on the upper portion of SAV were consistent with those on the lower portions, with the addition of percent cover of SAV for the lower portion of the plants (Table 5 1). Predictive models for percent cover of non -filamentous epiphytes on the lower portion of plants were inconsistent among months with SAV canopy height, water depth, and percent plant cover influencing the model results in March, only SAV canopy height influencing the model in May and no variables significantly contribut ing to model results in February or April (Table 5 1). Analyses for percent coverage of benthic algal mats identified four significant independent variables that contributed to the model: transect number water depth, SAV canopy height, and ratio of canop y height to leaf length (Table 5 1). Mean percent cover was lower at greater (2.0 to
113 2.5 m) depths (Figure 5 7 ). Lowe st mean percent cover of mats was present in the deepest portion s of the channels along T ransects 3 7 and 12 with open patches of sand and rock present in Transects 3 and 12 (Figure 5 8). Along the western side of Transect 3, representing the outside bend of the river, percent cover of algae was also low. Higher levels were observed along T ransects 16 and 20, where no distinct, deep cha nnel was present and water depths were more consistent across the width of the river (Figure 5 8) SAV c anopy height and the ratio of canopy height to leaf length only contributed to the model in two of four months, February and May and March and April respectively Epiphyte Biomass Mean dry weight s of epiphytes on the individual S. kurziana were not significantly different among sites, with the exception of the highest mean weight (0.902 g) at S ite 16 and lowest mean weight (0.021 g) at S ite 3 (Table 5 2). Epiphyte biomass values normalized to plant weights w as significantly greater at Sites 16 and 20 than at Sites 3, 7, and 12 (Table 52). Discussion Previous research on the abundance and distribution of epiphytic and benthic algae in lotic ecosystem s has emphasized growth and mortality within the context of different nutrient and light regimes ( Chetelat et al. 1 999, Biggs 2000). This study explored patterns of epiphytic and benthic algal distributions at different spatial scales and their relationsh ip to river channel characteristics. Epiphyte Distribution Little research has been conducted on the distribution of epiphytes along the vertical profile of SAV. Based on personal observations that the upper portions of plants are more influenced by wate r movement than their lower portions, epiphyte distribution was investigated along the profile of Sagittari a kurziana Percent cover of filamentous epiphytes was
114 significantly less on the upper than lower portions of Sagittari a kurziana throughout the Rai nbow River. This is consistent with Comte et al (2005), who observed fewer algae on the tips of leaves due to effects of water movement. Conversely, Whitford (1956) found that due to growth patterns of Sagittaria kurziana, the older apex of leaves devel oped thicker, more complex, three -dimensional epiphytic communities. The abundance of filamentous epiphytic and benthic algae was investigated at the lateral spatial scale of five meters along cross channel transects. Percent coverage along 20 transects was highly variable. This was consistent with percent coverage of epiphyt ic algae in seagrass populations of Posidonia oc eanica (Piazzi et al. 2004) In lotic systems such as spring runs, high variability in the distribution of epiphytes might be expect ed due to the influence of water velocity, decreased light intensity from shading from shoreline tree canopies water depth and associated disturbance by human activities such as boat traffic swimming, and foot traffic at ingress and egress areas of river s In this study, sampling occurred at times and in locations when and where the eff ect of the latter was minimized. Algal abundance decreases with increased flow rates (Ghosh and Gaur 1994) due to effects of shear and export of biomass from the leaf sur face (Horner et al. 1990). High variability in water velocities in and around SAV beds has been measured in streams (Sand Jensen and Pedersen 1999). It was therefore hypothesized that the distribution of epiphytic and benthic algae should be associated w ith changes in structural characteristics of the river and S. kurziana community, including percent cover and plant height that influence water velocity. Logistic regression models between epiphyte abundance and environmental characteristics along the spring run indicated that percent cover of filamentous epiphytic algae on the upper portion of the plants was significantly affected by water depth, SAV canopy height, and the ratio
115 of SAV canopy height to plant length that was used as an estimate of leaf mo vement. Distribution along transects (Figure 5 4) followed three trends. First, at the upstream transects (3, 7, and 12), coverage was generally higher along the shore. Second, at transects 3 and 12, coverage was higher at two mid channel locations. Third, in downstream transects (16 and 20), percent cover of algae was higher across the entire river profile. Higher epiphyte coverage was predicted at shallower depths, peaking between 1 and 1.5 m (Figure 55). Compared to water velocities of 0. 16 to 0.32 m/s observed in the central channel, water velocities were lower in shallow shoreline areas. The second trend of high mid-channel coverage at Transects 3 and 12 can be explained by bottom substrate. Uncharacteristically, substrate in these two areas wa s made up of sand and rock with a low percent cover of S kurziana and no other SAV compared to dense S kurziana beds common throughout other transects. Epiphyte coverage was high on the few individual plants that were present compared to the dense beds common throughout the other transects. This high epiphyte cover is supported by the observation that large amounts of suspended materials can accumulate on artificial structures over a short period of time in the Rainbow River ( Appendix Table A 2 ). This may demonstrate the importance of the vertical structure of the SAV up into the water column which is consistent with the model prediction that epiphyte cover is influenced by SAV canopy height. Transect location was also determined to be significant li kely due to downstream changes in channel morphology, with Transects 3, 7, and 12 characterized by a deeper mid river channel and shallower areas near the shoreline and Transects 16 and 20 more uniformly shallow across the entire width of the river. The r atio between SAV canopy height to plant length, an estimate of leaf movement, also suggested that this may be a factor in export of epiphytes from leaf surfaces. Biggs and Stokseth (1996) showed that after colonization, epiphyte biomass of filamentous alg ae was lower at water velocity greater than
116 0.31 m/s when compared to lower water velocity. At high water velocities, shear stresses become too great for epiphyte colonization (Stevenson 1983). Water velocities comparable to this were measured in the Rai nbow River. This suggests that attachment and colonization of algal filaments to SAV at mid channel areas of the river may be limited by high water velocities. Non -filamentous encrusted epiphytes were observed on Sagittari a kurziana leaves in this study and quantified separately from filamentous algae The epiphytic community of spring runs has been described as a complex association including filamentous algae and diatoms (Whitford 1956). Mineral deposits including diatom frustules have also been obse rved on leaves of SAV species in Florida lakes (Zimba and Bates 1996). Water samples collected in the Rainbow River in July 2004 were dominated by epiphytic and benthic forms of pennate diatoms principally of the orders Naviculales, Achnanthales and Fra gillaria ( Cowell and Dawes 2008) versus planktonic taxa documenting that resuspension of diatoms into the water column and immigration onto substrate surfaces can be important to the composition and standing crop of benthic algal communities (Stevenson and Peterson 1991). Similar to the results for filamentous algae, the logistical regression model for percent coverage of non-filamentous epiphytes revealed SAV canopy height and water depth as significant factors, supporting the second hypothesis that distr ibution of epiphytic algae are associated with channel morphology and SAV structure. The basis for the observed model relationships can be viewed from the context of immigration and emigration rates of epiphytes. Model results between each component of epiphytic cover on the lower portion of the plants were similar to those of upper plants, with the additional contribution of percent plant cover on the lower plants in certain months (Table 5 1). Accumulation of algae is greater in refugia from flow crea ted by structure within channels (Mattaei et al 2003). Water velocity
117 determine s the size and densit y of materials transported between benthic substrates and the water column (Madsen et al 2001). Although no direct measurements of water velocity were t aken within Sagittari a kurziana beds, SandJensen and Pedersen (1999) demonstrated that water velocity within beds of different species of SAV were as low as 8 % of velocities just above the canopy. Plant densities in Sagittari a kurziana beds in areas of the Rainbow River with high percent coverage (96.2 to 99.5 %) in 1994 were measured at 40.8 and 48.8 plants/m2 (C. Cichra, unpublished data ). Decreased water velocities, mediated by structures such as SAV can decrease transport loss of fine particulate m aterials on the sediment surfaces within river channels ( Losee and Wetzel 1993, Schulz et al 2003). Contrary to percent coverage, mean filament length s of algae along the 20 transects were greater at the three downstream transects suggesting within-chan nel differences. This trend was consistent with higher downstream epiphyte biomass measurements. This may be the result of increased growth and accumulation downstream. Filamentous epiphyt ic algae are readily dislodged by the shearing effects of high fl ow rates (Biggs and Thomsen 1995). Concentrations of organic suspended solids (OSS) in the Rainbow River increase downstream (Holland and Cichra 1994) as in other rivers (Minshall et al. 1992). Suspended materials in the Rainbow River that accumulated qu ickly (30 minutes) on artificial structures were partially comprised of short algal filaments along with fine particulate materials. T herefore one explanation for longer filaments downstream may be their repeated resuspension and downstream spiraling, wi th filaments down river having a longer residence time to grow. This extended time frame allows for greater growth and reproduction of filaments. Benthic Algal Distribution Lyngbya sp. a filamentous cyanobacterium, was documented as a major component of benthic community of the Rainbow River (Cowell and Botts 1994). No large scale patterns for
118 benthic algal mat coverage or thickness were observed along the length of the Rainbow River with the exception of l ower levels observed at certain upstream tran sects. Differences in distribution were more evident at the smaller scale of individual transects. Logistic regression models revealed significant effects for transect number, water depth, canopy height and ratio of canopy height and plant length on be nthic mat coverage Transect location was the strongest contributing variable, being significant in three of the four months. Individual transect profiles showed that percent cover of benthic mats was lower along the west or outside bend of the river on Transect 3, and lower at the deepest portions of the river channel (> 2 m) of Transects 7 and 12. Acro ss Transects 16 and 20, where no deeper channel was present and water depth was consistent across the width of the river percent cover of benthic algae w as higher Lower flow can result in deposition of algae and fine particulates along the lower portion of plants and on the bottom (Jowett and Biggs 1997). The presence of s ignificant deposits of fine flocculent, organic se diments in the Rainbow River with thickness greater than 0.5 m suggests that sedimentation of fine particulates within SAV beds is occurring. This suggests that variability in distribution of mats is also correlated to channel morphology. S ediment composition and distribution is also influenced by channel morphology (Madsen et al. 2001). Evaluating Change in Epiphytic Communities in Lotic Ecosystems Epiphytes have long been recognized as an important component of lotic ecosystems, including spring runs (Whitford 1956 Odum 1957, Hyne s 1970, Mattson et al. 1995). Numerous studies have been conducted on epiphytic and benthic algae communities and their potential negative effects on SAV, including shading ( Tilley et al. 1985, Sand Jensen and Borum 1991, Morris and Virnstein 2004). Rece nt interest has centered on potential changes in algal biomass due to increased nutrient loads in ecosystems as a result of cultural eutrophication
119 (Stevenson et al 2004). However comparisons between current and historical data are complicated by hetero geneity in the distribution of algae lack of historical data, and differences in methods of analysis The results here confirm a high level of heterogeneity of epiphyte and benthic algae at different spatial scales. Distinctions between the upper and lo wer portions of plants manifest two distinct vertical habitats Distribution of epiphytes in lotic systems is mediated by the combined effects of growth conditions, immigration and emigration associated with flowing water ( McCormick and Stevenson 1991), a nd anthropogenic disturbance at specific locations. Lower percent coverage on the upper portion of the plants, relative to lower portion of the plants, suggests that the effects of flowing water contribute to the distribution of epiphytes on the Rainbow R iver This is also supported by differences in periphyton abundances observed between deeper mid -river and shallower near shore portions of the channel. Due to high resource availability, particularly light, many spring runs represent an ideal system to study distribution of epiphytic and benthic algae. However, other potential sources of variability must be considered. G rowth rate of Sagittari a kurziana can potentially influence the length of time for colonization and growth of epiphytes. The complexi ty and size of the epiphyte community can increase with the age of the leaf surface (Whitford 1956). The fact that growth of Sagittaria kurziana is limited to a few central leaves (Odum 1957), and that suspended epiphytic material can colonize quickly ont o structures (Appendix Table A -2), suggests epiphyte cover observed on Sagittari a kurziana may have a small influence on epiphytic colonization on the majority of the leaves Anthropogenic activities such as recreation can also disturb, damage, and uproot SAV ( Mumma et al 1996). Portions of the river where disturbance was frequent and Hydrilla common, such as the headsprings, downstream reaches of the river, and areas immediately along residential properties, were excluded from the study. They added add itional
120 sources of variability and the highly dissected leaf morphology of Hydrilla and dense surface mats potentially influence light availability, water velocities, and the growth, immigration and emigration of algae. At an ecological scale these factor s increase the spatial heterogeneity of the system. They are unlikely to improve our understanding of the Sagittaria community but are potentially important to understanding the changes occurring on a system wide scale The role of hydrologic effects on epiphyte distribution highlights the importance of minimum flows in management of lotic ecosystems (Suren et al 2003) Variability in long -term spring discharge levels ha s been documented (Rosenau et al 1977). Observed t emporal changes or fluctuations in river stage and discharge can cause temporal changes in the distribution of epiphytes due to potential changes in water velocity and its effect o n resuspension and sedimentation. Variability within epiphyt ic communities has been observed o ver different spatial and temporal scales (Krejci and Lowe 1987). As a result, conclusions about longterm changes in distribution drawn from sampling that is either spatially or temporally limited must be viewed with caution. A comprehensive understanding of distrib utional patterns of epi phyton in lotic ecosystems is critical to understanding whether long-term changes are in fact occurring and the degree to which changes are related to eutrophication or hydrology.
121 Figure 5 1. Portion of the Rainbow River, Florida, in which 20 transects were sampled for distribution of epiphytic and benthic algae in 2000 and 2001.
122 0 25 50 75 100 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 (upstream) Transects (downstream) Percent cover of epiphytes lower portion of leaves upper portion of leaves 0 2 4 6 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 (upstream) Transects (downstream) Epiphyte filament length (mm) lower portion of plants upper portion of plants B Figure 5 2. Distribution of filamentous epiphytic algae along 20 cross -channel transects in the Rainbow River, Florida during September 2000. Transects are presented in a downstream progression at an interval of 250 meters. A) Mean percent cover at transects, of epiphytes on the upper and lower halves of Sagittaria kurziana. B) Mean length (mm) of filamentous epiphytic algae on the upper an d lower halves of Sagittaria kurziana. Standard deviations are shown as brackets associated with each mean value. B A
123 0 25 50 75 100 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 (upstream) Transects (downstream) Percent cover of benthic mats A 0 5 10 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 (upstream) Transects (downstream) Thickness of benthic mat (mm) B Figure 5 3. Distribution of benthic algal mats at 20 cross channel transects in the Rainbow River, Florida during September 2000. Tr ansect are presented in a downstream progression at an interval of 250 meters. All values are means from measurements taken at 5 -meter intervals along the transects. A) Percent cover of mats. B) Thickness of mats (mm). Standard deviations are shown as brackets associated with each mean value.
124 -2.5 -2 -1.5 -1 -0.5 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 Depth (m) 0 20 40 60 80 100 Epiphyte percent cover Transect 3 -2.5 -2 -1.5 -1 -0.5 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 Depth (m) 0 20 40 60 80 100 Epiphyte percent cover Transect 7 -2.5 -2 -1.5 -1 -0.5 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 Depth (m) 0 20 40 60 80 100 Epiphyte percent cover SAV canopy water depth epiphytes Transect 12 Figure 5 4. Distribution of filamentous epiphytic algae on the upper portion of SAV relative to water depth and SAV canopy height, measured at 5 transects along the Rainbow River, Florida. Sampling occurr ed monthly from February to May 2001. Transect data are presented at 2 -meter intervals from the west to east bank of the river. Standard deviations are shown as brackets associated with each mean value.
125 -2.5 -2 -1.5 -1 -0.5 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Depth (m) 0 20 40 60 80 100 Epiphyte percent cover Transect 16 -2.5 -2 -1.5 -1 -0.5 0 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 Depth (m) 0 20 40 60 80 100 Epiphyte percent cover SAV canopy water depth epiphytes Transect 20 Figure 5 4. Continued.
126 0 20 40 60 0 0.1 > 0.1 0.2 > 0.2 0.3 > 0.3 0.4 > 0.4 0.5 > 0.5 0.6 > 0.6 0.7 > 0.7 0.8 SAV canopy height (m) Percent cover A 0 20 40 60 > 0.5 1.0 > 1.0 -1.5 > 1.5 2.0 > 2.0 2.5 Water depth (m) Percent cover B Figure 5 5. R elationship of mean percent cover of filamentous algae on the upper half of Sagittaria kurziana blades to A) plant canopy height and B) water depth. Graphs represent summary of measurements made at 2 meter intervals along five transects along the Rainbow River, Florida from monthly samples taken during February, March, April, and May 2001. Standard deviations are shown as a bracket on top of each bar.
127 0 20 40 60 0 0.1 > 0.1 0.2 > 0.2 0.3 > 0.3 0.4 > 0.4 0.5 > 0.5 0.6 > 0.6 0.7 > 0.7 0.8 SAV canopy height (m) Percent cover A 0 20 40 60 > 0.5 1.0 > 1.0 -1.5 > 1.5 2.0 > 2.0 2.5 Water depth (m) Percent cover B Figure 5 6. Relationship of mean percent coverage of non-filamentous algae (bar) on the upper ha lf of Sagittaria kurziana blades to A) SAV canopy height and B) water depth. Graphs represent summary of measurements made at 2 -meter intervals along 5 transects along the Rainbow River, Florida from monthly samples taken during February, March, April, a nd May 2001. Standard deviations are shown as a bracket on top of each bar.
128 0 20 40 60 80 100 > 0.5 1.0 > 1.0 -1.5 > 1.5 2.0 > 2.0 2.5 Water depth (m) Percent cover A 0 5 10 15 > 0.5 1.0 > 1.0 -1.5 > 1.5 2.0 > 2.0 2.5 Water depth (m) Thickness (mm) B Figure 5 7. Relationship of mean A) percent cover and B) thickness of benthic algal mats to mean water depth (m) along 5 cross channel transects in the Rainbow River, Flor ida. Graphs represent summary of measurements made at 2 -meter intervals along 5 transects along the Rainbow River from monthly samples taken during February, March, April, and May 2001. Standard deviations are shown as a bracket on top of each bar.
129 -2.5 -2 -1.5 -1 -0.5 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 Water depth (m) 0 20 40 60 80 100 Percent cover Transect 3 -2.5 -2 -1.5 -1 -0.5 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 Water depth (m) 0 20 40 60 80 100 Percent cover Transect 7 -2.5 -2 -1.5 -1 -0.5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Water depth (m) 0 20 40 60 80 100 Percent cover SAV canopy Water depth Benthic mats Transect 12 Figure 5 8. Distribution of benthic algal mats relative to water depth and SAV canopy height, measured at 5 transects along the Rainbow River, Florida sampled monthly from February to May 2001. Transect data are presented at 2 -meter intervals from the west to east bank of river. Standard deviations are shown as brackets associated with each mean value.
130 -2.5 -2 -1.5 -1 -0.5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Water depth (m) 0 20 40 60 80 100 Percent cover Transect 16 -2 -1.5 -1 -0.5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Water depth (m) 0 20 40 60 80 100 Percent cover SAV canopy Water depth Benthic mats Transect 20 Figure 5 8. Continued.
131 Table 5 1. Results of logistic regression analysis between percent coverage of algae and measured environmental vari ables Environmental variables showing significant effect (p<0.5) using stepwise selection procedure are included for each measured category of algae for each of the fo ur sampling months i n 2001. Algae Environmental February March April May type parameter p value estimate p value estimate p value estimate p value estimate Upper portion of S. kurziana Filamentous Water depth 0.0089 0.0311 0.0035 0.0214 SAV canopy height 0.0431 0.0460 SAV canopy/plant length 0.0484 9.9297 0.0163 4.5728 N onfilamentous SAV canopy height 0.0098 0.0626 <0.0 001 0.0854 0.0073 0.0510 <0.0001 0.1009 Water depth 0.0023 0.0154 0.0332 0.0116 0.0008 0.0225 Lower portion of S. kurziana Filamentous Water depth 0.0004 0.0177 0.0008 0.0145 <0.0001 0.0278 Transect number <0.0001 0.1363 0.0123 0.0819 0.0017 0.5603 % plant cover 0.0016 0.4503 SAV canopy/plant length 0.0341 4.6151 Nonfila mentous SAV canopy height 0.0089 0.1058 0.0202 0.2002 Water depth 0.0004 0.0612 % plant cover 0.0275 2.1039 Benthic algae mats Transect number <0.0001 0.1736 0.0001 0.1419 <0.0001 0.1775 Water depth 0.0300 0.0096 0.0159 0.0105 SAV canopy height <0.0001 0.0779 <0.0001 0.0755 SAV canopy/plant length <0.0001 10.3705 0.0012 6.5073
132 Table 5 2. Biomass of epiphytic materials and Sagittaria kurziana plants at five si tes adjacent to respective transects, on the Rainbow River, Florida in July 2002. Tukeys Multiple Range Test was used to compare mean values. Means with different letters are significantly different (p<0.05) (Standard deviations are in parentheses). Site 3 7 12 16 20 Epiphyte biomass 0.021 0.062 0.135 0.902 0.401 dry weight (g) (0.038) (0.051) (0.064) (0.634) (0.312) B AB AB A AB Plant biomass 38.926 30.415 34.223 25.814 15.173 fresh weight (g) (19.768) (11.215) (9.404) (7.354) (4.140) AB BC AB BC C Ratio of epiphyte/ 0.0009 0.00204 0.00394 0.0349 0.0264 plant fresh weight (0.002) (0.003) (0.002) (0.020) (0.020) biomass A A A B B Water 1.32 1.38 2.05 1.26 1.51 depth (m) CD C A D B Water velocity (m/s) 0. 16 0 32 0. 19 0. 18 0. 24
133 CHAPTER 6 SUMMARY The Rainbow River was used as a case study to investigate the ecology of Flo rida spring runs within the context of the overall question of ecosystem homogeneity and lotic system theory The focus was on the dominant macrophyte Sagittaria kurziana because of its critical role in the structure and function of the ecosystem, and the associated distribution of epiphytic and benthic algae. Results of this study suggest that the Rainbow River, one of Floridas largest spring runs, is subject to the similar types of structural heterogene ity in plant and algal communities as other lotic systems. These observations provide caveats to the more general characterization of springs as relatively homogeneous and temporally stable systems. T hi s finding extends a broader view of variability in the structure and function of lotic systems to spri ng dominated river runs. SAV communities in lotic systems are heterogeneous with patchy distributions resulting from variability in light and nutrient availability and hydrodynamic conditions. The latter impacts the ability of SAV to colonize or survive due to sheer stresses Compared to most lotic system, SAV cover age in Rainbow River is high greater than 75 % of benthic surface coverage (Sleszynski 2000) suggesting the presence of favorable conditions for plant growth. This might be expected due to the constant year round temperature, high water clarity, and high volume of water exchange from the spring discharge. T he dominant aquatic macrophyte in the Rainbow River S kurziana, however exhibited spatial differences in structure and growth. Size and morphology of S kurziana along the main channel of the river were consistent but statistically different from shallower side areas characterized by low water velocities and high cover of epiphytic algae. Spatial differences in relative growth rate ( RGR) of S kurziana were also observed in the headsprings area and along
134 the spring run. Differences in growth in the headsprings may be related to several factors including heterogeneity in light levels caused by tree canopies (Canfield and Hoyer 1988), water velocities within the river channel, and differences in water chemistry amongst individual spring vents (Jones et al 1996). In the headspring, maximum growth was observed in plants inserted in mid -channel locations which were characterized by full sun light and high water velocity (0.45 m/s). This result is consistent with plant growth observed in situ at sites downstream of the headsprings. At the mid river sites, RGR was higher in the main channel exposed to flows of approximately 0.3 m/s, than in shallower adjacent areas w here flow rates were less than 0.1 m/s The range of RGR (2.1 9.8 mg/g/d) at mid river sites in the Rainbow River were relatively low compared to 2/s PAR to approximately 20 mg/g/d at over 2/s PAR for Vallisneria americana (Blanch et al. 1998) and less than 10 mg/g/day to over 40 mg/g/d for Elodea canadensis growth in sediments of differing fertility (Pagano and Titus 2004) This suggest s some limitation in resource availability in the Rainbow River Light availability does not appear to explain the differences in growth rates since light levels are high in the Rainbow River due to shallow water depths (< 3 m) and low light attenuation in the water column. Relative S kurziana tissue nutrient concentrations of C:N of 12:1 and N:P of 1:1 suggest that neither nitrogen nor phosphorus limits growth, however more detailed studies on nutrient limitations are needed. The ra nge of RGR of S. kurziana however suggested that growth conditions were heterogeneous between the deeper and shallow locations along the river channel. Under the set of conditions present in these studies, higher water velocities appeared to have a positi ve affect on growth of S kurziana influencing the spatial variability in growth Flowing water improves nutrient availability to SAV, and eliminates metabolites that can inhibit
135 photosynthesis (e.g., supersaturated O2) by the continuous replacement of th e water surrounding leaves (Losee and Wetzel 1993) The distribution of epiphytic and benthic algae in the Rainbow River was also heterogeneous at different spatial scales. Mean percent cover of epiphytes was higher along downstream transects than tran sects nearer to the headsprings which might be expected in an autochthonous lotic system where organic carbon accumulates downstream with autotrophic producti on (Odum 1957). C haracteristics associated with the river channel (i.e., structure of plants wi thin SAV beds and profiles of the river channel) were correlated to the distribution of epiphyton. Epiphyte levels were generally higher in areas of reduced flow whether at the lower portions of the SAV beds or in shallow areas outside of the main channe l. O ther studies have shown that epiphyte biomass of filamentous algae increase with increasing water velocity facilitating colonization At higher water velocities biomass decreases (Ghosh and Gaur 1994, Biggs and Stokseth 1996) where the effects of shear become too great, and algal biomass is exported from the leaf surface (Horner et al. 1990). Based on the results of this study I hypothesized that heterogeneity in channel morphology and the resultant impacts on water velocities can influence the dist ribution of epiphytic algae on S kurziana, which should have implications on in -channel and out -of -channel effects and seasonal changes in river stage or spring discharge. One of the potential impacts of the proliferation of epiphytes is the potential for decreased light availability for SAV (Sand Jensen 1977), causing decreased plant growth (SandJensen and Borum 1991). The potential effect on S kurziana has not been previously studied. The photosynthetic response of S kurziana leaf tissue to light gr adients, in this study, suggests that the species is tolerant to low light levels. In s ubmersed plant genera, like Hydrilla
136 Myriophyllum and Ceratophyllum photosynthesis is saturated at light levels as low as 28 to 33% of full sunlight flux (Van et al. 1976) and plants continue to grow at light levels between 2 and 10% of available surface light (Sheldon and Boylen 1977, Salvucci and Bowes 1982). S. kurziana became saturated at 6 to 15 % of full sunlight flux. It may be hypothesized that productivity of S kurziana should be adaptable to some shading by epiphton, unless the overgrowth becomes very dense in which case shading may reach levels that reduce the rate of photosynthesis. Given the spatial differences in the amount of epiphyte cover along the Rainbow River, their impacts on shading o f S kurziana may vary between regions of the river. Another area of interest regarding the ecology of Florida springs is the increased nitrate concentration in spring discharge (Florida Springs Task Force 2000). From the standpoint of the potential negative physiological effects of nitrates at high concentrations, results of the i n vitro research show no indication of detrimental effects on growth of S kurziana, with the exception of root length at nitrate conce ntrations far above levels currently observed in the Rainbow River. Results also indicated that both nitrate and ammonium are readily assimilated by the plants High ammonium levels had a greater negative effect on S. kurziana than nitrate, specifica lly on root elongation and growth. A potential implication of these results may be that bioaccumulation of nitrogen in sediments may influence the macrophyte community more than the direct effects of increased nitrate in the water column. Ammonium levels of 0.32 mMol/L just under the inhibitory level observed in this study, ha s been measured in the pore water of sediments at Manatee Springs (Stevenson et al. 2004). Composition and distribution of sediments have received little attention in spring runs. F locculent, organic sediment layers greater than 0.5 m thickness observed in the Rainbow River. Fertility of sediments can have a negative effect on growth of SAV ( Carr and Chambers 1998).
137 Increased organic content can increase sediment density decreasing rate of nutrient movement through pore spaces. Decreased oxygen and redox potential in organic sediments can also increase mineralization of nitrogen forms resulting in higher availability of ammonium, which decreased root lengths in vitro Decreased ro ot length in situ could affect the ability of plants to remain anchored in the sediments. Rooted aquatic plants can be impacted by uprooting from loosely consolidate d sediments by high water velocities (Chambers et al 1991) or dislodged by physical distu rbance, as observed for Vallisneria americana rosettes (Titus and Hoover 1991). Subsequently, the distribution of these sediments may be important to the primary producers, both SAV and algae. The spatial heterogeneity in soil characteristics is importan t to understanding the ecology of these ecosystems. Lotic ecosystems Lotic systems are often characterized as spatially and temporally heterogeneous with geomorphic features such as channels and bars creating a diversity of aquatic and riparian habitats (W ard 1998). Spatial complexity and fluvial dynamics of the system are critical to this diversity (Ward and Tockner 2001). Factors influencing this heterogeneity are multidimensional including longitudinal, lateral, vertical, and patterns of disturbance (W ard 1998). At the longitudinal scale, t he River Continuum Concept (RCC) hypothesizes that as stream size increases downstream, the ecology shifts from allochthonous dominated carbon balance based on l eaf litter and other external inputs of organic carbon to auto chthonous dominated carbon inputs (Vannote et al 1980). Florida spring runs do not fit this model since autochthonous processes are the dominant sources of organic carbon even in the headwaters, due to the abundance of benthic primary producers. In addition, low order streams are characterized by high thermal homogeneity, but low light due to canopies, and low nutrient availability.
138 At the lateral scale, the cross section of a river can be described as a gradient from aquatic to terrestrial hab itats, with plant communities exhibiting distinct zonation patterns from aquatic to terrestrial habitats. At small spatial scales the hydraulic forces influence biodiversity by creating microhabitats both along vertical and lateral gradients and within fe atures such as riffles, pools, runs and glides (Ward 1998, Shoffner and Royall 2008). Water levels play a critical role in lotic systems shifting the mosaic of habitats within the river. Increased and decreased river stage lead to shifts in boundaries cr eating a balance between changing habitats, and at a finer scale, species organize according to micro sites (Ward and Tockner 2001). Spatial heterogeneity is maintained by dynamic factors operating at different temporal scales creating a patch work of bar s, islands, ponds, and riffles with differing turnover times. However, these processes appear to be limited in spring runs likely due to the relatively stable river stage and spring discharge. While the stability of the Rainbow Rivers submersed communit y, dominated by one species suggests an environment more spatially and temporally homogeneous than most lotic ecosystems, the heterogeneity in plant size a nd growth appear to represent a divergence of habitats within the submersed community similar to othe r lotic systems At an ecological scale, low biological diversity is predicted in ecosystems with low disturbance ( Connell 1978) such as spring runs, and when productivity is high, species survival is due to competitive exclusion (Kautsky 1988). In high ly productive ecosystems with high levels of disturbance species diversity is maximized (Huston 1979). Ecosystem expansion and contraction, observed with changes in river stage, discharge and water velocity cause disturbance to plant communities which res ults in successional shifts among the communities (Ward and Tockner 2001). Sagittaria kurzianas distribution is limited to spring runs in Florida, with the exception of a potential population in Guam (Godfrey and Wooten 1979), suggesting that S.
139 kurziana developed under a limited set of environmental conditions. Results here suggest that the S. kurziana community is spatial heterogeneous similar to other lotic systems but the ranges in variability are much smaller and therefore less easily observed. Sim ilar to other lotic systems, zonation of emergent plant communities can be observed along a water depth gradient in the Rainbow River, but differences are less apparent in the submersed communities. Small variations in water depth potentially result in ch anges in water velocity, epiphytic levels and subsequently light and nutrient availability. The extent of heterogeneity within spring run ecosystems and the ability of the dominant species to respond to these changes is critical to the long -term ecologica l stability. Future Research Needs Accurately defining responses of plant and algal communities to changing nutrient levels require a robust understanding of the natural heterogeneity and dynamic character of these ecosystems. Changes in growth rates r elated to shifting light availability, flow rates, and nutrient availability could lead to changes in the composition and abundance of primary producers. A lot of attention has been focused on increasing nitrate levels and the long -term effects on the spring ecosystems (Florida Springs Task Force 2000). The question of longterm nutrient storage and cycling needs to be further explored within these ecosystems. Primary producers store nitrogen entering the system from groundwater, but the interaction betw een water velocity and primary producers influence whether leaf biomass and algal biomass turnover is stored in the sediments, recycled by SAV, or exported downstream out of the system or to areas with lower energy. I t appears that the transport of epiphy tic, benthic, and suspended materials interact with sediments and benthic communities and may be an important component of nutrient cycling within the system. High water velocities increase export rates of nutrient from the system downstream
140 while decreas ed rates increase sedimentation and long term storage in the sediments. This should be placed in the context of minimal flow research for these ecosystems. It is hypothesized that changes in spring discharge, channel flow rates, and the subsequent effect on sedimentation, sediment type, and nutrient storage effect the structure and function of spring-fed ecosystems and should be a focal point of future research.
141 APPENDIX A ADDITIONAL DATA Table A 1. Chemical analysis of river sediments collected in the Rainbow River upstream of K.P. Hole and approximately 3 km from the headsprings in 2001. Analyses conducted by University of Florida IFAS soils testing laboratory. Mehlich 1 extraction method used for P, K, and Mg analyses. EPA Method 350.1 (modified) us ed for ammonium analyses. EPA Method 353.2 used for nitrate analyses. (+ SD) Site P K Mg pH NH4N NO3N (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) 1 100.45 49.32 204.4 7.93 26.34 2.11 (10.04) (4.08) (24.62) (0.35) (9.53) (0.68) 2 66.51 50.47 137.4 7.93 9.53 1.31 (5.42) (4.96) (7.92) (0.06) (18.84) (0.47) 3 269.60 4.95 34.65 7.37 8.05 0.69 (56.74) (3.23) (2.81) (0.06) (6.69) (0.17) 4 151.32 6.65 8.72 7.5 0 11.33 0.45 (51.37) (0.70) (0.97) (0.10) (5.45) (0.05) 5 342.27 7.12 59.01 7.87 7.93 0.48 (65.31) (1.71) (11.89) (0.35) (6.19) (0.08)
142 Table A 2. Mean dry weights for materials accumulated from the water column of the upper Rainbow River over 4 hours on September 23 and October 2, 2002. Materials accumulated onto a 0.5 x 0.5 m mesh screen with 3 mm wide openings. ( + SD) Site Algal Plant Water velocity Loading Dry weight weight(g) weight(g) (km/hr) rate (g/hr) ( g/L) September I 2.47 (0.52) 0.93 (0.55) 3.3 (0.4) 0.62 (0.13) 0.744 (0.898) II 3.00 (1.06) 0.21 (0.16) 2.2 (0.5) 0.75 (0.26) 1.435 (0.651) III 3.65 (0.68) 0.26 (0.26) 1.6 (0.4) 0.91 (0.17) 2.389 (0.318) October I 2.73 (0.96) 0.79 (0.40) 3.6 (0.2) 0.68 (0.24) 0.753 (0.252) II 2.20 (0.64) 0.18 (0.11) 2.0 (0.4) 0.55 (0.16) 1.103 (0.303) III 2.43 (1.24) 0.22 (0.18) 1.6 (0.2) 0.61 (0.31) 1.483 (0.677)
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154 BIOGRAPHICAL SKETCH Peter Sleszynski grew up in F lorida acquiring, an attachment to its natural resources and a desire to protect them. In pursuit of that goal, he received the Bachelor of Science degree in biology at Eckerd College in St. Petersburg. The degree represented a broad spectrum of microbio logy, botany, zoology, physiology and ecology. After working for a few years, he attended the University of Florida to receive the Master of Science degree in environmental engineering sciences. His research centered on the seed reserves of the cypress p rairies of Big Cypress National Preserve. It was associated with a project to develop restoration strategies for oil -exploration platforms. He then acquired practical experience working in the field, helping to manage different aquatic resources in north central Florida. While working, he began taking additional classes at the University of Florida, to strengthen his background. This led to his eventual return to the University of Florida to pursue his Doctor of Philosophy degree.