Production temperature effects on anatomy, morphology, physiology and postharvest longevity of leatherleaf fern (Rumohra...

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Title:
Production temperature effects on anatomy, morphology, physiology and postharvest longevity of leatherleaf fern (Rumohra adiantiformis (Forst.) Ching)
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xvi, 122 leaves : ill. ; 28 cm.
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Stamps, R. H ( Robert Huguenor ), 1948-
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Thesis (Ph. D.)--University of Florida, 1984.
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Includes bibliographical references (leaves 108-120).
Statement of Responsibility:
by Robert Huguenor Stamps.
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Typescript.
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Vita.

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PRODUCTION TEMPERATURE EFFECTS ON
ANATOMY, MORPHOLOGY, PHYSIOLOGY AND POSTHARVEST LONGEVITY OF
LEATHERLEAF FERN [Rumohra adiantiformis (Forst.) Ching]











BY

ROBERT HUGUENOR STAMPS


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


1984































Copyright 1984

by

Robert Huguenor Stamps































TO THE MEMORY OF MY PARENTS,
NINA M. HUGUENOR AND FREDERICK W. STAMPS,
AND TO LORETTA















ACKNOWLEDGEMENTS


I would like to sincerely thank my graduate committee chairman, Dr.

Terril A. Nell, for his guidance, support and criticism during my

graduate career at the University of Florida. His well-considered

advice helped me on many occasions.

Hearty thanks are also extended to the other members of my

committee, Dr. James E. Rarrett, Dr. Charles A. Conover, Dr. Frederick

S. Davies and Dr. Terry W. Lucansky, for their advice, assistance and

friendship. Special thanks go to Ms. Debbi A. Gaw for her considerable

assistance to this "commuting" student.

To the myriad other faculty, staff, friends and fellow students, at

Gainesville and Apopka, who contributed to this endeavor, many thanks.

Thanks are offered to Dr. Carlos Blazquez, Mr. George Edwards and Mr.

Leonard Blesius at Lake Alfred for the use of the LMS.

Special gratitude is extended to Dr. Charles A. Conover for

encouraging me along this path and for allowing me the leave of absence

that made this possible.

Above all, I am grateful to my wife, Loretta Satterthwaite.

Without her support and help the completion of this dissertation could

not have been successful given the time constraints involved.













TABLE OF CONTENTS


Page

ACKNOWLEDGEMENTS . . ... ...... iv

LIST OF TABLES . . ... ... viii

LIST OF FIGURES . . . x

KEY TO SYMBOLS AND ABBREVIATIONS . ... xiii

ABSTRACT . . ... . xv

INTRODUCTION . . ... . 1

CHAPTERS

I LITERATURE REVIEW . .. 6

Growth .. .. ... .. .. 6

Morphology and Anatomy. . ... 8
Leaf length and surface area . 8
Leaf thickness . . 8
Specific leaf weight and leaf density thickness. 9
Stomatal distribution . 9
Stomatal frequency . 9
Cuticle thickness and integrity .. 10
Epidermis . . 10
Endodermis . . 11
Tracheids . . 11

Physiology. . .... ... 11
Carbon exchange . .... 11
Carbohydrates . .. 17
Chlorophyll . .... 18
Transpiration . ... 18
Water use efficiency . .... ..18
Diffusive conductance . ... 18
Hydraulic conductivity . ... 19

Postharvest . . 21








Page

Plant Material . .. .. 23

II TEMPERATURE AFFECTS THE DEVELOPMENT AND POSTHARVEST
LONGEVITY OF LEATHERLEAF FERN FRONDS .... 24

Materials and Methods . .... 26

Plant material and treatments . ... 26

Growth and development . .... 28
Frond length . .... 28
Sori development . .... 28

Morphology and anatomy . ... 29
Frond surface area . .... 29
Frond thickness . ... 29
Stipe cross-sectional area .... 29
Stomatal density .. ....... 29
Cuticle thickness and number of epidermal
cell layers ..... ....... 30
Tracheid numbers and cross-sectional areas 30

Physiology . . 31
Carbon exchange . .. 31
Transpiration . ..... 38
Chlorophyll content . 39
Diffusive conductance . 39
Carbohydrates . .. .. 39
Stipe hydraulic conductivity ... 40

Postharvest . ... .. 41
Postharvest water uptake . ... 42
Postharvest weight changes .... 42
Postharvest longevity . .... 42

Results and Discussion . . .. 43

Experiment 1 . . 43

Experiment 2 . . 51

Experiment 3 . . 65

Experiment 4 . . 80
Harvest I . . .. 80
Harvest 2 . . 83

Conclusions . ... . 92







Page

APPENDIX . . .. .100

LITERATURE CITED . . . 108

BIOGRAPHICAL SKETCH .. .. .. 121















LIST OF TABLES


Table Page

0-1 Annual change in movement of leatherleaf fern in
Florida for crop years 1977-78 through 1983-84 2

2-1 Production temperatures affect sori development on
leatherleaf fern fronds grown in controlled environ-
ment chambers 45

2-2 Physiological characteristics for leatherleaf fern
fronds grown under low and high temperature regimes 49

2-3 Anatomical, morphological and postharvest character-
istics of leatherleaf fern fronds grown under low and
high temperature regimes 56

2-4 Anatomical, morphological, physiological and post-
harvest characteristics for leatherleaf fern fronds
grown under low and high temperature regimes 73

2-5 Effects of former production temperature treatments
(FT) and latter production temperature treatments (LT)
on leatherleaf fern frond characteristics. Temperature
treatments were changed February 26, 1984, crosiers were
tagged March 4, 1984, and fronds were harvested May 5,
1984 85

2-6 Association of vase life and frond morphological
characteristics of leatherleaf fern fronds harvested
May 5, 1984 86

2-7 Effects of former production temperature treatments
(FT) and latter production temperature treatments (LT)
on water uptake of cut leatherleaf fern fronds. Temper-
ature treatments were changed February 26, 1984, crosiers
were tagged May 5, 1984, and fronds were harvested
July 4, 1984 88

2-8 Effects of former production temperature treatments (FT)
and latter production temperature treatments (LT) on
leatherleaf fern frond characteristics. Temperature
treatments were changed February 26, 1984, crosiers
were tagged May 5, 1984, and harvested July 4, 1984 91


viii








Table Page

A-i Association of vase life, water uptake, and leatherleaf
fern frond anatomical, morphological and physiological
characteristics for Experiment 2. Fern was grown under
high temperature regime (30 day/250 night) or low
temperature regime (200 day/150 night) 100

A-2 Association of vase life, water uptake, and leatherleaf
fern frond anatomical, morphological and physiological
characteristics for Experiment 3. Fern was grown under
high temperature regime (300 day/250 night) or low
temperature regime (20 day/150 night) 102

A-3 Association of vase life, water uptake, and leatherleaf
fern frond morphological and physiological character-
istics for Experiment 4, harvest 1. Plants had been
grown under 1 of 2 former temperature treatments (FT)
and fronds were produced under 1 of 2 latter
temperature treatments (LT). The temperature treat-
ments were low (200 day/150 night) temperature regime,
LTR, and high (300/250) temperature regime, HTR 104

A-4 Association of vase life, water uptake, and leatherleaf
fern frond morphological and physiological character-
istics for Experiment 4, harvest 2. Plants had been
grown under 1 of 2 former temperature treatments (FT)
and fronds were produced under 1 of 2 latter
temperature treatments (LT). The temperature treat-
ments were low (200 day/150 night) temperature regime,
LTR, and high (300/250) temperature regime, HTR 106















LIST OF FIGURES


Figure Page

0-1 Association of cooling degree days (18.30 C base)
and the percentage of fronds that curled or yellowed
12 days postharvest 4

2-1 Photomicrograph of vascular bundle in stipe of leatherleaf
fern frond (top), digitized image of the same vascular
bundle (middle), and enhanced digitized image of the
lumina of the tracheids in that vascular bundle (bottom) 33

2-2 Schematic diagram of open system used to measure
carbon exchange and transpiration of leatherleaf
fern fronds 34

2-3 Acrylic plastic cuvette used in carbon exchange and
transpiration determinations of leatherleaf fern fronds 37

2-4 Effect of production temperatures in controlled
environment chambers on growth of leatherleaf fern
fronds 44

2-5 Abaxial diffusive conductances (A), leaf temper-
atures (B), and transpiration (C) of leatherleaf fern
fronds grown in controlled environment chambers under
temperatures of 200C day/150 night, or 30
day/250 night, ---- and relative humidities at the
time of measurement (D) 46

2-6 Effect of photosynthetic photon flux density (PPFD) on
carbon exchange (CER) of leatherleaf fern fronds grown
under 2 temperature regimes 48

2-7 Quantum efficiencies of leatherleaf fern fronds grown
under 2 temperature regimes 50

2-8 Effect of photosynthetic photon flux density (PPFD) on
transpiration (T) of leatherleaf fern fronds grown
under 2 temperature regimes 52








Figure Page

2-9 Photomicrographs of leatherleaf fern pinnules showing
A) abaxial pinna surface with stomata, B) adaxial pinna
surface, C) close-up of a stoma and D) cross section of
a pinnule showing stomatal complex and substomatal
chamber 54

2-10 Association of fresh weight and surface area for
leatherleaf fern fronds grown under 2 temperature
regimes 57

2-11 Pinnae from high (300C day/250 night) temperature
regime, HTR, frond (left) and low (200 day/150 night)
temperature regime, LTR, frond (right) showing
reduced venation and increased marginal incision of
HTR pinnules 59

2-12 Scanning electron micrographs of cross sections of
pinnules of leatherleaf fern grown under low (200C
day/150 night) temperature regime (top) and high
(300 day/250 night) temperature regime (bottom) 61

2-13. Postharvest water uptake of cut leatherleaf fern fronds
grown under 2 temperature regimes 63

2-14. Postharvest weight changes of cut leatherleaf fern
fronds grown under 2 temperature regimes 64

2-15. Postharvest water uptake of cut leatherleaf fern fronds
grown under 2 temperature regimes 66

2-16. Effect of recutting stipe bases 1 or 2 days post-
storage on water uptake of leatherleaf fern fronds
grown under temperatures of 200 C day/15 night,
or 30 day/250 night, ---- 67

2-17. Effect of recutting stipe bases 3 or 5 days post-
storage on water uptake of leatherleaf fern fronds
grown under temperatures of 200C day/15 night, --
or 30 day/250 night, --- 68

2-18. Postharvest decline of relative conductivity, k, of
cut leatherleaf fern frond stipe bases 70

2-19. Changes in abaxial diffusive conductance and
transpiration due to recutting stipe bases of
leatherleaf fern fronds 6 days postharvest.
Fronds were grown under temperatures of 200C
day/15 night, or 300 day/250 night, ---- 71








Figure Page

2-20. Postharvest weight changes of cut leatherleaf fern
fronds grown under 2 temperature regimes 72

2-21. Scanning electron micrographs of a leatherleaf fern
stipe showing A) a cross section with vascular bundles
(vb) containing tracheids, B) the location of tracheids
(t) in a vascular bundle, C) close-up of tracheids and
D) scalariform pitting of the cell walls of tracheids 76

2-22. Cross sections of vascular bundles in stipe bases of
leatherleaf fern fronds, grown under 200C day/150
night (top) and 30 day/250 night (bottom) in
controlled environment chambers, showing the greater
thickening of the outer tangential wall of the
uniseriate endodermis of the 200/150 grown frond 78

2-23. Poststorage water uptake of cut leatherleaf fern fronds
grown under 1 of 2 former temperature treatments
and 1 of 2 latter temperature treatments 81

2-24. Abaxial diffusive conductance and transpiration during
the first 90 hr after recutting stipes of leatherleaf
fern fronds stored for 1 day 82

2-25. Poststorage weight changes of cut leatherleaf fern
fronds grown under 1 of 2 former temperature
treatments and 1 of 2 latter temperature treatments 84

2-26. Postharvest water uptake of cut leatherleaf fern fronds
grown under 1 of 2 former temperature treatments and
1 of 2 latter temperature treatments 87

2-27. Postharvest weight changes of cut leatherleaf fern
fronds grown under 1 of 2 former temperature
treatments and 1 of 2 latter temperature treatments 90

2-28. Plot of actual versus predicted weight changes of
leatherleaf fern fronds determined using the
transpiration and water uptake from Experiment 4,
harvest 1 96














KEY TO SYMBOLS AND ABBREVIATIONS USED IN TEXT


Where appropriate, magnitudes or typical units are indicated in
parenthesis.



Quantity Description

a total lumen area (mm2)

A cross-sectional area of stipe (cm2)

CER carbon exchange rate, carbon flux density, or

Pnet (mg CO2 dm2 hr-1)
chl chlorophyll

n viscosity (MPa-s, 0.9142 for water at 240C)

EY early yellowing

FCS frond curl syndrome

FT former production temperature treatment

g gram
res
gres residual conductance to carbon dioxide
2
gwv diffusive conductance to water vapor
c
g cuticlar diffusive conductance to water vapor

leaf leaf diffusive conductance to water vapor
hr hour

HTR high temperature regime (300 day/250 night)

Ic light compensation point, LCP mol. s- m-2)


xiii







KEY TO SYMBOLS AND ABBREVIATIONS (continued)


Quantity Description

Is light saturation point, LSP (imols- *m-2)

k relative conductivity (cm-2)

LDT leaf density thickness (g fresh wt-area- )

LT latter production temperature treatment

LTR low temperature regime (200 day/150 night)

Jm micrometer (10-6m)

PPFD photosynthetic photon flux density (pmols-1.m-2)

Rd dark respiration (mg C02*dm2 hr-1)

r w boundary layer resistance to water vapor (s*cm- )
wv
a conductivity

SLW specific leaf weight (g dry wt-area-1)

T transpiration, E (mg H20*dm 2*hr1)

VPO vapor pressure difference

WUE water use efficiency (mg C02:mg H20)


xiv













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



PRODUCTION TEMPERATURE EFFECTS ON
ANATOMY, MORPHOLOGY, PHYSIOLOGY AND POSTHARVEST LONGEVITY OF
LEATHERLEAF FERN [Rumohra adiantiformis (Forst.) Ching]

by

ROBERT HUGUENOR STAMPS

December 1984

Chairman: Terril A. Nell
Major Department: Horticultural Science

Leatherleaf fern, Rumohra adiantiformis (Forst.) Ching, was grown

under 2 temperature regimes in controlled environment chambers. The

chambers had the same photosynthetic photon flux density, but half the

chambers had high (300C day/250 night) and the other half had low

(200/150) temperature regimes. These regimes approximate those found

in Florida during the months when postharvest longevity of leatherleaf

fern fronds are low and high, respectively.

Fronds produced under the high temperature regime (HTR) grew faster

initially and produced sori sooner than low temperature regime (LTR)

ones. Fronds from both treatments were hypostomatous, anomocytic, and

stipe tracheids had scalariform pitting.

Light saturated carbon exchange, quantum efficiences, and dark

respiration were lower for HTR grown fronds than LTR fronds when

measured at 30.50. Light compensation points, water use efficiency,







photosynthetic efficiency, and soluble sugar and starch content were

similar for fronds from both treatments. Abaxial diffusive conductance

(gwv) of HTR fronds was lower than for fronds grown under the LTR. The
lower g may have been due to greater physiological age or to

preconditioning of HTR fronds.

Temperature treatments did not affect frond weights, surface areas,

water content, stomatal density, cuticle thickness, or number of

epidermal layers, but leaf density thickness, specific leaf weights,

pinnule thickness and vascularization, endodermal wall thickening, and

stipe vascular bundle numbers and cross-sectional areas were reduced

for HTR fronds. Relative conductivities of freshly harvested stipes

were 39% lower for HTR fronds than LTR fronds.

Postharvest water uptake of HTR fronds was 36 to 50% lower than LTR

uptake. In 3 experiments, vase life of HTR fronds was reduced 28 to

66% compared to LTR fronds. HTR fronds lost weight more rapidly after

harvest. Vase life was positively correlated with stipe

cross-sectional area and initial water uptake. Stipe recutting 1 to 6

days postharvest increased gwv and water uptake of both frond types.

Plants were switched from one temperature regime to the other.

Former production temperature effects predominated for the first

harvest of fronds produced under the latter temperature regime. The

second crop of fronds was mainly influenced by the latter production

temperature regime.













INTRODUCTION


Temperature is one of the more important environmental factors

influencing the development and physiology of plants. Production

temperatures may affect crop performance both before and after harvest,

and can have both beneficial and detrimental effects, depending on the

crop and other environmental factors.

Leatherleaf fern, Rumohra adiantiformis (Forst.) Ching (151), is

one of the most important ornamental crops produced in Florida.

Estimates place the annual wholesale crop value at approximately

$60,000,000 (133), with leatherleaf fern accounting for approximately

85% of cut foliage use nationally (129). In the past several years

leatherleaf fern has become one of Florida's major farm exports (49)

and is one of the few remaining floricultural cut crops whose

production is predominantly domestic and is increasing (Table 0-1).

The preeminence of Florida in the production of this crop is

threatened by many factors. The most immediate problems threatening

the industry are the occurrence of frond curl syndrome (FCS) and early

yellowing (EY) of fronds. Both conditions greatly reduce vase life

(112, 137). Florists are looking for other sources of leatherleaf fern

fronds and/or other cut foliage crops to replace leatherleaf fern

because of these problems (129). The incidence of FCS and EY is quite

seasonal and occurs mainly during the months of July, August,

September and October (32, 98). Fronds harvested during these months





















Table 0-1. Annual change in movement of leatherleaf fern in
Florida for crop years 1977-78 through 1982-83 (133).



p Y Shipments Change
SYear (cartons) (%)


1977-78 1,057,000

1978-79 1,286,000 +22

1979-80 1,480,000 +15

1980-81 1,615,000 + 9

1981-82 1,723,000 + 7

1982-83 1,983,000 +15

1983-84 2,367,000 +19








develop during the 4 hottest months of the year (June, July, August,

September). Figure 0-1 shows the association of temperature, expressed

as base 18.30 C cooling degree days, and FCS plus EY. Previous

research (112) suggests that some factors) other than postharvest

dessication predispose(s) the fern to frond curl. It therefore seems

possible that production temperatures may be a factor involved in the

reduction of vase life. A preliminary experiment (Stamps,

unpublished), conducted using controlled environment chambers to

simulate production temperatures during those periods when vase life

was found to be greatest and least, indicated that vase life of fronds

produced at high temperatures was reduced 36% compared to those grown

at lower temperatures. This difference in vase life due to production

temperatures was still present after all the plants were grown together

under the same conditions for 1 week in a greenhouse.

The ability to predict and/or decrease the incidence of reduced

vase life would benefit the leatherleaf fern industry. Almost no data

are available on the effects of production temperatures on leatherleaf

fern development and physiology. No studies have been made on the

effects of this factor on the postharvest longevity of harvested

fronds. Indeed, not a great deal of research has been done on the

physiology of fern sporophytes in general. For example, Dyer (40), in

his book The Experimental Biology of Ferns, does not devote any space

to carbon exchange rates, transpiration, dark respiration or other

physiological aspects of fern sporophytes. These and other

physiological factors, as well as anatomical and morphological factors,

could effect the postharvest longevity of leatherleaf fern fronds.

These experiments were undertaken to examine some of the effects of












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production temperatures on the developmental, morphological,

anatomical, physiological and postharvest aspects of this important

crop, leatherleaf fern.













CHAPTER I
LITERATURE REVIEW


Effects of Production Temperatures on development,
Physiology and Postharvest Longevity of Plants



Most chemical reactions and physiological processes respond to

temperature. Therefore, considerable research has been carried out to

study the effects of production (preharvest) temperature on plant

development and physiology. Considerable research has also been

directed at storage (postharvest) temperature effects on many

agricultural commodities (91, 158). Until recently, however, little

research has addressed the question of what are the effects of

production temperatures on the post-production quality and longevity of

horticultural commodities even though it was shown over three decades

ago that production temperatures might affect the postharvest

respiration rates of a certain variety of greenhouse tomato (1). No

such production temperature studies have been carried out for

leatherleaf fern; however, there is no a priori reason to expect that

leatherleaf fern would respond differently from other plants,

especially other C3 plants.


Growth


Most processes of living organisms are controlled by enzyme

reactions and, therefore, growth phenomena tend to exhibit temperature








response curves similar to those for enzymes (149). In addition to

affecting enzymatic processes, temperature may affect physical

processes, such as oxygen diffusion (115), which may affect growth.

Many studies have shown that increased production temperatures, day

and/or night, soil and/or air, increase growth and developmental rates

provided other factors such as light, CO2 and water are not limiting

and temperatures are not so high as to cause thermal injury. Went

(156) found that growth of tomato plants at a constant 260 C day

temperature increased as night temperatures were increased from 40 to

200. Friend et al. (54) found that raising the temperature by 50

intervals between 100 and 250 resulted in progressively higher rates of

emergence and expansion of wheat leaves. Similarly, Ballantine and

Forde (9) found that soybean plants grown in high temperature (27.50

day/22.50 night) controlled environment conditions grew more rapidly

than those at lower (20.00 day/12.5 night) temperatures. Woledge and

Jewiss (161) presented data from Robson showing increased relative

growth rates of tall fescue plants grown at high (200 day/150 night)

versus low (100 day/50 night) temperatures. Kramer (84) found that the

growth of red oak improved with increasing temperature up to 300.

Caladiums (31), Campanula (106), cucumbers (103), Dipladenia (60),

loblolly pine and red oak (84), roses (20, 104, 165), Salvinia-an

aquatic fern-and sunflower (16) and tropical foliage plants (126) are a

few of the crops that exhibit increased growth and developmental rates

at moderately high temperatures compared to lower ones. Staghorn fern

sporophytes grown over the temperature range of 120 to 300 grew best at

260 (144). Therefore, most plants respond to increasing temperatures

with increased growth and development rates, provided the temperatures

are not excessive.







Morphology and Anatomy


Leaf length and surface area. Leaf length and surface area are

important because the leaf is the major light collecting and water

vapor radiating organ of most terrestrial plants. Friend et al. (54)

found that winter wheat leaf area was greatest when grown at 200 than

when grown at higher or lower temperatures. Plants grown at 250 had

longer leaf laminae compared to plants grown at 100, 150, 200 or 300.

In a later study, Friend and Pomeroy (55) found that leaf length of

wheat increased with increasing production temperatures over the range

from 100 to 250. Leaf length and surface area are particularly

important for cut foliage crops due to their use as decorative filler

in floral arrangements.

Leaf thickness. Numerous authors have found that leaf thickness

decreases with increasing temperature. Chabot and Chabot (25) found

that Fragaria vesca leaf thickness decreased with increasing production

temperatures up to 300 day/200 night. Higher temperatures caused cell

damage. Peet (120) reported a decrease in Phaseolus leaf thickness

with increasing temperature. Charles-Edwards et al. (28) also found a

similar decrease in leaf thickness for Lolium grown over the

temperature range of 100 to 280. Leaf thickness of Marquis wheat

decreased with increasing temperature in other studies (53, 54).

However, Nobel (113) did not show a decrease in leaf thickness with

increasing temperature for Plectranthus.

Leaf thickness may be of physiological importance because Pieters

(122) and Wilson and Cooper (160) have shown that carbon exchange (CER)

is positively correlated to leaf thickness.







Specific leaf weight and leaf density thickness. Specific leaf

weight (SLW, leaf dry weight area- ) and carbon exchange rate are

positively correlated in many plants (38, 100, 122). Holmgren (74)

found that SLW was highly correlated with mesophyll [i.e., residual

conductance of Solidago leaves and suggests that increasing

cross-sectional area (per unit leaf area) of the pathways of CO2

transfer increases residual conductance and photosynthesis. Specific

leaf weights of Fragaria increased with increased temperature from 100

day/20 night to 300/200 (25). McMillen and McClendon (102) prefer leaf

density thickness (LDT, leaf fresh weight area-1) to SLW and state

that LOT is important in photosynthetic adaptation of plants.

Blackman's data (16) showed that LDT for Helianthus and Lemna was lower

for leaves grown at 240 than 150. Blackman et al. (17) found that

sunflower LDTs decreased seasonally from May through September due to

the rising temperature.

Stomatal distribution. Stomata may occur on one (epistomatous,

hypostomatous) or both (amphistomatous) leaf surfaces (149). Parkhurst

(117) found that hypostomatous leaves occurred most frequently in mesic

habitats, less frequently in hydric ones, and least frequently in xeric

habitats. Stomata generally occur on the abaxial surface of leaves of

leptosporangiate ferns (52, 89, 116). Of the 35 fern species studied

by Linskens and Schoof-van Pelt (89), Ludlow and Wolf (90), Pisek et

al. (123), Nobel (114) and Biswal et al. (11) all were essentially

hypostomatous even though the fern ranged from a desert fern,

Notholaena parryi, to ferns of mesic habitats.

Stomatal frequency. Stomatal frequency can vary greatly (61).

Verduin (153), using data of Eckerson (41), reported that wheat had a








-2
stomatal frequency of 14-mm-2. Davies et al. (36) found stomatal

frequencies as high as 634*mm-2 for Rhus typhina. Lin et al. (88)

found a range of densities from 377 to 1180.mm-2 for different species

of Pistacia. Typical fern stomatal densities range from 10mm-2 for

Phyllitis scolopendrium (123) to 169-mm-2 for Alsophila australe (113).

However, Starzecki (142) reports stomatal densities exceeding 300.mm-2

for fern, Asplenium trichomanes and A. ruta-muraria, growing at a cave

entrance. Friend and Pomeroy (55) report higher stomatal densities for

Kharkov winter wheat grown at 32,280 lux (approximately 375

pmol.m-2 s- ) at high (250) versus low (150) temperatures. At light

levels of 5380 lux (approximately 62.5 umol*m-2 s- ) there were no

differences in stomatal density due to temperature.

Cuticle thickness and integrity. Water permeability of cuticles of

terrestrial plants is very low (135); however, cuticular transpiration

can exceed 10% or more of total transpiration of some plants (75, 86,

149). Cuticle thickness across species is not a reliable indicator of

water permeability (135) but may be of value when comparing plants of a

given species. As leaves age, cracks may develop and cause an increase

in water permeability (115). Holmgren et al. (75) found that cuticular

conductance (g v) of three species was greatly increased by an increase

in temperature from 170 to 220 and leveled off or decreased slightly at

higher temperatures.

Epidermis. The epidermis is the outer layer of cells of the

primary plant body. The epidermis is usually one layer of cells in

thickness (44) and functions in water vapor and gas exchange as well as

in protection. Studies relating production temperatures with the

epidermis are not available.








Endodermis. The endodermis is the innermost layer of the cortex

and forms a sheath around the vascular region of the stems and roots of

lower vascular plants (44). Possible functions of the endodermis of

the stem are the storage of materials and as a barrier to gas exchange

and the entrance of pathogens. The highly suberized endodermis between

the ground tissue (cortex, pith) and the stele is an effective

waterproof barrier to apoplastic water transport across the endodermis

(149). Studies of temperature effects on the endodermis were not

found.

Tracheids. Tracheids, the characteristic water conducting cells in

lower vascular plants, have thick, lignified secondary cell walls (44).

Typical fern tracheids are long, slender, tapered and scalariformly

pitted (157). Scalariformly pitted tracheids are considered to be the

primitive type of tracheid in fern (157). Huber and Schmidt (77)

measured vessel diameters from 16 um for Carpinus betulus to 400 Um for

Robinia pseudacacia. Petty (121) found a mean vessel diameter of 59 pm

for birch wood. Jeje and Zimmermann (81) measured Plantago vessel

diameters from 5.4 um to 11.6 um and found that ring thickness and

spacing caused changes in resistance to flow. Nobel (114) reports fern

stipe tracheid lumen diameters of 7.8 um in stipes of Notholaena

parryi. Woodhouse and Nobel (163) reported ranges for tracheid

diameters from 7.9 pm to 18.9 um and for the number of tracheids from

27.7 to 228 in stipes of 7 fern species.


Physiology


Carbon exchange. Considerable research has dealt with the effects

of temperature on carbon exchange (CER, carbon flux density) and







photorespiration. Optimum temperatures for CERs of C3, C4 and CAM

plants have been determined (15). However, much less research has

dealt with the effects of production temperatures preconditioningg) on

subsequent CERs. Temperature preconditioning effects should be

considered in planning or evaluating measurements of CERs (85, 107).

Fragaria vesca grown at moderate temperatures (100/20, 200/100,

300/200; day/night) showed a general trend towards increased CERs with

increased production temperatures, even though CERs were measured at

the same temperatures (25). Plants grown at 400/300 had a reduced CER

at low temperatures and only at 350 did their CERs equal those of

plants grown at 300/200. Strawberry plant CERs varied significantly

when plants were grown at a common mean temperature (250) but different

day/night amplitudes (250/250, 300/200, 350/150). Chabot and Lewis

(26) found that, when day/night temperatures were asymmetrically

distributed around a daily mean, CERs of Quercus rubra seedlings

acclimated to those temperatures experienced for the major portion of

the 24 hr period such that CER was most favorable at the predominant

temperature. Nobel (114) found that the temperature optimum for CERs

of a desert fern, Notholaena parryi, shifted from 130 in midwinter

(daily mean air temperature of 110) to 190 in early fall (air

temperature of 230). Blackman et al. (17) determined that CERs of

sunflower were positively correlated with temperature. Many studies

have shown that the temperature of maximum CER increases with

increasing growth temperatures (27, 108, 134, 146, 154, 161). Rook

(131) grew Pinus radiata seedlings at 150/100 and 330/280 and then

switched some plants from each chamber to the other. He found that

most of the adaptation of the seedlings occurred within 2 days and

after about 5 days at the new temperatures the seedlings were







similar in CER behavior to seedlings that had been raised entirely

under the changed conditions. Not all studies have shown significant

acclimation in the temperature dependence of CER for plants grown under

different temperature regimes (43).

Endogenous factors influenced by temperature, such as leaf

physiological age and residual conductance (gC05), can affect CER.

CERs generally increase as immature leaves develop, reach a maximum

when leaves fully expand, and decline as the leaves age (see 148 for

references). Jewiss and Woledge (82) found that the CER of tall fescue

progressively declined with increasing age. Leaves of greenhouse roses

have been shown to exhibit a similar decline with age (19). Silsbury

(136) reports that light saturated CER of ryegrass leaves decreased

when leaves began to senesce. Holmgren (74) suggests that mesophyll

[residual] conductance increases with increased cross-sectional area

(per unit leaf area) of the pathways of CO2 transfer in the mesophyll

from cell surfaces to reaction sites. Higher temperatures generally J/

lead to smaller cells and up to a 40% higher ratio of the total area of

the cell walls of mesophyll cells that is exposed to the intercellular

air spaces to the area of one side of the same leaf (Ames/A) (115).

Charles-Edwards et al. (27) found that, within a given grass variety,

plants grown at a higher temperature had a lower CER. In a later study

(28) they found that the stimulation of CERs per unit leaf area of

grasses disappeared when the data were expressed on a volume basis due

to the thicker leaves of grasses grown at the low temperature.

McClendon (100) and McMillen and McClendon (102) report that leaf

density thickness is positively correlated to CER. Dornhoff and

Shibles (38) suggest that soybean varietal differences in CER were







mainly a result of differences in diffusive conductances. Leaf density

thickness increased linearly during the test period (July 11 to August

4) and CER increased starting August 4. Since the CER increase

coincided with the beginning of seed filling, increased sink demand was

probably the cause of the CER increase in this experiment.

Light saturation (Is or LSP) of CERs of shade-adapted leaves is
-1 -2
usually in the vicinity of 280 umol*s- *m (149). CER of weeping figs

grown under 75% light exclusion was light saturated at about 300

umol-s-1*m-2 (45). Alocasia macrorrhiza and Cordyline rubra growing on

the rainforest floor reached light saturation at irradiance levels
-1 -2
below 100 umol-s *m (14). Many ferns have I s between 100 and 200

umols-1.m-2 (71, 90, 113, 114), with the Is for leatherleaf fern being
-1 -2
reported as 500 umol*s *m2 (97).

Light saturated CERs under natural conditions range from 1 to 4 mg

C02*dm-2 hr-1 for some CAM plants to 35-70 mg C02*dm2* hr-1 for C4
plants (132). Light saturated CERs for C3 species such as leatherleaf

fern are generally between 5 and 40 mg C02*dm2hr-1 (43). For

example, reported Is CERs for a typical C3 crop such as soybeans range

between 12 and 50 mg C02*dm-2*hr- depending on the variety (34, 38).

Light saturated CERs for ferns are generally lower, 3 to 5 mg

C02'dm-2hr1 (86). Assuming 1 g fresh weight is approximately equal

to 0.5 dm2 of leaf surface area (132), Hew and Suan (70) recorded I

CERs from 2.2 mg CO 2dm-2*hr- for cut fronds of Asplenium nidis to 12
2 -1
mg C02*dm-2hr1 for cut fronds of Gleichenia linearis. CERs at Is for

intact nonsenescent fern fronds range from 0.9 for Adiantum pedatum to

27.6 mg C02*dm-2'hr-1 for Alsophila australis (71, 90, 113, 164).







Maximum CER for shadehouse grown Rumohra adiantiformis is reported as

7.5 mg C02.dm-2-hr-1 (97).

Survival of plants [or plant parts] under low light depends [in

part] upon the efficiency with which leaves capture and utilize

available light, and upon control of respiratory losses (45). The

quantum efficiency (slope of light intensity curve below

photosaturation) of a plant is, to a large extent, dependent on leaf

morphology (79). Ehleringer and Bjorkman (42) found that typical

quantum yields of C3 plants were 0.0524 mol C02/absorbed mol photons.

In a later study (43) they found that species of Encelia with high

photosynthetic rates had quantum yields (on an incident light basis) of

0.033 to 0.041 nmol CO2/mol photons. The quantum efficiency for an

Alocasia leaf in situ was found to be 0.07 mol C02/mol photons (14).

Ouantum efficiencies for wheat grown at 50 to 70 or 250/200

temperatures were not different when measured at 250 (134). Quantum

efficiencies of 6 grasses were also not affected by different growth

temperatures (28).

Photosynthetic efficiency (CO2 fixed per unit chlorophyll per unit

time) can vary among species (85) and according to growth environment

(66). Light saturated photosynthetic efficiencies of 1.5 to 0.8 mg

CO2mg chl- 1hr- for Pteris ferns have been reported (66).

The light compensation point (Ic or LCP), the light intensity where

photosynthesis just equals respiration, is especially important when

plants or plant parts are grown in or moved to very low light

environments (132). Light intensities in home and office environments

are usually low and low Ics may be beneficial under such conditions.

Light compensation points for C3 species are usually on the order of







-1 -2 -1 -2
11 Umolos *m for shade-adapted leaves and 31 ymolos *m for

sun-adapted leaves (149). Greenhouse grown tropical foliage plants

were found to have Ics from 14 to 34 ymol*s- *m-2 except for a monocot
-2 -1
that had an I of 11q9 mol.m *s- (51). Alocasia in extreme shade
-1 -9
habitats are reported to have I s of 0.5 to 2 Umol.s l m -? (14).

Bannister and Wildish (10) measured Ics for detached fronds of 4 fern

species of 0.5 to 2.0 ymolos-1 m-2 and found that specific leaf areas

showed a significant negative correlation with Ics. Similar extremely

low Ic values for Pteris fern have been reported (66). Many authors

attribute very low light compensation points to low rates of

respiratory CO2 release (10, 14, 51, 101, 118). Salisbury and Ross

(132) state that differences in Ics are caused primarily by differences

in respiration rates. Most Ic values for fern are in the 6 to 40
-1 -2
umol-s *m range (62, 71, 90, 118) and the one report of an Ic for

shadehouse grown leatherleaf fern was 44 umol.s-.m-2 (97).

Ting (149) writes that dark respiration (Rd) by green leaves is

generally 1 to 10 mg C02*dm-2 hr-1. Studies of the Rd of the ferns

Nephrolepis (118) and Rumohra (97) fit this range; however, studies of

cut fronds of 6 fern species (70) and attached fronds of 14 others (90,
-2 -1
164) yielded Rd values from 0.13 to 0.45 mg C02odm-2hr-.

Factors such as substrate availability, temperature, and type and

age of plant affect respiration (132). Azcon-Bieto et al. (8)

concluded that the level of respiratory substrate in leaves of spinach

and wheat determines their Rd. Wager (154) found that the Rds of

arctic plants were higher than those of temperate plants and suggested

that the differences were due to differences in carbohydrate

concentrations rather than to differences in enzyme activity. Warren








Wilson (155) reports similar results. Rook (131) found that Rds of

Pinus seedlings grown under 150/100 conditions were double those of

plants preconditioned at 240/190 or 330/280. Woledge and Jewiss (161)

and Bjtrkman (12) report similar results and attribute the higher Rds

to higher carbohydrate levels. Chabot and Chabot (25) found that Rd

expressed on an area basis was positively correlated with SLW and leaf

thickness, but when expressed on a weight basis it was negatively

correlated with both morphological variables. The rate of respiration

of an organ decreases as it ages (154). Bozarth et al. (19) state that

Rd of rose leaves decreased throughout most of their development. The

greater rates of decline in Rd due to higher temperatures may, in fact,

be due to increased aging (59).

Strain and Chase (145) measured reduced Rd rates at 4 prevailing

temperatures (100,200,300,400) for high temperature (400/250) grown

desert shrubs. They hypothesized that either a depletion of

respiratory substrates or a change in enzyme activity with increasing

temperature is a possible explanation (128). Alban et al. (1) showed a

trend for fruits from one variety of tomato, but not for another, to

have higher postharvest respiration rates when grown at higher

temperatures. However, their data were not analyzed statistically.

Carbohydrates. Carbohydrates are the direct products of

photosynthesis and foliar levels of non-structural carbohydrates can

vary greatly on diurnal (8) and seasonal (85) cycles. Temperature

affects carbohydrate concentrations of plants. Sawada and Miyachi

(134) found total sucrose in wheat grown at low temperatures was higher

than in high temperature grown plants. Ballantine and Forde (9) showed

that soybeans grown at high temperatures had reduced starch content







compared to low temperature grown soybeans. Carbohydrate

concentrations of ostrich fern were lower when grown at 240/180 than at

180/12' (127).

Chlorophyll. Published chlorophyll contents for fern range from

0.81 to 55 mg chlorophyll-dm-2 (43, 65, 90, 114). Some studies have

shown decreases in chlorophyll content (on an area basis) due to high

temperatures (9), while other studies have not (43).

Transpiration. Water loss is an inevitable consequence of stomatal

opening necessary for CO2 uptake. Usual daytime transpiration flux

densities (T) are in the range of 0.1 to 2.5 g H20*dm-2 hr (0.15 to

3.9 mmol *m 2s- ) (149). Transpiration values for soybeans were higher

(2.75 to 3.79 g H20*dm-2hr-1) (38). Nobel (114) calculated maximum T

of 1.47 g H20'dm-2 hr-1 (2.27 mmol*m-2*s 1) for the xeric fern

Notholaena parryi.

Water use efficiency. Water use efficiency (WUE) relates the

amount of CO2 fixed to the amount of water lost. WUE on a mass basis

of a leaf of a representative mesophyte is 4.9 x 103 mg C02.(mg H20)-1

(115). The WUE reported for a desert fern during the daytime in situ

was 5.8 x 10-3 mg C02.(mg H20)-1 (114).

Diffusive conductance. Abaxial water vapor diffusive conductance
-2 -1
(gw) for crops when stomata are open range from 80 to 400 mmol*m *s

(115). Abaxial g wvs for trees are generally lower (20 to 120
-~2 -1 leaf
mmol *m -s ). Leaf conductance (g a ) of C and C plants commonly

increases during the morning, reaches a peak in late morning or early

afternoon and decreases during the rest of the day (29, 88). Two

epiphytic CAM ferns had leaf of 3.3 to 80 mmol'm-2s-1 and exhibited
the typical CAM reverse pattern of low g during the day and high
the typical CAM reverse pattern of low gleaf during the day and high
WV







leaf leaf
leaf at night (162). Preharvest leatherleaf fern abaxial gea were
354 and 1333 mmol*m n*s- and values were 69 and 286 mmol*m *s-1 3 hr
leaf d-2 -1
postharvest (112). After 4 days gea dropped to 14.5 mmol*m s.

Davis et al. (37) found that diffusive conductance of bean leaves

exposed to constant light decreased continuously with age. Stomatal

conductance (g s), one component of g is largely independent of

transpiration rate [flux density] from the leaf as a whole (80).

Fisher (50), using a leaf disc assay to provide a uniform environment,

found that the ability of stomata to open reached a maximum for newly

fully expanded leaves and declined with aging.

Other factors, besides leaf age, that affect stomatal functioning
leafleaf
influence g wf. Hall and Kaufmann (64) found that gle of sesame

plants decreased when the humidity gradient between leaf and air was

increased. The decrease was mainly due to reductions in stomatal

aperature; however, stomatal response to humidity was not present at
leaf
high (340) leaf temperatures. Lasko (87) showed that CERs and gwv of

apple trees were positively correlated with each other and that the

leaf water potential required to close stomates decreased by 2.5 MPa

between May and September.

Hydraulic conductivity. Much confusion exists in the literature

regarding definition and calculation of conductivity (used in a general

sense). Relative conductivity, k, formerly called specific

conductivity (47), describes the flow of water through a stem or

petiole of given cross-sectional area and length and under a known

pressure. Relative conductivity is calculated as follows:


k = Qln/Ap








where 0 = flow (volume*time-)
1 = length
n = viscosity
A = cross-sectional area
p = pressure


and has the dimensions 12 (67). Published k values often are not

corrected for n (47, 119, 163). Assuming a n value of 0.9142 MPa.s,

Woodhouse and Nobel's reported relative conductivities for 7 fern

species range from 2.1 to 61.7 cm2 (163).

Alsophila australis had the highest relative conductance and also

the greatest tracheid number and diameter of the 7 species studied.

Carlquist (22) states that longer and wider tracheids could be said to

have a conductive advantage of fewer, longer overlap areas per unit

length of conductive tissue and this could make for more rapid

conductivity per unit transaction. Woodhouse and Nobel (163) contend

that low conductance is an advantage for ferns exposed to drought and

may allow species with such an adaptation to survive in a greater range

of habitats.

Conductivity, a, as defined by Heine (67), differs from relative

conductivity in that it is based on lumen area rather than the cross-

sectional area of the plant part. Conductivity is calculated as

follows:


a= Ql/ap


where a = total lumen area


Murroz et al. (109), using Huber's (78) definition of specific

conductivity, found that hydraulic conductivity of detached peach stems

decreased logarithmically over time. The authors suggest that initial








reductions in relative conductivity possibly were due to increased sap

viscosity resulting from enzymatic activity upon cell wall material.

Decreased conductivity over time was positively correlated with a

decrease in the percentage of functional vessels and negatively

correlated with an increase in the number of plugged vessels.


Postharvest


Vase life of many cut flowers and cut foliage is terminated

because proper water balance cannot be maintained (39, 56, 63, 112,

130, 141). Maintenance of satisfactory water balance depends on the

ratio between water uptake and water loss. Uptake of untreated water

by cut flowers and foliage generally declines rapidly after about the

first or second day postharvest (23, 33, 93, 112, 141). This decline

is usually attributed to stomatal closure and/or vascular blockage (58,

63, 93, 109). Halevy and Mayak (63) review the factors such as

solution pH and quality, microbial and physiological plugging, and

solution constituents that may contribute to vascular blockage.

Research has shown that pulsing and holding solutions can increase

rates of solution uptake of leatherleaf fern. However, high rates of

solution uptake do not appear to be an important factor in extending

longevity of leatherleaf fern (138, 141). A similar lack of

correlation between high rates of solution uptake and flower longevity

has been reported for roses (33) and peaches (35). Camprubi and

Fontarnau (21) did not find a correlation between the effects of

chemicals on the water conductance in carnation stems and the effects

of the chemicals on flower longevity. On the other hand, other







researchers (56, 94, 152) have found floral preservative chemicals

decrease vascular blockage and increase longevity of roses and

maidenhair fern.

A partial explanation for these differences may be that some

chemicals influence stomatal closure. Marousky (94) reported higher

vascular conductance and greater stomatal closure for roses treated

with chemicals and this treatment resulted in better maintenance of

fresh weight and increased longevity of cut roses. Chemicals which

increase solution uptake but reduce longevity may interfere with

stomatal closure, as evidenced by the rapid weight loss of leatherleaf

fern fronds in one study (141). In that study and another (138), the

fronds that had the highest solution uptake had the shortest vase life.

As mentioned previously, stomatal closure by cut leatherleaf fern

fronds is slow (112). This may be why antitranspirants have enhanced

the vase life of leatherleaf fern during periods when frond curl

syndrome is a problem (96, 111).

When mechanical rather than chemical methods are used to increase

water uptake, leatherleaf fern fronds increase in weight. Henny (69)

has shown that recutting the base of the stipe of leatherleaf fern

fronds can cause increased uptake and increased frond weight. Marousky

(95) found that postharvest retrimming of stipes greatly reduced frond

curl. One study (57) showed no benefit from recutting the stipe base

of leatherleaf fern, but the fern in that study did not exhibit

symptoms of frond curl syndrome (FCS) and had normal longevity.

Cut leatherleaf fern fronds generally have a vase life of 2 weeks

or more (32, 56, 68, 97, 98, 137, 140). Longevity is reduced during

certain times of the year, especially late summer and early fall (32,







98), due to the occurrence of FCS (112). Attempts to correlate FCS

with the presence of disease organisms or level of nematode infestation

have not been successful (32). A similar seasonal reduction in

longevity, which may be due to reduced substrate levels, has been

observed for carnations (46). Moe (105) found that production

temperature affected longevity of cut roses. Roses grown at high

(270C) temperatures had reduced longevity compared to roses grown at

lower (240, 210, 180) temperatures. Treatment of leatherleaf fern

fronds with floral preservatives, with and without carbohydrate

sources, has not been beneficial (Marousky, unpublished; Stamps,

unpublished). Treatment of cut fern fronds with ethylene synthesis and

action inhibitors did not increase vase life (141) and exposure to high

(1%) atmospheric concentrations of ethylene did not reduce vase life

(Marousky, personal communication). Poole et al. (125) found a

negative correlation between frond age and vase life. Conover et al.

(32) suggest that the basic physiology of the fern is altered during

the summer to produce weak stems with large thin walled cells and that

this may be a factor in FCS.

Plant Material


Leatherleaf fern, Rumohra adiantiformis (Forst.) Ching, is a

leptosporangiate fern and is a member of the order Ficales or "true

ferns" (52). Although taxonomists have placed leatherleaf fern with

the Davalliaceae (76) and Dryopteridaceae (83), the systematic position

of leatherleaf fern remains unclear.

Leatherleaf fern is primarily circum-austral in distribution (151)

and is terrestrial, rupestral and epiphytic (110, 151). It grows in a

variety of habitats from open sandy strand and dunes to forests (151).













CHAPTER II
TEMPERATURE AFFECTS THE DEVELOPMENT
AND POSTHARVEST LONGEVITY
OF LEATHERLEAF FERN FRONnS


Leatherleaf fern, Rumohra adiantiformis (Forst.) Ching (151), is

the cut foliage most frequently used in floral arrangements in the

United States (129). The majority of the world's production of

leatherleaf fern occurs in Florida where it is grown under 60-80% light

exclusion provided by polypropylene shade fabric, brush, lath, or oak

trees (30, 68, 137). Vase life of cut leatherleaf fern fronds is

usually 2 weeks or longer (32, 57, 68, 98, 99), even if stored for a

month prior to use (68, 140). However, studies have shown that

postharvest longevity of leatherleaf fern is greatly reduced when

harvested during certain months of the year, especially July, August,

September and October (32, 98). During these months the average daily

temperatures in the major production areas of Florida generally exceed

270 C (2, 3, 5, 6). A similar reduction in postharvest longevity

during this period of the year has been observed for carnations in

Colorado (46). Roses grown at 270 had reduced postharvest longevity

compared to ones grown at lower (240, 210, 180) temperatures (105).

Reduced postharvest longevity of leatherleaf fern is due mainly to the

occurrence of frond curl syndrome, FCS, (112) and to a lesser degree to

earlier yellowing, EY, of noncurling fronds (98).

Commercial postharvest handling of cut fronds is essentially the

same throughout the year (68). Harvesting starts around 0800 hr and

24








may continue until 1600 hr. Fronds are cut by hand using clippers,

stacked in bunches of 20 to 25 and rubber-handed together. Bunches are

picked up every 1 to 4 hr and transported in bulk, either covered or

uncovered, to packing sheds. Upon arrival bunches are sprayed with or

dipped in water and are packed into waxed nonperforated corrugated

fiberboard cartons. The water in which the fronds are dipped may

contain a fungicide. Research (140) has shown that these fungicide

treatments do not affect vase life. Most packed fern is stored at 20

to 50 prior to shipment.

Frond curl, although influenced by postharvest frond desiccation

(112), does not appear to be a problem of postharvest origin. However,

postharvest trimming of stipe bases reduced the severity but did not

prevent frond curl in one study (95) and in another study frond curl

could be reversed by recutting the stipe base when fronds began to curl

(69). Mathur (96) reports that leatherleaf fern fronds given a 5

minute dip in any of 3 different antitranspirants lasted 20 days longer

than untreated control fronds. Fronds were held at 300 and all the

untreated fronds had yellowed by day 4. Other researchers (Conover,

unpublished; Nell, unpublished) have had more ambiguous results when

treating fronds with antitranspirants.

Data on the effects of production temperature on leatherleaf fern

prior to and following harvest are lacking. These experiments were

conducted to study the effects of production temperatures on the

development, physiology and postharvest longevity of leatherleaf fern

fronds.







Materials and Methods


Four experiments were conducted to study the effects of 2

production temperature regimes on leatherleaf fern. The experiments

are briefly outlined below and the following sections describe in

detail how the numerous types of data were taken in each experiment.

Experiment 1. Growth and physiological characteristics of intact

fronds of similar chronological ages were compared.

Experiment 2. Anatomical and morphological attributes and

postharvest behavior of detached fronds were studied.

Experiment 3. The effects of stipe recutting 0, 1, 2, 3 and 5 days

postharvest on water uptake, diffusive conductance and frond longevity,

as well as hydraulic conductivity changes over that time period were

determined.

Experiment 4. Pots of leatherleaf fern that had been grown under

one temperature regime were switched to the other regime and

morphological and postharvest characteristics of detached fronds were

evaluated 9 weeks and again 18 weeks after the switch.


Plant Material and Treatments


On Aug. 22, 1982, leatherleaf fern growing in 15.3-cm plastic pots

were repotted into 25.3-cm pots using a 1:1:1 (peat:sand:perlite) mix

amended with 5.6 kg dolomite, 2.9 kg superphosphate, and 1.8 kg PERKT

(a micronutrient blend manufactured by Estech General Chemical Corp.,

Chicago, IL). Twenty pots, 10 for each temperature regime, were placed

into controlled environment chambers (Sherer Controlled Environment

Lab. Model CEL 512-37, Sherer-Gillett Co., Marshall, MI) set for








day/night temperatures of 200/150 (low temperature regime, LTR) and

30/250(high temperature regime, HTR). The day/night temperature

fluctuations were kept the same (50) for both regimes because the

amplitude of temperature variation in controlled environments has been

shown to affect the development and physiology of plants (26).

Day/night relative humidities were 75/80% 10% and 65/75% 15% for

the low and high temperature chambers, respectively. These relative

humidities and temperatures are similar to those found during the

months of March and July (6) when the incidence of frond curl is low

and high, respectively (98).

Lighting in each chamber consisted of eight 2.4-m cool white

fluorescent lamps (Sylvania Lifeline F96T12/CW/VHO, Sylvania Lighting

Products Group, GTE Products Corp., Danvers, MA 01923) and four 60 watt

incandescent bulbs for a photosynthetic photon flux density (PPFD) at

the top of the plant canopy (35.6 cm above the top of the pot) of 120
-1 -2
Vmol*s *m2 as measured before and after each growth cycle with a

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

68504). Fronds from these temperature treatments were used as the

experimental units in experiments 1, 2 and 3. The temperature regimes

in the chambers were reversed February 26, 1984, and one half of the

pots at each temperature regime were switched to the other regime.

Fronds from these switched regimes were the experimental units in

experiment 4, harvest 1. On May 13, 1984, the pots were moved to

different controlled environment chambers (Plant Growth Chamber E 30B,

Percival Manufacturing Co., Boone, IA 50036) where the temperature
-1 -2
regimes were maintained and the light levels were 180 pmolos -m-2

Light in each of the second set of chambers consisted of six 60.9-cm







cool white fluorescent lamps (GE F24T12.CW.HO, General Electric Co.,

Nela Park, Cleveland, OH 44112) and two 25 watt tubular incandescent

bulbs. In these chambers, as well as the previously-mentioned ones,

the total watt input provided with incandescent lamps was kept in the

10 to 20% range recommended by Cathey and Campbell (24). Fronds from

these chambers were used in experiment 4, harvest 2.

Plants were fertilized with 1 liter of complete liquid fertilizer

(Peters Florida Special 20-10-20, W. R. Grace & Co., Horticultural

Products, Cambridge, MA) at a concentration of 400 or 500 ppm N Ix/week

for the low and high temperature treatments, respectively.

Fertilization maintained conductivity readings and pHs with a 2:1

(volume:volume, water:medium) extract procedure between 400-600

micromhos'cm-1 (Hach Model 2511, Hach Chemical Co., Ames, IA) and

5.5-5.9, respectively. Plants were watered daily. Just emerging

crosiers (fiddleheads) were tagged on September 4 and October 13, 1983,

and March 17 and May 5, 1984. Same aged fronds were used in each of

4 experiments to reduce variability and because research (95, 124, 125)

suggests that frond age is an influencing factor in frond longevity.


Growth and Development


Frond length. Measurements of the lengths of tagged fronds, 2

fronds per pot, were made at weekly intervals starting September 11,

1983.

Sori development. Dates when fronds first developed sori visible

to the unaided eye were recorded.







Morphology and Anatomy


Frond surface area. Surface areas were measured using area meters

(LI-COR Portable Area Meter Model LI-3000 with Accessory Belt Conveyor

LI-3050A, LI-COR Model LI-3100).

Frond thickness. Frond thickness was measured from the video

display of a scanning electron microscope (Hitachi S-450, Hitachi,

Ltd., Tokyo, Japan) operating at an accelerating voltage of 20 kV.

Pinnules obtained from a middle pinna of the rachis were fixed in 3%

glutaraldehyde in sodium cacodylate buffer (pH 6.9), post-fixed in

buffered 1% osmium tetroxide, dehydrated using an ethanol dehydration

series, and critical point dryed (Tousimis Model No. Samdri-regulated,

Tousimis Research Corporation, Rockville, MD) using liquid CO2.

Samples were then attached to aluminum stubs with low resistance

contact cement (Ernest F. Fullam, Inc., Schenectady, NY) and sputter

coated with a 50 nm layer of gold-palladium (Technics Hummer V,

Technics EMS, Inc., Springfield, VA).

Stipe cross-sectional area. Stipe diameters, narrow and wide for

each stipe, were measured 14 cm below the lowest pinna using a

micrometer. Stipe cross-sectional areas were approximated using the

formula for an ellipse:

(narrow diameter/2 x wide diameter/2) x r.

Stomatal density. Stomatal densities were measured using

photographs obtained using the scanning electron microscope (SEM) as

outlined above for frond thickness. Stomatal numbers were determined

for 2 fields for each frond.







Cuticle thickness and number of epidermal cell layers. Cuticle

thickness and number of epidermal layers were determined as described

for frond thickness above.

Tracheid numbers and cross-sectional areas. Tracheid numbers and

cross-sectional areas were determined from stained sections mounted in

Permount" (Fisher Scientific, Pittsburgh, PA) using a video image

analysis system (Linear Measuring Set system, Measuronics Corporation).

The stipe sections used were those from the hydraulic conductivity

experiments. The tissue was fixed in FAA and then embedded in medium

grade LR White resin (London Resin Co. Ltd., Hampshire, England) using

an aliquot mixer (Model 4651, Ames Co., Div. Miles Laboratories, Inc.,

Elkhart, IN) to enhance infiltration. Conventional paraffin embedding

techniques are generally not suitable for use with leatherleaf fern

stipe sections due to the sclerenchymatous nature of the stipe and the

great range in tissue hardness across the stipe (D. B. McConnell,

personal communication). Gelatin capsules were used to hold the tissue

and resin. The resin was polymerized using heat (600) and the embedded

tissue was affixed to aluminum stubs using epoxy cement. Sections were

obtained using a steel knife on a rotary microtome (AO", American

Optical Co., Buffalo, NY). Section thickness ranged from 1 to 5 um.

Sections were stained in an aqueous 1% toluidine blue 0 solution made

with 1% sodium tetraborate (48, 73, 150).

Photomicrographs on 35 mm color transparency film were made of each

vascular bundle in the stipe sections. A stage micrometer (American

Optical Co.) was also photographed at each magnification used to

photograph the vascular bundles using the same light microscope

(Olympus BH-2, Olympus Optical Co., Tokyo, Japan) and photography








system (Olympus AD exposure control unit and C-35A camera). The

micrometer transparencies were used to calibrate the video image

analysis system. The transparencies were placed on a light stage

(Omega type DII enlarger condenser, Simmons Bros., Long Island, NY)

covered with opal glass. A high resolution color video camera (RCA

with Canon TV zoom V6x18 lens equipped with a #4 close-up lens) and

video recorder (Hitachi VT-6500A) were used to generate a video image

for image analysis using the LMS digitizer. The LMS was interfaced

with a computer (Apple II plus, Apple Computer, Inc., Cupertino, CA

95014). The digitized images were corrected and enhanced using system

software and a light pen prior to the extraction of the geometric

information. Figure 2-1 shows a representative photomicrograph of a

vascular bundle and the digitized and enhanced digitized images of the

same bundle.


Physiology


Carbon exchange. An infrared gas analyzer (IRGA) (Anarad model

AR-600R, Anarad, Inc., Santa Barbara, CA) in an open system was used to

measure net CO2 fluxes of individual leatherleaf fern fronds (Figure

2-2). Standard gases of 265 and 350 ppm CO2 in nitrogen were used to

calibrate the IRGA for CO2. An internal calibration wedge was used to

calibrate for water vapor. Flow meters (Dwyer Instruments, Inc.,

Michigan City, IN) were used to regulate flow rates from 1 to 4

litermin-1. High density polyethylene tubing was used throughout the

system because of its relatively low cost, water absorption and CO2

permeability (18). The incoming air stream was saturated with water

vapor using an air-stone submerged in deionized water. A circulating































Figure 2-1. Photomicrograph of vascular bundle in stipe of leatherleaf
fern frond (top), digitized image of the same vascular
bundle (middle), and enhanced digitized image of the
lumina of the tracheids in that vascular bundle (bottom).













JL


0
(I)
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CO

LU


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pump (Model 907CA182, Thomas Industries Inc., Power Air Division,

Sheboygan, WI) operating at a flow rate of 21.5 liter.min-1 and a fan

(Acme 600", Acme, Miami, FL) with a 10.2-cm blade were used to mix the

air in the 45-cm by 45-cm by 5-cm acrylic plastic cuvette (Figure 2-3).

This system exhibited reciprocity at the flow rates used. At high

photosynthetically active photon flux densities the high flow rates

were used to limit CO2 concentration reductions to 25 ppm or less. The

fronds were supported on a galvinized wire fabric with a 6-mm square

mesh. A polystyrene base held the wire above the fan blade and was

colored black to reduce the albedo. The turbulence caused by the fan,

the circulating pump and the air flowing through the cuvette were

intended to increase boundary layer conductance to physiologically

insignificant levels (147). Light was supplied from a fixture (HI-TEK,

Division of Lithonia Lighting, Crawfordsville, IN) equipped with a 400

watt high pressure sodium vapor lamp (Sylvania Lumalux LU400). The

lamp was allowed to warm up to full output (approximately 30 min)

before any readings were made. Light compensation points were
-1 -2
determined by reducing intensities from a maximum 673 pmol*s m-2

using layers of cheesecloth until the net CO2 flux was zero. Net CO2

fluxes were measured at up to 21 light levels per plant. Dark

respiration measurements were made when the recorder (Varian Model

9176, Varian Aerograph, Walnut Creek, CA) reached a stable reading

after the lamp was extinguished. Temperatures were maintained at 30.50

1.50 using a water filled heat sink below the light and a

temperature regulating water bath (Lauda K-21R, Brinkman Instruments,

Inc., Westbury, NY). These temperatures, which are representative of

the average daily high temperatures during the months when curl is most
































Figure 2-3. Acrylic plastic cuvette used in carbon exchange and
transpiration determinations of leatherleaf fern fronds.




































































































































I







severe (6), were monitored using copper-constantan thermocouples and a

digital thermometer (Model AD2036, Analog Devices, Norwood, MS). Yadav

et al. (164) have also found that 300 is the optimum temperature for

CER and dark respiration of 8 fern species in India. Barometric

pressure was determined using a barometer (Airguide Instrument Co.,

Chicago, IL). Carbon exchange was computed using the equation


CER = (C a SA) x ((FxMW) MV) x (273 T) x (P 0.1013)


where C = CO2 differential (vpm x 10-6)
SA = surface area, 1 side (dm2)
F = flow rate (l.hr-1)
MW = mole wt. of CO2 (44,010 mg)
MV = mole volume of CO2 (22.414 1)
T = temperature (0K)
P = barometric pressure (kPa)


The order of running CER determinations was randomized over treatments

to eliminate bias due to possible hysteresis or biological rhythms

(45). CER determinations were made, 1 replication per day, during the

period from November 18, 1983, to December 18, 1983 (Experiment 1).

Plants were thoroughly watered the day before and again the day

readings were made.

Transpiration. Net fluxes of water vapor in the air stream during

the CER measurements were determined using the above system.

Transpiration (T or E) was determined as follows:


T = H x F SA


where H = H20 differential (ugoml-I)
F = flow rate (ml*hr-1)
SA = surface area, 1 side (dm2)







Chlorophyll content. Chlorophyll determinations were made using a

modification of MacKinney's (92) and Arnon's (7) procedures. Two

0.27-cm2 leaf discs, obtained using a cork borer, were punched from

pinnules of each frond used for CER measurements. The discs were

quartered using a razor blade and placed in 5 ml of acidified (10% HC1)

methanol. Dark extraction was for 48 hr at -15. Optical density was

measured at 652 nm using a spectrophotometer (Spectronic 710, Bausch &

Lomb, Rochester, NY). Optical density (OD) was converted to mg/liter

using Arnon's (7) formula,

-1
(OD x 1,000) 34.5 = mg.liter-.


Milligrams*liter- were corrected for sample size as follows:

-1 2
mg*liter- x 0.005 liter x 187.3 leaf disc samples/dm2


Diffusive conductance. Diffusive conductance, transpiration and

pinnule temperatures were measured using a steady state porometer

(LI-COR LI-1600) with 0.6- and 1-cm2 apertures. Tests indicated that

adaxial transpiration was about 10% of total transpiration during the

lighted portion of the day so only abaxial readings were made.

Measurements were made on dark green, mature, non-sporulating fronds at

a terminal pinnule of the central pinna on attached and detached fronds

in growth chambers and postharvest holding rooms, respectively.

Temperatures and relative humidities were measured in the growth

chambers and holding rooms using the porometer.

Carbohydrates. Fronds used for CER determinations were

freeze-dried at -400 and 4.0 Pa (Virtis Model 10-MR-TR, Virtis

Freezemobile II, The Virtis Co., Gardiner, NY 12525) immediately after







CERs and surface areas were measured. Freeze-drying lasted 72 hr or

more and tissue was then stored in a desiccator at -150. Tissue was

then ground through a 20 mesh screen (Wiley Mill, Arthur H. Thomas Co.,

Philadelphia, PA), boiled in 80% ethanol and centrifuged at 10,500 rpm

(Model HT Centrifuge, International Equipment Co., Division of Damon)

for 1 hr. One-half milliliter of supernatant was diluted for soluble

sugar determinations with 9.5 ml deionized water. The centrifuged

pellet was combined with 5 ml of enzyme solution (40 ml of 20 mM

phosphate buffer + 20 mg a-amylase + 20 mg amyloglucosidase + 17.6 mg

CaCI2) and incubated for 12 hr at 340 using a constant temperature bath

(Magni Whirl Constant Temperature Bath, Blue M Electric Co., Blue

Island, IL). The sample was centrifuged as above and 0.5 ml of

supernatant was diluted with 9.5 ml of deionized water and starch

content of the sample was determined using a phenol-sulfuric acid

assay. One-half milliliter of 5% phenol and 2.5 ml of concentrated

H2SO4 were added to 0.5 ml of each diluted sample and allowed to cool;

then optical density was measured at 490 nm using a spectrophotometer.

Standards were prepared using D-glucose and deionized water.

Stipe hydraulic conductivity. The amount of time required to force

0.2 ml of deionized water through a stipe section 4-cm long using a

pressure of 0.5 MPa was determined using a pipet, a stopwatch and a

pressure chamber (Soil Moisture Equipment Corp., Santa Barbara, CA)

powered by compressed nitrogen gas. Section orientation was maintained

as when attached to the frond, proximal end of the stipe down, and the

bases were placed in a deionized water reservoir inside the pressure

chamber. The stipe sections were obtained from the base of fronds

subsequently used for postharvest evaluation. Previous research (69)







has shown that removal of 1 cm from the base of the stipe can cause

curled fronds to recover and removal of 2 cm gave no added benefit.

Relative conductivity, k, was calculated as defined by Farmer (47) and

subsequently modified by Heine (67):


k = Q1n/Ap


where Q = flow (ml.s- )
1 = stipe length (cm)
n = viscosity (MPa.s)
A = cross-sectional area (cm2)
p = pressure (MPa)


Conductivity, a, was calculated using the lumen area rather than the

cross-sectional area of the plant part (67):


a = Ql/pa


where a = total lumen area


Postharvest


Fronds were harvested with clippers by cutting the stipe near the

rhizome. Each stipe was recut with a razor blade to a 14-cm length and

placed through a small hole in Parafilm@ "M" (American Can Co.,

Greenwich, CT) which covered the opening of a 100-ml graduated

cylinder filled with deionized water. Harvested fronds were held in

holding rooms that approximated home or office conditions.

Temperatures were maintained at 24 1, relative humidities were 60%

15%, and light levels were 17 Pmol.s-*m-2 obtained using cool white

fluorescent lamps.







Postharvest water uptake. Water uptake for each frond was

determined by observing the change in water level in each cylinder and

refilling the cylinders to the 100-ml line. This was done daily for

the first week and when fronds were terminated. One tagged frond from

each pot, the same age as those used for CER determinations, was

harvested December 10, 1983, and the stipes were cleaned of scales

(Experiment 2).

Fronds for subsequent postharvest experiments were handled

similarly except as noted below. Forty fronds from each growing

temperature, 5 fronds from each of 8 pots, were harvested January 8,

1984 (Experiment 3). This second group of fronds, as well as a third

group harvested May 5, 1984 (Experiment 4), was stored in polyethylene

bags at 40 for 1 day prior to being placed in graduated cylinders. A

fourth set of fronds, from the second set of growth chambers, was

harvested July 4, 1984 (Experiment 4) and handled the same as the first

group.

Postharvest weight changes. Initial frond weights were taken

before fronds were placed in the graduated cylinders. Fronds were

placed in the cylinders which were then filled to the 100-ml line with

deionized water and weighed. Cylinders were thereafter weighed with

the water level at the 100-ml line. This procedure obviated the need

to remove the fronds from the water which might have caused the

formation of air embolisms. Preliminary tests showed that cylinders

could be refilled to the line with little variation ( 0.05 g).

Postharvest longevity. Fronds were checked daily and were

discarded if they showed signs of yellowing (>5% of frond yellowed),

curling infoldingg of pinnae along the midvein) (68, 112, 137), or

overall desiccation (wilting accompanied by graying).







Results and Discussion

Experiment 1


Growth of fronds was greater at the high temperature regime, HTR,

than at the low one, LTR (Figure 2-4). Poole et al. (125) have found

that, in shadehouses, crosiers emerging during the warmer months also

grew more rapidly. Both HTR and LTR growth curves were logarithmic and

had similar slopes; however, early growth of fronds produced under the

HTR was greater as evidenced by the different intercepts 1 week after

fronds were tagged. Also, HTR fronds produced visible sori sooner

(Table 2-1). Sori development of the LTR fronds had reached that of

the HTR fronds by 5 weeks after emergence of fronds. Increased growth

and development due to higher production temperatures have been

reported for many crops (9, 16, 53, 60, 84, 104, 126, 161).

Abaxial diffusive conductance (g w) and leaf temperatures increased

during the light period (Figure 2-5A,B). Both measurements were

different for fronds at the 2 temperature regimes throughout the day

cycle, with the diffusive conductance lower for HTR grown fronds.

Abaxial g ws of LTR fronds were on the low side for crops and abaxial

g ws for LTR and HTR were similar to those of many trees (115), many of
which are hypostomatous. Diffusive conductances for fronds at both

regimes were similar to those for 2 epiphytic CAM ferns (162) and

considerably lower than those previously reported for field grown

leatherleaf fern fronds (112). The differences for leatherleaf fern

g ws may have been due to the lower light levels and relative
humidities in the controlled environment chambers. Since potential

vapor pressure increases with temperature and the relative humidities






44






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Table 2-1. Production temperatures
leatherleaf fern fronds
chambers.


affect sori development on
grown in controlled environment


Day/night production Frond age (days)
temperatures
(C) 7 14 21 28 35

Fronds with sori (%)

200/150 0 0 0 0 53.3
300/250 0 0 0 52.9 58.8


Significance level
based on t test


1.000 1.000 1.000 0.007


0.612










--a--


A


31" B
30

29

28

27

26

25

24

23

22

21

20

19

18

17

16
1i5


10 1-


48


46


44


.- /


0-2 L__, 38[
800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 8(
TIME OF DAY


Figure 2-5.


a













b.
I'b
i/



0 I


a





0


)0 900 1000 1100 1200 1300 1400 1500 1600 1700 1800
TIME OF DAY


Abaxial diffusive conductances (A), leaf temperatures (B),
and transpiration (C) of leatherleaf fern fronds grown in
controlled environment chambers under temperatures of 200C
day/15 night, or 30 day/250 night, -, and
relative humidities at the time of measurement (D).
(Letters are means of 6 replications and different letters
indicate significant differences for t test comparisons at
the 2% level within time of day for treatments.)


W
LJ
i~2
ha

LL
-I


50 t


35-


N. ,


bbb b




b


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E
E 0.8

z
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were lower in the high temperature chambers (Figure 2-50), the vapor

pressure deficit (VPD) was greater in the high temperature chambers.

This greater VPD resulted in there being no transpiration differences

between treatments in spite of the lower gwv s for HTR grown fronds

(Figure 2-5C).

The CER curves were logarithmic and CERs for fronds grown at the 2
-1 -2
temperature regimes were different at PPFDs above 430 umols -*m-2

(Figure 2-6). At light saturation (Is), the CER for HTR fronds was 34%

lower than for LTR ones (Table 2-2). The LTR I CER was about 14%

lower than that previously reported by Mathur and Bhagsari (97) for

leatherleaf fern grown in a shadehouse at higher light intensities than

were used in this study. Numerous studies have documented increased I

CERs for plants grown at higher light intensities compared to plants of

the same species grown under lower production light levels (13, 45, 53,

159).

Quantum efficiencies, on an incident light basis, were different

(P < .01) for HTR and LTR grown fronds, as determined by a test of

homogeneity of the slopes (143) of the CER curves below photosaturation

(Figure 2-7). Quantum efficiencies for HTR and LTR fronds were 0.0195

and 0.0223 mol C02/mol, respectively. Chlorophyll content was also

lower for HTR fronds, and this is probably the reason for the lower

quantum efficiencies. Chlorophyll is the primary photon trap in both

photosystems I and II (149). Light saturated CER efficiencies

(chlorophyll basis) were the same for LTR and HTR fronds, and these

efficiencies indicated that there were probably no qualitative

biochemical differences in photosynthesis due to production

temperatures (Table 2-2).






48






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0 ao





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49


Table 2-2. Physiological characteristicsz for leatherleaf fern fronds
grown under low and high temperature regimes.


Day/night production temperature
(C)

Significace
200/150 300/250 level


Light saturated CER
(mg CO2 dm-2 hr-1) 6.42 0.77

Chlorophyll (chl)
(mg dm-2) 6.91 0.48

CER efficiency
(mg CO2 mg chl1 hr-1) 0.92 0.08

Light compensation
point (pmol s-1 m-2) 13.0 2.58

Dark respiration
(mg CO2 dm-2 hr-1) 0.51 0.12

Soluble sugars
(mg g dry wt-1) 208 25.0

Starch
(mg g dry wt-i) 34.3 6.23

Nonstructural
carbohydrates
(mg g dry wt-1) 242 27.2

Transpiration (at I )
(mg H20 dm-2 hr1) 564 25.4

Water use efficiency
(mg CO2 : mg H20 10-2) 1.30 0.15

ZMeans of 10 replications SE.
YPlants were grown in controlled environment
and 12 hr nights.
XSignificance based on t test.


4.25


5.20


0.81


7.4


0.17


191


35.1



226


475


1.06


0.51


0.21


0.08


2.13


0.03


16.7


2.56



18.4


35.4


0.12


0.030


0.007


0.343


0.114


0.022


0.583


0.910



0.631


0.067


0.354


chambers with 12 hr days




















/
/ /











0.035 x y= 0.015 + 0.031x
r =0.99***
00/








or













---A-- GROWN AT 300/250 C (DAY/NIGHT)
-o- GROWN AT 200/150 C (DAY/NIGHT)


0 9 18 27 36 45 54
PPFD (pmol-s'- m2)


Figure 2-7.


63 72 81 90


Quantum efficiencies of leatherleaf fern fronds grown
under 2 temperature regimes. (*** indicates significance
at the 0.1% level.)


y = -0.166 +
r = 0.99**


E


O
E
LU



0


U.


0.3


0.0


-0.3


-0.6







Light compensation points were low and not different, but dark

respiration rates (Rds) were different and lower for HTR fronds.

Soluble sugars, starch and nonstructural carbohydrate levels were

similar for both temperature treatments and, therefore, substrate

levels do not seem responsible for the differences in Rd rates. The

reduced Rds for HTR fronds may be due to increased (physiological)

aging of HTR compared to LTR fronds due to more rapid development at

the higher production temperatures (59). Dark respiration has been

shown to decrease with aging (19, 59, 154).

The transpiration (T) curves were logarithmic and similar in shape

and orientation to those for CERs (Figure 2-8). Transpiration was

lower (P < .05) for HTR fronds at PPFD levels between 183 and 431 and
-1 -2
below 32 Umol-s *m The ability of stomata to open, as measured by

the size of the stomatal aperature, has been shown to decrease as

leaves age (50). If the HTR fronds were significantly older,
st
physiologically, gw could be responsible for the reduced T. The

stomata of HTR fronds may also have been preconditioned to lower

conductivity. Transpiration and WUE (mass basis) at Is were similar

for fronds from both temperature treatments (Table 2-2).


Experiment 2


Fronds from both temperature treatments were found to be

hypostomatous and anomocytic, i.e., with no specialized subsidiary

cells associated with the guard cells (Figure 2-9). Cracks in the

cuticle were not detected for either treatment. No differences in

initial fresh weights, surface areas, adaxial and abaxial cuticle

thickness, upper and lower epidermal cell layers or stomatal densities
















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a) C C4 .3




CU- t
r Sc t-







t : JQ
o J o
t- 0
4- 4 t


\
\


o0
0


0 0
tO ,D
%I-


I I I I I I 1 I ly)































Figure 2-9. Photomicrographs of leatherleaf fern pinnules showing
A) abaxial pinna surface with stomata, B) adaxial pinna
surface, C) close-up of a stoma and D) cross section of a
pinnule showing stomatal complex and substomatal chamber.




54








due to the production temperatures were noted (Table 2-3). The

association of frond fresh weights to surface areas was strongly linear

for fronds grown at both temperature regimes (Figure 2-10). The test

of the homogeneity of the 2 slopes (143) was not significant (P < .20).

The surfaces (laminae) for water loss were, therefore, somewhat

similar; however, pinnules from HTR fronds had more incised margins,

less pronounced venation (Figure 2-11) and were 24% thinner than LTR

fronds (Table 2-3, Figure 2-12). Chabot and Chabot (25),

Charles-Edwards et al. (28), Friend (53), Friend et al. (54) and Peet

(120) have reported similar decreases in leaf thickness with increased

production temperatures. Carbon exchange (Experiment 1 fronds) appears

positively correlated with leaf thickness (Experiment 2 fronds) since

fronds for both experiments were tagged and produced concurrently in

the same pots. Such a correlation has been reported previously for

other crops (122, 160).

The stipe of the fronds differed markedly due to production

temperature treatments. Stipe diameters, cross-sectional area and

relative conductivity were reduced for HTR grown fronds (Table 2-3).

Vase life was positively correlated with stipe narrow diameter

(r = 0.58, P < 0.007) and cross-sectional area (r = 0.52, P < 0.018).

Differences in stipe conductivity may have significance to the water

balance and postharvest longevity of leatherleaf fern fronds. The

ratio of the surface area (one side) of the fronds to the stipe

cross-sectional area for HTR fronds was about 30% greater than that of

LTR fronds (Table 2-3). This ratio was negatively correlated

(r = -0.43) with vase life at P < 0.061.








Table 2-3. Anatomical, morphological and postharvest characteristicsz
of leatherleaf fern fronds grown under low and high
temperature regimesy.



Day/night production temperature
(C)

Significance
200/150 300/250 levelx


Fresh weight (g)

Surface area = SA (cm2)

Adaxial cuticle thickness
(p)m)

Abaxial cuticle thickness
(Nm)

Upper epidermal layers

Lower epidermal layers

Stomatal density (*mm-2)

Leaf thickness (um)

Stipe narrow diameter (cm)

Stipe wide diameter (cm)

Stipe (cross-sectional)
area (cm2)

Relative conductivity
(cm2)

Ratio of SA:stipe area
(.102)

Uptake (ml frond-1)

Vase life (days)

Discard weight

(% of initial weight)


15.9

430


1.29

33.0


1.27 0.12


1.29

1.50

1.00

169

191

0.31 +

0.37


0.15

0.17

0.00

13.0

8.35

0.01

0.02


0.09 0.01


1.04 0.10


48.8

122

25.6


2.02

13.0

1.33


90.1 2.24


15.3

430


2.00

54.7


1.18 0.11


1.02

1.60

1.00

161

144

0.26

0.32


0.04

0.15

0.00

8.33

3.09

0.02

0.01


0.07 0.01


0.63 0.11


63.6

78.2

16.3


3.56

9.04

1.51


89.2 3.15


zMeans of 10 replications t SE.


YPlants were grown in controlled environment
and 12 hr nights.
XSignificance level based on t test.


chambers with 12 hr days


0.820

1.000


0.592


0.103

0.655



0.603

0.0001

0.048

0.073


0.048


0.012


0.002

0.013

0.0002



0.822











-0- GROWN AT 200/150C (DAY/NIGHT)


A o
/ I


500

475

450

425

400

375

350


y = 11.44+ 27.34x.
r = 0.93***


-o
/
4'


-y =23.57+25.63x
r =0.98***


------ GROWN AT 300/250C (DAY/NIGHT)


I I


I I I I i ,
4 5 6 7 8 9 10 II 12 13 14 15 16 17

FRESH WEIGHT (g)




Figure 2-10. Association of fresh weight and surface area for
leatherleaf fern fronds grown under 2 temperature
regimes. (*** indicates significance at the 0.1% level.)


/ /O
A /
/


325


300

275

250

225

200

175


150

125

100


































Figure 2-11. Pinnae from high (30C day/250 night) temperature regime,
HTR, frond (left) and low (200 day/150 night) temperature
regime, LTR, frond (right) showing reduced venation and
increased marginal incision of HTR pinnules.





59






























Figure 2-12.


Scanning electron micrographs of cross sections of
pinnules of leatherleaf fern grown under low (20C
day/150 night) temperature regime (top) and high (30
day/250 night) temperature regime (bottom).




























































~V~wQ~


" ~L ~j
4;n
-
I* i








Water uptake by HTR fronds was lower than that of LTR ones starting

3 days postharvest and both curves were negatively logarithmic (Figure

2-13). Water uptake 7 days postharvest was positively correlated with

stipe wide diameter (r = 0.55, P < 0.012) and cross-sectional area

(r = 0.46 P < 0.043). Postharvest weight changes of cut fronds were

similar for LTR and HTR fronds for the first 9 days postharvest, but

HTR fronds appeared to be losing weight more rapidly (Figure 2-14).

The 2 lines appeared to be diverging, and this may be due to the

observed differences in water uptake and/or to differences in rates of

water loss. Mean overall water uptake per frond was 36% less for HTR

fronds than that of LTR fronds (Table 2-3).

Vase life was reduced 36% for HTR fronds (Table 2-3). LTR fronds

lasted almost 4 weeks and were discarded due to yellowing. Fifty

percent of the HTR fronds yellowed and 50% showed symptoms of

dessication. Frond curl syndrome did not occur on fronds produced

under either the HTR or LTR conditions.

Stipe narrow and wide diameters, stipe cross-sectional area and

frond surface areas of LTR fronds were all positively correlated with r

values of 0.9 or greater (Table A-i, Appendix). Leaf thickness was

positively correlated with adaxial cuticle thickness (r = 0.83) and

number of upper epidermal layers (r = 0.68). Total frond water uptake

was positively correlated with stipe narrow (r = 0.87) and wide

(r = 0.91) diameters, stipe cross-sectional area (r = 0.90) and frond

surface area (r = 0.91). No factors were correlated with vase life of

LTR grown fronds.

The results were similar for HTR grown fronds. Stipe narrow and

wide diameters, cross-sectional area, number of upper epidermal layers




63










-- GROWN AT 20/15C
(DAY/NIGHT)
--- GROWN AT 300/250C







y =0.088- 0.045 In x
r =0.94***










\ y = 0.071- 0.0371n x




b b a*rZO.94b
b -b


I 2 3 4 5 6 7 8 9


DAYS POSTHARVEST


Figure 2-13.


Postharvest water uptake of cut leatherleaf fern fronds
grown under 2 temperature regimes. (Letters are means of
10 replications and different letters indicate
significant differences for t test comparisons within
days postharvest for treatments. *, **, and *** indicate
significance at the 5%, 1% and 0.1% level, respectively.)


IoF




















,O


104


103


102


101-


100


99


98


97-


96


95


94


93


'-0


--- GROWN AT
--- GROWN AT


200/150 C
(DAY/NIGHT)
30/25C


I 2 3 4 5 6 7 8 9


DAYS POSTHARVEST


Figure 2-14.


Postharvest weight changes of cut leatherleaf fern fronds
grown under 2 temperature regimes. (Letters are means of
10 replications and indicate t test comparisons at the 5%
level within days for treatments.)


a a
0L


0^-







and frond surface area were positively correlated with r values from

0.68 to 0.97 (Table A-i, Appendix). Total frond water uptake was

positively correlated with stipe narrow (r = 0.75) and wide (r = 0.83)

diameters, stipe cross-sectional area (r = 0.83) and frond surface area

(r = 0.80). The association of vase life with relative conductivity

for HTR fronds was negative with an r value of -0.79. The HTR fronds

with the highest relative conductivity had the shortest vase life.

The discard weights (weight at termination initial weight) for

LTR (90.1%) and HTR (89.1%) fronds were not different which indicates

that HTR fronds lost weight more rapidly than LTR ones. This

similarity suggests that HTR fronds lack effective postharvest stomatal

function and water loss control.


Experiment 3


Water uptake by cut leatherleaf fern fronds (Figure 2-15) was very

similar to that in Experiment 2 (Figure 2-13). Day 1 poststorage in

this experiment is equivalent to day 2 postharvest in the previous

experiment due to the storage of the fronds for 1 day. Initial (day 1)

water uptake was positively correlated (r = 0.49, P < 0.0001) with vase

life. Water uptake by HTR fronds was approximately 50% of the uptake

observed for LTR fronds. Recutting stipe bases 1, 2 (Figure 2-16) and

even 3 or 5 days (Figure 2-17) poststorage caused water uptake to

return to nearly the day 1 poststorage levels. The rate of decline

(slope of the curve) in uptake after stipe cutting was similar for HTR

fronds regardless of when they were recut. Comparison of the water

uptake curves shows that the same was true for LTR fronds; however, the

uptake for LTR fronds was higher than for HTR fronds.








































d



C -
0

II II


*0-
o -























I -








o ..
I )


X
_-
CM

0
*

rto
n co
0 0)
d d
to II


ro cN 0


- LD I0 Tf


t O


L0

ot
0
F-
U)


0
'-

U)


E V
1/)





C-- U
E --
.-r-- a

..- L- a)
4) ~- C L

-C a)
LU *r-
ac4- U,
E *r- -0
a)CCL
4 _> n ro a)







c x r
La)

C4-) CU

0 *
CC C II
3 *- 4-

SC 4 >
CD LE









"-"-
1"- 4-) ro "-

LOLn



L 0 .-
4- 4- CL a)





4- *
) 4-) -
.- -o A a)
SC 4- C >








r- ro ro
-C oC-
.o c





a1 0 0 -
r- .- to
4- 0-&
o a) 4
L (r- C-
0) 3


to
4-) 4- C I3

n 0 0-













L Cj L0--
CL 4- In
a-) U,(




: 0
4c U










a)
in


U-


L I I I 1 I I I


(Oz--_wUo'.iwu) 3>vidln d31VM



























































Figure 2-16.


-y= 0.049-0.0251n x
r =0.97**


Na


-y=0.037-0.019 In x
r=0.97**
.-. .
a a
a-
a -- --- --- a


y = 0.049-0.025 In x


-y=0.032 -0.018 In x
r =0.97**


'b \ **



b -b
bb ^- ---- a* -


I 2 3 4 5 6 7 8

DAYS POSTSTORAGE


Effect of recutting stipe bases 1 or 2 days poststorage
on water uptake of leatherleaf fern fronds grown under
temperatures of 200C day/150 night, -- or 300 day/250
night, --- (Letters are means of 8 replications and
different letters indicate significant differences for t
test comparisons within days poststorage for treatments.
*, **, and *** indicate significance at the 5%, 1% and
0.1% level, respectively. x = days after stipes recut.)





** Ts


\ Is
S













S0.051- 0.0251n x
S0.99**


S
T
PI
A E

R

T
0 S
\ 0


.y 0.050 0.0271n x
r =0.99***


0.035-0.02
-v= 0.035-0.02 In x


\ **


"b --
b --b


1 2 3 4 5 6 7 8


DAYS POSTSTORAGE


Figure 2-17.


Effect of recutting stipe bases 3 or 5 days poststorage
on water uptake of leatherleaf fern fronds grown under
temperatures of 200C day/15 night, or 30 day/250
night, ---- (Letters are means of 8 replications and
different letters indicate significant differences for t
test comparisons within days poststorage for treatments.
*, **, and *** indicate significance at the 5%, 1% and
0.1% level, respectively. x = days after stipes recut.)


I I







Relative conductivity, k, also declined logarithmically with time

(Figure 2-18); however, there were no differences between HTR and LTR

fronds on any date. This lack of relative conductivity differences

suggests that there may be no qualitative difference between the

hydraulic conductivity of HTR and LTR stipes.

Figure 2-19 illustrates the effect of stipe recutting 5 days

poststorage on gleaf and T. Both statistics increase within 15 minutes
wv
and after 1 hr begin to decline slowly. Transpiration and gleaf reach
wv
near zero values 2.7 days after recutting. Within about 2 hr of stipe
leaf
recutting, gleaf values for HTR fronds were lower than LTR ones, as was

found for attached fronds in Experiment 1 (Figure 2-5). Assuming that

internal leaf relative humidity was 100% (4), T also differed after

about 6.5 hr (Figure 2-19). High temperature regime fronds lost weight

more rapidly than LTR fronds (Figure 2-20), indicating that, in spite
Sleaf
of reduced gwv HTR fronds were losing water relative to uptake at a

higher rate than LTR fronds.

Morphological characteristics of HTR and LTR fronds were similar to

those observed in Experiment 2. Initial fresh weights, dry weights,

surface areas and frond water content were not different due to

production temperatures (Table 2-4). Leaf density thickness (LDT),

specific leaf weights (SLW), stipe narrow and wide diameters, and stipe

cross-sectional areas were lower for HTR fronds. Initial water uptake

was positively correlated with LDT (r = 0.83, P < 0.0001), SLW

(r = 0.38, P < 0.0006), stipe narrow (r = 0.38, P < 0.0005) and wide

(r = 0.38, P < 0.0005) diameters, and stipe cross-sectional area

(r = 0.38, P < 0.0006). Vase life was also positively correlated with

LDT (r = 0.63, P < 0.009), stipe narrow (r = 0.43, P < 0.0001) and wide











2.0


1.8


1.6


I 2 3
DAYS POSTHARVEST


Figure 2-18.


Postharvest decline of relative conductivity, k, of cut
leatherleaf fern frond stipe bases. (Each point
indicates the mean of 8 replications and indicates
significance at the 5% level.)


-0- GROWN AT 200/15C
(DAY/NIGHT)
--A-- GROWN AT 300/150C



















= 1.62-1.02 In x
= 0.94*


\k-y = 1.64-0.97 In x
\r= 0.95*




n0
0 0


S1.4


5 1.2
C-)

I 1.0
z
0

w 0.8


S0.6


0.4


0.2


0.0

















/
/
/
/

/
/
/
I
I
/


r- 0 oo 0 0 01 0 0 0
SN N -D -- Q Q
o o o oo o o o


(4S.Z.uJ.IOUJJ) NOIIV IdSNVJI


f( o
o0 0 0
coo~


4-

o o0

aw C\j 4-
U) 0

a)oE


V 4-- 6


*n L
c- 4-




4--)





C 0 .. m
o ac)










0r-"



*c- C
L a) -A



)C Ct
=o m. 4-'





40 I 0 r-











U t-- L-

LCn
-o 0



*r- U
4 L4 -C




to t *
w0 0) L

4- )L I
Cr I -
















r- 4J *-
'4 t 4 0
+ C C I

a) a) a)
c *-- Lu




mn ) c




> e 0 4-1



3 C--e c



i-4- C






- 4 4 O-





0 CO >, Q.0
NCI-0
c drh


0 U.o 0 o Q o )0 P 0 o nm 0
o r- r0 t ui 0 'N d d
c(s u N3 N NvONOO -
(is. wu.io uIu) 33NtifnGN03 BAISfJJdIO


t I I i I I I


<










-a


-aa

a-a
o .- a


a
a


bb
\\

b
\

\b
\\
\\


GROWN AT 200/150C
(DAY/NIGHT)
GROWN AT 30/250C


DAYS POSTSTORAGE


Figure 2-20.


Postharvest weight changes of cut leatherleaf fern fronds
grown under 2 temperature regimes. (Letters are means of
8 replications and different letters indicate significant
differences for t test comparisons at the 5% level within
days for treatments.)


101.0


100.5


100.0


99.5


99.0


98.5


98.0


97.5


97.0


96.5


96.0









Table 2-4.


Anatomical, morphological, physiological and postharvest
characteristics for leatherleaf fern fronds grown under
low and high temperature regimes


Day/night production temperature
(C)

Significance
200/150 300/250 level


Fresh weight (g)

Dry weight (g)

Water content (%)

Surface area SA (cm2)

Leaf density thickness
(g fresh wt/cm2- 10-2)

Specific leaf weight
(g dry wt/cm2 10-3)

Stipe narrow diameter (cm)

Stipe wide diameter (cm)

Stipe (cross-sectional)
area (cm2)

Ratio of SA:stipe area
( 102)

Tracheid number

Tracheid lumen area
(mm2 10-1)

Parenchyma cell area
(m2. 10-3)

Average lumen area
(mm2. 10-4)

Vascular bundle number

Conductivity
(cm2 MPa-15s-1.102)

Vase life (days)

Discard weight
(% of initial weight)


12.7

2.96 +

76.2

347 +


12.8

2.60 +

78.8

356


3.73 0.13


8.46

0.29

0.33


1.79

0.20

1.18

23.5


3.15 0.06


0.21

0.007

0.009


0.08 0.004


45.2 1.34

379 82.2


1.60 0.42


4.61 0.44


4.16 0.27

9.56 0.26


1.47 0.49

27.5 1.14


88.6 t 3.51


Z
Means SE.
YPlants were grown in controlled environment
and 12 hr nights.
x
Significance level hased on t test.


7.27 t

0.25

0.28 +


0.20

0.006

0.008


0.06 0.003


65.2 2.28

346 75.3


1.03 0.16


5.44 0.45


3.04 t 0.16

8.38 0.40


0.74 0.57

19.9 0.92


87.7 2.25


chambers with 12 hr days


0.961

0.182

0.141

0.761


0.001


0.0001

0.0001

0.0001


0.0001


0.0001

0.786


0.276


0.225


0.022

0.048


0.388

0.0001


0.839







(r = 0.43, P < 0.0001) diameters and stipe cross-sectional area

(r = 0.43, P < 0.0001). The frond surface area to stipe

cross-sectional area ratio was 38% greater for HTR fronds. As was

found in Experiment 2, this ratio was negatively correlated (r = -0.23,

P < 0.011) with vase life.

Tracheids of stipes of leatherleaf fern were scalariformly pitted

(Figure 2-21). Differences in tracheid numbers and total tracheid

lumen area per stipe cross section were not detected (Table 2-4) and

this was probably due to the limited sample number (3 replications).

The number of tracheids per stipe cross section were higher than

reported for other fern species (163). However, the ratio of frond

surface area to tracheid numbers in this research is the same as was

found for the smaller-leaved fern species examined in that study.

Lumen areas appear to differ in size due to the temperature treatments.

However, this may be an artifact of the LMS system which tends to

underestimate tracheid numbers in stipe sections and, therefore,

overestimate average lumen areas under the low magnification necessary

for the large vascular bundles of LTR fronds. Lumen areas reported

here are larger than Woodhouse and Nobel (163) found for 6

smaller-leaved species of fern. Total tracheid lumen area comprised

2.06% and 1.87% of stipe cross-sectional areas of LTR and HTR fronds,

respectively. Vascular bundles were less numerous in HTR stipes than

in LTR stipes. The secondary thickening of the outer tangential wall

of the endodermal cells was greater for LTR fronds (Figure 2-22). This

thickening may increase the structural strength of the stipe and also

reduce movement of water out of the stele and into the ground tissue of

the stipe. This could increase the amount of water available to distal





























Figure 2-21. Scanning electron micrographs of a leatherleaf fern stipe
showing A) a cross section with vascular bundles (vb)
containing tracheids, B) the location of tracheids (t) in
a vascular bundle, C) close-up of tracheids and
D) scalariform pitting of the cell walls of tracheids.








































DI.




























Figure 2-22.


Cross sections of vascular bundles in stipe bases of
leatherleaf fern fronds, grown under 200C day/150 night
(top) and 30 day/250 night (bottom) in controlled
environment chambers, showing the greater thickening of
the outer tangential wall of the uniseriate endodermis of
the 200/150 grown frond. (x850) e: endodermal cell,
s: sieve cell, t: tracheid.






78


















b h












t r zr ~ rop



.. t4L








~gt" ; rci .eel








tissues of the lamina. Frond curl syndrome usually starts at the

periphery of the frond and progresses downward and inward. The size of

the parenchyma cells of the ground tissue were similar (Table 2-4).

Conductivity, a, was not different between treatments and this suggests

that there are no qualitative differences, such as differences in

tracheid cell wall pitting, in the vascular tissue of LTR and HTR

fronds.

Vase life of HTR fronds was 28% less than for LTR fronds (Table

2-4). Since the discard weights (termination weight initial weight)

of LTR and HTR fronds were the same, the reduction in vase life of HTR

fronds was due to their losing weight faster than the LTR fronds and

not to any bias during termination evaluations. This supports results

observed in Experiment 2. Stipe recutting did not affect vase life,

and there was no interaction of temperature treatment and stipe

recutting. The stipe bases were recut once in this experiment. In an

experiment where stipes of fronds grown under a single environmental

regime were recut daily, the recut fronds did not lose weight over an

18 day period, whereas the control plants lost 19% of their initial

weight (Henny, unpublished). None of Henny's recut fronds exhibited

FCS, but 55% of the control fronds were terminated due to

curling/dessication.

Numerous correlations existed between frond anatomical and

morphological characteristics for LTR fronds (Table A-2, Appendix). No

characteristic was highly correlated with vase life. Surface area

(r = 0.35, P < 0.045), relative conductivity (r = 0.32, P < 0.045) and

initial (day 1) water uptake (r = 0.35, P < 0.027) were weakly

positively correlated and specific leaf weight was weakly negatively







correlated (r = -0.38, P < 0.016) with vase life (Table A-2, Appendix).

Stipe relative conductivity was positively correlated with the number

of tracheids in the stipe (r = 0.80, P < 0.02) and conductivity and

relative conductivity were positively correlated with tracheid lumen

area (r = 0.99).

There were numerous correlations between frond anatomical and

morphological characteristics for HTR fronds (Table A-2, Appendix).

Specific leaf weight (r = -0.38, P < 0.017) and water uptake on the

eighth day poststorage (r = -0.35, P < 0.028) were negatively

correlated with vase life.


Experiment 4


Harvest 1. Water uptake curves in this experiment were similar to

those in Experiments 2 and 3 (Figure 2-23). The main effect of the

former temperature treatment (FT) was significant (P < 0.044) for the

first 90 hr poststorage (post-stipe recutting) and fronds from pots

that were formerly grown under HTR had reduced uptake compared to

fronds formerly grown under LTR. The temperature treatment under which

the tagged fronds developed (LT) had no effect on uptake and no

interactions were found between the former and latter temperature

treatments. Abaxial diffusive conductance and transpiration were not

different during the first 90 hr as determined by analysis of variance

(Figure 2-24). Abaxial diffusive conductance values were considerably

lower than have been found for cut field grown leatherleaf fern (112)

and may have been partially due to stomatal closure during storage and

to differences in environmental conditions mentioned in Experiment 1.

Weight loss effects due to FT were detected (P < 0.035) 90 hr after the
















































0.0


Figure 2-23.


TEMPERATURE DURING GROWTH (DAY/NIGHT)
FORMER LATTER
-----0 200/150 200/150
n----- 300/250 300/250
----- 300/25" 200/150
----- 207/150 300/25











y=0.0040-0.0009 In x
r =0.96**
y=0.0041-0.0010 In x
Sr =0.96**
y=0.0031-0.00071n x
r = 0.95*
r y=0.0029-0.0007 In x
S/ r=0.96**


I I I I I I I I I i
0 10 20 30 40 50 60 70 80 90
HOURS


Poststorage water uptake of cut leatherleaf fern fronds
grown under 1 of 2 former temperature treatments and 1 of
2 latter temperature treatments. (Circles and triangles
represent the means of 5 replications. and ** indicate
significance at the 5% and 1% levels, respectively.)


4.0 r


3.5 1


3.0 F


2.5 -


2.0 F


1.5 1


1.0 -


0.5 1