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Ecological Interactions in a Longleaf Pine-Native Woody Ornamental Intercropping System

Permanent Link: http://ufdc.ufl.edu/UFE0022713/00001

Material Information

Title: Ecological Interactions in a Longleaf Pine-Native Woody Ornamental Intercropping System
Physical Description: 1 online resource (74 p.)
Language: english
Creator: Hagan, Donald
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: agroforestry, competition, ecological, florida, forestry, interactions, intercropping, longleaf, native, ornamentals
Interdisciplinary Ecology -- Dissertations, Academic -- UF
Genre: Interdisciplinary Ecology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The cultivation of ornamentals to produce woody floral products (the fresh or dried stems that are used for decorative purposes) may be an attractive option for southeastern landowners looking to generate income from small landholdings. Since many shrubs native to the understory of the longleaf pine (Pinus palustris Mill.) ecosystem have market potential, one possibility is the intercropping of select species in the between-row spacing of young longleaf pine plantations. The development of a new intercropping system, however, is dependent upon an understanding of how the associated species interact in the context of a managed, mixed-species setting. Thus, the overall objective of this study was to evaluate how interspecific competition affects the productivity of three native shrub species when intercropped with longleaf pine. Field studies were conducted over the course of a single growing season in a 15-year-old longleaf pine plantation in Santa Rosa County, Florida, USA. In the first study (Chapter 2) we evaluated the effect of shading and competition for water on the three shrub species: American beautyberry (Callicarpa americana L.) (Verbenaceae), wax myrtle (Morella cerifera (L.) Small) (Myricaceae), and inkberry (Ilex glabra (L.) A.Gray) (Aquifoliaceae). In the second study (Chapter 3) we quantified the uptake and use-efficiency of applied 15N fertilizer in the same system. In both studies, the effect of intercropping was assessed via comparisons with a monoculture (treeless) treatment in an adjacent open field. Increased mortality and large reductions in growth suggests that resource limitations brought upon by interspecific competition with longleaf pine were severe in the intercropping treatment. Since all intercropped species allocated a greater percentage of their carbon to roots, it is likely that the most limiting resources were belowground. Indeed, through-canopy PAR transmittance was high (only I. glabra was adversely affected by shading), but soil moisture in the upper 20 cm in this treatment was significantly reduced. Stomatal conductance decreased with decreasing soil moisture for I. glabra and M. cerifera, but not for C. americana, indicating that this species is less susceptible to moisture stress. Fertilizer uptake and use-efficiency were lower in the intercropping treatment and were most likely due to the reductions in growth caused by water limitation. It is clear, based on the results of this study, that the effective management of competition is essential to the viability of a longleaf pine/native woody ornamental intercropping system. Conventional silvicultural practices such as thinning would be a logical first step, considering the apparent severity of competition in this system. Irrigation, trenching or the installation of root barriers have also proven effective at reducing belowground competition and should be considered in future studies.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Donald Hagan.
Thesis: Thesis (M.S.)--University of Florida, 2008.
Local: Adviser: Jose, Shibu.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022713:00001

Permanent Link: http://ufdc.ufl.edu/UFE0022713/00001

Material Information

Title: Ecological Interactions in a Longleaf Pine-Native Woody Ornamental Intercropping System
Physical Description: 1 online resource (74 p.)
Language: english
Creator: Hagan, Donald
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: agroforestry, competition, ecological, florida, forestry, interactions, intercropping, longleaf, native, ornamentals
Interdisciplinary Ecology -- Dissertations, Academic -- UF
Genre: Interdisciplinary Ecology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The cultivation of ornamentals to produce woody floral products (the fresh or dried stems that are used for decorative purposes) may be an attractive option for southeastern landowners looking to generate income from small landholdings. Since many shrubs native to the understory of the longleaf pine (Pinus palustris Mill.) ecosystem have market potential, one possibility is the intercropping of select species in the between-row spacing of young longleaf pine plantations. The development of a new intercropping system, however, is dependent upon an understanding of how the associated species interact in the context of a managed, mixed-species setting. Thus, the overall objective of this study was to evaluate how interspecific competition affects the productivity of three native shrub species when intercropped with longleaf pine. Field studies were conducted over the course of a single growing season in a 15-year-old longleaf pine plantation in Santa Rosa County, Florida, USA. In the first study (Chapter 2) we evaluated the effect of shading and competition for water on the three shrub species: American beautyberry (Callicarpa americana L.) (Verbenaceae), wax myrtle (Morella cerifera (L.) Small) (Myricaceae), and inkberry (Ilex glabra (L.) A.Gray) (Aquifoliaceae). In the second study (Chapter 3) we quantified the uptake and use-efficiency of applied 15N fertilizer in the same system. In both studies, the effect of intercropping was assessed via comparisons with a monoculture (treeless) treatment in an adjacent open field. Increased mortality and large reductions in growth suggests that resource limitations brought upon by interspecific competition with longleaf pine were severe in the intercropping treatment. Since all intercropped species allocated a greater percentage of their carbon to roots, it is likely that the most limiting resources were belowground. Indeed, through-canopy PAR transmittance was high (only I. glabra was adversely affected by shading), but soil moisture in the upper 20 cm in this treatment was significantly reduced. Stomatal conductance decreased with decreasing soil moisture for I. glabra and M. cerifera, but not for C. americana, indicating that this species is less susceptible to moisture stress. Fertilizer uptake and use-efficiency were lower in the intercropping treatment and were most likely due to the reductions in growth caused by water limitation. It is clear, based on the results of this study, that the effective management of competition is essential to the viability of a longleaf pine/native woody ornamental intercropping system. Conventional silvicultural practices such as thinning would be a logical first step, considering the apparent severity of competition in this system. Irrigation, trenching or the installation of root barriers have also proven effective at reducing belowground competition and should be considered in future studies.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Donald Hagan.
Thesis: Thesis (M.S.)--University of Florida, 2008.
Local: Adviser: Jose, Shibu.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022713:00001


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1 ECOLOGICAL INTERA C TIONS IN A LONGLEAF PINE NATIVE WOODY ORNAMENTAL INTERCROPPING SYSTEM By DONALD LEE HAGAN A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2008

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2 2008 Donald Lee Hagan

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3 To my family.

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4 ACKNOWLEDGMENTS I would like to thank my committee chair and cochair Shibu Jose and Mack Thetfo rd for securing the funding for my research and for their support and guidance over the past two years I would also like to thank my 3 rd committee member, Kimberly Bohn, for her assistance with my statistical analyses and for providing helpful editorial feedback I am very thankful for the assistance provided by the staff at the West Florida Research and Education Center and Jay Research Farm particularly Marti Occhipinti, Barry Ballard, Melvin Gramke and Doug Hatfield. The efforts of Jimmie Jarratt, Gerardo Celis, Pedram Daneshgar, Michelle Mack Grace Crummer and Meghan Brennan, who contributed in various capacities, are also greatly appreciated. Above all, I thank my family, especially my wife Thea, for their love and support.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ ........... 4 LIST OF TABLES ................................ ................................ ................................ ...................... 7 LIST OF FIGURES ................................ ................................ ................................ .................... 8 ABSTRACT ................................ ................................ ................................ ............................... 9 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ ............. 11 Introduction ................................ ................................ ................................ ........................ 11 The Longleaf Pine Ecosystem: Past and Present ................................ ......................... 11 Is Intercropping with Woody Ornamentals an Option? ................................ ................ 12 Ecolog ical Interactions in Mixed Species Systems ................................ ....................... 13 Objectives and Hypotheses ................................ ................................ ................................ 15 2 PRODUCTION PHYSIOLOGY OF THREE NATIVE SHRUBS INTERC ROPPED IN A YOUNG LONGLEAF PINE PLANTATION ................................ ................................ 16 Introduction ................................ ................................ ................................ ........................ 16 Materials and Methods ................................ ................................ ................................ ....... 18 Study Site and Experimental Design ................................ ................................ ............ 18 Fertilizer Application and Plot Maintenance ................................ ................................ 19 Light Transmittance and Soil Water Content ................................ ............................... 20 Biomass, Chlorophyll and Leaf Area Sampling ................................ ........................... 20 Pine Root Length Density ................................ ................................ ............................ 21 Gas Exchange Measurements ................................ ................................ ...................... 21 Tree Growth ................................ ................................ ................................ ................ 22 Data Analysis ................................ ................................ ................................ .............. 22 Results ................................ ................................ ................................ ............................... 23 Light Transmittance and Soil Water Content ................................ ............................... 23 Survival, Growth and Biomass Allocati on Patterns ................................ ...................... 24 Photosynthesis and Stomatal Conductance ................................ ................................ .. 24 Tree Growth and Mortality ................................ ................................ .......................... 25 Discussion ................................ ................................ ................................ .......................... 25 Conclusions ................................ ................................ ................................ ........................ 29 3 PARTITIONING OF APPLIED 15 N FERTILIZER IN A LONGLEAF PINE NATIVE WOODY ORN AMENTAL INTERCROPPING SYSTEM ................................ ................. 42 Introduction ................................ ................................ ................................ ........................ 42 Materials and Methods ................................ ................................ ................................ ....... 44

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6 Study Site and Experimental Design ................................ ................................ ............ 44 Fertilizer Application and Plot Maintenance ................................ ................................ 45 Harvest and Sampling ................................ ................................ ................................ 45 Data Analysis ................................ ................................ ................................ .............. 47 Results ................................ ................................ ................................ ............................... 47 Biomass ................................ ................................ ................................ ...................... 4 7 Tissue Nitrogen Concentrations and Content ................................ ............................... 48 Recovery of Fertilizer N in Soil ................................ ................................ ................... 49 Fertilizer N and Total N in Pine Foliage ................................ ................................ ...... 50 Discussion ................................ ................................ ................................ .......................... 50 Conclusions ................................ ................................ ................................ ........................ 54 4 SUMMAR Y AND CONCLUSIONS ................................ ................................ ................. 62 APPENDIX A MARKETABLE YIELD ................................ ................................ ................................ .... 65 B SOIL PROPERTIES ................................ ................................ ................................ .......... 66 LIST OF REFERENCES ................................ ................................ ................................ .......... 68 BIOGRAPHICAL SKETCH ................................ ................................ ................................ ..... 74

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7 LIST OF TABLES Table page 2 1 Su rvival (%) by species treatment combination ................................ .......................... 30 2 2 Leaf area, specific leaf area (SLA) and chlorophyll concentration (Chl). ........................ 31 2 3 Parameter estimate s from the photosynthesis model ................................ ...................... 32 3 1 Leaf stem, root and total biomass ................................ ................................ ................. 56 A 1 Marketable yield ................................ ................................ ................................ ............ 65 B 1 Soil properties ................................ ................................ ................................ ............... 67

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8 LIST OF FIGURES Figure page 2 1 Mean transmittance (by month) o f photosynthetically active radiation (PAR). ............... 33 2 2 Typical patterns of incident PAR over the course of a cloud f ree day in June 2007 ....... 34 2 3 Soil water potential ( k Pa) in the two treatments at depths of 20 cm and 50 cm. .............. 35 2 4 Mean volumetric water content (%) at 0, 60 and 120 cm from shrub base. ..................... 36 2 5 Above and belowground biomass ................................ ................................ ................. 37 2 6 Mean root length density (RLD) for longleaf pine at three distances from a tree (40, 8 0 and 120 cm) and at three depths (30, 60 and 90 cm) ................................ .................. 38 2 7 Photosynthetic light response curves fitted using parameter estimates obtained from the nonlinear Mitscherlich model. ................................ ................................ .................. 39 2 8 Treatment comparisons (by species) of biweekly incident photosynthesis measurements. ................................ ................................ ................................ ............... 40 2 9 Relationshi p between soil water potential and stomatal conduc tance ............................. 41 3 1 Mean nitrogen concentration (by tissue) .. ................................ ................................ ...... 57 3 2 Total nitrogen content (by tissue) ................................ ................................ .................. 58 3 3 Percent nitrogen derived from fertilizer (NDF) (by tissue). ................................ ............ 59 3 4 Percent utilization of fertilizer nitrogen (UFN) (by tissue) ................................ ............ 60 3 5 Recovery of fertilizer nitrogen in soil (RFNsoil) at three depths (30, 60 and 90 cm). ...... 61

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9 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science ECOLOGICAL INTERACTIONS IN A LONGLEAF PINE NATIVE WOODY ORNAMENTAL INTERCROPPING SYSTEM By Donald Lee Hagan August 2008 Chair: Shibu Jose Major: Interdisciplina ry Ecology The cultivation of ornamentals to produce woody floral products the fresh or dried stems that are used for decorative purposes may be an attractive option for southeastern landowners looking to generate income from small landholdings. Sinc e many shrubs native to the understory of the longleaf pine ( Pinus palustris Mill.) ecosystem have market potential, one possibility is the intercropping of select species in the between row spacing of young longleaf pine plantations. The development of a new intercropping system, however, is dependent upon an understanding of how the associated species interact in the context of a managed, mixed species setting. Thus, the overall objective of this study was to evaluate how interspecific competition affec ts the productivity of three native shrub species when intercropped with longleaf pine Field studies were conducted over the course of a single growing season in a 15 year old longleaf pine plantation in Santa Rosa County, Florida, USA. In the first st udy (Chapter 2) we evaluated the effect of shadi ng and competition for water on the three shrub species : American beautyberry ( Callicarpa americana L.) ( Verbenaceae ), wax myrtle ( Morella cerifera ( L.) Small) (Myricaceae), and inkberry ( Ilex glabra (L.) A. Gray) (Aquifoliaceae) In the second study (Chapter 3) we quantified the uptake and use efficiency of applied 15 N fertilizer in the same system In both studies, t he effect of intercropping was assessed via comparisons with a

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10 monoculture (treeless) treatm ent in an adjacent open field. I ncreased mortality and large reductions in growth suggests that resource limitations brought upon by interspecific competition with longleaf pine were severe in the intercropping treatment Since all intercropped species allocated a greater percentage of their carbon to roots, it is likely that the most limiting resources were belowground. Indeed, through canopy PAR transmittance was high (only I. glabra was adversely affected by shading), but soil moisture in the upper 20 cm in this treatment was significantly reduced. Stomatal conductance decreased with decreasing soil moisture for I. glabra and M. cerifera but not for C. americana indicating that this species is less susceptible to moisture stres s. Fertilizer uptak e and use efficiency were lower in the intercropping treatment and were most likely due to the reductions in growth caused by water limitation. It is clear, based on the results of this study, that the effective management of competition is essential to the viability of a longleaf pine/native woody ornamental intercropping system. Conventional silvicultural practices such as thinning would be a logical first step, considering the apparent severity of competition in this system. Irrigation, trenching or the installation of root barriers have also proven effective at reducing belowground competition and should be considered in future studies.

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11 CHAPTER 1 INTRODUCTION Introduction Concerns over the ecological and economic sustainability of conventional f orestry practices have led to a renewed interest in alternative production strategies (Franklin 1989). This is especially true for small landowners who, due to economies of scale, are increasingly disadvantaged in the competitive global marketplace (Rosse t 2000). In order to stay viable, they will likely have to adopt new management techniques and seek out markets for niche products that are not well suited for large scale production. The development of a longleaf pine native woody ornamental intercrop ping system is one such possibility Such a system would not only generate income, it would also provide an incentive for landowners to reintroduce native understory species, thereby enhancing the biodiversity of plantation forests (Hartley 2002). Th e Longleaf Pine Ecosystem: Past and Present Encompassing some 37 million hectares and a range of sites from moist flatwoods to xeric sandhills, the longleaf pine ecosystem was once the dominant forest type of the southeastern coast al plain (Jose et al. 20 06). Frequent low intensity fires and other disturbances kept this ecosystem in a perpetual sub climax state, effectively excluding late successional hardwood species and maintaining a nearly monospecific overstory of longleaf pine. The wide spacing and open, irregular canopy that were characteristic of this ecosystem allowed for high light transmittance which, in concert with frequent disturbance, sustained a diverse groundlayer of early successional grasses, forbs and shrubs (Walker and Silletti 2006). Human activities, however, have reduced longleaf pine forest cover to approximately 1 million hectares a reduction which, in terms of total area, represents a loss of over 97%. This decline began in the late 1800s with the near complete exploitation of old growth forests for timber and continued

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12 through the 1900s with the exclusion of fire and the conversion of forestlands to agricultural fields and to plantations of faster growing timber and pulpwood species such as slash ( Pinus elliottii Engelm.) and loblolly pine ( Pinus taeda L.). Today, most of the remaining longleaf pine acreage is found in protected forests or in degraded remnants on private land (Outcalt and Sheffield 1996). While much of the original longleaf pine forest has been lost, the inter est in longleaf pine silviculture has gro wn in recent years (Hainds 2002 ; Guldin 2006). This is primarily due to the strength of the market for poles and high quality sawtimber (Kush et al. 2006) and the fact that longleaf pine is less susceptible than ot her southern pines to damage from fire, fusiform rust or bark beetles (Hainds 2002 ). The downside to this species, however, is its slow growth rate. While slash and loblolly pine can be harvested within 20 years, longleaf pine may take 70 or more years t o reach valuable sawtimber sizes ( Borders and Bailey 2001 ). Longleaf pine silviculture, at least in the conventional sense, therefore entails a multi generational commitment, while providing little opportunity for income generation between final harvests Is Intercropping with Woody Ornamentals an Option ? In the eyes of many landowners, the need for economic returns in the short term overrides the potential benefits of a long term investment in longleaf pine (Alavalapati et al. 2002). It would be a more a ttractive option, however, if it were possible to generate income between thinnings perhaps by incorporating a short rotation crop into the between row spacing of the site. One exciting possibility is the production of specialty products for the floral i ndustry. This growing industry has consistently identified new product research as one of its top priorities, with particular emphasis o n woody florals the fresh or dried ornamental stems used for decorative purposes such as wreaths and flower arrangeme nts (Stamps et al. 1998 ; Venrick 2003). Considering the diversity of this market and its potential for growth, any species with a

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13 colorful or unique stem, bark, flower or seedpod could become a woody floral product (Josiah et al. 2004). Native species wo uld be a logical choice for a longleaf pine intercropping system, given the abundance of woody ornamentals indigenous to the longleaf pine understory that meet the above criteria. Indeed, many species from genera including Ilex Vaccinium Morella Lyonia Callicarpa Gaylussacia and Diospyros are likely either already established in plantations due to previous unsuccessful attempts at elimination (Hartley 2002) or would be easily obtainable from local distributors or other sources. Ecological Interactions in Mixed Species Systems Mixed species systems such as agroforestry and intercropping have proven to be effective at generating multiple income streams from a single plot of land while providing environmental benefits such as soil and water improvement (G arret and Buck 1997 ; Alavalapati et al. 2004; Nair and Graetz 2004). By increasing resource use efficiency, a well designed mixed species system can also be more productive per unit land area than a monoculture (Sullivan 2003 ; Jose et al. 2006) Unfortun ately, mixed species cropping, which is commonly practiced in the tropics, has not been widely adopted in the temperate zone. This is largely due to the scarcity of available information on how best to design, implement and manage temperate systems ( Jose and Gordon 2008 ) As multi strata, multi species cropping arrangements, these systems are as analogous to natural ecosystems as they are to conventional cropping systems. As such, the development of a new system is dependent on an understanding of how int eractions between component species affect productivity (Garret and Bu ck 1997; Gillespie et al. 2000) Interspecific interactions in mixed species systems occur both above and belowground as intercropped species attempt to capture resources. These interact ions are typically classified as either yield enhancing (facilitative) or yield depleting (competitive), with the net balance of the two ultimately determining the productivity of the system. Of particular importance are the

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14 competitive interactions, whic h occur when there is overlap between the spatiotemporal resource requirements and/or physical structures of the component species (Jose et al. 2006). Shading is arguably the most important of aboveground interactions, as it can greatly impact the producti vity of an intercropped species by reducing both the quantity and quality of photosynthetically active radiation (PAR) available for interception (Sa et al. 1999). The degree of shading present in a mixed species system varies by season and time of day an d depends on the height and canopy characteristics of the overstory species. The effect of a reduction in PAR on the photosynthesis of an understory species depends largely on its inherent shade tolerance, CO 2 uptake (A max (Boardman 1977). Individual species, however, can adapt to a range of light levels by reducing or increasing their photosynthetic rate accord ingly. Shade species (or shade acclimated individuals), to an extent, make up for their reduced A max by increasing their photosynthetic efficiency at lower light levels. Plants with the C 3 photosynthetic pathway ( i.e., most woody plants) typically are better adapted to shaded conditions than are C 4 plants (Jose et al. 2004 ; Kho 2007). rooting habit. Thus belowground interactions, particularly competition for water and nutrients, occur when the root systems of the intercropped species exp loit the same soil horizons. Ideally a mixed species system would have a stratified rhizosphere, in which the deep rooting system of one species underpinned the shallow rooting system of the other. Belowground competition, however, is difficult to preven t, as most plants (even deeply rooted trees such as pines) have a large portion of their fine roots in the nutrient rich uppermost 30 cm of the soil profile. While root plasticity as a response to interspecific competition has been observed (Wanvestrout e t al.

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15 2004) inherent differences in root architectures and temporal uptake patterns should also be considered during species selection, system design and management. This helps to maximize complementarity between species (Schroth and Zech 1995) and improv e resource use efficiency. reducing the amount of nutrients lost to leach ing (van Noordwijk et al. 1996; Allen et al. 2004a). Objectives and H ypotheses Thi s study was conducted to elucidate how above and belowground interspecific interactions affect the productivity of three woody ornamentals intercropped into the between row spacing of a 15 year old longleaf pine plantation in the Florida Panhandle. Selec ted species were American beautyberry ( Callicarpa americana L. ) ( Verbenaceae ), wax myrtle ( Morella cerifera ( L. ) Small ) (Myricaceae) and inkberry ( Ilex glabra (L.) A. Gray ) (Aquifoliaceae)) The specific objectives of this study were: 1. Determine how PAR tra nsmittance and soil water content vary in monoculture and intercropping systems 2. Determine growth and biomass allocation patterns of the three shrub species with respect to shading and belowground competition from longleaf pine trees 3. Quantify the effect o f above and belowground competition on leaf level physiological processes for the three shrub species. 4. Compare the fate and use efficiency of applied 15 N labeled fertilizer in monoculture and intercropping systems. It was hypothesized that, as species na tive to the longleaf pine understory, all plants would be minimally affected by the shaded conditions of an intercropping system. Interspecific competition was expected to encourage the shrubs to derive a greater percentage of their nitrogen from fertiliz er and would leave less fertilizer remaining in the soil at the end of the growing season. Reductions in growth and nitrogen uptake, if observed, would likely be due to interspecific competition for water.

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16 CHAPTER 2 PRODUCTION PHYSIOLOG Y OF THREE NATIVE S HRUBS INTERCROPPED I N A YOUNG LONGLEAF PINE PLANTATION Introduction The interest in alternative cropping practices such as intercropping has been increasing in the United States over the years. However, the knowledge base required for the proper design an d implementation of such systems is limited (Jose and Gordon 2008). This is due to the fact that the science and practice of temperate intercropping is relatively new, and that these systems, with their potential for interspecific interactions, are much m ore complex than conventional monocultures (Garret and Buck 1997; Gillespie et al. 2000). The productivity of a mixed species cropping system is ultimately determined by the type and extent of interactions that occur within it (Jose et al. 2006). In the broadest sense, these interactions ca n be classified as either competitive or facilitative and divided into two main categories: aboveg round and be lowground (Ong et al. 1991; Schroth 1999; Jose et al. 2004). Paramount among aboveground interactions is s hading (Boardman 1977), which, depending on the degree of canopy closure, the shade tolerance of the understory crop, and interactions with below canopy microclimate, can have either a competitive or facilitative effect (Chirko et al. 1996 ; Jose et al. 200 4). The typical leaf level response to shading is a reduction in photosynthesis tolerance but this reduction in CO 2 uptake may be offset by increased photosynthetic efficiency a t lower light levels. Plants also adapt to reduced light conditions by increasing their specific leaf area (leaf area per unit leaf mass) or by increasing carbon allocation to aboveground tissues (Chapin et al. 2002 ). The ability to quantify the relations hip between shading and plant productivity is key to selecting the species that are best adapted to reduced light conditions and for developing an understanding of how best to manage mixed species system.

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17 Resource limitations that arise due to belowground competition can result in an adjustment of carbon allocation patterns to favor root development over shoot development. The ratio of root biomass to shoot biomass is, therefore, a helpful diagnostic tool for determining whether aboveground or belowground competition is most prevalent in a given system (Chapin et al. 2002). Competition for water can cause loss of turgor and induce stomatal closure (Kho 2007). This reduces photosynthetic efficiency resulting in decreased carbon uptake. Competition for wa ter can also affect the mobility and thus the availability of soil nutrients (Baldwin 1975) which can further hinder photosynthesis and tissue development. Tissue analyses, particularly those that assess foliar nitrogen and chlorophyll concentrations, ar e effective means of quantifying plant nutrit ional status (Porro et al. 2000; Netto et al. 2005). As such, they are also useful in assessments of belowground interspecific competition in mixed species systems (Caton et al. 2003). Instantaneous gas exchan ge measurements correlated with environmental parameters such as soil moisture can also be good indicators of belowground competition in a system (Miller and Pallardy 2001), but have not been extensively empl oyed in field studies. The inherent complexity o f intercropping systems makes them more analogous to natural ecosystems than to conventional cropping systems. The most sustainable and productive intercropping systems, therefore, are often those that are modeled after native plant communities (Ewel 1999 ). Since many shrubs native to the understory of the longleaf pine ( Pinus palustris Mill.) ecosystem have market potential as woody floral products, one exciting possibility is the intercropping of select species in the between row spacing of young longle af pine plantations. Such a system would provide yearly income, which would supplement the long term returns from longleaf pine timber sales. The development of a longleaf pine native woody ornamental

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18 intercropping system, however, is dependent upon an u nderstanding of how the trees and shrubs interact in the context of a managed, mixed species setting. Thus, the overall objective of this study was to evaluate how above and belowground competition affects the productivity of three native shrub species : A merican beautyberry ( Callicarpa americana L.) ( Verbenaceae ), wax myrtle ( Morella cerifera ( L.) Small) (Myricaceae), and inkberry ( Ilex glabra (L.) A.Gray) (Aquifoliaceae) in such a system. The three specific objectives were: 1. Determine how PAR transmittanc e and soil water content vary in monoculture and intercropping system s. 2. Determine growth and biomass allocation patterns of the three shrub species with respect to shading and belowground competition from longleaf pine trees 3. Quantify the effect of above a nd belowground competition on leaf level physiological processes for the three shrub species Species native to the understory of the longleaf pine ecosystem were chosen for this study. It was hypothesized, therefore, that all would be well adapted to the shaded conditions of an intercropping system. Reductions in growth and yield, if observed, would likely be due to belowground competition with longleaf pine. Materials and Methods Study S ite and E xperimental D esign This study was conducted on a private 1 5 year old longleaf pine plantation in Santa Rosa with mild winters and hot, humid summers. Mean annual precipitation is 1645 mm. The soil is an ultisol and classified as a Fuquay sand (loamy, kaolinitic, thermic Arenic Plinthic Kandiudult), a deep, well drained sand over loamy marin e or fluviomarine deposits Trees in the study site were uniformly spaced, with approximately 3 meters between rows and 1.5 me ters between stems within the row. Mean diameter at breast height (DBH) at the

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19 initiation of the study (December 2005) was 8.3 cm. Mean basal area was 14 m 2 ha 1 In December 2005, containerized native woody ornamental shrubs identified as having market potential were incorporated into the existing between row spacing of the site, and as an equivalently spaced monoculture treatment in an adjacent open field. Selected species were American beautyberry ( Callicarpa americana ), wax myrtle ( Morella cerifera ) and inkberry ( Ilex glabra ). Shrubs were given a year for proper establishment with dead or dying shrubs being replaced in the winter of 2006, prior to the initiation of the study. The effect of intercropping on shrub productivity in this system was ass essed via comparisons with the monoculture treatment. The trial was laid out as a split plot completely randomized design with treatment (monoculture or intercropped) as the whole plot factor and shrub species as the split plot factor. There were four re plications, each consisting of six subplots (one for each species by treatment combination) with eight shrubs each. Subplots were 2 alleys wide (or equivalent distance in the monoculture) with shrubs planted in two rows of four at a spacing of 3 meters. As a control, four subplots of the same dimensions were established in the plantation and not planted with shrubs. Fertilizer A pplication and Plot M aintenance To simulate the effect of a slow release fertilizer, three applications of ammonium sulfate ferti lizer (NH 4 ) 2 SO 4 (21% N) each at a rate of 146.5 kg N ha 1 were uniformly hand applied at approximately 60 day intervals in a circular area of 325 cm 2 at the base of each shrub. The first application was on 21 March 2007, shortly after bud swelling and lea f emergence were first observed. Pesticide and herbicide application, along with manual weed removal, were conducted as needed throughout the growing season. Plots were non irrigated, but supplemental water was uniformly provided to all shrubs when at le ast 20% showed signs of extreme drought stress.

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20 This occurred on three occasions during a particularly dry period from mid May to early June 2007. Light Transmittance and Soil Water Content Two Hobo quantum sensors, wired to Micro Station data loggers (O nset Computer Corporation, Bourne, MA, USA) were installed at a height of 105 cm above ground level in each of the two experimental treatments (intercropping or monoculture). Automated measurements of photosynthetically active radiation (PAR) were taken a t 30 minute intervals from May 2007 until October 2007. Soil water potential ( k Pa ) measurements were taken in conjunction with gas exchange measurements using tensiometers (Soil Measurement Systems, Tucson, Arizona, USA), set at depths of 20 and 50 cm a t 20 cm from the base of one shrub (or shrubless control) per sub plot. Biweekly m easurements were taken from May 2007 until October 2007 Volumetric s oil water content was measured using a 12 cm electronic time domain reflectometry (TDR) probe (Campbell Scientific Inc. Logan, UT, USA). Readings were taken for each shrub at three distances in the intercropping treatment (at the base of the tree, midway between tree and alley center and at alley center), and equivalent distances in monoculture plot s Mea surements were taken at monthly intervals, beginning shortly after leaf emergence in early April and continuing until shrubs were harvested in September and October. Biomass, C hlorophyll and L eaf A rea Sampling In order to shed light on the physiological pr ocesses that affect growth and yield in this system, two shrubs per species plot combination (48 total) were selected for detailed analyses. For these shrubs, 20 leaves were randomly selected and analyzed for chlorophyll concentration with a hand held SPA D 502 meter (Minolta Corp., Japan). Stem subsamples from each of the four cardinal directions were then harvested and separated into stem and leaf and (when

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21 applicable) fruit components. The remaining aboveground biomass was then harvested and all sample s were transported to the lab where they were separately weighed. In the lab, subsample leaf area was determined on fresh leaves using a LICOR Li 3100C leaf area meter (Lincoln, Nebraska, USA). Belowground biomass of the same 48 shrubs was harvested lat er For this, a hole with a 70 cm radius centered on each shrub was excavated and roots were separated from th ose of non target species in the field on the basis of texture and color. Further separation was done in the lab, where roots were washed with w ater over a 1 mm mesh screen to remove soil and debris. All tissu es were dried separately at 70 C for 48 hours. Specific leaf area (SLA) was determined by dividing LA by dry leaf weight. The ratio of leaf area to subsample biomass (g) was multiplied by the aboveground dry biomass of the respective shrub to obtain an estimate of whole plant LA. Dry weights were used to determine root:shoot biomass ratio for each shrub. Pine Root Length Density Soil cores (8 x 90 cm) were taken in control (shrubless) p lots at 40, 80 and 120 cm from a tree, divided into 30 cm sections and sifted to separate pine roots from soil. Root length was determined by using the line intercept method described by Tennant (1975) and divided by soil core volume to determine root len gth density (RLD). Sampling was conducted after the growing season ended (November 2007) to prevent interference with water and nutrient uptake. Gas Exchange Measurements A LICOR 6400 (Lincoln, Nebraska, USA) infrared gas analyzer (IRGA) was used to creat e photosynthetic light response curves during the peak of the growing season (July 2007). These were done using the internal LED light source at 8 pre set levels of descending PAR (1600, 1000, 700, 400, 100, 50, 25 and 0 mol cm 2 sec 1 ) on 6 plants per sp ecies by treatment 2 s 1 and set to control

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22 chamber CO 2 concentration at 400 ppm. An effort was made to maintain chamber humidity as close as possible to ambient levels. Measurements were t aken over a 4 day period during which several rainfall events maintained soil moisture at or near field capacity. This, it was assumed, would ensure that water stress would not be a major determinant of photosynthesis, thereby helping to isolate light lev el as the variable of interest. Curves were fit using a nonlinear Mitscherlich model, as described by Peek et al. (2002). The LICOR 6400 was also used to measure net photosynthesis ( A 2 m 2 s 1 ) and stomatal conductance ( g ) (mm m 2 s 1 ) of two shrubs per species plot combination (48 total). Measurements were taken twice monthly on clear days between 10:00 and 1:00, beginning with the full expansion of new leaves in late May 2007 and continuing until the latter part of the growing season in September 2007. No measurements were taken within 48 hours of any significant rainfall event. The same plants were used for each set of measurements to facilitate repeated measures statis tical analyses. The IRGA was operated in a survey mode with a transparent 0.785 cm 2 2 s 1 and with reference CO 2 set at 400 ppm. Tree Growth Diameter at breast height (DBH) was measured in February of 2006, 2007 and 2008 on all trees in the intercropping plots to monitor annual increment al growth Data A nalysis SPAD units were converted to chlorophyll concentration ( g Chl cm 2 ) as described by Markwell et al. (1995). Data for biomass root length density, specific leaf area and chlorophyll concentration were analyzed using a two way analysis of var iance (ANOVA) procedure in JMP IN 5.1 for Windows (SAS Institute, Cary, NC, USA). Time integrated measurements (gas exchange, soil moisture and PAR) were analyzed with a repeated measures ANOVA using the

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23 PROC MIXED procedure in SAS 9.1 (SAS institute, Car y, NC, USA). With the exception of RLD, all analyses were conducted within the framework of a split plot, completely randomized experimental design. Specifically, treatment effects (intercropping vs. monoculture) were compared for each shrub species for each variable of interest. Log transformations were performed when necessary to improve data normality. Differences between m eans were considered significant at comparisons. Results Light Transmittance and Soil Water Content Overall, PAR transmittance below the pine canopy averaged 57.7% over the 6 month time period from May to October 2007 The highest transmittance levels (64.8 and 62.0%) were observed in June and July, respectively. Values for other months were significantly lower with August being the lowest at 52.4% (Figure 2 1). Significant variability was observed on a daily time scale, with pe riods of near 100% transmittance alternating with periods where transmittance was greatly reduced by shading (Figure 2 2). Soil water potential varied by date ( P < 0.0001) and depth ( P < 0.0001) and there was a significant treatment by depth interaction ( P = 0.0165). At 20 cm, soil moisture was generally lower in the intercropping treatment, with the difference becoming statistically significant in late August. At 50 cm, soil moisture was significantly higher in the intercropping treatment in late June an d in early September (Figure 2 3). Volumetric water content showed significant variation by date ( P < 0.0001) and distance from shrub base ( P < 0.0001) and there was an interaction between treatment and distance ( P < 0.0001) (Figure 2 4).

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24 Survival, Growth and Biomass Allocation Patterns Mortality was higher for all shrub species in the intercropping treatment particularly so for C. americana (Table 2 1). Growth was also affected, with reductions in biomass in the intercropping treatment of 75 .5 % ( P = 0.0 030), 50.6 % ( P = 0.0200), and 68.7 % ( P = 0.0012) for C americana M cerifera and I glabra respectively. Differences in biomass allocation patterns were also observed, with root:shoot ratios being higher by 14 % for C. americana ( P < 0.0 001), 6 % for M. cerifera ( P = 0.0020) and 11 % for I. glabra ( P < 0.0001) in the intercropping treatment (Figure 2 5). Overall, leaf area was higher in the monoculture, with reductions of 81.4 % ( P = 0.0136) and 78.3 % ( P = 0.0022) observed in the intercropping treatment for C. americana and I. glabra respectively. SLA was significantly higher for all species in the intercropping treatment. Observed differences were 18.0% for C. americana ( P = 0.0303) 14.2% for M. cerifera ( P = 0.0021) and 12.4% for I. glabra ( P = 0.0 449) Chlorophyll concentrations were 42.6% lower for C. americana in the intercropping treatment ( P = 0.0114) but there were no treatment effects for M. cerifera or I. glabra ( Table 2 2 ) Root length density for longleaf pine varied by distance in the alleyway ( P = 0.01) and depth ( P < 0.0001). Values decreased with increasing depth, and were highest (at all depths) at 120 cm from the trees a distance which coincides with the middle of the alley (Figure 2 6). In total, 81.1% of longleaf pine fine r oots were confined to the uppermost 30 cm of the soil profile. Photosynthesis and Stomatal Conductance Significant treatment differences in net photosynthesis (A max ) were not observed for C. americana or M. cerifera A significant reduction in A max, howev er, was observed in the intercropping treatment for I. glabra Quantum yield (A qe ) and light compensation point (LCP) values did not differ between species or treatments (Table 2 3 and Figure 2 7). Incident

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25 photosynthesis varied significantly by species ( P < 0.0001), treatment ( P = 0.0042) and date ( P < 0.0001), and there were significant species*treatment and species*treatment*date interactions ( P = 0.0218 and 0.0014, respectively) (Figure 2 8). Both M. cerifera and I. glabra had positive relationsh ips between stomatal conductance and soil water potential ( Figure 2 9). Tree Growth and Mortality Annual increment for longleaf pines in the study plots was 0.24 cm in 2006 and 0.01 cm in 2007. Species (shrub) effects were not observed between species or between species and control. There was no mortality in 2006 and 2% mortality in 2007 (7 trees). Discussion Contrary to our hypothesis that shade tolerant native understory species would perform well under longleaf pine trees, we observed increased mo rtality and reduced growth for all three shrub species in the intercropping system. Apparently, competition with longleaf pine was a major determinant of shrub productivity in this treatment (Jose et al. 2006). Despite supplemental fertilization, annual incremental growth of longleaf pine also decreased substantially, suggesting that competition was a major stressor, even on the deeply rooted, 15 year old trees. This competition may have been magnified by water stress, as total rain fall for March Septe mber 2007, at 55.2 cm, was only 47.1 % of the 44 year average (NOAA National Climate Data Center). While instantaneous gas exchange measurements at the leaf level do not adequately account for the factors ( e.g. carbon allocation patterns, temporal variabi lity in CO 2 uptake, etc .) that affect plant growth and mortality (Givnish 1988), they are useful for comparing instantaneous rates of CO 2 uptake un der different field conditions The typical photosynthetic response of plants grown under reduced light condi tions is a reduction of light saturated photosynthesis (A max ) and light compensation point (LCP) and an increase in quantum yield

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26 (A qe ). For light demanding plants, the reduction in A max can be substantial and result in significant decreases in carbon upt ake. This is particularly true for plants with the C 4 photosynthetic pathway, which have a near linear relationship between photosynthetic rates and PAR interception. C 3 plants, however, typically reach A max at 25 50% of full sunlight a characteristic which presumably makes them better adapted to reduced light conditions (Jose et al. 2004). For shade tolerant or shade demanding C 3 plants, reductions in A max are often minimal (compared to plants grown in full sun) and may be compensated for, in terms of carbon uptake, by the decreased LCP, increased A qe and an increase in photosynthesis p er unit leaf mass (Bazzaz 1979; Poorter and Evans 1998; Niinemets and Tenhunen 1999). Observed patterns of PAR transmittance were comparable to those reco rded in longl eaf pine forests Light transmittance estimates reported by Battaglia et al. (2003), for example were between 40 and 78 % with variability on a daily time scale largely attributed to the irregular canopy structure of the overstory We observed an average transmittance of 57.7% in the intercropping treatment with similar daily variability As C 3 plants native to the partial shade of the longleaf pine ecosystem, C. americana M. cerifera and I. glabra were assumed to be well adapted to these conditions. Photosynthetic curves created for C. americana and M. cerifera under field capacity largely supported this assumption, as neither species had a significantly reduced A max in the intercropping treatment. There was, however, a significant reduction in A max for I. glabra suggesting a lower level of shade tolerance for this species. It should be emphasized, however, that all species had higher specific leaf area in the intercropping treatment a typical response to shading (Chapin et al. 2002). Furthermore observed differences in total leaf area indicate that light capture, and thus whole plant carbon uptake, was reduced for all species (Givnish 1988). Quantum yield and light compensation point did not vary between

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27 treatments. Ambient photosynthetic rate s for all species were consistently lower than their respective A max values. This is not unusual, as A max is a potential maximum level that is rarely attained due to resource limitations and/or environmental constraints (Bazzaz 1996). The fact that all species allocated a greater % of carbon to roots than to shoots supports the argument that shading was not a major determinant of productivity in the intercropping treatment (Chapin et al. 2002). Belowground competitive vectors therefore, are likely more responsible for the observed differences between treatments. Studies have shown that longleaf pine, once established, develops an extensive shallow lateral root system, often extending well beyond the area covered by the canopy (Heyward 1933 ; Brockway an d Outcalt 1998). Since resource uptake is strongly correlated to root length density (van Noordwijk and Lusiana 199 6 ; Green and Clothier 2002) th is can result in significant intra and interspecific competition in the comparatively nutrient rich but ofte n water deprived upper soil horizons (Callaway and Walker 1997). The proportion of longleaf pine fine roots in the upper 30 cm of soil of this system was more than double than that reported by Jose et al. (2006) a difference that is likely due to age, spacing or soil characteristics. A highly uneven fine root distribution such as this indicates the presence of a shallow zone of very intense competition and a deeper zone where resources, particularly water, are underexploited An intercropped shrub wit h a deeper root system would likely be able to exploit this niche and coexist favorably with longleaf pine. The shrub species chosen for this study, however, appear to have lacked such belowground complementarity. Water stress can affect photosynthesis by inducing stomatal closure (Farquhar and Sharkey 1982), which in turn may inhibit gas exchange (Bennett and Sinclair 1998). It can also inhibit cell expansion and differentiation (Hsiao 1973) resulting in reduced growth.

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28 Interspecific competition for wa ter therefore appears responsible for observed treatment differences in CO 2 uptake and growth for M. cerifera and I. glabra two facultative wetland species. In temperate agroforestry systems, mixed species plantings, and natural longleaf pine forests, c ompetition for water appears to be the rule, rather than the exception ( Miller and Pallardy 2001; Harrington et al. 2003; Wanvestraut et al. 2004; Jose et al. 2006). This competition further magnifies the stresses created by drought, possibly requiring ma nagement interventions ( i.e., effects on the growth and yield of component species (Harrington et al. 2003; Wanvestraut et al. 2004 ; Zamora et al. 2008 ). The productivity of C. americana an upland species, was less a ffected by competition for water than the other two species, possibly due to a rooting habit that allowed it to tap moisture rich deep soil horizons. Nonetheless, high mortality and reduced growth in the intercropp ing treatment suggest that C. americana is, indeed, adversely affected by competition from longleaf pine Reduced chlorophyll content, while apparently having little effect on photosynthesis, could be evidence of interspecific competition for nitrogen. N itrogen is an integral component of chlorophyll (Chappelle et al. 1984) and is essential for the synthesis of amino acids, enzymes and prot ei ns (Sugiharto et al. 1990). While nitrogen deficiency may or may not affect photosynthetic capacity at the leaf le vel, it can slow the rate of leaf expansion, as well as limit leaf area and number (Ciompi et al. 1996). Nitrogen based amino acids also serve as important overwinter reserves (Chapin et al. 1990). Competition for nitrogen would therefore have a deleteri ous effect on growth and yield particularly for a deciduous species such as C. americana which likely has a high early season nitrogen demand. A companion study involving the stable isotope 15 N (Hagan 2008) seeks to quantify the effect of interspecific co mpetition for nitrogen in this system.

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2 9 Conclusions Increased mortality and large reductions in growth were observed for each of three shrub species intercropped with longleaf pine. This suggests that resource limitations brought upon by interspecific co mpetition were severe and will require management intervention. Since all species in the intercropping treatment allocated a greater percentage of their carbon to roots, it is likely that the most limiting resources were belowground. Indeed, through cano py PAR transmittance was high (only I. glabra was adversely affected by shading), but soil moisture in the upper 20 cm in this treatment was significantly reduced. This depth corresponds not only to the zone at which the highest root length density for lo ngleaf pine was reported, but also the zone most likely to be exploited by the shrubs for water and nutrients. Stomatal conductance decreased with decreasing soil moisture for I. glabra and M. cerifera but not for C. americana indicating that this speci es is less susceptible to moisture stress. The reduced chlorophyll concentration observed for C. americana may, however, be indicative of interspecific competition for nitrogen a possibility that is further explored in the following chapter.

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30 T able 2 1 Survival (%) by species treatment combination Treatment 1 Species MC IC C. americana 97 53 M. cerifera 94 81 I. glabra 78 75 1 MC = monoculture, IC = intercropped

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31 Table 2 2 Mean l eaf area, specific leaf area (SLA) and chlorophyll concentrat ion (Chl) for three species in a longleaf pine native shrub intercropping system in Florida, USA Species Treatment Leaf area (cm 2 ) SLA (cm 2 g 1) Chl (g Chl cm 2 ) C. americana Monoculture 4896.9 82.94.0 14.9 1.1 C. americana Intercroppe d 908.2 101.2 4.8 8.2 1.3 (0.0 136 ) 1 ,2 (0.0303) (0.0114) M. cerifera Mon o culture 1806.3 59.7 1.3 13. 70.9 M. cerifera Intercropped 898.8 68. 1 1.2 13. 30.8 (0. 1106 ) (0.0 021 ) (0. 8576 ) I. glabra Monocultu re 3125.3 62.52.6 32. 42.6 I. glabra Intercropped 676.9 70.3 2.3 28 0 2.3 (0.0 022 ) (0.04 49 ) (0.2 462 ) 1 P values given in parentheses. 2 Leaf area P values determined from log transformed data.

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32 Table 2 3 Parameter est imates from the photosynthesis model: light saturated photosynthesis (A max ) quantum yield (A qe ), and light compensation point (LCP) for species in a longleaf pine native shrub intercropping system in Florida, USA Means and standard errors Species Trea tment A max A qe LCP C. americana Monoculture 15.760.42 32.783.04 38.874.84 C. americana Intercropped 12.430.35 39.644.37 37.244.94 (0.0681) 1 (0.7717) (0.9223) M. cerifera Monoculture 17.270.44 34.663.21 35.824.63 M. c erifera Intercropped 13.790.39 31.973.03 48.425.03 (0.0626) (0.7531) (0.4516) I. glabra Monoculture 17.700.63 29.403.57 27.927.07 I. glabra Intercropped 11.770.44 34.724.71 35.476.78 (0.0028) (0.8604) (0.7125) 1 P values given in parentheses.

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33 Figure 2 1 Mean transmittance (by month) of photosynthetically active radiation (PAR) below the longleaf pine canopy in an intercropping system in Florida, USA. Me ans with different lowercase letters are significantly different at

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34 Figure 2 2 Typical patterns of incident PAR over the course of a cloud free day in June 2007 in a longleaf pine native shrub intercropping system in Florida, USA.

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35 F igure 2 3 Soil water potential ( k Pa) in in a longleaf pine native shrub intercropping system in Florida, USA A) at 20 cm, B) at 50 cm A B

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36 Figure 2 4 Mean (March to October) volumetric water content (%) at 0, 60 and 120 cm from shrub base in a longleaf pine native shrub intercropping system in Florida, USA. Within treatment means with different uppercase letters are statistically different at < 0.05 Between treatment means (by distance) with different lowercase letters are statistically different at

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37 Figure 2 5 Above and belowground biomass for C. americana (CA), M. cerifera (MC) and I. gl abra (IG) in a longleaf pine native shrub intercropping system in Florida, USA. 1 Numbers above bars represent root:shoot ratios.

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38 Figure 2 6 Mean root length density (RLD) for longleaf pine at three distances from a tree (40, 80 and 120 cm) and at thr ee depths (30, 60 and 90 cm) in a longleaf pine native shrub intercropping system in Florida, USA.

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39 Figure 2 7 Photosynthetic light response curves fitted using parameter estimates (Table 2 3) obtained from the nonl inear Mitscherlich model.

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40 Figure 2 8 Treatment comparisons (by species) of biweekly incident photosynthesis measurem ents in a longleaf pine native shrub intercropping system in Florida, USA

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41 Figure 2 9 Relationship between soil water potential ( k Pa) and stomatal conductance (mol H 2 O m 2 s 1 ) for the three species. Closed circles represent the monoculture treatment and open circles represent the intercropping treatment.

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42 CHAPTE R 3 PARTITIONING OF APPL IED 15 N FERTILIZER IN A LO NGLEAF PINE NATIVE W OODY ORNAMENTAL INTERCROP PING SYSTEM Introduction The diversity of groundlayer vegetation is what makes the longleaf pine ( Pinus palustris Mill.) ecosystem one of the most species rich p lant communities outside of the tropics (Walker and Silletti 2006). Interestingly, many of these species have potential as woody floral products the fresh or dried stems used for decorative purposes such as wreaths and flower arrangements ( Stamps et al. 1998; Venrick 2003 ; Josiah et al. 2004). While concerns over sustainability would likely rule out the wild harvest of stem material, the intercropping of select species in the between row spacing of a longleaf pine plantation could be an attractive option for some landowners. Such a system would not only generate income, it would also provide an incentive to reintroduce native understory species, thereby enhancing the biodiversity of plantation forests (Hartley 2002). By optimizing the use of resources in space and time, a well designed intercropping system can be highly productive as well as ecologically and economically sustainable. Achieving this balance, however, is dependent upon the understanding, and subsequent management, of the interspecific i nteractions that affect the productivity of its component species. Of particular importance is minimizing competition, the interaction that occurs when both species simultaneously seek the same limiting resource. Competition in intercropping systems comm only occurs aboveground in the form of shading, or belowground in the form of overlapping zones of resource depletion i n the rhizosphere (Schroth 1999; Jose et al. 2004). The open canopy and high light transmittance that is characteristic of longleaf pine suggests that properly selected shrubs, when intercropped in the alleys between tree rows, would be minimally affected by shading (Battaglia et al. 2003; Hagan 2008). The extensive lateral root

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43 system of this species, however, creates the potential for in terspecific competition belowground (Hagan 2008). Competition for nitrogen, typically the most limiting macronutrient in temperate cropping systems (Jose et al. 2004), could be intense under these conditions. This competition could be ameliorated or avoi ded, to some extent, through fertilization and by selecting species with patterns of nutrient uptake that differ, spatially or temporally, from longleaf pine. Ideally, the deeply rooted trees capture nutrients which leach beyond the shallow rooting zone of the sh rubs (van Noordwijk et al. 1996; Allen et al. 2004b; Jose et al. 2006; Zamora et al. 2008). Increasing the fertilizer use efficiency of a system in this manner effectively reduces the amount of nitrogen that leaches down into groundwater a common problem with ornamental production systems (Ristvey et al. 2004), which typically require higher fertilization rates than do conventional agronomic crops. In this stud y, the nitrogen dynamics in a longleaf pine native woody ornamental intercropping system were examined using 15 N labeled ammonium sulfate ((NH 4 ) 2 SO 4 ) fertilizer. Despite limited use in temperate intercropping applications, 15 N labeling techniques have proven to be effective means of tracing the movement of nitrogen in the tree cro p soil system (Jose et al. 2000; Allen et al. 2004a; Allen et al. 2004b; Zamora et al. 2008). Knowledge of how fertilizer is cycled, in turn, can be used to determine what, if any, management interventions must be implemented to improve both crop yield and ecological sustainability. The specific objective of this study was to examine how competition from longleaf pine affects fertilizer uptake and use efficiency by three common native shrub species: American beautyberry ( Callicarpa americana L.) ( Verbenaceae ), wax myrtle ( Morella cerifera ( L. ) Small ) (Myricaceae), and inkberry ( Ilex glabra (L.) A.Gray) (Aquifoliaceae). We hypothesized that

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44 interspecific competition would force the shrubs to derive a greater percentage of their nitrogen from fertilizer and would leave less fertilizer remaining in the soil at the end of the growing season. Reduced fertilizer uptake or use efficiency by the shrubs (if observed) would likely be du e to differences in biomass brought about by other resource limitations. Materials and M ethods Study Site and Experimental Design This study was conducted on a private 15 year old longleaf pine plantation in Santa Rosa with mild winters and hot, humid summers. Mean annual precipitation is 1645 mm. The soil is an ultisol and classified as a Fuquay sand (loamy, kaolinitic, thermic Arenic Plinthic Kandiudult), a deep, well drained sand over loamy m arine or fluviomarine deposits Trees in the study site were uniformly spaced, with approximately 3 meters between rows and 1.5 meters between stems within the row. Mean diameter at breast height (DBH) at the initia tion of the study (December 2005) was 8.3 cm. Mean basal area was 14 m 2 ha 1 In December 2005, containerized native woody ornamental shrubs identified as having market potential were incorporated into the existing between row spacing of the site, and as an equivalently spaced monoculture treatment in an adjacent open field. Selected species were American beautyberry ( Callicarpa americana ), wax myrtle ( Morella cerifera ) and inkberry ( Ilex glabra ). Shrubs were given a year for proper establishment with d ead or dying shrubs being replaced in the winter of 2006, prior to the initiation of the study. The effect of intercropping on the nitrogen dynamics of this system was assessed via comparisons with the monoculture treatment The trial was laid out as a s plit plot completely randomized design with treatment (monoculture or intercropped ) as the whole plot factor and shrub species as the split plot factor There were four replications, each consisting of six

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45 subplots (one for each species by treatment combi nation) with eight shrubs each. Subplots were 2 alleys wide (or equivalent distance in the monoculture) with shrubs planted in two rows of four at a spacing of 3 meters. As a control, four subplots of the same dimensions were established in the plantatio n and not planted with shrubs. Fertilizer Application and Plot Maintenance To assess competition for nitrogen between component species, 15 N ammonium sulfate ((NH 4 ) 2 SO 4 ) at 5% atom enrichment was applied to two shrubs within each subplot. To simulate the effect of a slow release fertilizer, three applications at 146.5 kg N ha 1 were applied at approximately 60 day intervals in a circular area of 325 cm 2 at the base of each shrub. The six remaining shrubs in each plot received non enriched (NH 4 ) 2 SO 4 at the same application rate. The first application was on 21 March 2007, shortly after bud sw elling and new leaf development were first observed. Pesticide and herbicide application, along with manual weed removal, were conducted as needed throughout the grow ing season. Plots were non irrigated, but supplemental water was uniformly provided to all shrubs when at least 20% showed signs of extreme drought stress. This occurred on 3 occasions during a particularly dry period from mid May to early June 2007. Harv est and Sampling At the end of the growing season, 90 cm soil cores were taken using a manual soil auger at the site of each plant that received labeled fertilizer. Cores were subdivided into 30 cm segments and subsamples of approximately 5g were taken. Additionally, each plant that received 15 N fertilizer was harvested and separated into leaf, stem, root and (when applicable) fruit components. C american a was harvested in mid September, prior to leaf senescence while I. glabra and M cerifera were harv ested with the onset of cool weather (end of the growing season) in late October. Also following the growing season, pine foliar samples were harvested

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46 with a telescoping pruning saw from the four trees (two on each row) closest to the site of 15 N applica tion. For this, the canopy was visually divided into upper and lower halves and samples collected from the four cardinal directions in each half (8 total samples/tree). Needles from the four trees were composited into a single sample. All plant material was dried to constant weight at 70 C weighed, subsampled and ground with a coffee grinder to a fine (< 1 mm) particle size. The grinder was thoroughly cleaned and dried between samples to prevent cross contamination. Soil subsamples were dried at 105 C and ground with a mortar and pestle until they reached a flour like consistency. All tissue and soil samples were analyzed by the Stable Isotope Facility at the University of California Davis (Davis, California, USA). A nalyses were conducted using a PDZ E uropa ANCA GSL elemental analyzer interfaced to a PDZ Europa 20 20 isotope ratio mass spectrometer (Sercon Ltd., Cheshire, UK). The results of these analyses were then used to calculate percent plant nitrogen derived from fertilizer (NDF) percent utiliza tion of fertilizer nitrogen (UFN) and percent recovery of fertilizer nitrogen in soil (RFN soil ) Percent plant nitrogen derived from fertilizer (NDF), a measure of the amount of fertilizer that a plant obtains from labeled fertilizer was calculated usin g the following formula (Allen et al. 2004a): NDF (%) = 100* (a b)/(c d), where a = % 15 N abundance in plant tissue; b = percent abundance in control (unlabeled) plant tissue; c = % 15 N abundance of fertilizer (5%); and d = natural abundance of 15 N (0. 3663%). Percent utilization of fertilizer nitrogen (UFN), a measure of fertilizer use efficiency, was calculated using the following formula (Allen et al. 2004a): UFN (%) = (%NDF S)/R, Where %NDF = the percentage of plant nitrogen derived from fer tilizer;

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47 S = the amount of nitrogen (g) in plant tissue; and R = the amount of nitrogen (g) applied to each plant. Percent recovery of fertilizer 15 N in soil (RFN soil ), a measure of 15 N fertilizer remaining in soil at the end of the growing season was d etermined at each depth using the following formula (Allen et al. 2004a): RFN soil (%) = 100 ((a c)/(b c)) (Np/Nf) Where a = % 15 N abundance in soil that received 15 N fertilizer; b = % 15 N abundance in fertilizer (5%); c = background 15 N abundance i n unfertilized soil; Np = total N of soil sample (g); and Nf = total amount (g) of 15 N applied to soil as fertilizer Data A nalysis Data were analyzed using JMP IN 5.1 for Windows (SAS Institute, Cary, NC, USA). Analyses were conducted using two way ANOV A procedures for a split plot completely randomized experimental design. Between species comparisons were conducted for all isotopic analyses to determine which species were most effective at capturing and utilizing applied fertilizer. L ogarithmic or arc sin transformations were performed when necessary to improve data normality. and differences between means were declared significant at Results Biomass Biomass production was significantly lower in the intercropping treatment compared to the monoculture (Table 3 1) Total biomass in the intercropping treatment was lower by 76.9%, ( P = 0.0030), 53.8% ( P = 0.0200) and 67.4% ( P = 0.0012) for C americana M cerifera and I glabra respectively. For foliage, reductions (in the above order) were 83.0% ( P = 0.0002), 56.9% ( P = 0.0331) and 76.0 % ( P = 0.0030). Stem biomass was reduced by 72.3% ( P = 0.0065) for C. americana and 75.2% ( P = 0.0023) for I. glabra The 59.1% reduction observed for M.

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48 cerifera was not statistically significant. Root biomass was 67.2% lower for C. americana ( P = 0.0052) and 60.7% lower for I. glabra ( P = 0.0098) in the intercropping treatment. The 43.2% r eduction observed for M. cerifera was not s tatistically significant. Comparisons of fruit biomass for C. americana and I. glabr a were not possible as only one individual from each species produced fruit in the intercropping treatment Tissue Nitrogen Con centrations and Content Comparisons of nitrogen concentration showed no treatment differences, for any tissue, for either M. cerifera or I. glabra A significant treatment effect ( P = 0.0015), however, was observed for C. americana roots, which had 1.01% nitrogen in the intercropping treatment compare d to 2.55% in the monoculture (Figure 3 1). For C. americana tissue nitrogen content was lower in the intercropping treatment for leaves ( P = 0.0049), stems ( P = 0.0183) and roots ( P = 0.0173). A similar pat tern was observed for I. glabra ( P = 0.0155, P = 0.0014 and P = 0.0318, respectively). Nitrogen content for M. cerifera was lower in the intercropping treatment for leaves ( P = 0.0148) and stems ( P = 0.0036), but no statistically significant difference wa s observed for roots (Figure 3 2). Foliar nitrogen derived from fertilizer ( NDF ) values (by species) were 50.8% higher for C. americana ( P = 0.0482) and 66.7% lower for M. cerifera ( P = 0.0294) in the intercropping treatment compared to the monoculture. A similar pattern was observed for M. cerifera stems ( P = 0.0494) and roots ( P = 0.0190), which had significantly lower NDF values in the intercropping treatment (63.7% and 64.4%, respectively). No significant treatment differences were observed for I. glabra for any tissue Within treatments, M. cerifera was the only species that was significantly different, with NDF values for all tissues being significantly lower than C. americana and I. glabra in the intercropping treatment (Figure 3 3).

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49 Total utiliz ation of fertilizer nitrogen ( UFN ) (all tissues combined) was significantly lower in the intercropping treatment ( P < 0.0001), with species wise reductions of 82.2%, 81.7% and 78.3% for C. americana M. cerifera and I. glabra respectively. Significant re ductions in UFN were observed for all species, and were 77.8%, 71.4% and 83.1% for C. americana 85.7%, 81.7% and 81.9% for M. cerifera and 76.9%, 79.0% and 76.4% for I. glabra for folige, stems and roots, respectively. Within treatments, no significant differences in UFN were observed between species (Figure 3 4). Recovery of Fertilizer N in Soil RFN soil varied by species ( P = 0.0007) and depth ( P < 0.0001) and there was an interaction between treatment and species (P = 0.0001). For C. americana no di fferences between treatments were observed at any depth. For M. cerifera no treatment differences were observed at 30 or 90 cm, but RFN soil was higher in the intercropping treatment at the 60 cm depth. RFN soil was significantly higher, at all depths, fo r I. glabra in the intercropping treatment, with differences of 61.9% at 30 cm and 79.1% at 60 cm. The magnitude of the difference at 90 cm (while significant) could not be determined, as negative RFN soil values were observed in the monoculture indicati ng a lower level of 15 N enrichment than background soil. Between species, no significant differences in RFN soil were observed, at any depth, in the intercropping treatment (Figure 3 5). In terms of total RFN soil (RFN summed across the three depths) the re was a significant species effect ( P = 0.0265) and an interaction between treatment and species ( P = 0.0290). The 33.2% RFN soil observed for C. americana was 41.2% higher than that observed for I. glabra and 37.7% higher than M. cerifera I. glabra wa s the only species for which a significant treatment difference was observed, having 3.2 times more fertilizer remaining in the intercropping treatment than in the monoculture. Overall, mean RFN soil in the intercropping treatment was

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50 31.3% for C. american a 20.6% for M. cerifera and for 29.7% I. glabra Differences between species were not statistically significant. Fertilizer N and Total N in Pine Foliage Mean nitrogen concentration for pine foliage was 1.58%, 0.27% of which was derived from fertilizer. Extrapolating to canopy level as described by Baldwin and Saucier (1983) revealed that 20.9% of applied fertilizer N was in pine foliage at the end of the growing season. There was no effect of shrub species on nitrogen co ncentration or NDF in pine folia ge Discussion Biomass production and allocation patterns observed in our study suggest that competition for resources wa s an important determinant of productivity for all three shrub species in the intercropping system. All species in the intercropping t reatment produced less biomass and exhibited reduced carbon allocation to aboveground tissues and increased allocation to roots, a pattern which suggests that the limiting resources in this system we re belowground (Chapin et al. 2002). Reductions in biom ass due to belowground interspecific competition are common in temperate intercropping systems, particularly those involving crops intercropped with large trees with shallow lateral root systems. In a pecan ( Carya illinoensis K. Koch) cotton ( Gossypium hi rsutum L.) alleycropping system in NW Florida, a 58% reduction in aboveground cotton biomass (compared to a root barrier treatment) was attributed to competition for nitroge n and water (Allen et al. 2004b; Wanvestraut et al. 2004). Similar effects were ob served for maize ( Zea mays L.) when intercropped with black walnut ( Juglans nigra L.) and red oak ( Quercus rubra L.) (Jose et al. 2000). While longleaf pine is known for its deep tap root, it too has an extensive lateral root system (Brockaway and Outcalt 1998). In a companion study conducted in the same plantation, Hagan (2008) found that 81.1% of longleaf pine fine roots were in the

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51 uppermost 30 cm of soil the same horizons exploited by the root systems of the intercropped shrubs. Interspecific compe tition for water was apparent in the companion study, which had the most pronounced effects on M. cerifera and I. glabra productivity. Treatment effects on tissue nitrogen concentrations were observed only in C. americana roots a fact that suggests that this species was more adversely affected by interspecific competition than the other two. Nitrogen stored in roots at the end of the growing season serves as an important reserve for spring tissue development (Chapin et al. 1990), especially in deciduous species (Lamaze et al. 2003). Deciduous C. americana likely has a high early season nitrogen requirement which, due to this decrease in storage, may have force d them to tap soil N sources, thus increasing the likelihood of competition with longleaf pine. While differences in nitrogen concentration between treatments were minimal, total nitrogen content was lower for all species, and most tissues, in the intercropping treatment. The only exception was M. cerifera roots, for which there was no treatment ef fect for either biomass or total nitrogen content. The observed treatment differences were primarily due to the reductions in total biomass. It is generally believed (and was the basis of our hypothesis) that competition, by depleting native soil nitrog en levels, encourages intercropped plants to derive a greater proportion of their nitrogen from fertilizer sources. Substantial increases in NDF in this manner were observed in the above mentioned intercropping systems (Jose et al. 2000 ; Allen et al. 2004 b; Zamora et al. 2008) C. americana however, was the only species in this system which supported our hypothesis, deriving 50.8% more of its foliar nitrogen from fertilizer in the intercropping treatment than in the monoculture. Since leaf development f or this species was complete by May 15, it is possible that the most intense interspecific competition occurred in the weeks immediately following the first fertilizer application (March 21), thereby resulting in

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52 increased fertilizer utilization. The reas ons why this pattern did not hold true for C. americana stems and roots, which had no treatment differences, is unknown. The fact that no treatment differences were observed for any I. glabra tissue suggests that interspecific competition for nitrogen wa s less severe for this species. Perhaps this wa s the result of spatial or temporal complementarity between shrubs and trees or evidence of greater competitive ability (Schaller et al. 2003). The large decrease in NDF (despite no differences in N concentr ation) observed for all M. cerifera tissues in the intercropping treatment could be evidence of another trend. As a nitrogen fixing actinorhizal shrub (Young 1992), M. cerifera derives a percentage of its nitrogen from the atmosphere, which at 0.3663% ato m enrichment has 15 N concentrations ( Busse 2000; Robinson et al. 2001 ). Perhaps interspecific competition led this species to derive a greater percentage of its nitrogen from atmospheric sources instead of soil resulting in reduced NDF. This is an intriguing possibility that deserves further study. Differences in UFN for all species were likely functions of biomass differences, with plants in the intercropping treatment generally having lower values due to reduced growth, p ossibly caused by competition for water (Wanvestraut et al. 2004). As we hypothesized, these magnifying treatment differences for UFN (Allen et al. 2004b). The thick E horizon characteristic of the Fuquay soil series has a very low cation exchange capacity and thus very little ability to retain applied fertilizer. Soil cores from all species/treatment combinations confirmed this, illustrating a pattern of decre asing fertilizer RFN soil concentrations with depth. The combined effects of competition and spatiotemporal differences in nutrient uptake between species typically result in lower RFN soil values in

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53 intercropping systems ( Allen et al. 2004a; Allen et al. 2 004b), which was the foundation of our hypothesis. This pattern, however, was not observed. In this system, no treatment differences in total RFN soil were observed for C. americana or M. cerifera and the opposite (lower RFN soil in monoculture) was observ ed for I. glabra It is possible that the decreased uptake (lower UFN) observed for shrubs in the intercropping treatment was offset by uptake by longleaf pine. Unfortunately this scenario, while plausible for C. americana and M. cerifera does not adequ ately explain the differences observed for I. glabra Perhaps this can be attributed to ecophysiological differences between species. In the aforementioned companion study, Hagan et al. (2008) found I. glabra to be the only species that was adversely aff ected, in terms of carbon assimilation, by both shading and competition for water. This combined with the period of late season growth (August September) observed for this species in the monoculture, but not the intercropping treatment (Hagan 2008), may have contributed to the large disparity in total RFN soil between treatments. In the intercropping treatment, 83.9% more fertilizer ended up in pine foliage than in the shrubs themselves. This, however, is a conservative estimate of total fertilizer up take, given the likelihood of storage in pine roots, stems and branches, which were not sampled. On one hand, fertilizer uptake by the pines represents nitrogen that was not lost to leaching, and therefore may ct one of the most commonly touted benefits of intercropping ( van Noordwijk et al. 1996; Allen et al. 2004a ; Jose et al. 2006 ). However, given the shallow fine root distribution of the longleaf pines, it is likely that much of the fertilizer was obtaine d via interspecific competition, not by spatial complementarities between root systems. Any benefit that the trees received from this secondary fertilization, therefore, could potentially have been at the expense of shrub productivity. There was no evide nce, based on RFN soil data, of

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54 significant fertilizer uptake by trees in the deeper soil depths, although it is possible that some uptake occurred at depths greater than 90 cm. It is clear that the effective management of belowground processes is essentia l for the viability of a longleaf pine/native woody ornamental intercropping system. Ideally this could be done in a manner that minimizes the deleterious effects of competition while retaining, to the greatest extent possible, the environmental benefits of intercropping. Of particular importance is the need to improve our understanding of how the nutrient requirements of selected species differ in space and time. This knowledge would not only aid in species selection, but also with nutrient management, as fertilizer applications could be better synchronized with demand, thus decreasing competition, increasing fertilizer use efficiency and decreasing loss. In this system, for example, only 24.3% of applied fertilizer could be accounted for in at the end of the growing season (3.4% in shrubs, 20.9% in trees). The remaining 75.7% either remained in soil or was lost, most likely due to leaching. It deserves reiteration, however, that the most commonly reported signs of competition for nitrogen (increased N DF and reduced RFN soil ) were, for the most part, not observed. This, combined with the low utilization of fertilizer nitrogen suggests that nitrogen was likely not the main determinant of productivity in this system. Future research should seek to furthe r elucidate the effect of interspecific competition for water and other belowground resources on shrub growth. Conclusions Results indicate that competition with longleaf pine had a deleterious effect on the growth and productivity of three common understo ry shrub species, with biomass allocation patterns suggesting that the strongest competitive vectors were belowground. Increased NDF, which would suggest competition for nitrogen, was observed only in C. americana leaves. Perhaps the fact that this specie s had a lower nitrogen concentration in roots in the intercropping

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55 treatment forced it to take up more fertilizer during leaf development rather than relying on stored reserves. No treatment effect for NDF was observed for C. americana stems or roots or f or any I. glabra tissue. Interestingly, NDF for all M. cerifera tissues was lower in the intercropping treatment. This suggests, since nitrogen concentrations were not different between treatments, that this species obtained its nitrogen from another sou rce possibly biological nitrogen fixation. NDF for M. cerifera in the intercropping treatment was significantly lower than the other two species. UFN was higher for all species in the monoculture, reflecting the differences in biomass and indicating gre ater fertilizer use efficiency in the absence of competition. RFN soil decreased with increasing depth, with little to no treatment differences observed for C. americana and M. cerifera and significantly greater recovery, at all depths, for I. glabra in t he intercropping treatment. Fertilizer uptake for pines, as a percentage of fertilizer applied, was estimated at 20.9%. Overall, while it is clear that interspecific competition was present in the intercropping system, the inefficiency of fertilizer use suggests that nitrogen was not the most limiting resource. Management interventions, particularly those that address competition for water, are likely critical to the success of this system.

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56 Table 3 1 Leaf, stem root and total biomass for C. americana M. cerifera and I. glabra in a longleaf pine native shrub intercropping system in Florida, USA. Means and standard errors. Species Treatment Biomass (g/plant) Foliage Stems Roots Fruits Total C. americana Monoculture 52. 9 9.0 43.210. 8 87. 8 11.6 20.05.1 206. 3 29.8 C. americana Intercropped 8.711.1 12.0 14. 5 28.815. 8 0. 2 50. 9 37. 4 (0.0 002 ) 1 (0.0 030 ) (0.0 052 ) (0. 0030 ) M. cerifera Monoculture 30.69.7 68. 6 11.6 82. 9 11.6 182. 0 32.3 M. cerifera Intercropped 13. 2 8 3 29.6 10. 8 47.011. 7 89. 8 27. 5 (0.0 331 ) (0.0520) (0.0768) (0.0 200 ) I. glabra Monoculture 42. 0 8. 3 86. 0 11.6 92. 1 12. 6 4.25. 6 220.629. 8 I. glabra Intercropped 9.78.2 21. 3 11.7 36.211. 6 0. 5 68.929. 9 (0.0 030 ) (0.0145) (0.0 052 ) (0 .0 012 ) 1 P values given in parentheses

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57 Figure 3 1 Mean nitrogen concentration (by tissue) for C. americana M. cerifera and I. glabra in a longleaf pine native shrub intercropping system in Florida, USA. Be tween treatment means (by species) with different letters are statistically different at 0.05

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58 Figure 3 2 Total nitrogen content (by tissue) for C. americana M. cerifera and I. glabra in a longleaf pine native shrub intercropping system in Florida, USA. Between treatment means (by species) with dif ferent letters are statistically different at

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59 Figure 3 3 P ercent nitrogen derived from fertilizer (NDF) (by tissue) for C. americana M. cerifera and I. glabra in a longleaf pine native shrub intercropping system in Florida, USA. Within treatment means with different uppercase letters are statistically different at Between treatment means (by species) with different lowercase letters are statistically different at

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60 Figure 3 4 Percent utilization of fertilizer nitrogen (UFN) (by tissue) for C. americana (CA), M. cerifera (MC) and I. glabra (IG) in a longleaf pine native shrub intercropping system in Florida, USA.

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61 Figure 3 5. Recovery of fertilizer nitrogen in soil (RFNsoil) at three depths (30, 60 and 90 cm) for C. americana M. cerifera and I. glabra in a longleaf pine native shrub intercropping system in Florida, USA

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62 CHAPTER 4 SUMMARY AND CONCLUSI ONS The cu ltivation of ornamentals to produce woody floral products the fresh or dried stems that are used for decorative purposes may be an attractive option for southeastern landowners looking to generate income from s mall landholdings. Since many shrubs nati ve to the understory of the longleaf pine ( Pinus palustris Mill.) ecosystem have market potential, one possibility is the intercropping of select species in the between row spacing of young longleaf pine plantations. By providing yearly income to suppleme nt the returns from timber sales such a system would also provide an incentive for landowners to reintroduce native understory species, thereby enhancing the biodiversity of plantation forests (Hartley 2002). By optimizing the use of resources in space and time, a well designed intercropping system can be highly productive as well as ecologically and economically sustainable. Achieving this balance, however, is dependent upon the understanding, and subsequent management, of the above and belowground in terspecific interactions that affect the productivity of its component species (Schroth 1999; Jose et al. 2004) This study therefore, was designed to assess how interspecific competition affec ted three native shrub species intercropped in the between ro w spacing of a longleaf pine plantation. In Chapter 2 we hypothesized that the shrubs, as native understory species, would be minimally affected by the partial shade of the young longleaf pine plantation. Indeed, PAR transmittance during the growing se ason averaged 57.7% and I. glabra was the only species for which a significant reduction in A max (compared to monoculture) was observed. However, increased mortality and large reductions in growth for all three species indicate that interspecific competit ion was severe in the intercropping treatment The fact that shrubs in this treatment had higher root:shoot ratios suggests that the limiting resources in this system and thus the strongest

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63 competitive vectors were belowground (Chapin et al. 2002) Soi l moisture in the intercropping treatment was lower than the monoculture at 20 cm This depth corresponds to the zone at which the highest root length density was reported for longleaf pine as well as the zone most likely to be exploited by the shrubs for water and nutrients (Jose et al. 2004) Stomatal conductance was found to decrease with decreasing soil moisture for I. glabra and M. cerifera but not for C. americana indicating that this species is less susceptible to moisture stress (Kho 2007) The reduced chlorophyll concentration observed for C. americana may, however, have been indicative of interspecific competition for nitrogen (Chappelle et al. 1984) a possibility that was further explored in Chapter 3. In Chapter 3, w e hypothesized that int erspecific competition with longleaf pine would force intercropped shrubs to derive a greater percentage of their nitrogen from 15 N labeled fertilizer (NDF) thus leaving less fertilizer remaining in the soil (RFN soil ) at the end of the growing season. An increase in NDF, however, was observed only in C. americana leaves. Perhaps the fact that this species had a lower nitrogen concentration in roots in the intercropping treatment forced it to take up more fertilizer during leaf development rather than rel ying on stored reserves (Chapin et al. 1990; Lamaze et al. 2003) No treatment effect for NDF was observed for C. americana stems or roots or for any I. glabra tissue. Interestingly, NDF for all M. cerifera tissues was lower in the intercropping treatmen t. This suggests, since tissue nitrogen concentrations were not different between treatments, that this species obtained its nitrogen from another source possibly biological nitrogen fixation (Young 1992) NDF for M. cerifera in the intercropping treat ment was significantly lower than the other two species. RFN soil decreased with increasing depth, with little to no treatment differences observed for C. americana and M. cerifera and significantly greater recovery, at all depths, for I. glabra in the int ercropping

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64 treatment. Utilization of fertilizer nitrogen ( UFN ) was higher for all species in the monoculture, reflecting the differences in biomass and indicating greater fertilizer use efficiency in the absence of competition. Fertilizer uptake for pine s, as a percentage of fertilizer applied, was estimated at 20.9%. Overall, while it is clear that interspecific competition was present in the intercropping system, the inefficiency of fertilizer use suggests that nitrogen was not the most limiting resour ce (Vitousek 1982 ; Allen et al. 2004b) It is clear, based on the results of this study, that the effective management of competition is essential to the viability of a longleaf pine/native woody ornamental intercropping system. Ideally this could be done in a manner that minimizes the deleterious effects of competition while retaining, to the greatest extent possible, the environmental benefits of intercropping. Conventional silvicultural practices such as thinning would be a logical first step, consider ing the apparent severity of both intra and interspecific competition in this system ( Derr and Enghardt 1969 ; Jokela et al. 2004) Irrigation, trenching or the installation of root barriers have also proven effective at reducing belowground competition ( Harrington et al. 2003; Wanvestraut et al. 2004 ; Zamora et al. 2008 ) and should be considered in future studies.

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65 APPENDIX A MARKETABLE YIELD Table A 1 Marketable yield Species Treatment Length Fresh weight Stems/plant C. americana 1 Monocul ture 37.6 16.4 7.9 C. americana Intercropped 24.5 9.7 0.9 M. cerifera 2 Monoculture 109.7 M. cerifera Intercropped 75.6 I. glabra 3 Monoculture 45.2 36.0 6.8 I. glabra Intercropped 32.2 14.6 3.3 1 Stems with fruit were cla s si fied as marketable (weighed with foliage removed) 2 All aboveground biomass (excluding main stem) was classified as marketable. 3 Undamaged stems (up to of total stem number) were harvested and classified as marketable.

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66 APPENDIX B SOIL PROPERTIES

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67 Table B 1 Soil p roperties Treatment N P 1 K Mg Ca S B Zn Mn Fe Cu CEC 2 %K 3 %Mg %Ca %H %OM Monoculture 537.24 5.98 14.85 14.48 100.13 12.89 0.11 2.23 11.12 30.92 0.86 2.84 0.58 1.91 7.85 89.83 0.98 Intercropped 536.27 6.09 13.73 13.24 93.78 9.53 0.12 0 .52 23.05 51.91 0.68 2.84 0.56 1.76 7.06 90.63 1.13 1 Units for all nutrients are kg ha 1 2 Units for CEC are meq/100 g. 3 Percent base saturation given for K, Mg, Ca and H.

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68 LIST OF REFERENCES Alavalapati J RR, Shrestha RK Stainback GA Matta JR ( 2004 ) Agroforestry development: An environmental economic perspec tive. Agroforestry Systems 61: 299 310 Alaval apati JRR, Stainback GA Carter DR ( 2002 ) Restoration of the longleaf pine ecosystem on private lands in the US South: an ecological economic analys is. Ecological Economics 40 (3): 411 419 Allen SC Jose S Nair PKR, Brecke BJ, Nkedi Kizza P, Ramsey CL ( 2004 a ) Safety net role of tree roots: evidence from a pecan ( Carya illinoensis K. Koch) cotton ( Gossypium hirsutum L ) alley cropping system in the southern United States. Forest Ecology and Management 192: 95 407 Allen SC, Jose S, Nair PKR, Brecke BJ, Ramsey CL ( 2004 b ) Competition for 15 N labeled fertilizer in a pecan ( Carya illinoensis K. Koch) cotton ( Gossypium hirsutum L.) alley cropping system in the southern United States Plant and Soil 263: 151 164 Battaglia MA Mitchell R J Mou PP, Pecot SD (2003) Light transmittance estimates in a longleaf pine woodland. Forest Science 49(5): 752 762 Ba zzaz FA ( 1979 ) The physiological ecology of plant s uccession. Annual Reviews in Ecology and Syste matics 10: 351 371 Bazzaz FA (1996) Plants in changing environments: Linking physiological, population and community ecology. Cambridge University Press, Cambridge, UK Boardman NK (1977) Comparative photosy nthesis of sun and shade plants. Annual Review of Plant Physiology 28: 355 377 Borders BE, Bailey RL ( 2001 ) Loblolly pine pushing the limits of growth. Southern Journal of Applied Forestry 25(2) : 69 74 Brockway DG, Outcalt KW (1998) Gap phase regenerat ion in longleaf pine wiregrass ecosystems. Forest Ecology and Management 106 (2 3): 125 139 Busse MD (2000) Suitability and use of the 15 N isotope dilution method to estimate nitrogen fixation by actinorhizal shrubs. Forest Ecology and Management 136: 85 9 5 Callaway RM, Walker LR ( 1997 ) Competition and facilitation: a synthetic approach to interactions in plant communities. Ecology 78(7) : 1958 1965 Caton BP Cope AE, Mortimer M (2003) Growth traits of diverse rice cultivars under severe competition: imp lications for screening for competitiveness. Field Crops Research 83 (2) : 157 172

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69 Chapin FS, Matson PA, Mooney HA (2002) Carbon input to Terrestrial Ecosystems. In : Principles of Terrestrial Ecosystem Ecology. Springer, New York pp 9 7 122 Chapin FS, Ma tson PA, Mooney HA (2002) Terrestrial Production Processes. In : Principles of Terrestrial Ecosystem Ecology. Springer, New York pp 123 149 Chapin F S, Schulze E D, Mooney HA (1990) The Ecology and Economics of Storage in Plants. Annu Rev Ecol Syst 21: 423 Chirko CP, Gold MA Nguyen PV, Jiang JP ( 1996 ) Influence of direction and distance from trees on wheat yield and photosynthetic photon flux density (Q p ) in a Paulownia and wheat intercropping system. Fo rest Ecology and Management 83:171 180 Ciompi S Gentili E Guidi L, Soldatini GF ( 1996 ) The effect of nitrogen deficiency on leaf gas exchange and chlorophyll fluorescence parameters in sunflower. Plant Science 118 ( 2 ):177 184 Classen N, Steingroge B ( 1999 ) Mechanistic Simulation Models for a Better Understanding of Nutrient Uptake from Soil. In : Rengel Z (ed) Mineral Nutrition of Crops. Philadelphia: Haworth Press, pp 327 362 Derr HJ, Enghardt HG (1969) Growth in a young managed longleaf pine plantati on. Journal of Forestry 67(7):501 504 Ewel JJ (1999) Natural ecosystems as models for the design for sustainable systems of land use. Agroforestry Systems 45:1 21 Farquhar GD Sharkey TD (1982) Stomatal conductance and photosynthesis. Annual Review of Plant Physiology 33:317 345 Franklin J ( 198 9 ) Toward a new forestry. Amer ican Forests 12:37 44 Garrett HE, Buck L (1997) Agroforestry practice and policy in the United States of America. Forest Ecology and Management 91: 5 15 Gillespie AR, Jose S Mengel DB, Hoover WL Pope PE Seifert JR Biehl e DJ Stall T Benjamin TJ ( 2000 ) Defining competition vectors in a temperate alleycropping system in the Midwestern USA: 1. Production physio logy. Agroforestry Systems 48(1):25 40 Green S, Clothier B (1999) The root zone dynamics of water uptake by a m ature a pple tree. Plant and Soil 206:61 77 Guldin JM (2006) Uneven aged silviculture of longleaf pine. In : Jose S, Jokela EJ, Miller DL (eds) The Longleaf Pine Ecosystem: Ecology, Si lviculture and Restoration. Springer, New York, pp 217 239

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73 Young DR ( 1992 ) Photosynthetic characteristics and potential moisture stress for the actinorhizal shrub Myrica cerifera (Myricaceae) on a Virginia barrier island America n Journal of Botany 79(1): 2 7 Zamora D, Jose S, Napolitano K (2008) Competition for applied 15 N fertilizer in a loblolly pine ( Pinus taeda L.) cotton ( Gossypium hirsutum L.) alleycropping system. Agriculture, Ecosystems and Environment (in pre ss)

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BIOGRAPHICAL SKETCH Donald Hagan sandhills, swamps and bayous of his native Florida Panhandle. In 2002, H e earned a degree in e nvironmental s tudies from the Universit y of West Florida F rom 2004 to 2006, he served as a Peace Corps agroforestry extensionist in Ecuador, where he worked with landowners to preserve some of the last remnants of coastal dry tropical forest. Upon returning to the U.S., he enrolled in the i n terdisciplinary e cology program at the University of Florida In August 2008 he began a Ph.D. program as an alumni fellow in the School of Forest Resources and Conservation.