• TABLE OF CONTENTS
HIDE
 Copyright
 Title Page
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Abstract
 Introduction
 Chlorophyll, carbohydrate, and...
 Factors affecting the absorption...
 Physiological comparisons...
 Reference
 Biographical sketch






Title: Photosynthetic characteristics of the submersed aquatic plants hydrilla, southern naiad, and vallisneria
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 Material Information
Title: Photosynthetic characteristics of the submersed aquatic plants hydrilla, southern naiad, and vallisneria
Physical Description: viii, 88 leaves : ill. ; 28 cm.
Language: English
Creator: Haller, William T., 1947-
Publication Date: 1974
 Subjects
Subject: Aquatic plants -- Florida   ( lcsh )
Hydrilla   ( lcsh )
Agronomy thesis Ph. D
Dissertations, Academic -- Agronomy -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Thesis: Thesis (Ph. D.)--University of Florida, 1974.
Bibliography: Bibliography: leaves 80-87.
Statement of Responsibility: by William T. Haller.
General Note: Typescript.
General Note: Vita.
 Record Information
Bibliographic ID: UF00084166
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: aleph - 000334492
oclc - 09408003
notis - ABW4134

Table of Contents
    Copyright
        Copyright
    Title Page
        Page i
    Acknowledgement
        Page ii
    Table of Contents
        Page iii
    List of Tables
        Page iv
    List of Figures
        Page v
        Page vi
    Abstract
        Page vii
        Page viii
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
    Chlorophyll, carbohydrate, and morphological characteristics of natural plant populations
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
    Factors affecting the absorption of carbon in photosynthesis
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
    Physiological comparisons and summary
        Page 74
        Page 75
        Page 76
        Page 77
        Page 78
        Page 79
    Reference
        Page 80
        Page 81
        Page 82
        Page 83
        Page 84
        Page 85
        Page 86
        Page 87
    Biographical sketch
        Page 88
        Page 89
        Page 90
Full Text

August 2007


11qrlc(


Internet Distribution Consent Agreement


In reference to the following dissertation:

Author: William T. Haller


Title: PHOTOSYNTHETIC CHARACTERISTICS OF THE SUBMERSED AQUATIC
PLANTS HYDRILLA, SOUTHERN NAIAD AND VALLISNERIA


Publication Date: 1974


I, William T. Haller as copyright holder for the
aforementioned dissertation, hereby grant specific and limited archive and distribution
rights to the Board of Trustees of the University of Florida and its agents. I authorize the
University of Florida to digitize and distribute the dissertation described above for
nonprofit, educational purposes via the Internet or successive technologies.

This is a non-exclusive grant of permissions for specific off-line and on-line uses for an
indefinite term. Off-line uses shall be limited to those specifically allowed by "Fair Use"
as prescribed by the terms of United States copyright legislation (cf, Title 17, U.S. Code)
as well as to the maintenance and preservation of a digital archive copy. Digitization
allows the University of Florida to-generate image- and text-based versions as
appropriate and to provide and enhance access using search software.

This grant of permissions prohibits use of the digitized versions for commercial use or
profit.


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Return this form to:


Cathy Martyniak
Preservation Dept.,
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PHOTOSYNTHETIC CHARACTERISTICS OF THE SUBMERSED AQUATIC PLANTS HYDRILLA,
SOUTHERN NAIAD, AND VALLISNERIA








By


William T


Haller


A DISSERTATION PRESENTED TO THE GRADUATE
COUNCIL OF THE UNIVERSITY OF FLORIDA IN PARTIAL
FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY




UNIVERSITY OF FLORID.
1974














ACKNOWLEOD:! F

This work was undertaken with the support of a grant provided by

the Florida Department of Natural Resources, Bureau of Aquatic Plant

Research and Control. The encouraging comments and confidence of

Dr. Alva P. Burkhalter, Director, are gratefully appreciated.

The graduate supervisory committee deserves special recognition

for their help during the course of this student's graduate study.

Dr. S. H. West, Assistant Dean for Research and chairman of the committee,

has been extremely patient and helpful in all aspects of this students

endeavors. A year of study with Dr. David L. Sutton, co-chairman of

the committee, is most appreciated, and an acknowledgement here is hardly

enough for the experimental insight gained. Dr. Leon A. Garrard deserves

recognition for his daily assistance in the laboratory and his help

in the initial review of the manuscript. The assistance of Dr. E, G.

Rodgers is also appreciated. The advice and encouragement of Dr. J. S.

Davis also has been very helpful.

Through five years of study at the same university it is impossible

to thank all who have helped in significant ways. The assistance of

Drs. E. B. Knipling and M. H. Gaskins is truly appreciated. The help

of M. Rutter, J. Michewicz, and C. Barlowe is gratefully acknowledged.

The assistance of the author's parents, Dr. and Mrs. Thurston W.

Haller, and of Margaret F. Knapp made this work possible. The author's

wife, Jean, and sons, Will and Doug, offered much encouragement and

demonstrated considerable patience and understanding.
ii













TABI.E OF CONiTENTS

Ai iC',L _L...'.... ........ .. .. -i i

LIST OF TABLES . . . . . iv

LIST OF FIGURES . . . . . . v

ABSTRACT . . . . . . . vi

CHAPTER I GENERAL INTRODUCTION AND REVIEW . . 1
Introduction . . . . . 1
Plant Biology and Distribution. . . . 4
Literature Review . . . . . 13

CHAPTER II CHLOROPHYLL, CARBOHYDRATE, AND MORPHOLOGICAL
CHARACTERISTICS OF NATURAL PLANT POPULATIONS . . .. 32
Introduction. . . . .... .. . 32
Methods and Materials . . . .... .32
Chlorophyll Studies . . . .. 32
Morphology Studies . . . . 34
Carbohydrate Studies . . . .. 35
Results and Discussion. . . . . 36
Chlorophyll Studies . . . .. 36
Morphology Studies . . . .... .44
Carbohydrate Studies . . . .. 48

CHAPTER III FACTORS AFFECTING THE ABSORPTION OF CARBON
IN PHOTOSYNTHESIS. . . . . 57
Introduction. ................. ..... 57
Methods and Materials . . . . . 57
Plant Culture . . . . 57
Effect of Photosynthesis on Water Chemistry. .... 57
Effect of pH on Carbon Uptake. . . . 58
Carbon Dioxide Compensation Points . . .. 60
Results and Discussion . . . . 61
Effect of Photosynthesis on Water Chemistry. . 61
Effect of pH on Carbon Uptake. . . 63
Carbon Dioxide Compensation Points . . 68

CHAPTER IV PHYSIOLOGICAL COMPARISONS AND SUMMARY . .. 74
Introduction . . . . . .. 74
Discussion . . . . . .. 74
Properties of Aquatic Plants . . .. 74
Summary . . . . . . 78

REFERENCES CITED . . . . . . 80

IOGRAPHICA SKETCH. . . . . .. 88













LIST OF TA\KLES


Table

1 Chlorophyll content of hydrilla, southern naiad, and
vallisneria grown in plastic pools . . .... .37

2 Chlorophyll content of hydrilla, southern naiad, and
vallisneria collected from the surface of drainage
canals in southern Florida. . . .. 39

3 Chlorophyll content of hydrilla and vallisneria as a
function of water depth. . . . ... 41

4 Growth, iron content, and total chlorophyll content of
hydrilla grown for 2 weeks in solutions of various iron
concentrations . . . . . 43

5 Production of roots and shoots (mg dry wt) by hydrilla,
southern naiad, and vallisneria grown for 12 weeks in
3.8-1 jars . . . . .. .. .. .45

6 Morphological characteristics of hydrilla and vallisneria
as determined from natural unmixed populations in earthen
ponds 1.5 M deep in Orange County, Florida . . 46

7 Comparisons of the photosynthetic properties of hydrilla
southern naiad, and vallisneria. . . ... 75

8 Photosynthetic characteristics of terrestrial and
submersed aquatic plants . . . . 77













LIT" OF FIG[URiJES


1 View of apical portion of southern naiad (Najaa
gudal upeunis (Spreng.) Magnus) . . . 6

2 Leaves of vallisneria (Vai.t nevia neotpopicaU0l
Marie-Vict.) . . . . . 9

3 Node of hydrilla (Hyd tila vettLc iata. (L.F.) Royle)
showing several branches . . . .... 12

4 The spectral distribution of solar energy as it
passes through successive meters of distilled
water. . . . . ... ... 16

5 Proportions of CO2, HC3, and CO in water at various
pH values . . . . . 21

6 The depth distribution of hydrilla and vallisneria
grown in ponds 1.5 m deep. . . . .... 49

7 Starch content of hydrilla (A) and vallisneria (B)
as a function of depth . . . .... .50

8 Sucrose content of hydrilla (A) and vallisneria (B)
as a function of depth . . . . 52

9 Reducing sugar content of hydrilla (A) and
vallisneria (B) as a function of depth . ... 53

10 Total non-structural carbohydrate (TNSC) content
of hydrilla (A) and vallisneria (B) as a function
of depth . . . . .. . 54

11 Carbohydrate components of southern naiad (A), and
a comparison of total non-structural carbohydrate
(TNSC) content of the three species in January 1974 (B). 55

12 The effect of photosynthesis on water chemistry of
culture solutions in 250-ml sealed vessels. .... 62

13 Loss of 1C from 50-ml test tubes containing
buffer solutions at various pH's as a function of time 64








Figure
1^
14 The effect of pH on the "C uptake of hydrilla,
southern naiad, and vallisneria. . . ... 66

15 Uptake of C by hydrilla c.ntaied 0in sealed vesse;. S,

16 UPtake o0 C by southern ;"iid contained in sealed
vess is . . . . . . .. 70

17 Uptake of 1C by vallisneria contained in sealed vessels 71
14
18 Loss of 1C metabolites by hydrilla, southern naiad,
and vallisneria contained in sealed vessels. . .. 73






































vi








Abstract of Dissertation Presented to the
Graduate Council of the University of Florida in Partial
Fulfillment of the Requirements for the Degree of Doctor of Philosophy

PHOTOSYiTHETIC CHARACTEIRISTCS OF THE SUBMiERSED AQUATIC Pi.AN;iS HYDRILL
SOUTiHERN AIAAO, ANID VALLiSilERIA

By

'lilliam T. Haller

August, 1974


Chairman: Sherlie H. West
Co-Chairman: David L. Sutton
Major Department: Agronomy


Chlorophyll content of hydrilla (Hydritta veticL ~ic ta (L.F.) Royle),

southern naiad (Naja" guadatupen ~ z (Spreng.) Magnus), and vallisneria

(VatELLneAia neo.ttopicaiU Marie-Vict.) plant samples varied widely under

different environmental conditions. The chlorophyll a to chlorophyll b

ratios for hydrilla and vallisneria were approximately 2.0 at the water

surface; however, hydrilla samples collected from field populations at

a depth of 1.5 m had a greater proportion of chlorophyll b. Hydrilla

appeared to be capable of chromatic adaptation.

The leaf area index of hydrilla and vallisneria samples taken from

populations grown in earthen ponds 1.5 m deep was 4.8 and 8.7, respect-

ively. In these ponds, the dried standing crop of hydrilla was estimated
-2 -?
to be 161.4 g m-2 and that of vallisneria was 400.1 g m-2. The horizon-

tal distribution of hydrilla is such that it forms an extensive canopy

which limits light penetration. Tissue analysis of samples of these

species collected in September 1973, and January 1974, showed a pronounced

seasonal variation in their carbohydrate content.

vii









The pH of culture solutions increased rapidly when these submersed

species were grown in sealed vessels under controlled conditions.

M!easurieents for carbon-14 i1n pla;t and cul ture- sojlutions in licated ti;at

free i(CO, vas u tii :ed ;-ost readily for pho tosyn r.hes s; however,, carbon

for subsequent photosynthesis was derived from HC03 which was added to

the culture solutions. Uptake of "C by southern naiad and vallisneria

gradually decreased from maximum at pH 4.0 to nearly zero at pH 8.5.

Hydrilla had the highest rate of 14C uptake in solutions between pH 5.0

to 8.5 with a maximum absorption in solutions of pH 6.0. No evidence

of direct HCO3 utilization was shown by any species studied. The CO2

compensation points of all the species were about 8.0 ul 1-1. Photo-

synthetic characteristics of submersed aquatic plants could not be used

to categorize these species into either the C3 or C4 plant groups.

Data indicated that these submersed aquatic plants were most like C3

species, but they possess distinct characteristics which may be attri-

buted to the adaptation of aquatic plants to growth under low light

intensities and low concentrations of free CO2.


viii















GENERAL INTRODUCTION AI'D RPEVEW

Introduction

One of the less obvious signs of American affluence is the

accelerated eutrophication of natural waters and the contributing

growth of submersed aquatic plants. Native plants which once helped

maintain a well balanced aquatic system now often occur in troublesome

and sometimes dangerous quantities. Nutrification of natural waters by

improper land management and waste disposal has undoubtedly increased

growth of aquatic plants. The introduction and sale of exotic and native

species by the pet fish and aquarium industry has resulted in the spread

of undesirable plants from one area to another (52).

Florida is the leading source of aquatic plants for sale to aquarium

owners, primarily because the mild winters permit the growth of these

plants throughout the year. The natural high fertility of Florida's

waters has also contributed to rampant aquatic plant growth.

Control of aquatic plants is necessary to prevent their interference

'inth fish production, recreation, irrigation, and navigation. In south

Florida, weed control is essential for maintaining water table levels and

allowing efficient drainage of water in the event of a hurricane. Pre-

sently, attempts to prevent weed interference with water use are being

studied, as are mechanical harvesting and techniques in water level ma-

nipulation. Due to high costs or lack of development of other methods,

1








herbicides provide the major means for aquatic plant management. How-

ever, a single chemical treatment costs from 50 to 150 dollars per ha,

chemical residue imay ;persist, e d pl 't re'rowth otn o rs n ess

th1 n 1 vyar. Pist research has r ohasized studies in :control ad h'as

largely ignored the ecology and physiology of submersed plants. The

absence of any substantial amount of physiologically oriented research

has prompted a widely recognized plant physiologist to state that "perhaps

rooted aquatic plants have an unusual metabolism" (11 p. 260). This

statement clearly emphasizes our lack of knowledge of the metabolism of

aquatic plants. Further questions concerning the presence or absence of

a transpiration stream, nutrient uptake, carbon absorption, and trans-

location have not been resolved.

Research in other aspects of lake biology has been extensive. Algal

physiology and biochemistry are well developed areas of specialization,

and journals have reported this research for many years. The portion of

primary productivity of lakes ascribed to the phytoplankton has been the

subject of numerous research articles. However, the portion of produc-

tivity resulting from aquatic macrophytes frequently has been ignored,

although they often constitute a much greater biomass than the phyto-

plankton (95). Recent reviews of aquatic macrophyte productivity and

ecology indicate the importance of these plants to lake systems (29).

The apparent lack of interest in aquatic macrophyte research results

from the less dominant role they once maintained, and because the

classical research methods of lake biology are not readily adaptable to

vascular plants. The introduction of exotic aquatic plants has compounded

the problem because they often originate, or are found primarily in less

developed tropical countries where research by necessity is concentrated


I









on food production, not on aquatic plant control, ecology, or physiology.

The submersed aquatic plant presently causing the most serious

problems in Florida is hydrilla (g'bn:" eLL t'iJ&ti (L.F.) oy) .

This species Aias introduced to Florida around 1950 and has very rapidly

spread to all parts of the state (14). It has become a much more serious

weed than the native species of vallisneria (VaivLU ,An a neo.tpopiccati

Marie-Vict.) or southern naiad (Najao guada upenzis (Spreng.) Magnus)

were prior to its introduction (94). Hydrilla is extremely competitive,

and soon after its introduction into a body of water it rapidly

dominates the submersed flora. By 1970 hydrilla was estimated to

occur in more than 30,000 ha of Florida's fresh waters (58), and

presently is believed to infest in excess of 40,000 ha, or about 5%

of Florida waters. Control measures are applied in only a small portion

of the total area. The overall capital outlay for hydrilla control is

difficult, if not impossible, to determine accurately because several

dozen federal, state, county, and municipal agencies are active in

aquatic weed control including weeds other than hydrilla. However, it

is estimated that hydrilla control in Florida costs taxpayers between 4

and 6 million dollars annually.1

There has been little research reported on the physiology and

ecology of the native species vallisneria and southern naiad, and even

less published on the exotic hydrilla. The factors responsible for

hydrilla's rapid dominance of aquatic systems will not be identified

until more basic research is completed. When the growth and metabolism



1 Dr. Alva P. Burkhalter, Florida Department of Natural Resources,
February, 1974. Personal Communication.









of these plants are better understood, more effective management prac-

tices likely will result.

The primary objective of this research was to identify som'e of t;e

ii:etbolic characteristics of hydri1la which permit it to dominate our

native submersed flora. Because growth and production are direct func-

tions of photosynthesis, most of the experiments conducted were closely

related to this physiological process.

Plant Biology and Distribution

Hydrilla, southern naiad, and vallisneria are common submersed

vascular plants which root in the hydrosoil and often grow to the

water surface. They are found throughout Florida and commonly inhabit

any body of water from ditches to the largest lakes. When localized

in small areas around a body of water, they are beneficial to fish

and wildlife (51). However, prolific growth covering the water's surface

results in numerous undesirable effects which necessitate some form of

management.

The three plants studied are all monocots. Southern naiad belongs

to the Najadaceae family, and vallisneria and hydrilla are members of the

Hydctochan taceae family. The importance of sexual reproduction in the

natural propagation of these species has not been studied, but vegetative

reproduction appears to be the major means of plant establishment.

Southern naiad (Figure 1) is monoecious and has opposite sheathing leaves

1.0 to 3.0 cm long and 0.5 to 1.0 mm wide. The stems are slender and

branch profusely. The flowers are unisexual, and pollination is accom-

plished completely underwater (hydrophilous). Southern naiad has a very

wide range in the western hemisphere extensing from Quebec to the Rocky

Mountains and southward across the equator into Argentina (3,26,59).




























Figure 1. View of apical portion of southern naiad (Najcc guadatupednzs
(Spreng.) Magnus) (2X).























V









Southern naiad is an important food for waterfowl and marsh birds

and also provides shelter and food for fish. It can produce trouble-

some growth, and in the period of rapid :gric'jltur:r development of

southern Florida it caused probl -fms in r.-e,l y ;cnstr::ced irrigation .ii

drainage canals. The need for control of southern naiad is completely

overshadowed by the need for control of hydrilla which has replaced

southern naiad communities where it had been introduced.

Vallisneria (Figure 2), commonly called eelgrass or tape grass, is

also indigenous to Florida. It has no stem, but several simple leaves

15 to 22 mm wide arise from a rosette rooted to the hydrosoil. Vallis-

neria spreads vegetatively by stolons and rootstocks. The plants are

dioecious, and pollination and "spiraling" of the peduncle after pollin-

ation show how well this species has adapted to the aquatic habitat

(45,59).

Taxonomists have had difficulty in the classification of ValttLiseLia

species. Fassett (26) briefly describes the history of the classifica-

tion schemes that have been proposed. Recent Floras and the University

of Florida Herbarium no longer recognize VaotLtneLa ameticana as a

separate species but consider these plants to be the same as VaMELnetLa

neotAopicaLis Marie-Vict. (48). The range of Va &isinetri neotrtopicatLs,

now including the range formerly belonging to Va. syin'Kia amecicana,

includes most of eastern North America from Canada to Cuba.

Vallisneria is one of the most beneficial submersed aquatic plants

for wildlife. Waterfowl and aquatic mammals eat nearly all parts of the

plant, especially winter buds and rootstocks. The leaves harbor minute

animals which fish prey upon, and they provide cover for spawning sport

fish (59).


1
































Figure 2. Leaves of vallisneria (Vanciineaia neo.topica&is Marie-Vict.).






9








Prior to the introduction of hydrilla, vallisneria was a serious

problem in many lakes in central Florida. Presently, hydrilla also has

replaced val!isneria in most of th-s: lekes.

h1Ydrilla (Ficiure 3) is a ew p' in the f ora ort Amrerica

and may soon become the mos serious submersed aquatic weed problem

in this country. Since its introduction some 15 years ago it has spread

from Florida to Louisiana, Alabama, Georgia, Texas, and Iowa. Its spread

through Florida is now nearly complete. It was found in Lake Seminole

on the Florida-Georgia border in 1967 and in Lake George in north central

Florida in 1968. Hydrilla was well established in Florida's largest

lake, Lake Okeechobee, by 1972 and in Orange Lake by 1973. It is common

in canals in southern Florida, including those of the Everglades. Major

infestations around Orlando, in the Conway Lake chain, have caused

severe control problems for several years. Reasons for its rapid move-

ment from one area to another include its ability to survive prolonged

periods of drying, production of vegetative propagules, and growth from

fragmentation (56). Much of its spread is thought to be directly re-

lated to man's activities involving the movement of boats, motors, and

trailers from one watershed to another.

Hydrilla flowers are unisexual, and each unilocular ovary produces

two to three minute seeds. The plants can be either monoecious or

dioecious. Leaves of hydrilla have serrated margins, are 6.0 to 15.0 mm

long, and are found in whorls containing three to eight sessile leaves

(32,48). Internodes may be over 20.0 cm long in deep water, but may be

only a few millimeters long at the water's surface. Many aquatic

plants produce various vegetative propagules, and hydrilla is no excep-

tion. Propagules are formed in the leaf axils of hydrilla stems






























Node of hydrilla (Hyd~Zza. veat-icLaltct (L.F.) Royle)
showing several branches. (2X).


Figure 3.


























H r


am.


leC


0?


ki/









(turions) and also at the ends of subterranean rhizomes (tubers). These

propagules, and possibly the underground roots and rhizomes, are the

rFa,- o," o, rce ofr i:he r'aiyM re'i fe taiL/ion which o s ,j* cfi re,-c ,i^'o'

ieasu-resU are re applied (13.

Hydrilla, believed to originate in Malaysia, has spread throughout

the tropics. It is causing serious problems in Lake Gatun and other

regions of the Panama Canal (33,34). It is believed to have been

introduced into Florida from Central America. Only the pistillate or

female plant has become established in the United States. Monoecious

(both sexes) and dioecious plants have been found in India and Indonesia,

and seeds have been collected. Seeds brought back to the United States

from these countries were found to be viable.2

When hydrilla was first found in Florida it was erroneously thought

to be Etodea canadens.Ls Michx. Several papers were published in the

1960's that reported results of research on EEodea cankadensis, but it

was soon recognized that the vegetative propagules and floral character-

istics were unlike any known Etodea. species. The plant was then thought

to be a new Elodea species and was called Florida elodea. In 1965,

specimens were sent to Harold St. John, a recognized authority on the

Hydfe.chcty:aceae family, and he properly identified the mystery plant (140).

Literature Review

The rapid movement of hydrilla throughout the State of Florida is

recorded in taxonomic records in the University of Florida Herbarium.

A true appreciation of the potential threat of hydrilla to Florida water




2 Dr. George Allen, University of Florida, March 1974, Personal
Communication.








resources can only be obtained by closely observing the domination of a

waterway by this species. In the early 1960's, hydrilla was just be-

coiiing established in the canals of southern Florida. White (96) studied

fi: r uo 'chese canals extensively. The ;:'ove;;-en u hydril i no ', o

of the canals is reported by Blackburn 2t at. (15). In 1962, one of

these canals had an 80% cover of southern naiad, but by 1974 it was

completely covered by hydrilla.

In July 1972, an 0.08-ha earthen pond in Orange County, Florida,

was divided into eight equal plots. Hydrilla, southern naiad, vallis-

neria, and Chata sp. were planted separately in each of two plots. One

year later, over 90% of this pond contained hydrilla. Two years after

planting, the pond was completely covered by hydrilla.

The size of a waterway had little effect on the establishment of

hydrilla. Rodman Reservoir is a large, shallow reservoir in north-

central Florida. In August 1970, Hestand et aE. (35) reported that

hydrilla was just becoming established in the reservoir. In August

1971, hydrilla covered about 5 ha; however, hydrilla presently is the

dominant species in the major part of the reservoir and is moving up-

stream, presumably with the aid of fishermen and motorboats. Presently,

the area covered by hydrilla exceeds 200 ha.

Several studies have shown that, in most waters, light is a major

limiting factor for the growth of submersed aquatic plants. Pearsall

and Ullyott (60) have emphasized that underwater light measurement and





3 Dr. David L. Sutton, Univ. of Fla., Agr. Res. Center, Ft. Lauderdale,
Fla. January 1974. Personal Communication.








interpretation of results is difficult. Light intensity decreases with

depth, but a complication arises because the absorption coefficient for

radiant ;. i-,-' of a specific wavelength is not the same in different

bodies of water, or even at different levels ii t same- body of w~ater.

For example, the differential penetration of light through distilled

water is presented in Figure 4. This figure represents the maximum

light penetration that can be expected at a given wavelength because

transparency of most natural waters is substantially reduced by

suspended and dissolved materials. Extensive studies of the physical

and biological aspects of light penetration in lakes have been reported

by Birge, Juday, and co-workers (7,8,9,10,43).

Pearsall and Hewitt (68) compared light penetration and vegetation

limits in the lakes of Windermere in 1920 to those measured in 1933.

The total radiation decreased during this period, and the lowest limit

of rooted aquatic plants decreased from 6.5 m to a depth of 4.3 m. The

percentage of full sunlight at the lower vegetation limits was 0.18 to

0.28 in 1920 and 0.11 to 0.18 in 1933. The names of the plants were

not mentioned, but it was reported the blooms of Cyanophytes and

Chysophytes significantly reduced the penetration of light of wave-
o
lengths below 5000 A. From related studies, Pearsall and Ullyott

(69,70) reported a rapid extinction of blue light in Windermere,

presumably due to the presence of phytoplankton. It was suggested that
o
blue light of wavelengths less than 5000 A may be a very important

factor influencing organisms living in fresh water habitats. Their

results indicated that blue light alone, or possibly the ratio of blue

light to total light, limits growth of aquatic vegetation. This

evidence was derived from data which showed that, in summer, phytoplankton


































V B G Y 0
4000 5000 6000 7000


8000


The spectral distribution of solar energy as it passes through successive i .eters
of distilled water. Adapted from Clarke (22).


UV
3000



Figure 4.


1








reduced blue light intensity at 4.3 m by more than 50% compared to

periods when phytoplankton was less abundant. The coincidence of heavy

p!:;ktonl hlooms with the period of potential m;axi .um growth of sub-

'rs.d plants suggests that c h abunda-nc of pianknon is one of several

interacting factors which limit the growth of rooted aquatic plants.

The differential penetration of water by light resulted in the

development of the "chromatic adaptation" theory proposed by Engelman

(25). This theory states that algae and other plants growing at differ-

ent depths and in different waters will adapt their pigment composition

to take advantage of differences in spectral composition. Thus, green

algae predominate in shallow waters which allow red light penetration,

red algae occur in deeper water where blue-green light predominates, and

various forms of brown algae occur at intermediate depths. Dutton and

Juday (24) reviewed chromatic adaption studies and presented four

conclusions derived from the literature; (1) that chromatic adaptation

results from differences in light quality; (2) that light quantity is

the major factor controlling this phenomenon; (3) that both light

quantity and quality are important in chromatic adaptation; and (4)

that the medium, particularly the nitrogen content, exerts an influence

on the pigment composition of algae. The differences of opinion con-

cerning the cause of chromatic adaptation result from the many different

kinds of plants used to study this response. There are the exceptions,

however, and some plants show no chromatic adaptation at all.

Wallen and Green (89,90,91) studied the effect of light quality

on several aspects of marine phytoplankton growth. They found that the

diatom ycclo.tet.ca nana (Hustedt) and the green alga DLuialeLta tettioaecta

(Butcher) grew much better under blue light than under white or green









light. When these organisms were exposed to carbon-14 (14C) under the

same light regimes, 60% of the absorbed 1C was in the ethanol-insoluble

fractionr) of algae grown ui.nder blue o' grcen light, wvhereH s o",;y ,01 ,ias

in t'e same fraction when the plants were grown under white ,ichrt. 'th

algae contained more chlorophyll a and less carotenoids when exposed to

blue light. The chlorophyll a:b ratios of VanaZieea. in green, white,

and blue light were 2.08, 2.00, and 1.75 respectively. Also, the uptake
14
of 14C as a function of water depth was studied in natural phytoplankton

populations. The greatest amount of 14C activity at the water's surface

was found in the ethanol-soluble fraction of phytoplankton, and in deeper

water the greatest activity was found in the ethanol-insoluble fraction.
Thus, the 14C in the ethanol-soluble fraction decreased with depth,

and the amount in the ethanol-insoluble fraction increased with depth.

Through an extensive series of laboratory studies, it was shown that

these differences were attributable to light quality rather than light

quantity.

The effect of light quality on the pigment content of vascular

aquatic plants has not been studied as extensively as it has been with

marine algae and phytoplankton. Dutton and Juday (24) attempted to

cor-alate the presence of several pondweeds ( Potamogeton spp.) with

depth and color of plants. The pondweeds ranged in color from deep

brown to bright green. They found no evidence of chromatic adaptation

in either the pigment content or depth distribution of the plants.

Further, they found no evidence of chromatic adaptation in vallisneria

and slender naiad ( Najas teaexiMi. Willd.). The pigment responsible

for the color changes among the pondweeds was thought to be rhodox-

anthin. Although their studies were negative with respect to chromatic









adaptation, Dutton and Juday indicated that such might exist in these

plants under different conditions. The lake they studied was exception-

j1-. "i1:,. ;: .v Ij ;t L, 1 1 o '/ r0 ;11i C- d ix f' (a t h 0 j; u 'I.... S c C..a 1t ir l

inhy -also ?Iphnsiz d tha~ chro;l-; ic idadcatio Woli.d be especial y

important to new growth in early spring when aquatic plants are growing

under a maximum depth of water.

Most light studies conducted on aquatic plants have been concerned

with determining their light compensation points. The purpose of these

studies was to elucidate the light limits for aquatic plant growth.

Blackburn t atl.. (12) grew Brazilian elodea (Egetia densa planch.) and

waterstargrass (HeUtcA antheA dabije (Jacq.) MacM.) under lights of

different spectral composition and at different intensities of white

light. Brazilian elodea produced the most growth under daylight fluores-

cent bulbs at an illuminance of 108 lux. White light above 1345 lux

resulted in the deterioration of Brazilian elodea due to solarization.

Optimum growth of waterstargrass occurred at illuminances at or above

5350 lux. Most plants of both species died when grown for 12 weeks

under blue light. Brazilian elodea and waterstargrass grew well under

red light, but waterstargrass grew best under green light. Wilkinson

(97,9,99) studied the effect of light on growth of coontail (CeAato-

phby,pwn dejnerwa.m L.) as well as waterstargrass. The maximum growth of

these species resulted when exposed to full sunlight (approx. 108 klux)

and during the longest days of the year (June 10 to July 8). The

optimum temperature for growth was 25 to 30 C. The light compensation

point for both species was 2.0 to 3.0% of the illuminance of sunlight,

but under red light was only 1.7'; and 1.0 to 3.8% of the illuminance








of full sunlight for waterstargrass and coontail, respectively. The

lower compensation point under red light supports the contention that

spectral selectivity is a very important factor in aquatic plant gr'owt~h.

A:.:on ,i;atic plants cind various algae there aar di X-reenc esponss

different light regimes. This fact does not necessarily support the

chromatic adaptation theory, but does indicate that certain light regimes

will favor the growth of one organism over another.

Several field studies on light compensation points and the growth

limit light imposes on aquatic plants have been reported (42,44,54,55,

76,77,96). The wide variation observed in these studies reflects

differences in water quality, time of year, plant species, and technique.

The overall impression seems to be that aquatic plants have a wide range

of adaptability under low light intensities.

The uptake of carbon by a few aquatic plants and many species of

algae has been reported, but several important questions are yet un-

answered. The direct uptake and subsequent utilization of bicarbonate

(HCOL) in the photosynthesis of aquatic flora is an area of continuing

controversy. The relative proportions of the various ionic forms of

carbon in equilibrium in natural waters is a function of pH (Figure 5).

It has been shown that aquatic plants prefer and readily utilize free

carbon dioxide (C02) in photosynthesis. The utilization of HCO3 in

photosynthesis was suggested by Ruttner (75) and Arens (4) on the basis

of the formation of carbonate (CO-) deposits on the leaves of some

aquatic plants. These deposits were only found on the upper sides of

the leaves. It was theorized that some aquatic plants absorb HCO3

resulting in an ion exchange which precipitates CaCO3.







100 .--




80 -

0







I-I



20--
o


60 -,
o



a 40-
a 0 jCO



20-





4 5 6 7 8 9 i0
pH

Figure 5. Proportions of CO2, HCO 3, and CO3 in water at various :i i";i!es (39).









Steemann Nielsen (83) reported that broadleaf milfoil (Myglophyll&u

hentiophyti.wn Michx.) was unable to utilize HCO3 but that the aquatic

i.w -. ,-.*',;,t ,:c. sp. u,; 1ii nd it eff cci,;ply. M.y making tw;o uinrfouncded

as:.'.: ins, Hood and Park (37) show, r: t Ci( uL :.,li Yj i .noiduya. uA:i v:ied

HCO! in photosynthesis. They assumed that the equilibrium formed between

free CO2 and added CO3 and HCO3 in solution was a slow process. When

radioactive 14HCO3 was added to a carbon-free system and 14C was taken

up by Chlo.etta instantaneously, they concluded that Chto:Letta utilized

HCO3. A second method used to discriminate between CO2 and HCO3 uptake

involved purging the culture solutions with N2 to remove 14CO2 faster

than it could be formed by dehydration of H214CO3. Watt and Paasche

(93) and Steemann Nielsen (84) sharply criticized the procedures, assump-

tions, and conclusions reached by Hood and Park. Watt and Paasche first

showed that equilibrium between CO HCO3, and CO2 can be achieved in a

very short period of time (80 sec at 25 C, pH 8.0). The production of
14 14 14 -
CO2 from added 1CO or H CO, is so fast that it invalidates the

theory of instantaneous uptake of H14CO3. Watt and Paasche demonstrated

that the free CO2 content of a solution cannot be lowered by air purging

without lowering the HCO fraction in a similar proportion.

Osterlind (61,62.63,64,65,65) conducted a series of experiments

orn the CO2 and HCO2 uptake by the algae Scz;ede=6mu quadiLcauda and

Ch ceMa p&jteno.doLa. He compared growth rates of these two algae in

solutions of varying pH. He discovered the Sceiedesmu6 had an optimum

growth rate at 6.5, and that growth decreased to about half the optimum

rate at pH 9.0. Because the CO2 content of the culture solution at pH

9.0 was much less than 1% of that of the solutions at pH 6.5, the conclu-

ded that Sccnede un s was utilizing HCO Growth of ChLouetta was








negligible at pH 9.0 and was apparently capable of utilizing only the

available CO2.

arbondiode s aivaiilible in very o'In concentrations at high p-IHs.

Tie iuili:,ation of CO2 by plants a t. high pH's is thought by some to b,

much faster than CO2 can be supplied by the equilibrium established with

iCO3. Carbonic anhydrase is believed to catalyze the degradation of

HCO3 into CO2 and hydroxide (OH-) ions. When the carbonic anhydrase

content of Scenedeamuz and ChtoteUa was assayed by Osterlind, no

differences in content of the enzyme were found. Likewise, Steemann

Nielson and Kristiansen (85) found no difference in the carbonic anhy-

drase content of EHodea canadensin (Michx.) and FontinaLeU, an aquatic

moss shown to utilize HCO3. Osterlind (62) suggested that the ability

of certain plants to utilize HCO3 may be due to differences in their

protoplasmic membranes.

Further studies of Osterlind showed that 5-day old cultures of

Sceendesmu.s readily assimilated HCO3, but 10-day old cultures had nearly

lost that capability. ChZtorela cultures of any age were unable to

utilize HCO3. Both algae utilized CO2 in direct proportion to the CO2

concentration between 10 and 100 uM. It was also discovered that

"photoactivation" was necessary for Scenedesmus to maximize HCO3 up-

take. Scciedc5 jius cultures were grown in light and at high pH for

several hours. When growth of these cultures was measured, it was

found to be considerably greater than cultures freshly placed at high

pH, or cultures grown at high pH in darkness. Further experimentation

showed that pH values of 3.0 to 9.0 had no effect on photosynthesis

other than affecting the ratio of C02:HCO3. Cyanide was found to be

more inhibitory to photosynthesis when the CO2 content of the culture








medium was low. Osterlind (66) called cyanide a competitive inhibitor

because greater inhibition occurred at high pH's where the CO2 content

w' s very low.

links (17) measured h o orn phoI-syntih i. for ; oe

than 20 species of marine algae. He found that seven species could

maintain photosynthetic activity up to pH 10.0, but only one species

required a photoactivation period. He suggested that CO3 deposition on

leaves must result from a secondary factor such as some characteristic

of the cell membrane. This was suggested because he discovered several

algae that apparently utilize HCO3, but fail to form CO3 deposits.

Shiyan and Merezhko (79) studied the uptake of radiocarbon by

Potcmogeton pe~o.&&UAtu L. and coontail in phosphate buffers of pH's

5.8 to 9.1. They found that a 30-minute exposure period was necessary

to obtain significant results. Carbon uptake by both species was highest

at lower pH's and was reduced 5 to 10 fold at pH 9.1. Carbon metabolism

appeared to be altered by high pH. At pH 9.1, a higher percentage of

absorbed 14C was found in more complex carbon molecules (organic acids,

amino acids, proteins, lipids, starch and cellulose) than at pH 6.2

where most activity was localized in simple carbohydrates.

Paasche (67) made an extensive study of the uptake of 1C by one

species of coccoiithophorid. These are free-floating marine plants which

form a delicate shell of CO3 through the reaction 2HCO3 = CO2 + CO + H0.

He found that tris(hydroxymethyl)aminomethane ("Tris") buffer had no in-

hibitory effect on carbon uptake at pH's of 6.0 to 9.1. Sea water has a

usual pH of 8.0 to 8.3; however, maximum carbon uptake occurred at pH 7.5.

At pH 9.1, carbon uptake decreased to about 30% of maximum.









The question of CO2 limitation to growth at high pH's and the

utilization of HCO3 is still a matter of controversy and produces theories
3
.l counter- theories. Recently, Shcpiro (78) theori ed that bl) -creen
'alga dominate eutrophic iwactrs of hign pH because these a!iae r'e mre

effective in utilizing CO2 than other algal groups. Goldman (30) refuted

Shapiro's contention on the basis that the total carbon in equilibrium

(CO2, H2CO3, HCO3, and CO:) is a massive reservoir for free CO2. He also

pointed out that pH changes affect the availability of various nutrients

and may possibly affect enzymes which transport them.

Interest in CO2 and HCO3 uptake by plants is not limited to aquatic

flora. In terrestrial plants, CO2 is absorbed from the atmosphere, but

it is ultimately taken up by plant cells from aqueous solution. Raven

(72,73) reviewed the significant literature on HCO3 utilization in plants

and suggested possible metabolic sequences involved at the cellular level.

He believes that HCO3 enters the cell by active transport, is dehydrated

to CO2 by the enzyme carbonic anhydrase, and is fixed by carboxydismutase.

Raven indicated that several problems of HCO3 utilization have yet to be

resolved. The diffusion of HCO3 through plant membranes is a slow pro-

cess, and no evidence of active transport has been found. In addition,

carbonic anhydrase is present in plants, but there is no evidence that

plants capable of utilizing HCO3 have a higher carbonic anhydrase con-

tent than plants which apparently cannot utilize HCO3. All plants are

capable of fixing CO2, and it diffuses rapidly across plant membranes.

The flux of CO2 formed from the dehydration of HCO3 inside a cell would

be away from the plant toward the culture solution of high pH which has

a high affinity for CO2. This is a potential short circuit, analagous to

the CO2 leakage that short circuits the "CO2 pump" in four-carbon (C4)









plants. The fixation of CO2 from HCO3 would be greatest if the dehy-

dration of HCO3 occurred near or in the chloroplast. Evidence support-

i,: *^-.i-i ipatii l arr'ngemen, -is th-e 1 'ocai : ti on o, carbonic,. rhyi dr s,-

in ti! chioropl. sts of typical pentose phosphate (C3) plants. Lo.C' -

ization of HCO3 dehydration near the chloroplast places released CO2

close to the carboxylative enzyme but increases the long diffusion path

of HCO3. Raven, using information from scant and conflicting literature,

formulated a likely explanation for HCO3 utilization. His conclusions

were in agreement with the idea of HCO3 utilization in single cell algae

where diffusion paths to chloroplasts are minimal compared to vascular

plants. The lack of significant cuticular material and the presence of

chloroplasts in the epidermis also would facilitate HCO3 utilization in

submersed aquatics.

Meyer (53) determined the daily cycle of photosynthesis in coontail

by measuring changes in oxygen content of the surrounding water. There

was a rapid rise in photosynthesis during the morning hours with maximum

rates occurring between 10 a.m. and noon. Photosynthesis rate was closely

correlated with solar intensity. The skewing of photosynthesis curves

toward the morning hours was attributed to internal factors which exert

an influence on the daily course of photosynthesis.

The internal factors described by Meyer probably included the accum-

ulation of CO2 in the aerenchyma of coontail. Laing (47) and others (6)

showed that on sunny days a negative 02 gradient and a positive gradient

of CO2 occurred between the leaves and roots of aquatic plants. Concen-

tration gradients between roots and leaves were much less pronounced in

the early morning. This indicated that the 02 content in the aerenchyma

had dropped to a uniform low level at night, and CO2 had increased to








about equal concentrations in the roots and leaves. Hartman and Brown

(31) measured the CO2, 02, N2, and CH4 content of aerenchyma in elodea

(F.t;Kl( C,~ ad,,.is .lMichx.) n d ccontil throughout a daily cycle of

photosyntihesi.;. Their work sh!o'wed ':hat research on dateLrmin;lin ;lgh:

compensation points in submersed aquatic plants by measuring photosynthesis

via 02 evolution may be erroneous. It was shown that, at low light in-

tensities, no increase in the dissolved 02 content of surrounding water

could be detected, although the internal 02 concentrations had increased.

Carbon dioxide is important in photosynthesis, but in addition acts

as a growth regulator. Several aquatic plants produce one type of leaf

under water and an entirely different type leaf above water (hetero-

phylly). Bristow (18) and Bristow and Looi (19) showed that the amphi-

bious leaves of several aquatic plants developed many of the character-

istics of submersed leaves when exposed to a stream of air containing

5% CO2. They concluded that concentrations of free CO2 higher than

those in air may be essential for the normal growth and development of

submersed amphibious plants. Dale (23) showed that the CO2 content of

water surrounding the roots of Brasilian elodea has a pronounced effect

on root production. Additional CO2 stimulates root production, but the

effect of lowered pH as a result of added CO2 was not determined.

There has been much conjecture but little research on other sources

of photosynthetic carbon besides inorganic carbon. Natural waters

contain an abundance of organic complexes which may provide carbon to

photosynthesizing organisms. Smith et at. (80) showed that marine

planktonic algae utilized the carbamino complex of alanine in prefer-

ence to inorganic forms of CO2. Steemann Nielson (84) criticized the

results of Smith et at. and discounted the possibility that alanine








is preferred to CO2 for use in photosynthesis.

Literature relating to physiological research of vascular aquatic

p lan.ts is widely scattered and covers a wi de ranqe (o topics. Fort- t

ace '!yv, a broad 1se of aq'!jat c r sfIairc! h1I ben n 'pnrcertd fr vrar'ious

algae; however, it is difficult to make conclusions concerning aquatic

plants based on algal research.

In recent years, a few studies have been completed on plants very

closely related to those in this report. Stanley (81) and Stanley and

Naylor (82) have made an extensive study of photosynthesis and carbon

metabolism in eurasian watermilfoil (MyiLophyLjLum 6pZicatum L.). The CO2

compensation point of eurasian watermilfoil was near zero. As water

temperature was increased from 10 to 35 C, photosynthesis also increased

and was maximum at 35 C. The initial photosynthetic products were

glycerate-3-P and glycolic acid, indicating this plant to be a typical

C3 plant. Assimilate accumulation reduced photosynthesis rates. In

addition, 0.5 M "Tris" buffer inhibited carbon uptake by about 50%.

Hough and Wetzel (38) developed an assay for photorespiration in

aquatic plants. They allowed axenic cultures of slender naiad to absorb
14C for 30 minutes, then measured the release of 14C from these plants in

light and dark vessels. A flow of water through the vessels was main-

tained, and aliquots were taken at regular intervals for determination of
l4f
'C activity. They obtained little evidence of photorespiration in

slender naiad, but they felt that they could induce photorespiration by

high oxygen tensions (25 mg 021-1). In none of their experiments was

photorespiration significantly greater than dark respiration. Some of

the problems encountered in this particular study may have been laminar

water flow near the plants, or refixation of photorespired CO2. It is









possible that photorespired CO2 never leaves the plant but is moved in

and out of a gas pool in the aerenchyma system. The low carbon compen-

tio ints ,atic p lans Fvors ei iher ,n photoyrespirtCorL :n

or recycling of photorespiredl CC2 n i rG 'Iy w, i chin the p :n t.

Ikusima (40) found the maximum rate of photosynthesis at light

saturation in hydrilla to be 38 mg 02 g dry wt- hr1. In general, the

photosynthetic activity of submersed macrophytes studied by Ikusima was

from only 10 to 50% of that of land plants on a leaf area basis. Two

types of profile structures were found in vallisneria and pondweed com-

munities. The profile of the linear-leaved vallisneria correlated closely

with typical grass communities. Generally, aquatic plants correspond

to herb-type communities by producing more biomass at the top of the

plant. The concentration of pondweed leaves at the surface is exag-

gerated by the floating habit of the shoot tips. Ikusima (42) made

an intensive study of a Vainetlia ieniatlata community in a ditch

1 m deep. The biomass ranged from a low of 82 g dry wt m-2 in May, to

a maximum of 212 g dry wt m2 in August. In the study period from May

to October, the chlorophyll content of vallisneria ranged from 0.51 g

m2 to 1.7 g m2, and the leaf area index (LAI) varied between 4.8 to

9.3. Photosynthesis of vallisneria was calculated on a leaf area basis

and at light saturation was 2.1 to 3.6 mg CO2 dm2 hr1. The photo-

synthetic activity of vallisneria seldom reached the potential rate

at light saturation because of light extinction in the water. The rate

of photosynthesis in the upper stratum was greatest; however, respiration

seemed equal throughout the depth of the community.








A fundamental problem in aquatic research has been the lack of

accurate, standardized methods. Biomass determination is an important

p.rax;eter, but is very difficult to obtain accurately. Fosber1g (27)

*i c:i 3.ad ? ^ 1 -i!i ,'a Lio ln O) 17 st cl'ed es or! .^'b-,iqcua i t c" t. -.-- 1 ; ipo .S ti

by the lack of an accurate sampling device. He reported on the various

types of sampling techniques and described an apparatus he designed

for sampling aquatic standing crop. He found the standing crop of
-2
coontail in two lakes was 280 and 360 g dry wt m-2. The water depths

at the sampling sties were 2 m and 3 m respectively. By successive

sampling throughout the summer growing period, he obtained growth

rates for coontail of 2.8 g dry wt m-2 day-1, and for the alga NWtetta

sp., 2.5 g dry wt m-2 day-1

Polisini and Boyd (71) determined the standing crop and nutritive

value of several aquatic plants; however, they did not determine the

standing crops of the submersed species because of the difficulty in

obtaining accurate samples. It was estimated that the standing crops
-2
of the submersed species studied were less than 0.5 kg dry wt m-2

Westlake (95) reviewed the literature on plant productivity of

several different terrestrial, aquatic, and marine communities.

He concluded that the littoral zones of rivers and lakes containing

emergent vegetation were among the most productive systems. In

contrast, submersed communities were among the least productive. The

maximum biomass reported for several submersed communities was less

than 1.0 kg dry wt m-2. In addition, Westlake (95) reported that

the terminology used by investigators was often conflicting and

difficult to interpret on a comparative basis. The term biomass






31


has been used to describe the mass of plants not including the roots,

as well as the weight of all the plant parts. The term standing crop

should beL uLsed for the Former rxaple, with th te term biomass corr(ctiL'

usd in the latter case. Further, Wiestlake suggested d consistent une

of standard terminology and techniques that will improve future research

and produce more comparable data.















CHLOROPHYLL, C, -' HYDRATEE, ANDi' RORPHOLOGICAL
CHARACTERISTICS OF NATURAL PLANT POPULATIONS

Introduction

Comparative studies of aquatic plants in their natural habitat are

difficult because of variability in the physical and chemical nature of

natural waters. This section presents a survey of the chlorophyll con-

tent of plants from three different habitats. Further, the carbohydrates

and selected morphological characteristics of two species at a single

site were studied in detail.

Methods and Materials

Chlorophyll Studies

Plants were collected from plastic growth pools at Ft. Lauderdale

in April 1972. The pools were planted 18 to 24 months previously and

had not been recently fertilized. The apical 20 cm of each species were

harvested, washed in tap water, and the chlorophyll content was deter-

mined on 4-cm sections taken from the midpoint of the harvested plant

piece. The method of analysis was that of Arnon (5). Plants from

canals near Ft. Lauderdale were collected also in April 1972 and analyzed

for chlorophyll content. The method of selecting tissue was the same as

for the pools, except that sections of southern naiad and hydrilla were

separated into leaf and stem fractions. Additional samples were taken

to determine dry weight

The chlorophyll content of hydrilla and vallisneria at different

water depths was determined using plants collected from adjoining earthen

32








ponds in Orange County, Florida. Plants were pulled from the hydrosoil

and 5-cm sections from depths of 0.0, 0.5, 1.0, and 1.5 m were placed in

jars containing pond water. The jars were placed in ic? in a ,losejd ice

.ches T.. plants iw re hrvested in a -'t it.:;rnoon un S'-ipte ber t 0, JO7,

and analyzed the following morning.

Chlorophyll content of hydrilla as a function of iron content of the

culture medium also was investigated. Plants were grown 14 days in 0.1-

strength Hoagland's solution (36) under controlled environment conditions

as described by Sutton et at. (88). The iron concentrations of nutrient

solutions were adjusted to 0, 2, 4, 8, 16, 64, and 128 ppmw (mg I-1).

Iron in the form of Sequestrene 330 was added to the 3.8-1 culture jars.

Two 6-cm apical sections of hydrilla (150 mg dry wt) were planted in

5 cm2 plastic pots. Each jar contained four pots. At the end of 14

days, the plants were removed from the culture jars and rinsed in tap

water. Representative plant sections ( about 40 mg fresh wt) from each

pot were weighed and their chlorophyll content determined. The remain-

ing plant material was dried and ground in a Wiley mill through a 40-

mesh screen. The iron content of the tissue was then determined by dry

ashing at 550 C. The ash was dissolved in 5 ml of 5N HCI and filtered

through Watman No. 2 filter paper. The filter paper was rinsed with

an additional 5 ml 5N HCi and then with 90 ml distilled water. The iron

content of the filtrate was determined by atomic absorption spectrometry.

The four pots in each treatment solution were considered replications

for statistical comparison.




4 Sequestrene 330 is a trade name for sodium ferric diethylenetriamine
pentaacetate, which contains 14.2% Fe as Fe203.








Morphology Studies

The production of roots relative to top growth was determined

e'peri,,ienta lly for hyd; ril l south rn nai,,:!, oiand v-i isn-ri ~P ants

(--{ ir'esh t) i ere plan ; d in 1 i0 c of acid-,ashed qcuar-z -ind in n .-

jars containing 0.1 strength Hoagland's solution supplemented with 50

ppm NdHCO3. After 6 weeks, the nutrient solution was decanted and

replaced. The jars were maintained under a greenhouse bench for a

total of 12 weeks, after which they were separated into root and shoots

and dry weights determined.

The accurate determination of leaf area index (LAI) and biomass

for submersed aquatic plants is almost impossible unless the area under

study can be drained. Earthen ponds (0.8 ha)in Orange County were

monitored over a 2-yr period and provided for LAI and biomass determina-

tions on hydrilla and vallisneria. The ponds were planted in July 1971,

and were drained in January 1974. During this period, hydrilla and

vallisneria had become well established. The LAI of vallisneria was

determined by harvesting four complete plants and placing the leaves on

blueprint paper which then was exposed to ultraviolet light. The dry

weight of the vallisneria leaves was also determined. By determining

the dry weight of a known area of paper, it was possible to determine

the area of leaf cut-outs. The ratio of area to dry weight of traced

plants multiplied by the dry standing crop weight would result in total

leaf area. The leaf area of terrestrial plants is expressed in terms

of one surface only and this rule was applied to these plants also.

The LAI of hydrilla was determined on the basis of only two plants

because of the difficulty in working with many small leaves. Further,

it was necessary to harvest whole plants because leaf size and internode









length increase with depth. All of the leaves were removed from two

plants and their branches. The leaves of each plant were mixed and a

s''b-sa ml ? consisLin: of t.bouLt 2cn -<~ves w'as t~akn. These leaves

,~e placed on bliueprint pair, cov-e' d ,i -: :iass to hold them N iat,

and exposed to ultraviolet light. The impressions were cut out with a

small scalpel and weighed. The traced leaves were dried and weighed, as

was done with vallisneria, to determine leaf weight to area ratio. The

remaining leaves and stems were dried and weighed to determine leaf area

to biomass ratio.

After the ponds (1.5 m deep) were drained, eight replicate samples

of each species were taken at random for biomass determinations. The

sampler was a 1-m2 frame covered with window screen and equipped with a

door in the center of the frame. After the frame was pressed down on

the plants, the door was opened and a 902-cm2 sample was easily cut

away with a long knife. After the top growth was harvested, the hydro-

soil was cut out to a depth of about 15 cm to obtain the roots. The

plants and roots were then rinsed and dry weight determined.

Several plants of vallisneria and hydrilla were harvested from the

Orange County ponds and cut into 10-cm portions from the hydrosoil to

the water surface. The plant portions were dried and weighed to deter-

mine the profile of the standing crop. The data are expressed on a

percent of the total plant weight at each 10-cm interval.

Carbohydrate Studies

The effect of depth on carbohydrate composition of vallisneria and

hydrilla was determined in September 1973, and January 1974, in plants

from the Orange County ponds. The sampling was conducted in a manner

similar to that used for chlorophyll analysis; however, the samples were









immediately frozen and maintained as such until they could be analyzed.

The carbohydrate content of southern naiad was determined for only

Jin!:,ry 197, Southern rnaid was collected from water 1.5 m deep in

iocnatn reservoir. The idetrmination oD the carbohydrate co milpopents

is described by Carter et aZ (21).

The frozen plants were thawed and approximately 0.5 g was extracted

in boiling 80% ethanol. Extractions were repeated until the tissue

was cleared of most pigmentation. The tissue was dried, weighed, and

homogenized in 0.1 M acetate buffer, pH 4.8. An aliquot of the homo-

genate was then digested with amyloglucosidase at 55 C to convert starch

to glucose. Glucose content was then determined colorimetrically by

the glucose oxidase method.5

The combined ethanol fractions (containing reducing sugars and

sucrose) were heated to remove the alcohol. The remaining aqueous

solution was brought to volume with distilled water. The Nelson-Somogyi

method then was used to determine the reducing sugar and sucrose con-

tent of the extract (60,86,87). Differentation between reducing sugar

and sucrose content was accomplished by hydrolyzing one set of duplicate

samples with invertase. The respective sugar contents were determined

colorimetrically then by comparison to standard curves.

Results and Discussion

Chlorophyll Studies

The chlorophyll content of hydrilla, southern naiad, and vallis-

neria grown in plastic pools is presented in Table 1. The total



5 Glucostat, Worthington Biochemical Corp., Freehold, N.J.






















Table 1. Chlorophyll content of hydrilla, southern naiad, and
vallisneria grown in plastic pools.



Species Chlorophyll content (mg g fr wt )a/ a/b
Sp s a b c ratio



Hydrilla 0.5730 b 0.3181 b 0.8911 b 1.80 a

Southern Naiad 0.4431 a 0.2239 a 0.6670 a 1.69 a

Vallisneria 0.5965 b 0.3522 c 0.9487 c 1.98 b


/Values in a column followed by the same letter are not sig-
ficantly different at the 5% level as determined by Duncan's
Multiple Range Test. Each value is the mean of four
replications.









chlorophyll content of all three species was less than 1.0 mg g fr wt-1

Vallisneria had the greatest amount of chlorophyll, and southern naiad

contained the least. Vali sneria hlso hd ai hi'jher chlorophyll a :

hi irophyl- b ratio (a:b ratio) than ei, Ther hydril or snthern id;

however, this ratio for all species was below 2.0.

Hydrilla and southern naiad grown in plastic pools had considerably

lower chlorophyll contents and a:b ratios than plants growing under more

natural conditions (Table 2). The chlorophyll content of vallisneria

plants did not seem to be adversely affected by long term growth in

plastic pools. It was recognized long ago that "healthy" aquatic plants

should be used for research purposes (16). Thus, it is important that

plants grown in plastic pools be properly maintained to obtain useful

research results.

The chlorophyll contents of hydrilla and southern naiad leaves and

stems are also presented in Table 2. The chloroplyll contents of the

leaves of these two species were much higher than the chlorophyll con-

tents of the stems. In addition, the chlorophyll components (a and b)

were different in these plant parts. Hydrilla stems contained a

greater proportion of chlorophyll b than hydrilla leaves. The a:b ratios

for hydrilla stems and leaves were 1.57 and 2.23, respectively. The

chlorophyll components of the leaves and stems of southern naiad were

reversed. The a:b ratios of southern naiad leaves and stems were 1.86

and 2.18, respectively. The percent dry weights of these submersed

species indicated that 90 to 92% of their fresh weight was water.

The importance of the different chlorophyll composition of hydrilla

and southern naiad leaves and stems is unknown. However, chlorophyll

analyses of hydrilla tissue taken from water depths up to 1.5 m indicate
















Table 2. Chlorophyll content of hycrilla, southern naiad, and vallis-
neria collected from the surface of drainage canals in
southern Florida.


Sp s Dry wt Chlorophyll content (mg g fr wt )a- a/b
%pees a b total ratio



Hydrilla

whole plant 9.67 1.1847 c 0.5532 c 1.7379 c 2.14 c
stem 7.41 0.2373 a 0.1514 a 0.3887 a 1.57 a
leaves 12.26 1.8685 e 0.3351 d 2.7036 e 2.23 c

Southern Naiad

whole plant 7.94 1.0655 c 0.5171 c 1.5826 c 2.06 bc
stem 6.11 0.3703 a 0.1701 a 0.5404 a 2.18 c
leaves 9.71 1.4996 d 0.8063 d 2.3059 d 1.86 ab

Vallisneria

whole plant 8.29 0.6728 b 0.3292 b 1.0020 b 2.04 bc


a Values in a column followed by the same letter are not significantly
different at the 5% level as determined by Duncan's Multiple Range
Tests. Each value is the mean of four replications.









that the chlorophyll composition of this species may be an important

photosynthetic factor.

T'!; chlorophyll co o iion of! hyv Iril a Oa j v11a isneria plants

grown in wa tr 1.5 m deep is compared in `iblI 3. Plt sai'ple- s For

chlorophyll analysis were taken from water depths of 0.0 (surface),

0.5, 1.0, and 1.5 m. The total chlorophyll content of hydrilla de-

creased 50% from the surface to a depth of 0.5 m. The total chlorophyll

content of vallisneria decreased by only 12% over the same depth. In

general, the chlorophyll content of both species decreased with increased

depth. The important difference between the two species was the differ-

ence in their a:b ratios. In vallisneria the ratios remained constant

at all water depths sampled. However, the a:b ratio of hydrilla de-

creased from 1.77 at the water surface to only 1.15 at 1.5 m. Both

the chlorophyll a and chlorophyll b content decrease with increasing

depth in hydrilla, but the chlorophyll a content decreases faster than

the chlorophyll b content. The differential change in chlorophyll

composition found in hydrilla suggests a possible "chromatic adaptation".

Hydrilla stems have a low a:b ratio in comparison to hydrilla

leaves (Table 2). Hydrilla sampled for chlorophyll analysis had longer

internodes at greater depths. Thus, the low a:b ratio at 1.5 m may

have resulted in part by the greater proportion of stems at this depth.

However, stems from the surface of canals had an a:b ratio of 1.57

(Table 2). Therefore, the low a:b ratio (1.15) of hydrilla sampled

at a depth of 1.5 m does not seem to reflect a simple change in the

proportion of stems in the samples.

Iron has been suggested as one of the limiting nutrients of hydrilla

growth in Florida's natural waters (74). Growth and total chlorophyll
















Table 3. Chlorophyll content of hydrilla and vallisneria as a function
of water depth.



Chlorophyll content (mg g fr wt-1)a/
Depth a/b
Species (m) a b total ratio




Hydrilla 0.0 0.7835 d 0.4420 c 1.2252 d 1.77 cd

0.5 0.3787 c 0.2408 b 0.6194 c 1.57 b

1.0 0.2887 b 0.1784 a 0.4667 b 1.54 b

1.5 0.1736 a 0.1508 a 0.3253 a 1.15 a


Vallisneria 0.0 0.5296 c 0.3012 c 0.8270 c 1.96 cd

0.5 0.5011 c 0.2392 b 0.7402 bc 2.09 d

1.0 0.4062 b 0.2262 b 0.6323 b 1.94 cd

1.5 0.0842 a 0.0411 a 0.1227 a 2.00 d



a/ Values in a column followed by the same letter are not significantly
different at the 5% level as determined by Duncan's Multiple Range
Test. Each value is the mean of four replications.








content of hydrilla were studied in plants grown in water with varying

iron concentrations (Table 4). No increase in hydrilla growth was

evident after 2 weeks growth in the treatment so"luions. The total

rl irroph.Hll conten t icreae ; < wu-Fid .s the iroan c.io cenrtratI ns o

the treatment solutions increased from 0 to 16 mg Fe 1-1. The iron

content of hydrilla tissue was maximum in solutions of 16 mg Fe 1-! and

then gradually decreased in solutions of higher iron concentration.

Iron concentrations above 16 mg Fe 11 inhibited hydrilla growth.

No significant differences were found in hydrilla growth or chloro-
-1
phyll content between 0 and 2 mg 11 treatments. However, the data

suggest that a reduction in variability by a longer growth period or an

increase in the number of replicates would result in significant differences

between the two lowest treatment solutions.

The importance of higher proportions of chlorophyll b in hydrilla

has not been studied. The absorption spectra of chlorophyll b is
o o
maximal at light wavelengths of 4200 A to 4800 A (100). Hydrilla could

be efficiently utilizing these wavelengths if light penetration in

Florida waters is similar to the light penetration in distilled water

(Figure 4). In light limiting systems, the pigment changes in hydrilla

could have a pronounced effect on production.

The a:b ratios of the aquatic plants studied were lower than

corresponding values for terrestrial plants. Black (11) categorizes the

a:b ratio of C3 plants between 2.4 and 3.2, and C4 plants between 3.3

and 4.5. The range of a:b ratios found for the submersed plants in this

study was 1.15 to 2.23. This also indicates that chlorophyll b

is an important pigment in aquatic plant production. Several other

pigments as carotenoids and xanthins and light penetration in Florida

waters should be studied to ascertain the importance of chromatic















Table 4.


Growth, iron content, and total chlorophyll content of
hydrilla grown for 2 weeks in solutions of various iron
concentrations.


Treatment Concn. Growth a/ Iron content a/ Total
chlorophyll a/
-1 -1
ppm mg dry wt mg g dry wtA mg g fr wt



0 130 b 1.3 a 1.495 ab

2 162 b 5.7 b 1.814 b

4 180 b 6.1 bc 1.805 b

8 166 b 8.0 c 1.978 b

16 128 b 14.0 f 2.748 c

32 52 a 12.6 ef 3.078 c

64 15 a 12.0 de 1.741 b

128 37 a 10.5 d 1.038 a



a/ Values in a column followed by the same letter are not significantly
di FFerent at the 5% level as determined by Duncan's Multiple Range
Test. Each value is the main of four replications.









adaption in aquatic vascular plants.

Morphology Studies

Poo production in aquacic vcsc;ilar p'la s ra,; ges ,''om pl ns v ic

hv, r'o roots (coontail) Lo piani- which form chick, ,,fu -i!ke sk d on

the hydrosoil (vallisneria). If two aquatic plants had equal photo-

synthetic capability and only one produced an excess of non-photosyntne-

tic tissue, the production of standing crop by the latter would be re-

duced.

The production of roots of hydrilla, southern naiad, and vallisneria

was compared after young plants were grown for 12 weeks in 3.8-1 jars

(Table 5). Total growth, from highest to lowest, of the three species

was southern naiad, vallisneria, and hydrilla. The ranking in respect

to shoot growth was southern naiad and hydrilla, followed by vallisneria.

The total growth of vallisneria was about as high as the other species,

but the high proportion of roots produced (15.7%) resulted in less

production of top growth.

The growth characteristics of hydrilla and vallisneria in earthen

ponds in Orange County, Florida, are presented in Table 6. The standing

crop biomass (top growth) data from the ponds were very different from

results obtained in 3.8-1 jars, illustrating the difficulty in simulat-

ing natural growth under controlled conditions. The standing crop bio-

mass of vallisneria grown in the ponds was almost three times greater
-2
than the standing crop biomass of hydrilla (400 vs 161 g m-2, res-

pecitvely). The total biomass of vallisneria was also much greater

than the total biomass of hydrilla. However, roots accounted for 40.6%

of the biomass of vallisneria, but only 12.4% in hydrilla. All of the

standing crop of vallisneria was leaf tissue, but 56.5% of hydrilla






















Table 5. Production of roots and shoots (mg dry wt) by
hydrilla, southern naiad, and vallisneria grown
for 12 weeks in 3.8-1 jars.a/



Species Roots Shoots Total Roots (%)



Hydrilla 8.5 353.4 369.1 2.5

Southern Naiad 7.8 402.5 410.3 2.0

Vallisneria 58.9 314.1 373.0 15.7


-/ Each value


is the mean of four replications.









Table 6. Morphological characteristics of hydrilla and vallisneria as
determined from natural unmixed populations in earthen ponds
1.5 m deep in Orange County, Florida.


Characteristics


Hydrilla Vallisneria


Dry Weight (g m-2)

standing crop

roots

biomass


Components of Biomass (%)

leaves

stems

roots


Surface Area

dm2 g dry leaf-1

leaf area index (LAI)

LAI range a/


Production (kg ha-1)

wet standing crop

dry standing crop

dry standing crop range a/


161.4

22.6

184.0




31.1

56.5

12.4




8.25

4.76

4.0-6.2


17678

1614

1280-2213


400.1

273.6

673.7




59.4



40.6




2.18

8.74

6.5-10.8


48262

4001

2976-4960


a/ Range determined on eight replications.


___ ~ __








standing crop was stem tissue. Hydrilla leaves are small and thin.

The area per gram of dry leaf tissue was 8.25 and 2.18 dm2 for hydrilla

and vallisnerid, respectively. The LAI of hydrilla was only half of

-he L_,'\, of v'ali sneria. 1 iie LAI of hydriia (4./5) ccONpares with the

LAI of corn (Zea mays L.) (1), and the LAI of vallisneria (8.74)

corresponds with LAI's of w.aterhyacinth (Eic.ho.nia cssipe. (mart.)

Solms) (46) and ryegrass (Lolmwn petene L.) (20,57). Loomis and

Williams (49) found that a LAI of at least 3.0 is necessary for 100%

interception of radiant energy. Gessner (28) determined the LAI of

turtle grass (Thatesia te,6tudinmwn Banks ex Konig), a saltwater

vascular plant, closely related to vallisneria. In an intertidal zone,

turtle grass had a LAI of 18.6. It was not specified if this value

represents one leaf surface or both. If it represents both leaf sur-

faces, the LAI of vallisneria is nearly the same as the LAI of turtle

grass. The LAI of vallisneria found in this study is similar to the

LAI of vallisneria reported by Ikusima (41).

The dry standing crop of hydrilla and vallisneria was much lower

than values normally found for terrestrial or emergent aquatic plants.

Standing crop is a function of depth, but dry matter accumulation

remains low in submersed aquatic plants growing in deep water because

of light extinction. The high water content of these species is the

major factor which makes mechanical harvesting an uneconomical control

procedure.

The horizontal distribution of hydrilla and vallisneria grown in

the Orange County ponds is compared in Figure 6. The depths at which

half of the standing crop was distributed above and below were 0.45 m








for hydrilla and 1.05 m for vallisneria. Vallisneria leaves did not

reach the water surface. The tips were necrotic and appeared that

either animals were feeding on the laves, or more .i v.i lli: ri?

'as :;;iabl~ to withstand the hih cight int, nsit y at :he surface (.;oiar--

ization).

Hydrilla formed an extensive canopy by floating on the water.

This is a major competition factor which permits hydrilla to rapidly

dominate a particular area. Few vascular plants, if any, could survive

under such a hydrilla canopy when, even without hydrilla shading, light

is a limiting factor for growth.

The location of the meristem is believed to be the factor governing

the horizontal distribution of aquatic plants (41). The meristem of

vallisneria is located at the base of the plant, while hydrilla has its

meristem at the shoot apex.

Carbohydrate Studies

The starch content of hydrilla and vallisneria was determined at

depths of 0.0 (surface), 0.5, 1.0, and 1.5 m in September 1973, and

January 1974 (Figure 7). The starch content of plant roots only was

determined in January 1974. The starch content of hydrilla tissue taken

from the surface and a depth of 0.5 m was similar in September and

January. However, samples harvested in September from lower depths

contained nearly three times more starch than the January samples.

Thus, hydrilla seems to be storing starch in the lower plant portions

in the summer.

Vallisneria generally had a higher starch content than hydrilla,

However, vailisneria appeared to be storing starch in the lower leaf

portion in January instead of in September.




















o Vallisneria
A Hydrilla


I 1 1


10
of Total P!anf


20


15
Biomcss


The depth distribution of hydrilla and vallisneria
grown in ponds 1.5 m deep.


35

E45
0



c865


O



- 95
0 Q?


F-


V


105-


115[

125"

135
1 5


5
Percent


Figure 6.


C


r*








































40 80 120 I10 90 i80 .270 3
rnmg tarch g dry wt-' mg starch g dry f-t"1

Figure 7. Starch content of hydrilla (A) and vallisneria (B) as a function of cd- .









The sucrose and reducing sugar content of hydrilla and vallisneria

was studied in the same manner as their starch contents. The sucrose

ronrLen, t both species .,as a proxinaiely the same in .adn ary, a,. ;)



content of the plants was higher in September and decreased with in-

creasing depth. The obvious error in the sucrose content of vallisneria

taken in September at 1.0 was apparently caused by mislabeling the 1.5

and 1.0 m samples. Allowing for this error, the sucrose content of both

species was similar.

The reducing sugar content of both plants was lowest at all depths

sampled in January (Figure 9). The reducing sugar content of September

hydrilla samples was highest at 0.5 m. In January, vallisneria accumu-

lated the greatest amount of reducing sugars near the base of the fol-

iage in proximity to the meristem.

Total non-structural carbohydrates (TNSC) is a summation of starch,

sucrose, and reducing sugars. The TNSC content of hydrilla and vallis-

neria samples is presented in Figure 10. Vallisneria contained more

TNSC than hydrilla. The TNSC content of vallisneria was highest in

January, whereas it was highest in hydrilla in September.

The non-structural carbohydrate components of southern naiad were

studied in January 1974 (Figure 11). The data are very similar to

hydrilla data for the same month. A final comparison of TNSC of the

three species is presented for the January sampling date.

The high accumulation of starch in the January vallisneria tissue

may be due to several environmental factors. The cooler water in

January might favor more efficient photosynthesis. This may explain

the occurrence of vallisneria primarily in springs and large lakes in











/7'
i
i


* Vallisneria, St i.
o Vallisnsria, Jan.


_____ I- I-1 ______ i__ -^ ..J
20 30 40 !0 20 30
rrm sucrose g dry wt-' mg sucrose g dry wt-'
Sucrose content of hydrilla (A) and valiisneria (B) as a function o :o,-th.


Figure 8.









A
Surface


20 40 60 80 30
mg RS g dry wt"'


60 90
mg RS g dry wt-'


Reducing sugar content of hydrilla (A) and vallisneria (B) as a funci, -
of depth.


Figure 9.








A B
SURoc< -.-- ----..J'^--.--------- --- ---






















S00 150 200 100
m-5SC g dry wt-I my TNSC g dry t-
\' / 0 \





R -1,oots -0 0 2 0 0 I-^0 0 2 _0 0 '0 0 ~o o" -
!ig TNSC g dry wt-' my TNSC g dry wt-' -!
Figure 10. Total non-structural carbohydrate (TNSC) content of hydrilla (A) and
vallisneria (B) as a function of depth.








































Figure 11.


i





















g dry wt-i mg TNSC g dry .t-i
Carbohydrate components of southern naiad (A), and a comparison of total non-:tr. tural
carbohydrate (TNSC) content of the three species in January 194 (B)
0 Sucrose 0 n Scuthcnr.- ik.,. *'

_ ____ .___------------ t 40 00 120 i60 100 200 300 4 0
mg g dry wt-r mg TNSC g dry a,/t-'
Carbohydrate components of southern naiad (A), and a comparison of total nc1-3;-t-.n-tural
carbohydrate (TNSC) content of the three species in January 1974 (B).









Florida. In addition, vallisneria is not widely distributed in southern

Florida.

FuLirt er specultin is t'hat p: otosynthlesis aly 'procd at I 'dal

i'rt es n summer cd win bu repir'io is sowed by Lhe ccol.r

winter temperatures, resulting in an accumulation of starch. In summer,

respiratory activity would increase, and starch storage would no longer

occur.

The literature contains no information on the carbohydrate status

of these or most other submersed aquatic plants. The data presented

here-suggest that the carbohydrate content and composition of aquatic

plants vary throughout the year. In addition, major differences occur

between plant species. Carbohydrates are among the primary structural

components of plants and are responsible for the formation of under-

ground rhizomes and propagules. The production of underground propagules

would be intimately associated with the carbohydrate status of the above

ground plant portions.

Denying accumulation of carbohydrates, or preventing sugar

translocation at critical periods of underground growth, could lead to

more efficient plant management. More complete studies on this and

related subjects need to be done on submersed aquatic plants.















FACTORS AFFECTING THE ASOSRPTION OF? CARBON IN PHFOTOSYNTHESIS

Introduction

There are many biochemical, physical, and chemical factors which

affect photosynthesis of submersed vascular plants. Past research has

emphasized the physical aspect of the aquatic environment. This chapter,

however, describes studies of the effect of photosynthesis on water

chemistry and the effect of pH on carbon uptake. In addition, carbon

compensation points were determined.

Methods and Materials

Plant Culture

Plants were collected originally from ponds and canals in central

and south Florida and planted at Gainesville in outdoor pools. The pH

of water in the culture pools remained at 7.5 to 8.5 throughout the

year. Excess plant material was harvested periodically, and the pools

were fertilized to maintain healthy plants and prevent accumulation of

algae. Plants used in laboratory experiments were selected from the

pools on the basis of general appearance and uniform size.

Effect of Photosynthesis on Water Chemistry

Nutrient solutions (0.1-strength Hoaglands) containing carbon were

prepared by bubbling through respired CO2 and adding NaHCO3. The

initial concentrations of HCO3 and CO2 were determined by titration with

0.02N HC1 to pH 4.5 and with 0.02N NaOH to pH 8.3, respectively (2).









Erlenmeyer flasks (250-mi) were filled with 230 ml of this culture

solution. Approximately 2.0 g fr wt of hydrilla, southern naiad, and

v:i Isnseri a ;re ::'laced in s.epara.e, tigh -iy s'oppered flasks. The apical

porLions of hy'rilla cnd s')otnrn naiad .-,ere used, but it wais necessaIry

to use complete vallisneria plants because vallisneria leaves soon die

after they are separated from their roots. Plants were washed 30

minutes in running tap-water to remove as much epiphytic algae as

possible. Four replications (flasks) of each species were harvested

1, 2, 4, 6, 8, and 10 days after initiation of the experiments. The

CO2, HC03, CO and OH- contents of the culture solutions were deter-

mined for each flask and averaged to obtain daily values. A separate

set of flasks containing no plant material served as controls to

monitor any changes in water chemistry not related to photosynthesis.

The flasks were placed in a growth chamber with provided 160

ueinsteins m-2 sec1 of light energy from incandescent and fluorescent

lamps. The photoperiod was 12 hr light-12 hr dark, and the temperature

was maintained at 30 C. On the harvest dates, flasks were removed and

the water analyzed near the end of the 12-hr light period.

Effect of pH on Carbon Uptake

The uptake of carbon within the pH range 3.0 to 9.3 was studied.

Solutions between pH 3.0 and 7.0 were made with 50 mM phosphate buffer,

and between 7.0 and 9.3 with 25 mM "Tris" buffer. Solutions of pH 7.0

were prepared with each of the buffers, and these were used to compare

the possible effects of the buffers on carbon uptake. The buffer con-

centrations were chosen because they were the lowest concentrations that

resulted in a pH change of less than 0.05 when NaHCO3 (29.76 umoles) was








added to 49 ml of buffer solution.

Test tubes 25 mm in diameter and 150 mm long were filled with 49 ml

of the respective buffer solutions (no nutrients added). The tubes were

Jed I .h ;2. to :-'ov' i-'re :hen kept 5ii;r -'l:.L

sections 12 cm long were rinsed in flowing tap-water for 30 minutes and

then placed in the tubes. Two replication (tubes) were run at each pH

for each species. After the plants were placed into the test tubes, 1 ml

of 29.76 mM NaH14CO3 (specific activity 9.08 uCi mmole-1) was added.

The test tubes were stoppered tightly, inverted several times to mix the

contents, and immediately placed into a water bath at 30 C. Two mercury

vapor and four Sylvania Gro-Lux lamps provided light intensity of 500
-2 -1
ueinsteins m sec

After a 30-minute light period, the plant sections were removed

from the test tubes, rinsed for 3 minutes in tap water, dried, and

weighed. After drying, the plant sections were homogenized in 5 ml of

25 mM "Tris" buffer, pH 7.8. The homogenate was decanted into a 50-ml

test tube. The homogenizer was then rinsed with a additional 5 ml of

buffer. The combined homogenate and rinse was mixed on a vortex mixer,

and a 0.5 ml aliquot was placed into a liquid scintillation vial con-

taining scintillation fluid composed of 100 g of napthalene, 7 g of

2,5-diphenyloxazoie (PPO), and 0.3 g of 1,4-bis-2-(5-phenyloxazolyl)-

benzene (POPOP) in 1.0 1 dioxane. Samples were counted at least twice

at 12 C. The radioactivity of the samples was converted to disinte-

grations per minute (dpm) with a programmed absolute activity analyzer.

The analyzer was programmed with the counting efficiency of various

automatic externalization ratios determined with standard samples.








The problem of tissue self-absorption was minimized by diluting

the sample from which the aliquot was taken for counting (92).

Generally, aliquots conTai ioa 1.0 -o 3.0 m; dry wit of tissue were

counted hen ce 'diu ct iity of -ie culture solutions was desired,

0.5 ml aliquots were counted.

The loss of 14CO2 from solutions of low pH by exchange with un-

labelled atmospheric CO2 was thought to present a problem in determining

the uptake of carbon by the plants. A series of solutions having a pH

of 3.0 to 9.3 was prepared in test tubes. Plants were not placed in

the tubes, but 0.5-ml aliquots were taken at various times to determine

the rate of 14C dilution. The test tubes were placed in a hood at room

temperature and were tightly stoppered except when aliquots were taken.

Carbon Dioxide Compensation Points

The CO2 compensation points for the three species were determined

in stoppered flasks containing plant tissue, buffered nutrient solution,

and 14C-labelled NaHCO3. Erlenmeyer flasks (125-ml) were filled with

123 ml of buffered, 0.1-strength Hoagland's solution (25 mM "Tris" pH

7.Z8. Washed plant sections weighing approximately 0.15 g dry wt were

placed separately by species into the flasks, and 2.0 ml of 29.26 mM

NaH14CO3 stock solution (specific activity 7.70 uCi mmole-I) were added

to each flask. The flasks were stoppered tightly and placed in growth

chambers under the same environmental regime as was used for determining

the effect of photosynthesis on water chemistry. Three replicate flasks

of each species and control flasks which contained no plants were re-

moved from the growth chambers 1, 2, 4, 6, 8, and 10 days following

initiation of the experiments. Plant sections were then rinsed in 200 ml

of tapwater for 3 minutes and dried. Three 0.5-ml water samples were








taken from each flask and counted. Three additional 0.5 ml water samples

were placed in empty scintillation vials and acidified with 3 drops of

glacial acetic acid to convert ll HCOC3 and CO. to free CO2. The acidi-

Ti2d' vias wer placed id on oven (70 C) to dry in order to r-move .1l

CO2. After the vials were completely dry, they were filled with scin-

tillation solution, shaken, and the remaining radioactivity determined.

The chemical composition of the substances retaining radioactivity was

not determined, but they were presumably various carbon metabolites

exuded by the plants. To correct the CO2 compensation points, the

radioactivity remaining in the acidified samples was subtracted from

the radioactivity of the aqueous samples. Dried plant samples were

homogenized, diluted, and mixed. The radioactivity was determined in

the same manner as described previously. Radioactive recovery was

determined by comparing the radioactivity added to the flask with the

sum of the radioactivities of plants, culture solutions, and rinse water.

In all instances involving 14C uptake, it was possible to account for

at least 90% of the added radioactivity.

Results and Discussion

Effect of Photosynthesis on Water Chemistry

The effect of photosynthesis on the carbon content of culture solu-

tions is presented in Figure 12. Data were taken for a period of 10

days, but only the first 6 days are presented because the major changes

in water chemistry occurred during this time. Data collected from the

vallisneria experiment are presented in Figure 12 and are representative

of results obtained with hydrilla and southern naiad. The principal

factor affecting the presence of carbon-containing ions at any given

time was the amount of plant tissue present in the flasks.



















OC
o


0


20 -






HC0 C0




0 I 2 Da4

Figure 12. The effect of photosynthesis on water chemistry of culture
solutions in 250-ml sealed vessels.


1









Free CO2 was utilized very rapidly. Detectable levels of CO2 were

not found on the first day following the initiation of the experiments.

i ; i! di sapp ranc of CO, w 3 cco on d hy a rapid pH ris i-

th' cutI~ :';e so ili ions. Fiecr3 sd HC, c ent correspondl ii th ii-

creased CO3 content of the culture solutions. The plants apparently

were utilizing CO2 from HCO3 according to the reaction, 2HCO3

CO2 + CO3 + H20. As the pH increased to 10.0 or slightly higher on

days 8 and 10, the production of CO3 slowed and low levels of OH were

detected. These changes in water chemistry were characteristic of all

three species.

By the tenth day of the experiments, the plants were nearly dead,

for their leaves were necrotic and almost transparent. Also, colonies

of algae began to appear in some of the flasks by the tenth day. Main-

taining algae-free cultures was difficult, particularly with southern

naiad. Whenever flasks contained visible algae, the results were dis-

carded. The reason for plant mortality is not known. Carbon in a suit-

able form for photosynthesis, or the availability of some other nutrient,

may have become limiting.

EFfect of pH on Carbon Uptake

One of the problems encountered in studying the uptake of carbon by

aquatic plants is the presence of varying ionic species containing carbon

in solutions of different pH. Another difficulty is the dilution of

dissolved 14C in water by exchange with atmospheric CO2.

The 14C loss from buffer solutions of different pH was studied to

allow for the correction of data fro-m pH studies. These results are

presented in Figure 13. Initially, all test tubes contained 50 ml of

buffer solution which had a radioactivity of 13,800 dpm ml-.
















0.15 hr
o -,--


36 hr


144 hr


Figure 13.


Loss of C from 50-ml test tubes containing buffer solutions at
various pH's as a function of time.









Periodically, the stoppered test tubes were opened, and the radio-

activity was determined. The radioactivity in solutions of low pH

!d!cr,-C-!,._ very' ;`-jii' ',,h n 4'i.- 'CUy; '.!, i :i aK -,dded :co the t 'j s,.

Ace-r .1.5 ir, solu-Lions of p0H 3 and i d IoS aboLt 1' o cheir

initial radioactivity. The loss of 1C from tubes of high pH was evident

after 1.5 hr, but the loss of radioactivity at high pH's was considerably

less than the loss at low pH's. After 36 hr, solutions of pH 3.0 had

lost nearly 67% of the added radioactivity, while solutions of pH 9.0

had lost only about 11%.

Plant sections were placed in freshly prepared solutions of the

same pH and the uptake of 14C was measured (Figure 14). In order to

minimize 14C dilution with atmospheric CO2, the treatment solutions

were prepared immediately before the plants were placed in them. The

total time between adding radioactive NaH14CO3 and the termination of

the experiments was about 1 hour.

Hydrilla, southern naiad, and vallisneria absorbed more 14C in

solutions of low pH where a greater proportion of carbon present was

free 14C02 (Figure 14). Southern naiad absorbed the greatest amount

of 14C in solutions of pH 4.0 to 5.0; above pH 5.0 there was a progressive

and rapid decline in 14C uptake. Vallisneria absorbed the least 14C

of all the species studied, and uptake gradually decreased as the

pH of the buffer solutions increased above 4.0. Overall, hydrilla

had the highest rate of photosynthesis or 14C uptake. Carbon uptake

by hydrilla was maximum in solutions near pH 6.0. The proportion of

C02:HCO3 at pH 6.5 is about 1:1. Whether this is what caused a high

uptake at these pH's, or whether the activity of some enzyme is maximum

at these pH's is not known. At pH values above 8.0 to 8.5, the uptake














CQ


C/ I



E0
.2 -I--






2




3 4 5 6 7 8 p
pH
Figure 14. The effect of pH on the 4C uptake of hydrilla, southern naia,
and vallisneria.








of 14C by all species essentially ceased. However, if 14C were plotted

against the proportion of free CO2 in solution, it would be evident

thot thes.- species utilize free CO., most e-s-ilI. these results are

S,,i';! ,nV -.'- c .hose c. .i :.yc:' K. -,y ? K:.che (5/) wher he :^t.j.H e ..+- .. p.d,;- Q d .

carbon at various pH's by a coccolithophorid.

Osterlind (64) found that a photoactivation period was required

by Scenedesmus in order for photosynthesis to occur in solutions of

high pH. It is possible that a photoactivation period would increase

the uptake of 14C by hydrilla, southern naiad, and vallisneria in

solutions of high pH. The low carbon absorption above pH 8.0 by

hydrilla was unexpected. Deposits of CO have been reported to occur

on hydrilla leaves, and this plant is commonly found in waters of pH

10.0 or higher (50).

Hydrilla's growth in waters of high pH does not necessarily mean

that HCO3 is being utilized directly in photosynthesis. In the Orange

County ponds, the pH of the water was above 10.0, but CO3 deposits on

hydrilla leaves were not evident.5 It is possible that CO2 supplied

by algal respiration and sediment oxidation was sufficient to maintain

hydrilla in a canopy where rapid growth was no longer necessary. High

respiration rates in these ponds was indicated by results obtained when

the diurnal oxygen content of the water was measured. The aerenchyma

in hydrilla probably stores CO2 at night, and this may be an important

carbon source the next day.




5 Sutton, D.L. 1974. Control of aquatic plant growth in earthen ponds
by the white amur. Agr. Res. Rep., Univ. of Fla. 75 pp.









When the Orange County ponds were first planted with hydrilla, the

ph of the water was 7.5 to 8.0. The pH has increased the past 3 years

n ;) 1 5. y... lr I s r iy-d In p nds

;.,;? '-;: .t r 'i-i y P d S Ur n d ri. u o, "hrs yr)rs -r

hydrilla growth. Hydrilla probably is not growing at a maximum rate

now that a canopy has formed, but does have to produce enough growth

to maintain its canopy. It the ponds were cleared with herbicide, the

additional CO2 derived from decaying vegetation likely would result in

a high rate of regrowth. Much of this reasoning is speculative, and

further studies need to be completed. The rapid increase in 14C absorption

by hydrilla between pH's 5.5 and 6.0 also should be examined more

closely.

Carbon Dioxide Compensation Points

The uptake of 14C in closed flasks and the resulting CO2 compen-

sation points for hydrilla, southern naiad, and vallisneria are presented

in Figures 15-17. Initially, the flasks contained 58.5 umoles (39.3 mg

1-1) of NaH1CO3, and the radioactivity was 11,800 dpm ml1. After 6

to 8 days, the radioactivity of the solutions attained a uniformly low

level of radioactivity (300 dpm ml ). The amount of NaH14CO3in solution

decreased to about 1.49 umoles (1.00 mg 1 -). The COO compensation

points for all three species were about the same. After correcting for

the relative proportions of carbon in solution, the results indicated CO2

compensation points of 0.52 mg 1 CO2, or on a volume basis, 8.01 ul 11

For comparison to the CO2 compensation points of terrestrial plants, the

latter value expressed on a volume basis should be used. There was no

visible evidence of algal growth in any of these flasks during the 10-

day experiments; therefore, the results represent the compensation points


1






















































I 2


Uptake of C by


'1
-7-












-3


4 6 8
Days
hydrilla contained in sealed vessels.


1


Figure 15.


























Solution Activity (dpm m 'x lO-3)
CFn r- 61)


C IQ- 0

c\J "~(i.-OlxjM Aip 5w wdp) fitA!jZ2 OflSi


U)







rci






a,




-Cd







U)

(0




Cd






ci,
5-


























































Days
Uptake of C by vallisneria contained in sealed


26





,22
m
6


is
.4-


E
V


E
2
o14

'10





C',

6


c;)

I-e
C)



'C)



Li






i:


Figure 17.


vessels.









of the vascular plants and not algae. When working with aquatic plants

from natural conditions, there are always some algae present. It was

dou tf ul however, that the CO m concen'tra' ios of tUheser s-l ti ions Ce:r

significantly affected in the firsY dci/s by iga/e.

The radioactivity of the plants (dry weight basis) varied between

species because the results were not corrected for differences in plant

weights used (tissue dilution). The radioactivity of the plants in-

creased rapidly until about the fourth day and then decreased after the

sixth day. The decrease in radioactivity of the plant tissue was

caused by the increasingly poor condition of the plants past the sixth

day. Some of the tissue were becoming necrotic, resulting in C leak-

age. The loss of various carbon metabolites from the plant tissue is

presented in Figure 18. Aliquots taken from the solutions were acidified
14 14 14 -
and dried to remove 14C02 H CO3, and 1CO Thus, values in Figure

18 are measures of the loss of 1C metabolites from the plant tissue.

These data also give an idea of the relative capability of these plants

to survive in closed systems. The greatest amount of radioactivity was

lost by southern naiad and vallisneria. The radioactivity lost by

hydrilla during the experiments was very low. This illustrates how well

hydrilla can survive conditions which are relatively unfavorable to the

growth of other aquatic plants.





















0






E
E4









1 2 4 6 8 1
Days
Figure 18. Loss of 14C metabolites by hydrilla, southern naiad, and
vallisneria contained in sealed vessels.












CHAPTER TV

PHYSIOLOGICAL COMPARISONS AND SUMMARY

Introduction

The objective of this chapter is to summarize the photosynthetic

characteristics of aquatic plants. Although few studies have been re-

ported on the physiology of aquatic plants, it is evident from these

data that they have several distinct characteristics which are very

different from their terrestrial counterparts. In order to understand

their uniqueness, some general comparisons are listed.

Discussion

Properties of Aquatic Plants

A comparison of some photosynthetic properties of hydrilla, southern

naiad, and vallisneria is outlined in Table 7. Probably the most impor-

tant factor which allows hydrilla to dominate other aquatic plants is

its relatively high rate of photosynthesis. Vallisneria had twice the

LAI of hydrilla. However, the photosynthetic rate of hydrilla was three

to four times higher than that of vallisneria. The potential advantage

of chromatic adaptation in hydrilla also could be an important photo-

synthetic property. Photosynthetic rates in these plants are much lower

than rates found in terrestrial plants. An increased level of chlorophyll

b would not be as important in plants which have high rates of CO2 fix-

ation, but this may have great significance in aquatics. The canopy

formed by the growth of the apical meristem of hydrilla would deprive

light to plants already growing in a light-limiting situation.

















Table 7. Comparisons of the photosynthetic properites of hydrilla,
southern naiad, and vallisneria.



Southern
Factor Hydrilla Naiad Vallisneria



Leaf area index (LAI) 4.8 nda/ 8.7

Dominant apical meristem yes yes no

Possible chromatic adaptation yes nda no

Chlorophyll content (field) 1.7 1.6 1.0
(mg g fr wt-1)
0.30
Photosynthetic rate 1 pH 6.0 1.41 0.71
(mg C g dry wt-1 hr ) pH 7.8 0.31 0.19 0.11

Root production (field) 12.4 nd1a/ 40.6
(%)

Root production (lab.) 2.5 2.0 15.7
(%)


a/ Not determined.


~_









The high LAI of vallisneria would be an advantage in its competition

with hydrilla. However, the low content of chlorophyll, low rate of CO2

fixation, and high production of 7on-photosynthetic tissue (roots) ore-

ventL; vallisneria from imainraining itself in the presence of hydri!iia.

The photosynthetic characteristics of terrestrial and submersed

aquatic plants are compared in Table 8. The presence of ribulose di-

phosphate (RuDP) carboxylase as the primary carboxylating enzyme and

products of photosynthesis (63,64) of submersed aquatic plants are

indicative of a typical C3 plant. However, the low CO2 compensation

points demonstrated for these plants are more typical of C4 plants. On

the basis of this anomaly, Black (11) stated that little is known about

the metabolism of aquatic species. The literature relates several

more unusual characteristics of aquatic plants that prevents their

categorization into a typical C3 or C4 scheme. The maximum rate of

photosynthesis is only 2 to 4 mg CO2 dm-2 hr1. Because of this, the

growth rates and dry matter production are also very low. The growth of

submersed plants seems very rapid to investigators who study them; how-

ever, they contain over 90% water and the resulting dry matter accumulation

is very low. The presence of photorespiration has not been demonstrated

in submersed aquatics. The low light intensities and low 02 tensions

in water do not favor the photorespiratory process. It is possible

that the mechanism of photorespiration exists; however, the presence

of aerenchyma tissue and low CO2 compensation points indicates that

the CO2 is not lost by the plant but is re-assimilated rapidly.

The properties of aquatic plants which are like those of C3 plants

are carboxylation predominately by RuDP carboxylase and photosynthetic

products typical of the pentose-phosphate pathway. The characteristics











Table 8. Photosynthetic characteristics of terrestrial and
submersed aquatic plants.


Characteristic


C3 a/


C a/ Submersed
4 Aquatic


Aquatic
Species


b/ Reference


Primary carboxylating
enzyme

CO2 compensation
point (ppm CO2)

Maximum rate of
photosynthesis
(mg CO2 dm-L hr-1)

CO2 loss by
photorespiration

Optimum temperature
for CO2 fixation (C)

Maximum growth rate
(g m-2 land area day-1)

Leaf chlorophyll
a:b ratio

Dry matter production
(tons ha-1 yr-1)


RuDP


30-70


15-40



Yes


15-25


16-23


PEP
RuDP

0-10


RuDP Hy,N,V


0-8 M,Hy,N,V


40-80 2-4


30-47 25+ M,He,C


17-44 2-3


C,Ni


2.4-3.2 3.3-4.5 1.8-2.3 Hy,N,V


20-25


22-56


a/ Data for terrestrial plants adapted from Black (11).
b/ Abbreviation code: Hy-hydrilla; He-Heteranthera; V-Vallisneria;
N-Najas; Ni-Nitella; M-Myriophyllum; and C-Ceratophyllum
c/ Preliminary enzyme analysis by this laboratory shows the RuDP
carboxylase content of aquatic plants is much higher than the PEP
carboxylase content.


C/


63,64

68



65


63,64,22


60,62


~









which suggest C4 classification are their CO2 compensation points,

apparent lack of photorespiration, and high optimum temperature for Co2

iixa;,ion. The rates of photosynthesis, dry iiiter production, iiax1imumii

rnrowth, and the a:b ratios are lowcr than those found in either C, or

C4 plants.

If the photosynthetic rates of aquatic plants were higher, they

probably would fit into the C3 category fairly well. The C4 character-

istics would then be adaptations to the low CO2 content and low light

intensity of the aquatic habitat.

The low photosynthetic rates found in submersed plants invites

speculation. Water certainly would not limit growth, and nutrients

likewise probably would not be a limiting factor. Therefore, light

has to be the major factor limiting aquatic growth. Further evidence

of this is the practice of fertilizing farm ponds to promote the growth

of algae which prevent growth of aquatic plants (presumably by shading).

The light saturation level of submersed plants is probably very low

as well as rates of photosynthesis at light saturation.

Summary

The object of these studies was to determine why hydrilla can

rapidly dominate the submersed vascular flora of a body of water. The

nature of the problem was such that several parameters were examined

in three submersed species. The lack of previously reported research

in this area necessitated studies of three plants in order to obtain

valid comparisons.

Hydrilla had a higher rate of photosynthesis than the other species.

The higher proportion of chlorophyll b in hydrilla also may be an im-

portant factor for growth. The morphology of the hydrilla canopy and








hydrilla's reproductive potential cannot be discounted in the expression

of dominance over other species. The lack of a significant production

of roots by hydrilla Favors rapid growth of the upper portions or) the

plant. No single factor can explain the dominance demonstrated by

hydrilla, but the physiological characteristics presented here, and

possibly others, make hydrilla well adapted for continued growth and

expansion in natural and man-made waterways.

Submersed aquatic plants are most similar to C3 plants, with the

exception of their extremely low productivity which probably results

from growth under low light intensities. Their low CO2 compensation

points and lack of photorespiration are undoubtedly further examples

of the adaptation of plants to their environments.













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87


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1














BIOGRAPHICAL SKETCH

William T. Hailer was born June 28, 1947 in Watertown, New York.

Elementary and high school education was obtained at LaFargeville

Central School. He received the New York State Regents Diploma in

1965. The requirements for the Bachelor of Science degree were

completed at Cornell University in June 1969. He entered graduate

school at the University of Florida in June 1969, and was awarded the

degree Master of Science in Agriculture in June 1971. In April 1972,

he received the Fred H. Hull Research and Achievement Award for out-

standing research in Agronomy. He completed his Doctor of Philosophy

degree in Agronomy in August 1974. He is married to the former Jean

L. Caswell and has two sons. Professional memberships include the

Ecological Society of America, Weed Science Society of America, and

the Hyacinth Control Society.


1








I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.






Sherlie H, West, Chairman
Professor of Agronomy and
Assistant Dean for Research

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.



72 /9 1/

David L. Sutton, Co-Chairman
Assistant Professor of Agronomy

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.





Leon A. Garrard
Associate in Plant Physiology

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.



------j

Earl G. Rodgers
Professor of Agronomy









I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.


Jo3oph S. Davis
Associate Professor of Botany




This dissertation was submitted to the Dean of the college of
Agriculture and to the Graduate Council, and was accepted as partial
fulfillment of the requirements for the degree of Doctor of Philosophy.

August, 1974


7/ g'y, ---


Dean, Coll, e of Agriculture


Dean, Graduate School




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