PLANT PHYSIOLOGY , Vol 111, Issue 3 909-919, Copyright © 1996 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
The Effect of Elevated [CO2] on Growth and Photosynthesis of Two Eucalyptus Species Exposed to High Temperatures and Water Deficits
J. S. Roden and M. C. Ball
Ecosystem Dynamics, Research School of Biological Sciences, Australian National University, Canberra, Australian Capital Territory 0200, Australia
Two species of eucalyptus (Eucalyptus macrorhyncha and Eucalyptus rossii)
were grown for 8 weeks in either ambient (350 [mu]L L-1) or elevated (700
[mu]L L-1) CO2 concentrations, either well watered or without water
additions, and subjected to a daily, 3-h high-temperature (45[deg]C,
maximum) and high-light (1250 [mu]mol photons m-2 s-1, maximum) stress
period. Water-stressed seedlings of E. macrorhyncha had higher leaf water
potentials when grown in elevated [CO2]. Growth analysis indicated that
increased [CO2] may allow eucalyptus species to perform better during
conditions of low soil moisture. A down-regulation of photosynthetic
capacity was observed for seedlings grown in elevated [CO2] when well
watered but not when water stressed. Well-watered seedlings grown in
elevated [CO2] had lower quantum efficiencies as measured by chlorophyll
fluorescence (the ratio of variable to maximal chlorophyll fluorescence
[Fv/Fm]) than seedlings grown in ambient [CO2] during the high-temperature
stress period. However, no significant differences in Fv/Fm were observed
between CO2 treatments when water was withheld. The reductions in
dark-adapted Fv/Fm for plants grown in elevated [CO2] were not well
correlated with increased xanthophyll cycle photoprotection. However,
reductions in the Fv/Fm were correlated with increased levels of
nonstructural carbohydrates. The reduction in quantum efficiencies for
plants grown in elevated [CO2] is discussed in the context of feedback
inhibition of electron transport associated with starch accumulation and
variation in sink strength.
