Wjs. Downton et Wjr. Grant, PHOTOSYNTHETIC AND GROWTH-RESPONSES OF VARIEGATED ORNAMENTAL SPECIES TO ELEVATED CO2, Australian journal of plant physiology, 21(3), 1994, pp. 273-279
Variegated and completely green cultivars of oleander (Nerium oleander
L.) and willow myrtle (Agonis flexuosa (Willd.) Sweet) were grown in
controlled environment cabinets for 3 and 5 months, respectively, unde
r either ambient levels of CO2 or with supplementary CO2 to a partial
pressure of 800 mu bar. Photosynthesis of entirely green leaves and th
e green portions of variegated leaves on both species was greatly stim
ulated by high CO2 and there was no evidence of downward adjustment (a
cclimation) of photosynthetic rates to high CO2 during the experiment.
Dark respiration rates of these leaves were lowered by high CO2. The
yellow portions of willow myrtle leaves showed a low level of photosyn
thetic activity which was stimulated by high CO2; however, dark respir
ation rates showed little response to elevated CO2. Green and yellow a
reas on variegated leaves of willow myrtle had much lower dark respira
tion rates than completely green leaves, but this difference was not e
vident for oleander. Yellow portions of oleander leaves showed little
evidence of photosynthetic capacity. This was also confirmed by a low
photochemical efficiency as determined by chlorophyll fluorescence. A
major effect of variegation was to slow overall plant growth compared
with completely green plants. The respective 3-fold and 6-7-fold diffe
rences in biomass between fully green and variegated cultivars of olea
nder and willow myrtle was closely related to estimated net carbon gai
n per day by the plant canopy. Variegation for both species averaged c
lose to 50:50, green:yellow areas. Variegated plants developed about t
wice the leaf area ratio and specific leaf area compared with their co
mpletely green counterparts. The relative growth response to high CO2
was significantly greater for the variegated plants compared to the co
mpletely green plants.