Ceulemans, R.

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ECOPHYSIOLOGICAL ASPECTS IN HORTICULTURAL RESEARCH R. Ceulemans Departmenf of Biology. University of Antwerpen Universiterisplein, 1 B-2610 - WILRIJK (A ntwerpen) BELGIUM INTRODUCTION Through their ages exchange processes (photosynthesis, transpiration and respiration) plants exchange rnajor inorganic elements (carbon, hydrogen, oxygen) with their environrnent. Therefore these processes have an irnportant influence on plant growth and productivity (i.e. accurnulated carbohydrates) as well as on the interrelationships between plants and their environrnent. The study of these gas exchange processes (ecophysiology) in relation to different environrnental conditions (both physical and physico- chemical) and to genetic differences arnong different cultivars or genotypes can provide interesting information in view of selection toward enhanced productivity, (greenhouse) clirnate control, etc. Different applications of ecophysiological studies in horticultural research could also be envisaged: the use of physiological indices in breeding and selection prograrns of horticultural plants, determination of optirnal or non- lirniting environrnental conditions (ternperature, hurnidity, CO, concentration) -which rnight certainly have irnportant significance in glasshouse horticulture- or the evaluation and prediction of technico-cultural or managernent applications (fertilization, salinisation, use of antitranspirants) on horticultural production. Exarnples of al1 these possible applications \11ill be given here under, but first some general methodological features will be given. METHODOLOGY In the laboratory gas exchange processes (transpiration, photosynthesis, respiration) are studied on single leaves, single plants o r  m a l l  vegetations in environment controlled gas exchange chambers (or cuvettes). Environmental conditions in these assimilation chambers (with an inner volume ranging from 6 dm' to 30 dm3 according to plant or leaf dimensions) are controlled by means o f  highly sophisticated electronic control systems. Further specific advantages of these laboratory techniques next to the simultaneous measurement of both CO, and water vapour exchange processes include the continuous and natural air movement over the plant material enclosed in the cuvette, as well as the non-destructive character of the measurements. Typical long-term experiments can be performed under ideal circumstances using these laboratory chambers. Under field or glasshouse conditions a portable gas exchange unit consisting of an infrared gas analyser, a twin set of membrane pumps and a small laboratory- constructed plexi gas exchanged cuvette is used. The dimensions, form and design o f  the gas exchange cuvettes can also be adapted to the specific plant or leaf characteristics. Contrary to  the above mentioned laboratory assimilation chambers, environmental conditions (e.g. temperature) in these cuvette types can only be partially controlled. A small inner fan provides a considerable wind speed over the enclosed plant organ. However, very fast and short-term sampling times make the use of highly sophisticated environmental control mechanisms unnecessary as well as bulky in the field or in the glasshouse. The so-called electrical analogon model originally described by Gaastra (1959) is used in order to split up the resistances to both gas exchange processes in boundary layer, stomatal and interna1 contributions. Together with some other underlying anato-morphological and biochemical leaf characteristics, these basic gas exchange resistances are very helpful in understanding the gas exchange processes. EXAMPLES AND RESULTS Use o f  ecophysiological studies as a preliminary growth or selection index For a number of azalea (Rhododendron simsii Planch.) cultivars net photosynthesis - light response curves were made up under optima1 and controlled environmental conditions. Good agreement was obtained between light satured net photosynthetic rate (expressed either per plant or per unit projected crown area) and growth performance of different cultivars. Growth was expressed in this case as crown diameter which determines -together with flower size- the azalea parket price. Similar considerable differences in net photosynthesis were observed among a population of seedlings of the New- Zealand laurier (Corynocarpus laevigatus) as well as among a number of Bromelia and Vriesea cultivars (fam. Bromeliaceas) with relation to their responses to light and temperature. Here it might be possible to select among a population for seedlings or cultivars that are optimally adapted to certain temperature and light conditions. lnfluence of light and temperature on plant growth or productivity In view of the rentability problems in horticulture caused by the increased energy (oil, gas) prices, the introduction of new cultivars or selections with low energy requirements (light, temperature) is a basic prerequisite. It has been shown that certain New-Zealand laurier (Corynocarpus laevigatus) and Ardisia crenulats seedlings performed optimal net CO, uptake and optimal growth at moderate temperature (10 to 15 OC) and light (ca. 23 klux) combinations. From the ecophysiological data obtained on these plants -that are both originating from New-Zealand with quite low mean annual temperature- it could be concluded that in winter time -when incoming light in the greenhouse is the main limiting factor -considerable heating and increase in air temperature is unnecessary. Moreover, it has been shown on some other ornamentals (Dieffenbachia spec., Schefflera arboricola, Ficus lyrata and Epiyrennum aureum) that optimal temperature for net photosynthesis is reflected in the main underlying biochemical CO, fixing reactions and processes at the chloroplast level (photophosphorylation, ATP- production ...). For Schefflera arboricola (cv. Compacta) optimal temperatures for net photosynthesis -hence for growth- were found at 25 OC under an incident photon flux density of 450 pmol m-2 s'. With increasing vapour pressure deficit transpiration increased while diffusive conductance as well as leaf temperature decreased. However, differences in vapour pressure deficit had no significant influence on net photosynthesis nor on xylem water potential. Effects of cultural management techniques or applications For Ficus benjamina and an azalea (Rhododendron simsii Planch.) cultivar the effects of different fertilization levels in several ecophysiological as well as morphological characteristics were studied. For Ficus benjamina optimal fertilizer concentration for maximum growth was indicated by minimal light compensation point while maximal photosynthetic rates fertilization level as optimal crown diameter, hence productivity class. The effect of antitranspirant application on transpiration, photosynthesis and growth of azalea could also be evaluated through ecophysiological studies. Because of the fact that both gas exchange processes were limited by the antitranspirant application, long-term use would reduce growth considerably. Finally, effects of salinity or water stress on gas exchange of Schefflera arboricola have been studied and indicated that stomatal conductance and leaf water potential were significantly influenced by salinity and water stress. However, Schefflem arboricola showed interesting prospectives for horticulture under saline irrigation conditions. 1 O 4 R X I L ' S  de I 'EK Sup d'4priculiura Barcelona CONCLUSIONS Through different examples on  several valuable in view of breeding and horticultura1 and ornamental species and selection programs, for determinations of  varietes it has been shown that optimal or non-limiting environmental ecophysiological gas exchange studies conditions (greenhouse climate control whether or  not in combination with programming), for preliminary evaluation morphological o r  plant architectural of cultural management strategies o r  rneasurements could provide interesting early indication of  water stress situations. and useful information that could be LITERATURE GAASTRA, P. (1959).- Phorosynrhesis of crop planls stomatol dflusion wsislonce. Mededel. Landb.  h as influenced by lighi, carbon dioxide, lemperolure and school, Wageningen. 59. 1-68. Research supported by the lnstitute tot Aanmoediging van het Wetenschappelijk Onderzoek in Nijverheid en Landbouw (IWONL, Brussels) as project nrs. 3624A and 4172A. 

Ecophisiological aspects in horticultural research

UPCommons

Revistes Catalanes amb Accés Obert

ECOPHYSIOLOGICAL ASPECTS 
IN HORTICULTURAL RESEARCH 
R. Ceulemans 
Departmenf of Biology. University of Antwerpen 
Universiterisplein, 1 B-2610 - WILRIJK (A ntwerpen) 
BELGIUM 
INTRODUCTION 
Through their ages exchange processes 
(photosynthesis, transpiration and 
respiration) plants exchange rnajor 
inorganic elements (carbon, hydrogen, 
oxygen) with their environrnent. 
Therefore these processes have an 
irnportant influence on plant growth and 
productivity (i.e. accurnulated 
carbohydrates) as well as on the 
interrelationships between plants and 
their environrnent. The study of these gas 
exchange processes (ecophysiology) in 
relation to different environrnental 
conditions (both physical and physico- 
chemical) and to genetic differences 
arnong different cultivars or genotypes 
can provide interesting information in 
view of selection toward enhanced 
productivity, (greenhouse) clirnate 
control, etc. Different applications of 
ecophysiological studies in horticultural 
research could also be envisaged: the use 
of physiological indices in breeding and 
selection prograrns of horticultural 
plants, determination of optirnal or non- 
lirniting environrnental conditions 
(ternperature, hurnidity, CO, 
concentration) -which rnight certainly 
have irnportant significance in glasshouse 
horticulture- or the evaluation and 
prediction of technico-cultural or 
managernent applications (fertilization, 
salinisation, use of antitranspirants) on 
horticultural production. 
Exarnples of al1 these possible 
applications \11ill be given here under, but 
first some general methodological 
features will be given. 
METHODOLOGY 
In the laboratory gas exchange 
processes (transpiration, photosynthesis, 
respiration) are studied on single leaves, 
single plants o r  m a l l  vegetations in 
environment controlled gas exchange 
chambers (or cuvettes). Environmental 
conditions in these assimilation chambers 
(with an inner volume ranging from 
6 dm' to 30 dm3 according to plant or 
leaf dimensions) are controlled by means 
o f  highly sophisticated electronic control 
systems. Further specific advantages of 
these laboratory techniques next to the 
simultaneous measurement of both CO, 
and water vapour exchange processes 
include the continuous and natural air 
movement over the plant material 
enclosed in the cuvette, as well as the 
non-destructive character of the 
measurements. Typical long-term 
experiments can be performed under 
ideal circumstances using these laboratory 
chambers. 
Under field or glasshouse conditions a 
portable gas exchange unit consisting of 
an infrared gas analyser, a twin set of 
membrane pumps and a small laboratory- 
constructed plexi gas exchanged cuvette is 
used. The dimensions, form and design 
o f  the gas exchange cuvettes can also be 
adapted to the specific plant or leaf 
characteristics. Contrary to  the above 
mentioned laboratory assimilation 
chambers, environmental conditions (e.g. 
temperature) in these cuvette types can 
only be partially controlled. A small 
inner fan provides a considerable wind 
speed over the enclosed plant organ. 
However, very fast and short-term 
sampling times make the use of highly 
sophisticated environmental control 
mechanisms unnecessary as well as bulky 
in the field or in the glasshouse. 
The so-called electrical analogon model 
originally described by Gaastra (1959) is 
used in order to split up the resistances 
to both gas exchange processes in 
boundary layer, stomatal and interna1 
contributions. Together with some other 
underlying anato-morphological and 
biochemical leaf characteristics, these 
basic gas exchange resistances are very 
helpful in understanding the gas exchange 
processes. 
EXAMPLES AND RESULTS 
Use o f  ecophysiological studies as a 
preliminary growth or selection index 
For a number of azalea (Rhododendron 
simsii Planch.) cultivars net 
photosynthesis - light response curves 
were made up under optima1 and 
controlled environmental conditions. 
Good agreement was obtained between 
light satured net photosynthetic rate 
(expressed either per plant or per unit 
projected crown area) and growth 
performance of different cultivars. 
Growth was expressed in this case as 
crown diameter which determines 
-together with flower size- the azalea 
parket price. 
Similar considerable differences in net 
photosynthesis were observed among a 
population of seedlings of the New- 
Zealand laurier (Corynocarpus laevigatus) 
as well as among a number of Bromelia 
and Vriesea cultivars (fam. Bromeliaceas) 
with relation to their responses to light 
and temperature. Here it might be 
possible to select among a population for 
seedlings or cultivars that are optimally 
adapted to certain temperature and light 
conditions. 
lnfluence of light and temperature on 
plant growth or productivity 
In view of the rentability problems in 
horticulture caused by the increased 
energy (oil, gas) prices, the introduction 
of new cultivars or selections with low 
energy requirements (light, temperature) 
is a basic prerequisite. It has been shown 
that certain New-Zealand laurier 
(Corynocarpus laevigatus) and Ardisia 
crenulats seedlings performed optimal net 
CO, uptake and optimal growth at 
moderate temperature (10 to 15 OC) and 
light (ca. 23 klux) combinations. From 
the ecophysiological data obtained on 
these plants -that are both originating 
from New-Zealand with quite low mean 
annual temperature- it could be 
concluded that in winter time -when 
incoming light in the greenhouse is the 
main limiting factor -considerable 
heating and increase in air temperature is 
unnecessary. Moreover, it has been 
shown on some other ornamentals 
(Dieffenbachia spec., Schefflera 
arboricola, Ficus lyrata and Epiyrennum 
aureum) that optimal temperature for net 
photosynthesis is reflected in the main 
underlying biochemical CO, fixing 
reactions and processes at the chloroplast 
level (photophosphorylation, ATP- 
production ...). For Schefflera arboricola 
(cv. Compacta) optimal temperatures for 
net photosynthesis -hence for growth- 
were found at 25 OC under an incident 
photon flux density of 450 pmol m-2 s'. 
With increasing vapour pressure deficit 
transpiration increased while diffusive 
conductance as well as leaf temperature 
decreased. However, differences in 
vapour pressure deficit had no significant 
influence on net photosynthesis nor on 
xylem water potential. 
Effects of cultural management 
techniques or applications 
For Ficus benjamina and an azalea 
(Rhododendron simsii Planch.) cultivar 
the effects of different fertilization levels 
in several ecophysiological as well as 
morphological characteristics were 
studied. For Ficus benjamina optimal 
fertilizer concentration for maximum 
growth was indicated by minimal light 
compensation point while maximal 
photosynthetic rates fertilization level as 
optimal crown diameter, hence 
productivity class. 
The effect of antitranspirant 
application on transpiration, 
photosynthesis and growth of azalea 
could also be evaluated through 
ecophysiological studies. Because of the 
fact that both gas exchange processes 
were limited by the antitranspirant 
application, long-term use would reduce 
growth considerably. 
Finally, effects of salinity or water 
stress on gas exchange of Schefflera 
arboricola have been studied and 
indicated that stomatal conductance and 
leaf water potential were significantly 
influenced by salinity and water stress. 
However, Schefflem arboricola showed 
interesting prospectives for horticulture 
under saline irrigation conditions. 
1 O 4 R X I L ' S  de I 'EK Sup d'4priculiura Barcelona 
CONCLUSIONS 
Through different examples on  several valuable in view of breeding and 
horticultura1 and ornamental species and selection programs, for determinations of  
varietes it has been shown that optimal or non-limiting environmental 
ecophysiological gas exchange studies conditions (greenhouse climate control 
whether or  not in combination with programming), for preliminary evaluation 
morphological o r  plant architectural of cultural management strategies o r  
rneasurements could provide interesting early indication of  water stress situations. 
and useful information that could be 
LITERATURE 
GAASTRA, P. (1959).- Phorosynrhesis of crop planls stomatol dflusion wsislonce. Mededel. Landb.  h 
as influenced by lighi, carbon dioxide, lemperolure and school, Wageningen. 59. 1-68. 
Research supported by the lnstitute tot 
Aanmoediging van het Wetenschappelijk 
Onderzoek in Nijverheid en Landbouw 
(IWONL, Brussels) as project nrs. 3624A 
and 4172A. 


Ecophisiological aspects in horticultural research

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Revistes Catalanes amb Accés Obert