Root-zone temperature and soil moisture effects on growth and physiology of container-grown 'Grande Naine' banana and Ix...

MISSING IMAGE

Material Information

Title:
Root-zone temperature and soil moisture effects on growth and physiology of container-grown 'Grande Naine' banana and Ixora chinensis L. 'Maui'
Physical Description:
xii, 172 leaves : ill. ; 28 cm.
Language:
English
Creator:
Ramcharan, Christopher, 1943-
Publication Date:

Subjects

Subjects / Keywords:
Bananas   ( lcsh )
Ixora chinensis   ( lcsh )
Horticultural Science thesis Ph. D
Dissertations, Academic -- Horticultural Science -- UF
Genre:
bibliography   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1987.
Bibliography:
Bibliography: leaves 160-171.
Statement of Responsibility:
by Christopher Ramcharan.
General Note:
Typescript.
General Note:
Vita.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 000951394
oclc - 16959530
notis - AER3637
sobekcm - AA00004845_00001
System ID:
AA00004845:00001

Full Text










ROOT-ZONE TEMPERATURE AND SOIL MOISTURE EFFECTS
ON GROWTH AND PHYSIOLOGY
OF CONTAINER-GROWN 'GRANDE NAINE' BANANA
AND IXORA CHINENSIS L. 'MAUI'





By

CHRISTOPHER RAMCHARAN


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


UNIVERSITY OF FLORIDA


1987














ACKNOWLEDGEMENTS


I want to especially thank my major advisor, Dr.

Dewayne. L. Ingram. He impressed upon me the art of

scientific writing, an enthusiasm for research and the will

to persevere. Also, I wish to thank the other members of my

committee, Drs. Terril Nell, James Barrett, Jerry Bennett and

William Wiltbank, for their encouragement and critical

evaluation of my work.

I am deeply grateful to the United States Department of

Agriculture whose financial support and grant made this

research possible and to the Department of Ornamental

Horticulture for support staff, equipment and services. The

contributions of Ms. Claudia Larsen for laboratory and

technical assistance and T.D. Townsend of the greenhouse

staff are highly appreciated.

I would like to thank Oglesby nursery for the generous

donations of banana plants and Mr. George Behren of Behren's

nursery for the ixora plants used in this study.

Last, but certainly not least, sincere thanks go to my

family. The support of my wife Senovia throughout the course

of these studies was invaluable. Finally, I wish to

acknowledge my children: they gave me the purpose for which

it was done.














TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS ...... ........................... ....... ii

LIST OF TABLES ......................................... v

LIST OF FIGURES ..................................... vii

ABSTRACT ......................... .................... xi

CHAPTERS

I GENERAL INTRODUCTION ......................... 1

II LITERATURE REVIEW ............................ 4

Introduction ... ...................... 4
Water Stress Physiology .................. 5
Physiological Effects of Root-Zone
Temperature ............... ............. 12
Root-Zone Temperature and Soil Moisture
Interactions ............................ 18

III EFFECTS OF IRRIGATION VOLUME ON BANANA
AND IXORA UNDER TWO GROWING CONDITIONS ....... 22

Introduction ....... ........... .o........ 22
Materials and Methods .................... 23
Plant Materials and General Cultural
Procedures ............................. 23
Greenhouse ........................... 23
Experiment 1 ...................... 23
Experiment 2 ....................... 26
Growth Room .......................... 26
Experiment 3 ....................... 26
Results and Discussion ................... 27
Greenhouse ......................... 27
Experiment 1--banana ............... 27
Experiment 1--ixora ................ 34
Experiment 2--banana ............... 40
Experiment 2--ixora ................ 42
Growth Room ........................... 42
Experiment 3--banana ............... 42
Experiment 3--ixora ................ 50


iii









IV ROOT-ZONE TEMPERATURE EFFECTS ON BANANA AND
IXORA UNDER TWO GROWING CONDITIONS ........... 56

Introduction ............................. 56
Materials and Methods .................... 57
Plant Materials and General Cultural
Procedures ............................ 57
Experiment 1--Greenhouse .............. 57
Experiment 2--Growth Room ............. 60
Results and Discussion ...................... 61
Experiment 1--Greenhouse .............. 61
Banana .............................. 61
Ixora .............................. 65
Experiment 2--Growth Room ............. 68
Banana ............................. 68
Ixora .............................. 72

V ROOT-ZONE TEMPERATURE AND SOIL MOISTURE
EFFECTS ON BANANA AND IXORA UNDER TWO
GROWING CONDITIONS ................. ... 77

Introduction .............................. 77
Materials and Methods .................... 78
Plant Materials and General Cultural
Procedures .............................. 78
Experiment 1--Greenhouse .............. 79
Experiment 2--Growth Room ............. 84
Results and Discussion ................... 86
Experiment 1--Greenhouse .............. 86
Physiological responses--banana .... 86
Growth responses--banana ........... 93
Carbohydrate analysis--banana ...... 100
Physiological responses--ixora ..... 104
Growth responses--ixora ............ 109
Carbohydrate analysis--ixora ....... 118
Experiment 2--Growth Room ............. 120
Physiological responses--banana .... 120
Growth responses--banana ........... 128
Carbohydrate analysis--banana ...... 132
Physiological responses--ixora ..... 137
Growth responses--ixora ............ 145
Carbohydrate analysis--ixora ....... 150

VI SUMMARY AND IMPLICATIONS ..................... 153

LITERATURE CITED .................................... 160

BIOGRAPHICAL SKETCH ............ ...................... 172














LIST OF TABLES


Page

5-1. Growth components of 'Grande Naine' banana
measured after 10 weeks at four root-zone
temperatures and two irrigation volumes under
greenhouse conditions ............................ 94

5-2. Dry weight components of 'Grande Naine' banana
measured after 10 weeks at four root-zone
temperatures and two irrigation volumes under
greenhouse conditions ............... ............ 98

5-3. Shoot and root carbohydrate distribution of
'Grande Naine' banana at four root-zone
temperatures and two irrigation volumes under
greenhouse conditions ............................ 101

5-4. Growth components of Ixora chinensis L.'Maui'
measured after 10 weeTks at four root-zone
temperatures and two irrigation volumes under
greenhouse conditions ............................ 112

5-5. Shoot and root carbohydrate distribution of
Ixora chinensis L. 'Maui' measured after 10 weeks
at four root-zone and two irrigation volumes
under greenhouse conditions ...................... 119

5-6. Growth components of 'Grande Naine' banana
measured after six weeks at four root-zone
temperatures and two irrigation volumes under
growth room conditions .......................... 129

5-7. Dry weight components of 'Grande Naine' banana
measured after six weeks at four root-zone
temperatures and two irrigation volumes under
growth room conditions ........................... 130

5-8. Shoot and root carbohydrate distribution of
'Grande Naine' banana at four root-zone
temperatures and two irrigation volumes under
growth room conditions ........................... 134








5-9. Growth components of Ixora chinensis L.'Maui'
measured after six weFes at four root-zone and
two irrigation volumes under growth room
conditions ........................................... 146

5-10. Dry weight components of Ixora chinensis L.'Maui'
measured after six weeks at four root-zone
temperatures and two irrigation volumes under
growth room conditions ............................. 147

5-11. Shoot and root carbohydrate distribution of
Ixora chinensis L. 'Maui' measured after six weeks
at four root-zone temperatures and two irrigation
volumes under growth room conditions ............... 151














LIST OF FIGURES


Page

3-1. Photosynthetic photon flux density and relative
humidity in the greenhouse during measurements
of physiological parameters ....................... 24

3-2. Effects of three irrigation volumes on the
diurnal physiological responses of 'Grande
Naine' banana under greenhouse conditions ......... 29

3-3. Effects of three irrigation volumes on the
diurnal water use efficiency of 'Grande Naine'
banana under greenhouse conditions ................ 33

3-4. Effects of three irrigation volumes on the
diurnal physiological responses of Ixora
chinensis L. 'Maui' under greenhouse
conditions ........................................... 36

3-5. Effects of three irrigation volumes on the
diurnal water use efficiency of Ixora
chinensis L. 'Maui' under greenhouse
conditions ........................................ 39

3-6. Effects of a 14 day drying cycle on leaf water
potential and leaf conductance of 'Grande Naine'
banana under greenhouse conditions ................ 41

3-7. Effects of a 14 day drying cycle on leaf water
potential and leaf conductance of Ixora
chinensis L. 'Maui'under greenhouse
conditions ........................................ 43

3-8. Effects of three irrigation volumes on the
diurnal physiological responses of 'Grande Naine'
banana under growth room conditions ............... 45

3-9. Effects of three irrigation volumes on the
diurnal water use efficiency of 'Grande Naine'
banana under growth room conditions ............... 49


vii








3-10. Effects of three irrigation volumes on the
diurnal physiological responses of Ixora
chinensis L. 'Maui' under greenhouse
conditions ......... .............................. 52

3-11. Effects of three irrigation volumes on the
diurnal water use efficiency of Ixora
chinensis L. 'Maui' under growth room
conditions ......... .. .... ..... ................... 55

4-1. Photosynthetic photon flux density and relative
humidity in the greenhouse during measurements of
physiological parameters ......................... 58

4-2. Effects of four root-zone temperatures on the
diurnal physiological responses of 'Grande
Naine banana grown under greenhouse
conditions ........................................ 63

4-3. Effects of four root-zone temperatures on the
diurnal physiological responses of Ixora
chinensis L. 'Maui' grown under greenhouse
conditions ............... ..... .................. 67

4-4. Effects of four root-zone temperatures on the
diurnal physiological responses of 'Grande
Naine' banana grown under growth room
conditions .................... .................. 70

4-5. Effects of four root-zone temperatures on the
diurnal physiological responses of Ixora
chinensis L. 'Maui' grown under growth room
conditions ........................................ 74

5-1. Photosynthetic photon flux density and relative
humidity in the greenhouse during measurements of
physiological parameters ................ .............. 80

5-2. Effects of four root-zone temperatures and a 50+5
ml daily irrigation volume per 555 cm3 container
on the diurnal physiological responses of 'Grande
Naine' banana grown under greenhouse
conditions ........................................ 88

5-3. Effects of four root-zone temperatures and a 100+10
ml daily irrigation volume per 555 cm3 container
on the diurnal physiological responses of 'Grande
Naine' banana grown under greenhouse
conditions ......................................... 90

5-4. Regressions of midday physiological responses of
container-grown 'Grande Naine' banana over
four root-zone temperatures and two irrigation
volumes under greenhouse conditions .............. 92


viii








5-5. Effects of four root-zone temperatures across
two irrigation volumes on leaf area of the third
newest leaf in container-grown 'Grande Naine'
banana measured over 10 weeks under greenhouse
conditions ........................................ 96

5-6. Effects of four root-zone temperatures and two
irrigation volumes on shoot/root ratio and root
dry weight of container-grown 'Grande Naine'
banana grown under greenhouse conditions .......... 99

5-7. Effects of four root-zone temperatures and two
irrigation volumes on root sugar/starch content
of container-grown 'Grande Naine' banana
under greenhouse conditions ....................... 103

5-8. Effects of four root-zone temperatures and a 50+5
ml daily irrigation volume per 555 cm3 containeF
on the diurnal physiological responses of Ixora
chinensis L. 'Maui' grown under greenhouse
conditions ........................................ 106

5-9. Effects of four root-zone temperatures and a 100+10
ml daily irrigation volume per 555 cm3 container
on the diurnal physiological responses of Ixora
chinensis L. 'Maui' grown under greenhouse
conditions .... ........... ......................... 108

5-10. Regressions of midday physiological responses of
container-grown Ixora chinensis L. 'Maui' over
four root-zone temperature and two irrigation
volumes under greenhouse conditions ............... 111

5-11. Main effects of four root-zone temperatures
across two irrigation volumes on growth of Ixora
chinensis L. 'Maui' grown under greenhouse
conditions ........................................ 115

5-12. Effects of four root-zone temperatures and two
irrigation volumes on dry weight components of
container-grown Ixora chinensis L. 'Maui'
grown under greenhouse conditions ................. 117

5-13. Effects of four root-zone temperatures and a 75+8
ml daily irrigation volume per 1200 cm3 container
on the diurnal physiological responses of
container-grown 'Grande Naine' banana grown under
growth room conditions ............................ 122

5-14. Effects of four root-zone temperatures and a 150+15
ml daily irrigation volume per 1200 cm3 containeF
on the diurnal physiological responses of container-
grown 'Grande Naine' banana grown under
growth room conditions ............................ 124








5-15. Regressions of midday physiological responses
of container-grown 'Grande Naine' banana over
four root-zone temperatures and two irrigation
volumes under greenhouse conditions ............... 127

5-16. Effects of four root-zone temperatures across
two irrigation volumes on chlorophyll
concentration of container-grown 'Grande Naine'
banana under growth room conditions ............... 133

5-17. Interactive effects of four root-zone temperatures
and two irrigation volumes on carbohydrate content
of container-grown 'Grande Naine' banana
under growth room conditions ...................... 137

5-18. Effects of four root-zone temperatures and a 75+8
ml daily irrigation volume per 1200 cm3 container
on the diurnal physiological responses of
Ixora chinensis L. 'Maui' grown under growth
room conditions ................................... 140

5-19. Effects of four root-zone temperatures and a 150+15
ml daily irrigation volume per 1200 cm3 container
on the diurnal physiological responses of
Ixora chinensis L. 'Maui' grown under growth
room conditions .................................. 142

5-20. Regressions of midday physiological responses
of container-grown Ixora chinensis L. 'Maui'
over four root-zone temperatures and two
irrigation volumes under growth room
conditions ..... ................ ................... 144

5-21. Effects of four root-zone temperatures and two
irrigation volumes on growth of container-grown
Ixora chinensis L. 'Maui' under growth room
conditions ........................................ 149











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

ROOT-ZONE TEMPERATURE AND SOIL MOISTURE EFFECTS ON GROWTH
AND PHYSIOLOGY OF CONTAINER-GROWN 'GRANDE NAINE'
BANANA AND IXORA CHINENSIS L. 'MAUI'

By

Christopher Ramcharan

May 1987

Chairman: Dewayne L. Ingram
Major Department: Horticultural Science

Studies to investigate the effects of root-zone

temperature (RZT) and irrigation volume (IRV) on growth and

physiological responses of 'Grande Naine' banana (Musa spp.

AAA) plantlets and Ixora chinensis L. 'Maui' were conducted

under greenhouse (GH) and growth room (GR) environments.

Leaf photosynthesis (PS), conductance (CS) and

transpiration (TR) in the GH were reduced 65%, 57% and 49%,

respectively, in banana under an IRV of 20+4 ml daily per 150

cm3 container as compared with the highest IRV of 40+8 ml

daily per container. Measured parameters were severely

reduced at an IRV of 10+2 ml per container. Physiological

responses of ixora were also reduced by decreased IRV. Leaf

wilting occurred at a leaf water potential (LWP) of -1.1 MPa

and leaves abscised below a LWP of -2.1 MPa.









In an RZT study, maximum midday PS in banana occurred at

the 330C RZT in a GH and a maximum midday PS of 0.74 mg CO2

m-2 s-1 was observed in 330 and 380C RZT-treated plants in a

GR. In ixora, a 330C RZT induced a maximum midday PS in the

GH but there were no apparent differences in PS between 280,

330 and 380C RZTs in the GR study.

Maximum PS in banana occurred at 380 and 330C RZTs under

a higher IRV of 100+10 ml daily in the GH. In the GR, maximum

PS occurred in 330C RZT-treated plants and the higher IRV but

at 380C RZT under a moderate IRV (75+8 ml daily). Increasing

RZT reduced leaf area under both IRVs. Carbohydrate (CHO)

partitioning between shoot and root was correlated with RZT-

induced changes in LWP.

Gas exchange processes in ixora were reduced by RZTs

above 330C RZT regardless of IRVY. RZT-induced shoot growth

was not associated with increased PS or TR but a hormonal

role was theorized. CHO partitioning was likely related to

the induced shoot growth and was influenced by environmental

conditions.

These findings could have significant applications to

banana production schemes using tissue-cultured plants. RZTs

above 330C could reduce the landscape and floricultural value

of container-grown ixora.


xii













CHAPTER I

GENERAL INTRODUCTION



Temperature and water are perhaps two of the most

important environmental factors affecting growth and

physiology of plants. Although soil moisture can be modified

by irrigation, altering temperature is more difficult.

Extreme temperatures produce deleterious but often subtle

effects. Soil temperature and water are interrelated since

both directly affect plant roots. Maintaining optimum water

relations and temperature may be difficult, especially with

container-grown species.

Hot and dry conditions often occur simultaneously in

crop situations and alleviating the latter is often

considered a remedy for the former. Although many drought

tolerant plants are heat tolerant (85), the interactions

between temperature and water stresses have not been well

defined (102). Suboptimal root-zone temperatures (RZT) stress

plants through reduced respiration, increased water viscosity

(82) and reduced absorption caused by decreased cell membrane

permeability (74). In this context, increased RZTs, within

limits, are believed to have the reverse effect and so

increase water (5,30) and possibly nutrient absorption

(39,44).









Within limits, increased soil temperatures have

generally increased shoot growth curvilinearly (30).

Restricted shoot or leaf elongation is usually the first

symptom of mild water stress (57). Reduced soil water might

offset increased shoot growth induced by increasing soil

temperature to within the optimum range. A similar induction

of increased nutrient absorption by increasing soil

temperature may occur thus permitting less than normal

nutrient application. Such a recommendation was made for

peppers (Capsicum annuum L.) grown at a supraoptimal RZT of

360C (44).

Water stress, by its immediate effect on shoot growth

but delayed action on photosynthesis (13), has been shown to

increase shoot carbohydrate concentrations (8,119). Increased

root temperature has also been shown to reduce shoot

carbohydrates (7), again suggesting the possibility of

interactive effects between the two stress factors. Indeed

some pasture grasses were of better quality because of higher

carbohydrate levels under high temperature and dry conditions

as opposed to being irrigated (18).

Interactive effects of soil water and RZT on

translocation and carbohydrate partitioning patterns have

been reported (7,8). Increased RZTs have altered

translocation rates due to increased sink demands of roots

(46). Water stress could reduce translocation by its effect

on reduced turgor pressure and the consequent effect on

decreased mass flow of assimilates.









Therefore, the overall objective of this study was to

identify the effects of supraoptimal RZT and water deficits

on two container-grown plants. The specific objectives were

to

1) Determine growth and physiological effects on 'Grande

Naine' banana (Musa spp. AAA) and ixora (Ixora chinensis L.

'Maui') and to elucidate whether the two stress factors act

independently or interactively.

2) Identify any compensatory type interactions that may

be exploited in container production of plants.

3) Determine if drought stress can be induced by high

RZT, identify critical RZTs and observe whether watering

offsets temperature-induced water stresses.

Banana and ixora were selected because they represent a

contrast in morphology, phenotype and horticultural usage.

The use of tissue-cultured banana plants in this study

represents a unique application of micropropagation as a tool

in plant physiology. The choice of banana was also in

anticipation of the stress problems that may arise in the

banana production schemes that convert to the use of tissue-

cultured plantlets.














CHAPTER II

LITERATURE REVIEW



Introduction



Temperature and water stress affect plant growth and

physiological processes. The literature is abundant with data

describing their independent effects but there have been few

attempts to separate the effects of these two stress factors

when applied in combination. Any attempt to determine

interactions between soil water and temperature on plants

must first review or determine their independent effects.

While it is generally accepted that water stress reduces

expansive growth and induces a progressive reduction in gas

exchange processes, the effects of supraoptimal RZTs have not

been clearly identified. Soil water deficits usually reduce

plant water status and supraoptimal RZTs may affect root

absorption and conductance and indirectly stomatal function.

However, plant water stress can occur even with adequate soil

water when ambient conditions favor excessive transpiration

or water absorption is inhibited by factors including high

RZT.

Since supraoptimal root temperature directly affects

root respiration and metabolism, its effect on partitioning







5

patterns within the plant seems likely more direct than that

of water stress.

Water stress physiology

Water stress basically results from an imbalance

between soil water absorption and that required by plants to

meet transpirational needs. Kramer (74) stated that plant

water stress is caused by either excessive water loss,

inadequate absorption or a combination of the two. In

general, an increase in water stress produces a two phase

response in photosynthesis, with a threshold water potential

above which there is little or no change in photosynthesis

and below which the rate decreases rapidly (114). A water

potential of -0.4 MPa reduced the photosynthetic capacity of

loblolly pine with assimilation being negligible at -1.1 MPa

(17). This effect was caused by stomatal closure which

reduced transpiration as well as photosynthesis. Water stress

may affect photosynthesis via three major mechanisms (131):

1) by stomatal closure, 2) by cellular dehydration which

reduces enzyme activity, and 3) by decreasing cell membrane

permeability to carbon dioxide and bicarbonate.

Although stomatal closure has been cited as the primary

method by which water stress affects photosynthesis

(13,78,132), there are several reports of non-stomatal

reductions in photosynthesis (14,23,49,114). Many species

that exert some degree of stomatal limitation on

photosynthesis at low water potentials characteristically

have high mesophyll resistance (50,141). When the components









of leaf resistance to C02 were measured for several species,

mesophyll resistance was found to be lower than stomatal

resistance but about ten times that of boundary layer

resistance (139). Soil water deficit also affects the diurnal

pattern of stomatal aperture (33) with progressively earlier

closing under prolonged drought conditions (93).

Stomatal closure affected photosynthesis mainly by its

effect on the carbon dioxide supply (13,17). However, some

researchers agree that photosynthesis is evident even when

stomata are closed (93). Because of their diffusive nature,

photosynthesis and transpiration are both affected by

stomatal closure, although transpiration may be affected more

than photosynthesis (48,120). Photosynthesis was reduced 25%

while transpiration decreased 50% in apple (Malus pumila

Mill.) under drought conditions (51). Zelitch (149) indicated

that partial stomatal closure reduced transpiration

relatively more than photosynthesis. Although the diffusive

resistance of CO2 was larger than that of water, CO2 also

encountered a vastly greater mesophyll resistance than water.

Consequently, the stomata represented a smaller portion of

the total resistance to CO2 than to water vapor.

Moorby et al. (95) found no effect of drought on the

activity of ribulose 1,5-diphosphate (RUDP) carboxylase or

carbonate dehydratase, two enzymes involved in CO2 fixation.

Ackerson et al. (1) however, reported that water stress

reduced the activity of photosynthetic enzymes of potato

(Solanum tuberosum L). Lawlor (84) indicated that ATP







7

synthesis through photophosphorylation was inhibited by water

stress while electron transport and reductant supply were

relatively insensitive. Boyer (14) demonstrated that

photosynthesis of water stressed sunflower (Helianthus annuus

L.) plants under growth chamber conditions was affected more

by photochemical activity than by CO2 diffusion or enzymatic

activity. Davies (33) showed that stomatal sensitivity to

decreasing leaf water potential in cotton (Gossypium hirsutum

L.) and soybean (Glycine max. L.) was greater for plants

grown in a growth chamber than in a greenhouse.

When soil moisture is adequate, diurnal fluctuations in

xylem pressure potential closely followed the daily trend of

atmospheric evaporative demand, whether expressed as

radiation, vapor pressure or humidity (22,71,121). As soil

moisture becomes limiting, early morning leaf water

potentials (LWP) begin at a lower value, decrease sharply and

then remain constant over several hours, reflecting the

influence of increased stomatal resistance (29,108).

Threshold relationships between diffusive resistance and leaf

water potential appear to be more common than linear or

curvilinear relationships (52,67,68). Brix (17) showed that

net assimilation rate (NAR) was closely related to LWP; NAR

began to decrease at -1.0 MPa and completely ceased at -3.5

MPa. Other reports (53,79,113) indicated that parallel

decreases in NAR and LWP were strongly linked to changes in

diffusive resistance. However, NAR changes in pear (Pyrus

communis L.) (77), Pacific silver fir (Abies alba Mill.) and







8

noble fir (Abies nobilis Lindl.) (55) did not always coincide

with changes in diffusive resistance indicating the influence

of mesophyll and or carboxylation resistance. It was

concluded that species vary considerably in their

physiological reactions to water deficits.

The majority of studies on water stress in banana have

dealt primarily with the effects on fruit bunch and yield

characteristics, but with few details reported on

morphological, phenological and physiological responses.

However, all reports agree that water stress causes a general

reduction in growth (19,111,136). Daniells (31) in Australia

indicated a dramatic reduction in growth, delayed bunch

emergence, inferior fruits and longer maturity time for

'Williams' banana under decreasing soil water levels.

Robinson and Albertson (116) reported that optimum growth and

yields were obtained by maintaining soil moisture levels at

16 to 34% of total available soil moisture (ASM).

Bhattacharyya and Rao (10) also reported optimum bunch and

yield characteristics with 20 to 40% ASM depletion levels. An

unimpeded supply of water was essential for development of an

efficient root system, rapid rate of leaf emergence,

continued production and partitioning of assimilates, and

synthesis of growth hormones such as cytokinins. In Honduras,

Ghavami (40) found an irrigation rate of 44 mm/week or a soil

moisture tension of 30 to 40 centibars resulted in the

highest yields of 'Valery' banana.







9
Perhaps the most detailed description of the effects of

soil water levels on banana physiology was recorded by

Shmueli (126) in his paper on the physiological activity of

banana in relation to soil moisture in Israel. Depletion of

soil moisture below a third of the available water capacity

was accompanied by marked yellowing of leaves and significant

reduction in stem diameter. Diurnal changes in stomatal

activity were clearly related to ASM. When soil moisture

decreased below two-thirds of total ASM, there was a

reduction in stomatal conductance which was confined mainly

to the morning hours. The impairment of plant water balance

became acute when soil moisture decreased to about one-third

of the total available. Although diurnal patterns of stomatal

conductance and transpiration generally paralleled each

other, the rate of transpiration was considerably more

influenced by environmental conditions. Soil moisture levels

below two-thirds of field capacity resulted in reduced leaf

osmotic potential. Overall, banana plants responded to

diminishing soil moisture by stomatal closure, reduced

assimilation and accelerated yellowing of leaves indicative

of starvation effects.

Current efforts to increase agricultural production,

coupled with conservation of limited high quality water, have

focused attention on the possibility of increasing water use

efficiency (WUE) of various crops (16,88,97). Fischer and

Turner (38) observed that under field conditions, WUE usually

remained constant or increased slightly with increasing soil







10

water limitations for C3 species. Reports on the effects of

water stress on WUE are conflicting. Some investigations

pointed to only small increases in WUE with water stress

(16,38,97). Reduction of water supply to wheat

(Triticum aestivum L.) such that transpiration was reduced by

70% of the controls was associated with a 20% increase in WUE

(41). On the other hand, WUE in maize (Zea mays L.) was lower

on days when there was increasing soil water stress (128).

Limited soil water resulted in yield losses but enhanced WUE

in grapefruit (Citrus paradisi L.) (16) and Shamouti orange

(Citrus sinensis Osb.) (97). Manning et al. (86) found a

positive correlation of WUE with soil moisture regime, plant

height, leaf area and seed yield in pea [Pisum sativum (L.)

Mer.].

Adequate irrigation was critical for vegetative growth

in coffee (Coffea arabica L.) (4,72) and water stress reduced

extension growth, node number and leaf area (138). Ten and 25

ml water/day/coffee seedling in 15 cm pots resulted in

drastic growth reduction, wilting and necrosis of the

terminal shoots compared to a 200 ml treatment which caused

water logging and induced leaf abscission (72).

Water stress has been shown to cause specific changes in

plant carbohydrate status. Decreased starch concentration

simultaneous with increased sugar content during drought

stress have been reported for sugar maple (Acer saccharum

Marsh.) (106) and black oak (Quercus velutina Lam.) (107). In

sugar maple total carbohydrates were not affected, indicating









a change in carbohydrate partitioning. Similar changes in

carbohydrates occurred in the inner bark of loblolly pine

(Pinus taeda L.) (56) and in cotton shoots (36). Water stress

induced increases in sugar concentration may serve several

purposes, of which two are of major significance. Increased

sugars increase the readily available substrate for

respiration (17). A second effect of increased free sugars

during water stress is to lower the osmotic potential of the

cell solution and hence maintain cell turgor. Concentration

and form of carbohydrates, organic acids or inorganic ions

are modified to promote osmotic regulation (74). A more

negative leaf solute potential with water stress was observed

in seedlings of English oak (Quercus robur L.) and silver

birch (Betula pendula Rodt.) but the degree of osmotic

regulation varied between species (105).

Munns and Pearson (98) found that reduced photosynthesis

as a result of water stress was not caused by accumulation of

photosynthates in potato leaves. Low leaf water potential

resulted in decreased translocation of carbohydrate, which

was proportional to the decline in net photosynthesis,

irrespective of whether tubers were present. A lower

proportion of labelled 14C02 was found in tubers of stressed

potato plants compared to non-stressed plants (125).

One of the earliest plant responses to water stress is

reduced elongation of leaves, stems and roots (57).

Boyer (13) found that leaf enlargement of corn and soybean







12

was inhibited earlier and more severely than photosynthesis

and respiration by decreasing water potentials.


Physiological Effects of Root-Zone Temperature

According to Levitt (85) the two major forms of stress

injury are direct and indirect injury. Direct heat injury

results from a short exposure to an extreme temperature and

is detectable immediately at the cellular level. Indirect

injury results from prolonged exposure to temperatures below

those causing direct injury.

Supraoptimal temperature stress may be defined as the

retardation or cessation of metabolic functions in response

to high temperatures. Alexandrov (3) reported that the first

symptom of high temperature was the cessation of protoplasmic

streaming. This was followed by a reduction in photosynthesis

with subsequent damage to the chloroplasts. Finally,

semipermeability of cell membranes was disrupted, so that

cellular compartmentalization was lost with mixing of

cellular contents.

Starvation, a common form of indirect heat injury in

plants, occurs because of a higher optimum temperature for

respiration than photosynthesis (85). The temperature at

which photosynthesis and respiration rates are equal is the

temperature compensation point. When plant temperatures

exceed this critical point, carbohydrate reserves become

depleted and starvation ensues. Other forms of indirect

metabolic injury (85) are toxicities resulting from







13

disturbance of specific metabolic processes and biochemical

lesions resulting from the accumulation of metabolites

necessary for plant growth.

Ingram and Buchanan (61,62) demonstrated that electrol-

yte leakage through root cell membranes in response to

increasing supraoptimal temperatures was sigmoidal and the

midpoint of this response was defined as the critical

temperature. Critical temperature was species and cultivar

specific and varied from 480 to 530C for a 20 minute exposure

time (61,62). Direct injury at high temperature was also

shown to be a function of exposure time (60).

Proteins are denatured by high temperature (2) and there

is evidence that high temperature disrupts membrane

structure. Inhibition of photosynthesis at high temperature

was correlated with the disruption of membrane associated-

processes including photosystem II (108),

photophosphorylation (123) and the change of chlorophyll

organization (122). The stability of membranes is mainly due

to the degree of fatty acid saturation which is linked to

membrane function and organelle association (145).

Environmental temperatures have been demonstrated to alter

fatty acid saturation ratios and membrane fluidity as

adaptive responses to high and low temperatures

(24,27,28,45,87).

There are several reports of the effects of growth

medium temperature on water uptake by roots (70,89,104,115).

Water conductivity through roots appears to be a temperature-









dependent process (117). Low temperature reduced

transpiration and stomatal conductance in chill-susceptible

species by reducing conductance through root cell membranes

(75,104,147). Such results are most likely due to increased

resistance to water at the endodermis layer (89).

Heating the root-zone to temperatures within the optimum

range generally improved plant growth (12,42,83) and heating

the root medium to 200C improved foliage plant production at

low greenhouse air temperatures (12). Root temperatures above

or below optimum may alter hydraulic conductivity and thus

indirectly affect stomatal conductance, photosynthesis and

subsequent carbohydrate translocation (66). Optimal root-zone

temperature in tomato (Lycopersicon esculentum Mill.) ranged

from 300 to 360C for nutrient translocation and water

absorption (42,58).

Using plants with heat-killed roots, Kramer (73) showed

that plant shoots remained alive and did not wilt for several

days even after root death. Transpiration decreased after

root death because of leaf injury and gum deposits from dead

cells. Citrus hydraulic root conductance increased linearly

with increasing root temperature (137) and Carrizo citrange

exhibited a log-linear decrease in conductivity over a

temperature range from 400 to 100C (146).

Cooper (30) published an extensive literature review in

1973 on RZT effects and reported important differences due

not only to species and cultivars but also to growing

conditions. High leaf photosynthetic rates in soybean grown








at increasing RZT were related to low stomatal resistance,

high transpiration rate and high phosphoenol pyruvate and

RUDP carboxylase content (35). Cucumber (Cucumis sativus L.)

leaves were larger, contained more chlorophyll and produced

greater amounts of ATP and NADPH when plants were grown at

250C RZT compared to 150 or 350C (26). Canopy photosynthesis

of pepper plants was closely related to shoot dry weight and

crop yield (44), although maximum growth and yields were

obtained at 300C RZT and maximum photosynthesis rates were

recorded at 360C RZT. The disparity between optimal RZTs was

explained by increased rates of respiration at the higher

RZT. High rates of photosynthesis at high RZT in tomato were

due not only to increased plant size but also to a

modification of the physiological and morphological propert-

ies of the photosynthetic apparatus (43). Chlorophyll content

(26), enzyme activity (35) and leaf hormonal content (91)

have been influenced by increasing RZT.

Although many physiological processes are influenced by

high RZTs (30), there is relatively little information on the

effects of RZT on endogenous hormone levels (76). High RZTs

have been reported to increase gibberellin and decrease

cytokinin translocated in the root exudates (47,64,129).

There is also evidence that high RZT may affect the

distribution of gibberellin in the shoot (76). Alternatively,

high RZT may have increased the activity in the roots of

gibberellins previously synthesized in the shoot as well as

influenced synthesis in the shoot (110).









In a study on flowering in coffee (92), ambient

temperatures above 330C induced formation of orthotropic

shoots and prevented flower initiation. Root-zone heating

delayed flowering and induced excessive vegetative growth in

peppers (44). Such an antagonism between vegetative and

reproductive growth prompted the authors to recommend a

reduction in night temperature or nitrogen fertilization when

pepper plants are grown at high RZTs.

Reduced biosynthesis of cytokinins induced by supraopti-

mal RZT was thought to reduce photosynthetic rates in bean

(Phaseolus vulgaris L.) (21) and grape (Vitis vinifera L.)

(129). Increasing RZTs from 180 to 300C in rice (Oryza sativa

L.) increased the translocation and rate of

photosynthetically assimilated 14C into the roots but

decreased root growth apparently by retarding protein and

cell wall synthesis (96).

Temperature has long been recognized as the main

environmental determinant of plant growth and phenology (81).

Increased soil temperatures have generally increased shoot

growth curvilinearly and reduced root growth (30,112). All

growth variables of Pittosporum tobira Thunb. were

substantially lowered by a 400C RZT for 6 hrs/day compared to

270C (65), and Ingram (59) noted marked growth inhibition of

woody plants stressed by 350 to 400C RZT for 6 hrs/day.

Gosselin and Trudel (44) reported maximum leaf area in

pepper at a RZT of 300C with a decline at higher

temperatures. Watts (144) demonstrated reduced leaf expansion







17
in maize with increasing RZT but could not explain this as a

result of increased plant water deficits. RZTs above 370C

restricted leaf growth and rate of emergence in pearl millet

(Pennisetum typhoides S&H) (103). Soil temperatures of 370C

and above, which are common in the tropics, reduced both root

and shoot growth of maize and cowpea (Vigna unguiculata L.)

(90). Well-watered potted eggplants (Solanum melongena L.)

exhibited decreased plant growth with increasing RZT from 250

to 400C (118). Shoot to root ratio, however, was constant

except at 400C, where root rot occurred.

Philpotts (109) reported a linear decrease in cowpea

nodulation and total plant dry weight with increasing RZT

from 310 to 400C. RZTs above 320C significantly reduced

vegetative growth of two cultivars of cowpea through their

effects on shoot, peduncle and root dry weight and, to a

lesser extent, leaf number (94).

Using a system of circulating water coils, Franco

(39) applied RZTs from 130 to 480C and observed the effects

on coffee growth, transpiration and mineral absorption.

Maximum transpiration occurred at 330C with a significant

decline at 430C. Similarly, RZTs above 330C reduced

absorption of several nutrients and induced leaf chlorosis.

Plants growing at 480C died and both shoot and root growth

were depressed above 330C. In another experiment using young

coffee seedlings grown at 330C RZT, he reported the

occurrence of small tumors at the base of the stem from which

new orthotropic or non-flowering shoots grew.








In an extensive investigation using 'William' banana

in sunlit growth chambers, Turner and Lahav (142) reported

heat injury at an air temperature of 370C. Total plant weight

was greatest at 280C while leaf area was maximum at 330C.

Temperature altered partitioning patterns in the whole plant

and at 330C more leaves and less stem and roots were

produced, giving increased shoot to root ratios. Lamina leaf

folding also occurred at high air temperatures and the

authors implied that induced high vapor pressure deficits may

have been the cause. Severe constraints on data measurements

were imposed by the large nature of the banana plants and

restricted growth chamber space. This could, in part, explain

why critical physiological data such as photosynthesis,

transpiration and leaf water potential were not recorded.

Assimilate partitioning results were estimated using relative

growth rate formulae and no analyses on tissue carbohydrate

status were performed.


Root-Zone Temperature and Soil Moisture Interactions

The complexity of responses of RZT and soil moisture

stress alone are such that few researchers have attempted

studies on their interactive effects. Lal (80) reported in

1974 that a RZT of 350C significantly decreased root and

shoot growth and transpiration in maize seedlings. Effects of

high RZT were aggravated by low soil moisture levels. Changes

in soil water supply and RZT were found to have predictable







19

effects on the relationship between leaf water potential and

transpiration rate in several tree species (37,54,68,135).

Kaufmann (69) evaluated the effects of RZT (60 to 200C)

and two soil drying cycles (9 and 12 day) on water relations

and growth of Monterey pine (Pinus radiata. Don) under

greenhouse conditions. The slope of the relationship of xylem

pressure potential to transpiration was influenced by RZT.

Under well-watered conditions, neither transpiration nor

stomatal conductance were affected by RZT because xylem

pressure potential was not low enough to cause stomatal

closure. At the end of 9- and 12-day drying cycles, however,

transpiration was lower than in the well-watered controls as

a result of stomatal closure. RZT apparently had no consist-

ent effect on transpiration rate. Reduced RZTs and soil

drying both significantly reduced shoot and root extension

after 28 days even though low RZT did not cause stomatal

closure.

In an earlier study with 'Monterey' pine, Babalola et

al. (5) measured photosynthesis, transpiration and

respiration at four soil water levels and four RZTs (100 to

270C ). They found that the rates of photosynthesis, respi-

ration and transpiration decreased with increasing soil water

deficits. However, only at soil water levels lower than -0.7

bars and at RZTs of 10oC and above were the rates of

photosynthesis and transpiration affected similar to changes

in stomatal conductance.








Barlow et al. (7) studied the effects of RZT and soil

water potential on corn seedlings. This investigation also

did not involve supraoptimal temperatures but there were

notable interactive effects. Rates of leaf elongation, net

photosynthesis, transpiration and leaf water potential were

simultaneously monitored under varying stress conditions. In

their first study, leaf elongation was found to be much more

sensitive to changes in root temperature (120 to 280C) than

either photosynthesis or transpiration and ceased at a LWP of

-0.9 MPa; physiological responses were not affected until

LWPs of -1.2 to -1.3 MPa were attained. A decrease in net

photosynthesis coincided with an increase in stomatal and

mesophyll resistance at low LWPs. The authors concluded by

emphasizing the need for whole plant studies so that stress

effects on photosynthesis, translocation and assimilate

partitioning could be better analyzed.

Two root temperatures (21.10 and 26.60C) and two soil

water potentials (-0.35 and -2.50 bars) were employed in

their second experiment (8). Leaf elongation and total dry

matter were decreased 44% and 26%, respectively, soluble

carbohydrates increased 42% while rates of transpiration

decreased 24% at the low soil water potential. There were

also some interactions between RZT and soil water content.

Dry weights for plants at 21.100C and -0.35 bars were similar

to those at 26.60C and -2.50 bars. Higher soluble

carbohydrate concentrations with increased water stress were

offset by increased RZT. Decreased total plant dry weight and







21

transpiration at lower soil water levels were slightly offset

by higher RZT, presumably through increased root conductance

and water absorption.

Most of the studies involving soil temperature and

moisture interactions on banana in the tropics have been

field oriented and have involved the use of soil mulches

which effectively reduce soil temperature and conserve soil

moisture (10,11). In most cases, mulching led to increased

WUE which was based on a yield to evapotranspiration ratio

rather than on the physiological parameters of photosynthesis

and transpiration. In the case of coffee, there are

independent studies on soil temperature (39) and soil

moisture (4,72,138), but no reports on their interactive

effects.














CHAPTER III

EFFECTS OF IRRIGATION VOLUME ON BANANA AND IXORA UNDER
TWO GROWING CONDITIONS


Introduction


Although 'Grande Naine' banana (Musa spp. AAA) is a

mesophytic, herbaceous plant requiring moist soils for

optimum production (127), it can be grown in marginal areas

where soil water is limiting. Irrigation scheduled when

available soil moisture depletion reaches 60% to 80% has been

shown to be optimum (10,11,31,116), but detailed

characterization of physiological responses in banana to

decreasing soil water levels is lacking.

Moisture stress is thought to be necessary for flower

induction (4) in coffee, a close relative of ixora (Ixora

chinensis L. 'Maui') within the Rubiaceae family (6), but

adequate irrigation (72) is essential for growth and mineral

absorption (138). Because of its importance as a major

beverage crop, there are several field (100,101) and

container studies (39,72,138,140) on the physiological

responses of coffee, but no work has been conducted on the

effects of varying soil water levels on container-grown

ixora. The present study investigated the physiological

responses of banana and ixora to three irrigation levels and







23

a 14-day drying cycle. Irrigation experiments were conducted

under both greenhouse and growth room conditions.


Materials and Methods

Plant Materials and General Cultural Procedures

Ten- to 12-cm tall tissue-cultured banana plants and

similar-sized, uniform ixora rooted cuttings were obtained

from commercial nurseries. Plants were hardened with

intermittent mist (6 sec min-1) in a glass greenhouse at 280C

under 80% light exclusion for one week, then moved to 40%

light exclusion for another week. Plants were transplanted to

white 4-cm diameter x 21-cm tall conical containers (150 cm3)

using Metro-Mix 300 growth medium (W.R. Grace and Co.,

Cambridge, MA). Plants were then moved to the experimental

greenhouse or growth room where they were watered to

container capacity daily and allowed to acclimatize for one

week prior to the initiation of the experiment.

Greenhouse

Experiment 1. Experiment 1 was initiated in July, 1985,

in an air-conditioned greenhouse in which maximum

photosynthetic photon flux density (PPFD) ranged from 700 to

800 umol m-2 s-1, and temperatures were 25 to 300C day and 18

to 210C night. Relative humidity varied from 40 to 80%

(Figure 3-1).

Plants were watered daily at 2200 hr with 10+2 ml (W1),

20+4 ml (W2) or 40+8 ml (W3) per container. These irrigation





















0--- orLIiaiunH 3nl1ui3a IN33aJ3d

0 00
D 0 a0 a a
Sa it N


4-
La







-C

*r-


00 4.-





0 0

0 c
r-










-
C) Q.









otn



0L C
4J O-









0
.C
CO





(4



*rC ..
P E



0 *I.


Q 0) <
*r l
LL. 0


0 0 0 0- 0d
0 0 0 0 0

>E--- C.. t-7 lowifi Oidd


~reL-








volumes provided 53% to 60%, 65% to 75%, and 85% to 100%

container capacity (CC) respectively, for banana and 52% to

64%, 68% to 80% and 90% to 100% CC, respectively, for ixora.

The comparatively smaller root mass of ixora was responsible

for the difference in growth medium waterholding capacities

between these plants. Water was applied automatically through

drip tubes by a battery-operated controller (Water Watch

Corp. Seattle, WA). One, two and four 1-mm drip

tubes/container constituted the W1, W2 and W3 irrigation

treatments, respectively.

After 14 days of irrigation treatments, diurnal

measurements of leaf photosynthesis (PS), transpiration (TR)

and leaf conductance (CS) were made using a portable

photosynthesis system (Model LI-6000, LI-COR, Inc., Lincoln,

NE). Measurements were initiated at 0800 hr EDT on a

cloudless day and taken every 2 hr until 1600 hr. A 1-liter

cuvette chamber was used for measurements and the mean of

eight consecutive 30-sec observations on each leaf

constituted a measurement. A zero check of the analyzer was

performed between treatments within each replicate.

Simultaneous measurements of LWP were made using a Scholander

type pressure chamber (PMS Instrument Model 600, Santa
Barbara, CA) as described by Barrett and Nell (9). The third

most recently expanded leaf in banana was selected for

measurements of both gas exchange and LWP. This leaf has been

shown to be the most responsive and the youngest with fully

developed stomata (127). Gas exchange processes in ixora were








measured on the most recently matured leaves but apical

shoots were sampled for LWP. Six plants per treatment were

sampled for all measurements.

Experimental design was a randomized complete block with

21 plants per water treatment within each of three blocks.

Six replicate plants were randomly selected at each sampling

time. Water use efficiency (WUE) was calculated from PS/TR.

Means and standard errors were calculated and plotted against

time of day.

Experiment 2. In order to further monitor physiological

responses of water stress and correlate these with visual

plant symptoms, water was withheld from banana and ixora

plants for 14 days beginning one week after transplanting.

This drying cycle study was conducted simultaneously with

experiment 1 in the same greenhouse and similar cultural

practices were used. Midday LWP and CS measurements were

recorded on five plants of each species at 2-day intervals

using the procedures described in experiment 1. A completely

randomized design was used in this experiment and means and

standard errors were calculated. There were five replicate

plants per treatment for each sampling date.

Growth room.

Experiment 3. Experiment 1 was repeated in a 3.0 m by

7.6 m walk-in growth room in order to investigate

physiological responses to water stress under more precisely

controlled environmental conditions. Irradiance of 1100 umol

m-2 s-1 PPFD, as measured by a quantum radiometer (LI-COR








Model LI-185A, LI-COR Inc., Lincoln, NE), was supplied at

plant canopy level by 1000 W phosphor-coated metal-arc HID

bulbs (GTE Sylvania Corp., Manchester NH) from 0600 to 1830

hr daily. Air temperatures of 280C day and 2100C night and a

relative humidity of 65% to 70% were maintained. Three

irrigation volume treatments were applied as in experiment 1

in a randomized complete block design with three blocks and

21 plants per water treatment per block. Species were treated

and analyzed as separate experiments. On the fifteenth day

after water stress treatments, diurnal measurements were

initiated at 0800 hr and continued at 2-hr intervals until

1800 hr. Leaf sampling methods and measurement procedures for

PS, CS, TR and LWP were employed as in experiment 1.


Results and Discussion

Greenhouse

Experiment 1--banana. Irrigation treatments influenced

daily PS, CS and TR maxima as well as diurnal patterns

(Figure 3-2A, 3-2B, 3-2C). Relatively high LWP were

maintained by plants in the W2 and W3 irrigation treatments

but there was a distinct decline in LWP by 1000 hr in plants

receiving the lowest irrigation volume, W1 (Figure 3-2D).

PS patterns of plants under the W3 and W2 irrigation

treatments paralleled the corresponding CS patterns, with a

rise in PS from 0800 hr to a peak at 1400 hr of 0.20 mg CO2

m-2 s-1 for the W3 treated plants. Maximum PS for plants in

the W2 irrigation treatment were reduced almost three-fold



















4- r C
*- B r- *r-
d0 0) C 0

*.- 4.) *
0 0 LLi
o CL )
r- 0Q
0 L. C )
*i- ) 0 *r- -C
u C 4) Oe 4-)
> 0 E8 4+)
C r- 3: C 4-

*r- 4- 0
r- Y0
EU C 0(U 0
C 0 r- E L.
L. U U Q.
W 0
*r 0Q O La.
0 W L")




C0 C 0-

O S. i- U
0) 4 *r- Ur-
U) E"

EQ a*- o.
3 0w
'- C ) r- >


C S- OO C
C 3 4-) + IG
00 0
*r- S- *" )

o 11 C
t0)o E U
*- CU e r-
S- E0 C 3 0.
S.. CEU








4- 4- + IL.
0 Um C

U--0 U
S. 0 C i- *5-
S )C 10 E








4. CO 0.
4- + I

U*- r- *r
4'* C +1






0 (0 m
0 S.. C C' Q4-
4W 4JM
4-- -)
LU *u- *U)
4)- U) r- C




ZM 40 11

m- 00 0
3 .4-. II(
0)W)0 0

LL. S- 0.3: EU






























L-s wo) 30NvIOflNoo AV31


(0-9 Z-Au G0 "u) SS3HLLNASOOHd


00 tO 10
(&-e 3-W OW H &4 NOLLVIdSN&Mt


(BdY-) MiNL3Od U31VM









below plants at W3 (Figure 3-2A). PS for the W1 treated

plants was significantly reduced compared to plants in the

other irrigation treatments with a midday rate of only 0.003

mg C02 m-2 s-1.
CS in plants receiving the highest irrigation volume,

W3, averaged 0.37 cm s-1 at 0800 hr, had more than doubled by

1400 hr and declined sharply to 0.17 cm s-1 at 1600 hr

(Figure 3-2B). CS in plants under the W2 irrigation followed

the same pattern, but was reduced by 50%, 47% and 49% at

1000, 1200 and 1400 hr, respectively. CS in plants at the

lowest irrigation level did not change appreciably throughout

the day and averaged only 0.08 cm s-1, suggesting that the

stomata remained nearly closed throughout the day.

Therefore, PS and CS were severely reduced by decreased

irrigation and both declined in parallel.

Although TR increased from 0800 hr to 1000 hr for both

W2 and W3 treated plants, TR in W2 and W1 plants was

significantly lower (Figure 3-2C). TR remained somewhat

stable between 1000 and 1400 hr for all treatments and

declined significantly between 1400 and 1600 hr under the W3

irrigation volume. Maximum TR was 44.4, 14.2 and 6.3 mg H20

m-2 s-1 for the W3, W2 and W1 treated plants, respectively.

LWP of plants under the W2 and W3 irrigation treatments

were fairly stable throughout the day, but LWP of plants at

the lowest irrigation level declined significantly after 0800

hr to a low LWP of -0.90 MPa at 1000 and 1200 hr (Figure 3-

2D). Although there was an increase in LWP for W1 treated







31
plants after midday, the LWP at 1600 hr of -0.62 MPa remained

significantly lower than the 0800 hr LWP. The reduction in CS

and the decline in gas exchange processes but not leaf water

status at midday and 1400 hr for the W2 treated plants,

indicated that there were factors other than leaf water

status controlling stomatal opening.

Water use efficiency (WUE) for plants under the W3 and

W2 irrigation levels increased almost linearly throughout the

day but did not differ between treatments until 1200 hr,

after which WUE in W2 treated plants was higher (Figure 3-3).

This indicated that TR in plants under the W2 treatment was

reduced more relative to PS. However, the WUE pattern for the

severely stressed W1 treated plants remained low throughout

the day. The leaf folding mechanism commonly observed in

field-grown banana plants at midday hours (127,136) was

observed in the W2 treated plants. Increased WUE values,

though calculated on a yield/evapotranspiration ratio, have

also been obtained for field-grown bananas under moderate

reductions in soil moisture levels (11).

Altered physiological processes in banana with

decreasing irrigation levels agrees with Shmueli's work (126)

in which TR and CS in Cavendish banana were reduced by

available soil moisture levels below 66%. Chen (25) also

found a similar effect at a soil water level of 50% to 60%

field capacity. These were both field studies in which soil

moisture effects could have been confounded by ambient vapor
















CM
+1



11 4J

V-4 0
.II C



*- 0 41-
4U 3) "



0 *4 0




_ U 0 =

10 c0
*r- U) 0 U


W 0 V)
3O0
rL r-








o ( L- .-





C 0 3- C>
o C




5- C C

5O 00
+I)



.) C 4
40- 0 0














4- 0L
0 .- 4)
"a +

4 O *r-





30
S O






0 %- -
4) 0Zr- C%
0 Cd0


















*r- o- S 4a
4- 1 0





.5- 11 04
4- 0Li
: c cr u


-r- r-













LL.
























C














L.








*-













0
(M
























C.

C
ej
cr






0











*I-





0
0
CO




0
c





Go
C


0) LO


o-Ol'OtH Gw/Z03 6w) 13N3I3IJ3 3Sn a3iUR


AF 0t





3l 3I :








pressure deficits to a greater extent than occurred in the

present greenhouse experiment. CS and TR reported for both

field studies, however, were closely correlated. Brun (20)

reported good correlation between PS and TR in intact banana

leaves in response to light intensity but CS was not

monitored in his study. Results in the present experiment

indicate that stomatal closure was associated with reductions

in PS and TR.

Severe growth reduction and leaf chlorosis have been

induced by soil moisture depletion levels below 50% in field

studies (126). These effects were generally attributed to

reductions in PS, although PS rates were not measured. The

present study substantiates these hypotheses, since the

lowest irrigation level produced similar water stress

symptoms and significantly decreased PS (Figure 3-2A).


Experiment 1--ixora. Although irrigation treatments

highly influenced measured parameters, diurnal patterns did

not necessarily parallel one another (Figure 3-4). Under the

W3 irrigation treatment, maximum PS and TR rates of 0.26 mg

C02 m-2 s-1 and 58.1 mg H20 m-2 s-1, respectively, occurred
at 1400 hr (Figure 3-4A, 3-4C). However, CS was somewhat

erratic, with a maximum at 1000 hr, followed by a decline at

1200 hr and a small rise at 1400 hr (Figure 3-4B). PS and CS

were significantly reduced by the W2 and W1 irrigation levels

through 1400 hr compared to W3 and under the W1 level CS and

TR appeared to be more closely related.















4-

0 4*

r-- 0
*i- C
4- *r-
0 < 0 0
U (1)
*r *4 *
0) 0 *e LIL
O C CL L V)
-O )

r0 S- C 4)
tfr +) 4.) -r4-

MC 4-'
0.0 0 C
U 4C- U )


*r- C ( 5-

0C )
M M C S.



.E S* 0 1- (0
M L Q.

C- 0 S -
0 1) *- 0
0 4 II- U

E)- -0 0-
IA C O )
L. 3 4->
o 0oa
> s- ( 0
y) S- o r_
c 4-) + IM
0- 0


0 CC
U- 4- M rL.
O c -C0c C


U rc 4r


4-3 (I) 3U 0


c '4.




4- 4- + 1I.
Sd 0 IIC C

r- o-ClA

L. .E A
4r- -# r-

I 4) tC o E


to >o a)
4) Ct + '4.


S- 00 4.-
= 04-) II

I.-


























(L- UK) 30NVOerNOOV31


Md) VWUMLOd 3LVM tV31


(-0 a-i COO w&u) 9sS3HmNASQLOHd


8 0 8 a
(L-* 9-ui OWH &u) NOiLVUdvSNVU









LWP was generally reduced by decreasing irrigation

volumes (Figure 3-4D). Midday LWP for the W2 and W1

treatments were 2 and 2.5 times less than for plants under

the W3 irrigation treatment, respectively. Irrigation

treatments, therefore, were well distinguished by measuring

LWP.

Reduced irrigation, however, decreased PS relatively

more than TR as reflected in the higher WUE in plants at the

W3 irrigation level compared to plants under the W2 and W1

levels (Figure 3-5). Non-stomatal inhibition of PS under

water stress conditions have also been reported in other

species (14,15) and may have contributed to the lower WUE

observed with water stress in this study.

Although midday declines in CS have been noted for

coffee (100,101,140) under well-watered field conditions, the

suggestion that light was responsible (101) would not seem to

apply to ixora. In the high light environment of the growth
room CS did not decline at midday (Figure 3-10B).

A high irrigation treatment of 200 ml/15 cm pot/day

induced flooding effects and caused leaf abscission in coffee

(72). Such effects were not induced in this study by the

highest irrigation treatment, W3, but the erratic midday

stomatal response referred to above might have been in

response to the high watering level.

















II




W
) 4

(n 0*3-
3Z" 0

L.*

4)C 5- *
t0 0 0) LU

.3- lf
0) 0







O CL
z-I U U)
*-E Qr




Q) CD0
S- Ln (A









> < L.










C 11
*r- r- C
L. +




0OO-
o* r- U










r 0 +
S0) C








4-



L C 0C
*i- 110

0 *r- a.















L. l
E QU











LM4- + 1
0 -

uL >3


)- I- 0

I-U E

Ol4- + lo

la.. O -I 4.

























*-s
































c





















I I I I
tt,-OOH / \3 3 3
I --- ^I --- > 1 ^ --






i-b i ^ i- --







0 10 U)
LO





(^-O'O^ uj~o 6"' JLN3I3JJ3 Sn ^101








Experiment 2--banana. LWP decreased linearly while CS

decreased in a sigmoidal pattern during the 14 days without

irrigation (Figure 3-6). Leaf folding along the midrib is a

common feature of water-stressed field-grown banana plants at

midday hours (127,136), but plant water status associated

with the mechanism has not been previously defined. In this

study, leaf folding occurred between day 4 and 6 and

coincided with a decline in LWP from -0.51 to -0.65 MPa and a

decrease in CS from 0.46 cm s-1 on day 4 to 0.051 cm s-1 on

day 6. In experiment 1, leaf folding was also observed in the

W2 treated plants at midday with comparable LWP and CS. This

response therefore, substantiated the irrigation-volume

method as a fairly accurate, practical means of imposing

water stress treatments in banana. Anatomical studies have

indicated a special band of cells along the midrib of the

banana leaf (130) which are responsible for the folding

response and it is likely that these cells are more

responsive to decreasing LWP than the other leaf cells.

Further reduction in LWP to -0.91 MPa and CS to 0.019 cm

s-1 probably impaired the PS mechanism since chlorosis

occurred indicating greater chlorophyll degradation than

synthesis (57). At day 14, when LWP declined to -1.34 MPa and

CS to 0.004 cm s-1, there was severe chlorosis and apparent

growth cessation. At this stage leaves remained folded

probably indicating a cessation in gas exchange processes and

complete stomatal closure.










41








4- J
0 4J



r- 0.-
*0 (
C CO
SC -V)


OC
40- *


Soaw

1--)j o-* Uo) SONV1io0f00 J a s ^




S000







Oto re
I3 q 4J S-4-













1 4- S-Q-
r-Q <










04-3

,0 0.










(0 I~ ~iV dv1 4- 0





I CE
43 -C

SC 4u




*'- 0 5.
a.. U 0
*r O5.







42

Experiment 2--ixora. LWP decreased linearly after day 2

but there was a steep decline in CS from 0.53 cm s-1 on day 2

to 0.14 cm s-1 on day 4 (Figure 3-7). Wilting of youngest

leaves occurred between day 4 and 6 and corresponded to

decreases in LWP from -1.08 to -1.71 MPa and in CS from 0.14

to 0.038 cm s-1. Severe wilting of top leaves and abscission

of bottom leaves were observed on day 8 at a LWP of -2.06 MPa

and a CS of 0.008 cm s-1. Plant water status between days 4

and 6 of the cycle was comparable to that at midday

(-1.2 MPa) in plants under the WI irrigation treatment in

experiment 1. This indicated that reducing irrigation volume

was an effective means of imposing water stress in ixora.

Beyond the day 8 stage, wilting and leaf abscision made it

difficult to record further data. Since stressed plants were

not rewatered it was impossible to determine whether stomatal

closure and leaf abscission observed in this study were

clearly mechanisms imparting stress tolerance that allowed

the plants to survive.


Growth Room

Experiment 3--banana. PS, CS and TR diurnal patterns

paralleled one another under the more controlled conditions

of the growth room (Figure 3-8) but irrigation treatment

effects were not quite as dramatic as in the greenhouse

experiment (Figure 3-2). Maximum PS, CS and TR occurred in

the growth room at 1000 hr followed by a gradual decline to
































C-um: CL-s UWO) 3ONV1ONOO JVT31


$ ^ % 0


Li




*4-

C 4-
*0 0 C
C *i- a)


*r- 0 4)


c CL
*r- L.






03 10
0. .0






to sr-
s. C L



3> tM 4J
-






OC



UO 0)0
Iu-o
4- 0.


L. C-





0 C

-J 06







-U-i



4U 0
10C 50C

4-301


t) 0 .



I C)




*r- r "
0 Ci



LL- U 0





















1- *- C
4- 0 4-)




o 0.S..*V)
r- a)
S*- (&- C*)
*r- -r-





0..r- Oc
-r- C
>T (C0 (0
0Oi 0 L





0 IMC L V)
r- 00.




0 C 4.







COO r-
10 5-cr- =
L4- U U4





0 E *r a -

E 0 0 L.
i0 a
C (d 0,->
V* C )-

2 CE Q

OO rE
> ci
*r- OD r-
C C 4) + 1>

r- S *0- *d

0o3 Ct


- C I C 0

5-C*
.0 U C 4







oC C0
*0 0
)0 Ia) C4
*4r- C (AC

a) S- m o. 4-
4- CD m0
4-- (0c
LL -3 U)(
4- (u03- C
o) a C + Igo

1 041 CI E


4) C I -4 W
S- 0- 03 0



























(L- u9) 3oNVYonNtoo YIn


IIt
5It


0c



C
C
I
BdP( N


dV

L-s i-au Oa Bu NOtLVldSNYVV


t-* ca-uS Bou 0) S9S13iNAS8OLHd






46

1800 hr (Figure 3-8) while maximum levels in the greenhouse

experiment were at 1200 to 1400 hr for CS and 1000 to 1400 hr

for TR. Higher light intensity early in the day in the growth

room could have resulted in earlier stomatal opening (33).

Both Shmueli (126) and Chen (25) reported CS and TR diurnal

maxima in banana at 1000 hr followed by declines and with

minor increases at 1400 hr.

Under the W3 irrigation treatment, maximum PS, CS and TR

were 0.596 mg C02 m-2 s-1, 0.720 cm s-1 and 89.2

mg H20 m-2 s-1, respectively at 1000 hr. PS, CS and TR were

reduced 25%, 48% and 35% at 1000 hr, respectively, by the W2

irrigation treatment compared to the W3 treatment (Figure 3-

8A, 3-8B, 3-8C). At the lowest irrigation level, all gas

exchange processes remained consistently low throughout the

day and maximum PS, CS and TR were 0.097 mg CO2 m-2 s-1,

0.181 cm s-1, and 38.2 mg H20 m-2 s-1, respectively.

LWP generally declined for all irrigation treatments

after 0800 hr for most of the day with an increase after 1400

hr for the W3 treated plants (Figure 3-8D). Midday LWPs were

-0.58 MPa, -0.66 MPa and -0.82 MPa for the W3, W2 and W1

treatments, respectively. LWP between 1000 hr and 1400 hr

were not different for the W3 and W2 treatments but LWP was

significantly reduced by the W1 irrigation level. Despite the

similar LWP between W2 and W3 at 1000 to 1400 hr, significant

differences in PS, CS and TR were observed.

Davies (33) reported increased stomatal sensitivity to

decreasing soil water levels for cotton and soybean under








growth chamber conditions but Boyer (14) found PS of

sunflower to be affected more by photochemical activity than

by stomatal conductance under similar conditions. In the

present study there were relative increases in PS but not CS

in plants grown in the growth room as compared to the

greenhouse.

Maximum CS and TR have been shown to occur in moderately

watered field-grown banana at 1000 hr with subsequent

declines and smaller peaks at 1400 hr (25,126). It is notable

that this response resembled the diurnal patterns that were

observed in the W2 treated plants in the present study. In

the growth room LWP were generally lower than in the

greenhouse and could have been responsible for the general

decline in PS, CS and TR after 1000 hr.

Under growth room conditions, the W3 irrigation

treatment generally maintained a constant WUE throughout the

day (Figure 3-9) reflecting the parallel changes in PS and

TR. Though WUE for the W2 treated plants declined at 1200 and

1400 hr compared to 0800 hr, it was still not significantly

different from that of the W3 plants during these hours. The

relative improvement in WUE at the lowest irrigation in this

experiment compared to the same treatment in the greenhouse

study was due mainly to increased PS. The W1 irrigation

treatment under growth room conditions therefore did not

depress physiological responses as much as that observed in

the greenhouse study.















CM
+1
o
D-
41

II L
-4J






41 *- (
E(A

C tfl



- 0 4 *
0 S-C.
c 0
0 S- +C

LE C4




31 = 0 Wn
r- O 6 0)







tO 0- 0 AL


4) 4) LO L.
U 0C 0t/


r- L-
O 0-




*r0 01 S-
go c- >)






S0 CO


Q) C
M- r- 1 r-




= m
0 -0 0


on
5C *41



4-) CC (0

GCM r- C
4- EQ


o +1iX
3 to






0r 4- E c
*- 4-I-

LL. WEE





































































SUCD

(V-OVOZH 6w/Zoj 6wU) J3N3[3JL3 3Sn 831Un


1: 0 1 1



N (M(
a 3 -1







50
Experiment 3--ixora. Under growth room conditions, the

W2 and W1 treatments did not consistently decrease

physiological parameters (Figure 3-10) as severely as in the

greenhouse study (Figure 3-4). At 1200 hr, there were no

differences in responses of plants under the W2 and W3

treatments but at the lowest irrigation treatment, all

parameters were significantly reduced over those at the

higher irrigation levels.

Maximum PS rates were 0.425, 0.388 and 0.151 mg CO2 m-2

s-1 for the W3, W2 and W1 irrigation treatments, respectively

(Figure 3-10A). These rates were 1.25, 7 and 10 times higher

than the respective rates in the greenhouse study and may

have reflected the influence of increased PPFD on PS in

ixora, particularly at the lower irrigation treatments. Light

levels in the greenhouse were probably below light saturation

levels for ixora.

There were no differences in CS between plants at the W2

and W3 irrigation levels from 0800 to 1400 hr but CS was

significantly reduced at these hours by the W1 irrigation

volume (Figure 3-10B). Midday CSs were 0.492, 0.382 and 0.190

cm s-1 under the W3, W2 and W1 treatments, respectively.

Compared with CS in plants in the greenhouse experiment

(Figure 3-48), these values were 34%, 49% and 87% higher at

the W3, W2 and W1 irrigation levels, respectively. The

increased response in stomatal opening, especially at the

lower irrigation levels corresponded with increases in PS.
















X
II *1-



r- *0 m -
*r- 4- )


r- o
S*r- + I E
*i- 4 4 0

>.0 .4
0.0
U Q- 0)





&-
SL0 0


*- 4-
.C u*r-)
4.)0 0
3 i. 0.
>0- *r-

c0 M u *
C C) 0S
4 -r)LOJ
0s.. 0 >1/)
U r- *r-

o 4").a r
53 C:4

*- C Ur 4

> 0 Sco <
4 E w
S.C 0 >
o 4u +
*r-- U0 Q.

0 3 0 S -I .

4 o 11. U
4.- X4-3
**-S U .I- 0

*r- C .0
-1 0 >
) 0i- r-
O = *r- (a
'..r- Co- 40


LL 1- L.
9- C E <
o )- >

'noe + 1
4.) OC


O4- 0) II 0


C 3r 0
004- 4 r-

0 OC

fO 0 4
( .Cr-
4) C &0E2


n 0 < + I0.
.9- 4) 0)0o4
Ll. S. r- CM S.














L U
2


sI
SF


3otWiuonloo. i3


8 S- 8 u) NOL
(!4- ;-*us OZH Bu0 NOUiVtISNVHL


(L-4 &-u =O


CL4 SwD


IS


r^ ^- >- ^ -








The high PS rate at 0800 hr under the W3 irrigation

resulted in a correspondingly high WUE (Figure 3-11) and

although WUE then declined at 1000 and 1200 hr for the

highest irrigation treatment, WUE values were basically the

same for all irrigation treatments through the rest of the

day. Under greenhouse conditions, W3 treated plants clearly

had higher WUE than plants subjected to lower irrigation

levels (Figure 3-5). The increase in WUE in the W2 and W3

relative to the W3 treated plants under growth room

conditions was due mainly to the increased PS rates in the

high light environment.

Growth room conditions, therefore, not only moderated

physiological responses of ixora to reduced irrigation volume

but also stabilized PS/TR changes as reflected by WUE values.

The increased photosynthetic response in plants grown under

the W1 and W2 irrigation volumes suggested that ixora could

probably better withstand decreased irrigation volume in the

growth room compared to greenhouse conditions reported in

this study.

















It








) r- .)
0 0 r4


4) 0 V

QOL

4. 0 0





*r- 4 -3 0
C 0U 4 0)


C0 L 0

TO 4- a)
4) 0 /)
I.- 35 u iu
0 0 4.) 4.)


O arS- mL
0 S. .-. &



0 0 0r-
a=3 a
- -r-4 -



C C(
- >
-r -r- r-v4>


cc CLO
*r- >






C) &
*r- 4- )




4-3 Q)EW 4
0 0 r-








4-. M 4)
4- M





O r-
0- 11


4) ca
00 E






II- II
S*r-a4 4-C


0. D -


'4- + lx
4- II





*.0 *-
I0 U U









55








(0










UI
aO
































o -I-















OD


(V,-OI 'OZH 5W6 0 6w) IJ3N3I3IJJ3 3Sn a31UM














CHAPTER IV
ROOT-ZONE TEMPERATURE EFFECTS ON BANANA AND IXORA
UNDER TWO GROWING CONDITIONS


Introduction


High root-zone temperatures (RZT) have been shown to

reduce plant growth (59,63,70) and affect many physiological

processes (43,46,64). Tropical and subtropical plant species

are often thought to be heat tolerant, but soil temperatures

as high as 520C have been recorded in the tropics (39), and

temperatures in this range can be lethal for some tropical

(39,63) and subtropical crops (62). An air temperature of

330C was reported as being optimum for growth and dry weight

partitioning in banana (Musa spp. AAA) (142) and mineral

composition was highly influenced by temperatures from 18 to

330C (143). A RZT of 330C was found to be optimum for growth

and transpiration in coffee (39), a member of the same

subfamily of the Rubiaceae to which ixora belongs (6).

However, there are no reports on RZT effects on growth and

physiology of container-grown banana or ixora.

It is essential to identify growth and physiological

effects of high RZT in container production systems before

control measures can be developed to alleviate such effects.

This study investigated the short-term effects of RZT on

56







57

container-grown 'Grande Naine' banana and Ixora chinensis L.

'Maui' under greenhouse and growth room conditions.


Materials and Methods

Plant Materials and General Cultural Procedures

Ten- to 12-cm tissue-cultured 'Grande Naine' banana

plants and similar-sized, uniform Ixora chinensis L. 'Maui'

rooted cuttings were obtained from commercial nurseries.

Plants were hardened in intermittent mist (6 sec min-1) for

one week under 80% light exclusion and then moved to 40%

light exclusion for another week. Plants were then

transplanted to 4-cm diameter x 21-cm high conical containers

(150 cm3) using Metro-Mix 300 growth medium (W.R. Grace and

Co., Cambridge, MA). Plants were fertilized weekly with a

soluble 20N-8.8P-16.6K fertilizer (Peters 20-20-20, W.R.

Grace and Co., Cambridge, MA) at 150 ppm N.

Experiment 1--Greenhouse

An experiment was initiated August, 1985 in an air-

conditioned glass greenhouse with a mean maximum PPFD of 600

to 700 umol m-2 s-1 PPFD, and a 250 to 300C day and 180 to

210C night temperature. Relative humidity was not controlled

and varied from 40% to 80% (Figure 4-1). Recently

transplanted banana and ixora plants were watered daily to

container capacity and allowed to acclimatize for one week.

RZT treatments were established within styrofoam-lined

wooden air bath boxes (1 m x 1 m x 20 cm) in which plant

containers were firmly inserted to within 2 cm from their






















0-----0 OIIOrUnH 3"i-1U3N iN33J3d





I I I I I


4.




>1

*r


E
=I



















*r* *,-
C
J 0u









r- .L
OE
t- e1


















4.


. C4
c a











4) r-
0









4- *C
C 5..













'Q
SIC















*r- S:
QI a
















>. s
VI
0 0>
LE

C $


^ ----- < Z-s I jo rf) 3Jdd









upper rims. Four equally spaced 100 watt aluminum foil-

covered incandescent light bulbs provided convective heating

of the enclosed root systems. Proper distribution of heat and

aeration within the boxes were ensured by two fans (IMC

Magnetics, Roch. NH) per box. The light bulbs in each box

were controlled by a pre-set thermostat and the temperatures

in each box were verified daily with a thermocouple

thermometer (TH 65, Wescor, Inc., Logan, UT). Electrical

power to the temperature boxes was controlled by Intermatic

Time Controls (Intermatic Inc. Spring Grove, Ill), providing

daily RZT treatments from 1000 to 1600 hr. Boxes were placed

on 1 m high benches and an automatic drip irrigation system

provided daily watering of all plants to container capacity

at 2200 hr.

RZT treatments established were 28+10, 33+10, 38+10 and

43+10C. Each temperature box contained six ixora and six

banana plants and there were three replicate boxes for each

treatment temperature arranged in a randomized complete block

design. Species were treated and analyzed as separate

experiments. Means and standard errors were calculated for

the six replicate plants measured at each sampling time.

After 14 days of RZT treatments, diurnal measurements of

leaf photosynthesis (PS), leaf conductance (CS),

transpiration (TR) and leaf water potential (LWP) were made

using a portable photosynthesis system (LI-6000 model, LI-

COR, Inc., Lincoln, NE). Measurements were initiated at 0800

hr EDT on a cloudless day and taken every 2 hr until 1600 hr.







60
A 1-liter cuvette was used and the mean of eight consecutive

30-sec observations constituted a measurement. A zero check

of the analyzer was performed between treatments within each

replicate. Simultaneous measurements of LWP were made using a

pressure chamber (PMS Instrument Model 600, Santa Barbara,

CA) as described by Barrett and Nell (9). The third most

recently expanded leaf in banana was selected for both

gaseous exchange processes and LWP measurements. This leaf

has been shown to be the most responsive and the youngest

with fully developed stomata (127). The most recently matured

ixora leaves were used for PS, CS and TR measurements and 4-

to 5-cm shoot tips were sampled for LWP.

Experiment 2--Growth Room

In order to further monitor the physiological responses

of ixora and 'Grande Naine' banana to RZT under more

precisely controlled environmental conditions, experiment 1

was repeated in a 3.0-m by 7.6-m walk-in growth room. Light

irradiance of 1100 umol m-2 s-1 PPFD, as measured by a

quantum radiometer (LI-COR Model LI-185A, LI-COR Inc.,

Lincoln, NE), was supplied from 0600 to 1830 hr at plant

canopy height by 1000 W phosphor-coated metal-arc HID bulbs

(GTE Sylvania Corp., Manchester, NH). Air temperature of 280C

day and 210C night and a relative humidity of 65% to 70% were

maintained.

Each conical container with a transplant was suspended

through a tightly fitting styrofoam ring within a specially









constructed root heating tube (RHT). Each RHT was 22.5 cm

high and constructed from 7.5 cm diameter metal pipe wrapped

with 60 watt 120 vac heating tape (Smith-Gates Corp.,

Farmington, CT) and 1.25 cm thick foam insulation. The RHTs

were connected to solid state electronic controllers which

maintained preset treatment temperatures by a thermistor

feedback mechanism. Each controller maintained treatment

temperatures in 16 tubes with four tubes at each of four

specified temperatures. Treatment temperatures were set and

also maintained at 28+0.30, 33+0.30, 38+0.30 and 43+0.30C.

Similar leaf number and sampling methods were used and the

same physiological measurements were recorded as in

experiment 1 after 14 days of root-zone temperature

treatments.

Experimental design was a randomized complete block with

36 plants of each species per temperature treatment arranged

in three blocks. Species were treated and analyzed as

separate experiments. Means and standard errors were

calculated from six replicate plants measured at each

sampling time.


Results and Discussion

Experiment 1--Greenhouse

Banana. At the 330 and 280C RZTs, PS increased to midday

maxima of 0.53 and 0.50 mg C02 m-2 s-1, respectively, and

then declined (Figure 4-2A). Maximum PS was 0.43 mg CO2 m-2

s-1 at 1000 hr in the 430C RZT treated plants, while PS was



















Or-


) 01

0 (-
*r- 4< t o




O* U
>, (cc

C. C to




"O 0

C0 M
C
0 L EU


0 4.*

C EU
C =C C
0 C 0 t0



W. 0) 4- 0



&. C *i-








0 U
o o

I CCO

0 C +P (4

0 40 UC




-i- .C
U3 04
4- D EU

0- 0.

4a) C *

L. 0 c 4
4- 4W .-
LaJ *i- 0Q
41- (4.& XC


I (4 =r- 4)
L*L 0S C E0 C





*r- 0 .C0 0
Lu. 5.. a .. 5.






























0(BdYO) YlLN3Od H1LVM d


00oo
000C CO C0
CMWac'2


(L-9 E- 03 Bu) SMtS3LNASO.LOHd


8







0^

0
0
oD



O
O-
O


(L-S Z-wu O&H ur) NOLLVadSNVUL


0-8 uo) 3ONvionaNoo -wm







64

0.31 mg CO2 m-2 s-1 for plants at the 380C RZT. These rates

were 20% and 42%, respectively, of the maximum PS recorded at

330C.

Midday CS for the 280 and 330C RZT treated plants were

0.43 and 0.34 cm s-1, respectively, with significant

reductions to 0.28 and 0.19 cm s-1 for plants at the 380 and

430C RZT (Figure 4-2B). TR diurnal patterns were closely

related to those for CS, with maximum rates of 54 and 52 mg

H20 m-2 s-1 at midday for plants at the 280 and 330C RZT,
respectively (Figure 4-2C). Midday TR was significantly

reduced by the 380 and 430C RZT compared to the other RZTs.

LWPs were generally not different throughout the day for

the 280, 330 and 380C RZT treated plants. Among these three

RZT treatments, a low midday LWP of -0.52 MPa was recorded at

the 380C RZT (Figure 4-2D). A significant reduction in LWP

was noted for plants at the 430C RZT at 1200 hr, with a

midday LWP of -0.76 MPa. Although transpirational water loss

was reduced in plants at the 430C RZT at midday compared to

plants at the 280 and 330C RZTs, LWP of plants at the highest

RZT were significantly lower than those of the other three

RZT treatments. At 380C, TR was less than at 280 and 330C RZT

but LWPs were the same between these treatments. These

responses may suggest impairment of the absorptive and/or

conductive capacity of roots in plants exposed to the 430C

RZT.

In summary, PS in banana plants was greatest at the 280

and 330C RZTs under greenhouse conditions. The 280, 330 and







65

380C RZT treatments resulted in the highest LWP and the 430C

RZT reduced all measured parameters. RZTs of 280 and 330C are

well within the range of RZTs reported as being optimum for

the growth of coffee (39), tomato (42) and pepper (44) while

380C RZT has reportedly decreased root conductance (146) and

transpiration (73).

Ixora. PS in plants at all RZT treatments increased from

0800 hr to midday (Figure 4-3) but PS, CS and TR were

greatest at midday in plants exposed to the 330C RZT. LWP

declined for most treatments at 1200 hr, with progressively

lower values from the 280 and 330C RZT to the 380 and 430C

treatments (Figure 4-3D).

Maximum midday PS rate was 0.41 mg CO2 m-2 s'1 for the

330C treated plants with reductions to 0.29, 0.28 and 0.25 mg

C02 m-2 s-1 for the 380, 430 and 280C RZT treatments,
respectively (Figure 4-3A). At 1400 hr, however, PS rates at

the 430 and 380C RZT were 0.26 and 0.23 mg CO2 m-2 s-1,

respectively, while PS at 330C RZT had declined to 0.17 mg

CO2 m-2 s-1. At 1600 hr, PS rates for the 280, 330 and 380C

RZT treated plants were not different. The 330C RZT clearly

resulted in the highest midday PS but because this RZT did

not alter morning rates and caused rapid post-midday

declines, mean daily PS at 330C was probably similar to that

at other RZT treatments.

CS and TR diurnal patterns were closely related, with

the midday maxima of 0.53 cm s-1 and 95 mg H20 m"2 s-1,

respectively, for both parameters occurring in the 330C RZT
















r4-



U
0
*r- *

O
i- W
0 U) S. L.
*r- C Qt cc
n 0 +j .0

*=4. 3:
0.- E r-
.O 4- U
r- C O *r-

C U a-
id0) 4-

0 V
0 r



0 4)
C 5. CC

*r- r-


00s L O
C *r4- CL

4. W
4i 4c *i-
OEU r-

E L. +)


Cox
4) E s-
O -r-



oI- CO

E 4-W
0-1 U C
= cc



OrEU




4- a ) L/
C- 4-)


4J *. *
4 Enr Q .


S1) O 0 4
4 C E C
E- t-





LLJ *-4 0 4)
- On Q. C.
n =: *




*- 0 0 c00
= 064-) 4) L-


LL. S-0 C.Q l






























(-8 uo) 3ONVioANoo JV


0
| | *


0000 0
000 0
c CO C0


(L-* -4U Z03 O) 834sUNAS.LOHdM


8
I--
0
0
0
0




(BdVO 7N1 3Jo1d 31VM .1V31


(L-8 a-u OZH &B) NOU.Vt5dSNVU.








plants (Figure 4-3B, 4-3C). Midday CS and TR were

significantly reduced in plants at the 430C RZT compared to

the 3300C RZT but the 380C RZT resulted in the lowest midday

TR and CS.

Mean midday LWP for plants at the 280 and 3300C RZT was

-0.71 MPa with progressive reductions by the 380C (-0.87 MPa)

and 4300C (-1.02 MPa) RZT treatments (Figure 4-3D).

The 330C RZT treated ixora plants exhibited highest

midday PS, CS, TR and had relatively good plant water status

compared with other RZT. Although PS was not measured, Franco

(39) reported that a RZT of 330C was optimum for coffee in

terms of TR and root and shoot dry weights. TR and plant dry

weights were reduced with increasing RZT above 330C and

plants died at 480C RZT.

Midday LWPs decreased significantly to -0.87 MPa by the

3800C RZT treatment and to -1.02 MPa by the 430C RZT

treatment, but visible symptoms of water stress were never

apparent in these plants. In contrast, water-stressed ixora

plants (experiment 2, chapter III) exhibited wilting around a

LWP of -1.08 MPa. Therefore, there may have been mechanisms

to maintain turgor under decreasing LWP in plants at the 380

and 4300C RZT or plants may have become conditioned to the

high RZTs.

Experiment 2--Growth Room

Banana. Plants held at the 3800 RZT under growth room

conditions (Figure 4-4A) had a maximum midday PS rate of 0.81

mg C002 m-2 s-1, which was a 54% increase over the

















r-

c04-


O
I- w
o < L- 5-

.-) 4.)to

( *O 4-
0.0 0
*i- 4- U

r *4)- O
C 0- 4.
LC 0)
0 *>

-0 o
E C
0) 010 t0
= 0 *r
4 O S- C In
4-)










4) M
S-


3 *









0 40
04-) 0 tO
0. L l.0.














0 C 4(

4- -ac
4 0 &0






04 0U







U M oC o
4- *r-






4-- O E
0- C 4-


I ) (A S- 4
*O) 0


3 01 0 C



LaJ r 0 *
4-- U) 0


cm WU 0
I U)4.0 (.



LOOsCQ


"r -W 0
La.- L 0 Q. L


























-8 o)
0- ")aovon8o C


I
I 3 I
000
000


L-8s -uw 00 B&i) SIS3UNASOlOHd


I
Cdd 3LV q -I
(BOVUJ 6JLN3Od EmJIVM --WM


-) NO d 8
Q.-9 t-ui OZH a"r) NOllVldSNF~aj.i








corresponding greenhouse rate (Figure 4-2A). The 330C RZT

induced a rate of 0.74 mg CO2 m-2 s-1 at 1000 hr while the

430C RZT treated plants had the lowest PS rate of 0.39 mg CO2

m-2 s-1 at 0800 hr and through the afternoon hours(Figure 4-

4A).

Maximum stomatal opening for the 280 and 330C RZT

occurred earlier in the day than for the higher RZT

treatments (Figure 4-4B). While maximum CS of 0.72 and 0.63

cm s-1 occurred in plants at 1000 hr under the 280 and 330C

RZT respectively, peak values for the 430 and 380C RZT were

0.52 at midday and 0.70 cm s-1 at 1400 hr, respectively

(Figure 4-4B). The 430C RZT caused significant reductions in

CS and TR from 0800 hr to 1000 hr and later in the day at

1800 hr. Highest TR rates occurred with the 380C RZT with

values of 94.2 and 92.7 mg H20 m-2 s-1 at 1000 and 1400 hr,

respectively (Figure 4-4C).

Diurnal patterns of LWP were significantly influenced by

RZT treatments (Figure 4-4D). The 280C RZT treated plants had

the highest midday LWP of -0.55 MPa, which was higher than

the LWP at the 330 and 380C RZT treatments. The lowest midday

LWP of -1.26 MPa was induced by the 430C RZT. Overall, LWP

were lower in plants in this experiment than those observed

in the greenhouse environment. This could be attributed to

the higher CS and TR rates that were exhibited by plants in

the growth room experiment compared to the greenhouse. In

both environmental conditions, however, the highest RZT of

430C induced the lowest LWP with higher LWP at lower RZTs.








Although the 380 and 430C RZTs appeared to induce water

stress in banana as reflected by low LWP, there was no leaf

folding and/or chlorosis as shown by plants that had been

water stressed to -0.52 and -0.66 MPa by irrigation

treatments under greenhouse and growth room conditions,

respectively (experiments 1,3 Chapter III).

Under growth room conditions, the 330 and 380C RZTs

induced the highest PS rates though at different times of the

day. Under sunlit growth room conditions, 330C air

temperature was reported as being optimum for growth and

partitioning in Cavendish banana but 370C caused leaf injury

(142). Since growth measurements were not recorded in this

study it was impossible to determine whether the increased PS

observed at 380C RZT resulted in increased growth or was

merely a response to the increased root sink demand for

photosynthates. The response of the banana plants grown at

380C RZT in the two environmental conditions would indicate a

greater tolerance to RZTs up to 380C under growth room

conditions. The 4300C treatment was supraoptimal under both

environments.

Ixora. Maximum PS, CS and TR at midday followed by

distinct declines were not as evident in ixora plants under

growth room conditions (Figure 4-5) as they were in the

greenhouse study (Figure 4-3). In plants subjected to the 280

and 330C RZT treatments, PS rates of 0.51 and 0.47 mg CO2 m-2

s-1, respectively, were recorded at 1000 hr and followed by a

gradual decline to 0.21 and 0.12 mg CO2 m-2 s-1,


















r- 0
0 -C
U



00

(A 4-) 4.)


*r- 0

I-- u *
0 LLE

s1-00
30 *r- 0


S *r-
S4.) *i- A4.)
-X 30. C

L. C
CL 4 -0 0



0 5-
S- C


0 CW u0
5- 3 C .0




4-) U -
*r- 4-

5.C 4)
0 x U >
N- 3
I *-0 -0
4. C C
0 -J 0 0
0 U


4- C











<4- X
L O
*r- 4
5U) (IO










4-3
u) 04






4-) O- i-
U L.\l -
0. 010.



4-4-
4- -H>t
LLa C


L) 0u)
I U)4.

U/) .C 0




*' l-- E
La.. -u-

































o-s wao) 3owNV100cOO iv3i


h.C
'"

I-
guiL


0
0








S*4
oo
0







I


'i


I
f0



O
IW-

0S
1

0^*
0
0 ^

0

a

0
0
O


SII


0000
0000
C9Ooo


(4-9 Z4u OH BuO NOliVUdSNVW L


(- 0 O
CL-s z-W ZOO 6u) S1S3H.NASOJ.OHd







75

respectively, at 1800 hr (Figure 4-5A). A PS rate of 0.57 mg

CO2 m-2 s-1 was observed at 0800 hr in the 380C RZT treated
plants and was followed by a significant decline at 1000 hr

with no further decreases for the rest of the day. PS rates

were reduced during the morning hours in plants treated with

the 4300C RZT relative to other treatments but increased to

levels comparable to other RZTs at 1400 and 1600 hr. Except

for shifts in time at which maximum daily PS occurred, there

appeared to be little differences in overall PS values

between RZT treatments.

Diurnal CS (Figure 4-58) and TR (Figure 4-5C) followed

the same general pattern. Maximum values for both parameters

occurred at 1200 and/or 1400 hr in plants treated with either

the 280, 330 or 380C RZT, with subsequent declines for the

rest of the day. Maximum CS recorded for these RZTs was

0.51 cm s-1 at 1200 hr which was comparable to the

corresponding midday CS in the greenhouse. However, a CS of

0.46 cm s-1 at 1400 hr in the growth room experiment

represented a 30% increase over the CS recorded at this hour

in the greenhouse. A similar pattern was observed for TR.

Maximum TR was 83.3 and 80.1 mg H20 m-2 s-1 at 1200 and

1400 hr, respectively. CS and TR were significantly reduced

throughout most of the day in the 430C RZT treated plants

(Figure 4-5B, 4-5C).

Under growth room conditions, therefore, RZTs of 280,

330 and 380C did not produce appreciable differences in

physiological responses in ixora. The relatively low PS, CS








and TR early in the day with subsequent increases at later

hours in the 430C treated plants suggested a lag effect of

this RZT on stomatal opening.

Midday CS and TR were comparable to those observed in

the greenhouse. However, higher values for these parameters

were recorded at 1400 hr and later in the growth room as

compared to the distinct post-midday declines in the

greenhouse. There was an apparent effect of the constant high

light intensity during the illumination period in the growth

room that maintained midday stomatal opening to later hours.

However, the eventual decline in gas exchange processes at

1800 hr in the growth room suggested that the stomata may not

have completely lost the diurnal rhythmic pattern evident

under greenhouse conditions.















CHAPTER V
ROOT-ZONE TEMPERATURE AND SOIL MOISTURE EFFECTS ON
BANANA AND IXORA UNDER TWO GROWING CONDITIONS


Introduction



High temperature and water stress often occur

simultaneously in crop situations and alleviating the latter

is often considered a remedy for the former. Although many

drought tolerant plants are also heat tolerant (85),

interactions and sometimes negative correlations occur

between heat and drought stress (102). Research has tended to

concentrate on water and temperature stress effects

separately with little emphasis on defining or separating the

characteristics of these two stress factors.

Suboptimal root-zone temperature (RZT) (7,8,18) and

temperate plant species (5,18,69) have been employed in most

of the reported investigations that involve RZT and soil

moisture interactions. Barlow (7) found that increased shoot

carbohydrate under reduced soil moisture was offset by

increasing RZT in corn seedlings. Kaufmann (69) found that

soil water deficits directly affected leaf water potential

(LWP) and transpiration (TR) in 'Monterey' pine seedlings but

RZT had no consistent effects on TR and CS. Water stress has







78
been shown to affect growth (31,116), yield, WUE (10,11,40)

and physiological responses (25,126) in banana (Musa spp.

AAA). Relatively fewer studies have been reported on

temperature stress effects (63,142,143). An air temperature

of 330C was reported as being optimum for growth and dry

weight partitioning in Cavendish banana (142) but the

investigators experienced some difficulty in separating the

stress effects of air temperature and induced vapor pressure

deficits. Investigations in banana involving both stress

factors simultaneously have not been reported. A similar

pattern of research exists for coffee, a major tropical crop

that belongs to the same subfamily as ixora (Ixora chinensis

L. 'Maui') (6).

This study investigated the effects of four RZTs and two

irrigation volumes on growth, physiology and carbohydrate

status of 'Grande Naine' banana and 'Maui' ixora under

greenhouse and growth room conditions.


Materials and Methods

Plant Materials and General Cultural Procedures

Ten- to 12-cm tissue-cultured 'Grande Naine' banana

plants and 12 to 15 cm uniform ixora rooted cuttings were

obtained from commercial nurseries. Plants were hardened in

intermittent mist (6 secs min-1) under 80% light exclusion

for one week and then moved to 40% light exclusion for

another week. Plants were transplanted to 6.5-cm diameter x

25.0-cm tall conical containers (555 cm3) using Metro-Mix 300








growth medium (W.R. Grace and Co., Cambridge, MA). Plants

were then moved to the experimental greenhouse or growth room

where they were watered to container capacity daily and

allowed to acclimatize for one week prior to the initiation

of the experiment.

Experiment 1--Greenhouse

Experiment 1 was initiated in August, 1985, in an air-

conditioned greenhouse in which maximum irradiance levels

ranged from 600 to 800 umol m-2 s-1 PPFD, and 250 to 300C day

and 180 to 210C night temperatures were maintained. Relative

humidity was not controlled and varied from 40% to 80%

(Figure 5-1).

Two irrigation volumes and four RZT treatments were

factorially combined in a split plot design experiment.

Plants were watered daily at 2200 hr with 50+5 ml (W1) and

100+10 ml (W2) per container (555 cm3). These volumes

represented 60% to 70% and 85% to 100% container capacity

(CC), respectively. Water was applied automatically through

drip tubes by a battery-operated controller (Water Watch

Corp. Seattle, WA). The W1 and W2 irrigation treatments were

applied by one and two 6-cm dramm irrigation rings/container,

respectively.

RZTs of 28+10, 33+10, 38+10 and 43+10C were established

in air-bath boxes as described in Chapter IV. Each

temperature box contained six ixora and six banana plants to

which the irrigation treatments W1 and W2 were randomly






















0--J--- LIrunH 3nAi138a i3N3a3d

0 0
CDLO ItrI


I I I I


A --- K (,-s -w lo"wn) Ojdd


Q*

r-



















CL
O1


4J
c




4-c 0
S
r- 0-
c ex




















00
C a
OL


0 0r


-C '4-

00
OE
T-)




























LL. c
0




Cf




0 0*


C 5L




I 0,


* cU
L3 <








assigned to three plants per species per treatment.

Temperature boxes were replicated three times. RZT treatments

were applied daily from 1000 to 1600 hr EDT and irrigation

was supplied at 2200 hr so that the imposition of temperature

and irrigation treatments did not overlap. Plants were

fertilized weekly with the appropriate volume of water and

concentrations of 20N-8.8K-16.6P fertilizer (Peters 20-20-20,

W.R. Grace and Co., Cambridge, MA) to apply 250 mg

N/container. Fertilizer was applied with a hand operated

injector (Chem-trol Inc, Kansas City, KS).

Plant height, leaf area, leaf number and stem diameter

for banana, and plant height, plant width, shoot number and

total axillary shoot length for ixora were recorded weekly.

Plant height was considered the distance from the soil

surface to the leaf apex in banana and to the stem tip in

ixora. Banana stem diameter was measured at pot rim level and

leaf area of the third newest leaf was calculated from 0.65

of leaf length multiplied by leaf width (127). Leaf numbers

were derived from the number of whole green functional leaves

and emerging leaves were assigned a value of 0.25, 0.50 or

0.75 depending on the fraction of the leaf lamina fully

exposed.

Ten weeks after the initiation of the experiment, leaf

photosynthesis (PS), leaf conductance (CS) and transpiration

(TR) were recorded on a cloudless day from 1000 to 1600 hr at

2-hr intervals using a portable photosynthesis system (Model

LI-6000, LI-COR Inc., Lincoln, NE). A 1-liter leaf cuvette








was used and the mean of eight 30-sec observations

constituted a measurement. A zero check of the analyzer was

performed between treatments within each replicate.

Simultaneous measurements of LWP were made using a pressure

chamber (PMS Instrument Model 600 Santa Barbara, CA) as

described by Barrett and Nell (9). The third most recently

expanded leaf in banana was selected for gas exchange

processes and LWP measurements. This leaf has been shown to

be the most responsive and the youngest with fully developed

stomata (127). The most recently-matured ixora leaves were

used for PS, CS and TR measurements but 4- to 5- cm shoot

tips were sampled for LWP.

After physiological measurements, leaf and root samples

were immediately collected for carbohydrate analysis. The

third newest leaf in banana and six of the most fully

developed leaves in ixora were sampled. A 5- to 7-g composite

sample of carefully washed roots was used for root

carbohydrate analysis. Plants were then separated into

leaves, stems and roots before drying for at least 48 hr in a

forced-air oven at 700C prior to recording dry weights.

Ethanol-soluble sugars and starch were determined

according to the procedure used by Stamps (133) in which free

sugars were extracted from a 50-mg sample with 80% ethanol.

Leaf and root tissues were first freeze-dried at -4000C

(Freezemobile II, Virtis Co. Gardner, NY) for at least 72 hr

and stored in a desiccator. Tissue was then ground through a

20-mesh screen (Wiley Mill, Philadelphia, PA) and a 50-mg







83

sample was boiled in 8 ml of 80% ethanol and centrifuged for

1 hr at 10,500 rpm (Model HT Centrifuge, International

Equipment Co., Division of Damon). A 0.5-ml sample of

supernatant was diluted from 10 to 20 times with deionized

water. One half milliliter of 5% phenol and 2.5 ml

concentrated H2SO4 were added to 0.5 ml of each diluted

sample and the mixture was allowed to cool. Absorbance was

then measured at 490 nm using a spectrophotometer. Free sugar

concentrations were determined from plots of absorbance by

standard solutions of D-glucose and deionized water. Starch

content was determined by incubating the centrifuged pellet

at 340C for 12 hr in 5 ml of an enzyme solution containing

sodium phosphate mono- and dibasic, alpha-amylase,

amyloglucosidase and anhydrous calcium chloride. After

incubation, samples were centrifuged for 1 hr and absorbance

determined using the same procedure as above.

The experiment was arranged in a split plot design with

three blocks in which RZT were main plots and irrigation

treatments represented subplots. Each species was treated and

analyzed as a separate experiment. Mean values of

physiological measurements were plotted across time to reveal

diurnal patterns and regression analyses of midday

physiological parameters over RZT were performed for each

irrigation volume treatment. Weekly leaf area data of banana

were used for growth over time plots and final growth and

carbohydrate measurements were used for regression analyses

over RZT and irrigation treatments. Single degree-of-freedom






84

orthogonal comparisons between treatment means were performed

and partitioning of interactions for linear, quadratic and

cubic models for final growth and carbohydrate data were made

using the General Linear Model procedure of the Statistical

Analysis System (134).

Experiment 2--Growth Room

In order to further monitor the physiological responses

of banana and ixora to RZT and irrigation treatments under

more precisely controlled environmental conditions,

experiment 1 was repeated in a walk-in growth room in August

and September, 1986. The growth room was described in

Chapters III and IV. Irrigation and RZT treatments were the

same as for experiment 1 but root heat tube (RHT) containers

as described in Chapter III were used. Similar plant

materials and cultural procedures were used as for experiment

1 except plants were first transplanted for one week into 4-

mil 7.5 cm diameter x 22.5 cm tall clear plastic bags (1200

cm3) that were inserted into similar sized lengths of PVC

tubes. One week prior to the initiation of treatments, the

plastic bags were transferred to RHTs in the growth room.

Irrigation volumes of 75+8 ml (W1) and 150+15 ml (W2) per

container were applied daily at 2200 hr as in experiment 1.

These volumes provided 60% to 70% container capacity (CC) and

85% to 100% CC, respectively. Water was applied automatically

by drip irrigation and one and two 1-mm drip tubes per

container constituted the W1 and W2 treatments, respectively.








There were 16 RHTs per electronic controller, four of

which were randomly assigned to each RZT of 28+0.30, 33+0.30,

38+0.30 and 43+0.30C. There were six replicate plants per

RZT-irrigation treatment arranged in a randomized complete

block design with three blocks. Species were organized and

treated as separate experiments. RZT treatments were applied

from 1000 hr to 1600 hr daily.

Six weeks later PS, CS, TR and LWP were measured at 2 hr

intervals from 0800 to 1800 hr and growth data and samples

for carbohydrate analysis were taken as described in the

greenhouse experiment. Chlorophyll concentration of leaves

used for physiological measurements was recorded using a Spad

501 chlorophyll light absorbance meter (Minolta Corp. Ramsey,

NJ) and expressed as umol m-2.

Means and standard errors were calculated from

physiological measurements of six replicate plants at each

sampling time and are shown with data points. Single degree-

of-freedom orthogonal comparisons between treatment means and

partitioning of interactions for linear, quadratic and cubic

models for growth, physiological and carbohydrate data were

made using the General Linear Model procedure of the

Statistical Analysis System (134).








Results and Discussion

Experiment 1--Greenhouse

Physiological responses--banana. Under the W1 irrigation

volume, maximum PS at 1200 and 1400 hrs was 0.285 and 0.263

mg C02 m-2 s-1, respectively (Figure 5-2A). Diurnal patterns
for CS and TR appeared to parallel each other under both

irrigation levels with maximum levels for both parameters

occurring at 1200 and 1400 hr (Figure 5-2, 5-3). LWPs were

generally higher in plants at the 280 and 330C RZTs under the

W1 irrigation volume except at midday when LWP averaged

-0.71 MPa over all RZTs (Figure 5-2D).

At the higher irrigation level, W2, a maximum PS of

0.330 mg CO2 m-2 s-1 was measured for the 330C RZT treated

plants at midday (Figure 5-3A) and another similar peak of

0.301 mg CO2 m-2 s-1 occurred in the 380C RZT treated plants

at 1400 hr. PS was significantly reduced at midday and

thereafter by the 430C RZT. LWPs were generally higher in the

330 and 380C RZT treated plants compared to those observed at

280 and 430C between 1000 and 1400 hr (Figure 5-3D).

Regression analyses of midday PS over RZT and irrigation

treatments revealed significant effects of RZT but not

irrigation treatments (Figure 5-4A). PS was highest at the

280 and 330C RZT treatments with progressive reductions at

the 380 and 430C RZTs. While highest midday PS was noted for

the 280 and 3300 RZTs, diurnal patterns showed a lag in

response for the 380C RZT with peak PS occurring after midday

(Figure 5-2A, 5-3A). Since there were also corresponding

















O 4- )
.r- 0 C
4->) W0) (0
o o
Mn c E
*r-
S. c .C


> 4- 0
S-0 (n S-
i- 0 0s>
W to

'- 0 44) Ul
*r- 1 4.

I- C C
E o *r-
0 O

+I1u o
o L. = *
LC 0.-- uJ
I- 0 /)
M 4-*r-

*r.- C .-
co 4-) 4)

C o0r- ) 4-3
00o 4-)
r- 04)
U 0 09 *r- a
1./ Lu


0 Q. 0 0 Q.
S.- L)-S
=- 0- 4-
, e *O
m C30 0- U


F*- U .0
C) "a (D


C 0 C-
00U 0
0 a) (A (t
N .= 3 U
I 4- *r-
4-) rC- 4-
0 OCC S-
000 0d
S.- OC >
L. 0
L. 0 Ct *
C 4- C
0 *r- S. 0 0
4- 00 .-
*r) a -- U(
4- C C CL+4

U Cc
4) C r-
4t)) 39 L. Q.
U E o0 4)
0)L0 0



LO C *-
00 -
CL S.- CU L -
1 010 oC 01
LO C-. 10 L.

0 0- U X


U)r- *r- C
*r- O 0 O-
LL > Z U 0






































(1-s uo) 3oNVJ3fONOO


C--I
VI31


r-
8 A


O'


(BdY) T~U ~d CaiM I
C'E'O 1LLNLd U31VM dY31


0
1c


F

0

0
0
9-


C1 C 4 c
4-8 Z-W OZH &u) NOLLVUWdSNVWL


9



000
ooo
CO CO CO


q
(L-8 3-M


1* 00


ZOO &u) 9S3HKLNASOO1Hd