PLANT PHYSIOLOGY , Vol 106, Issue 2 661-671, Copyright © 1994 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Photosynthetic Acclimation in Pea and Soybean to High Atmospheric CO2 Partial Pressure
D. Q. Xu, R. M. Gifford and W. S. Chow
Commonwealth Scientific and Industrial Research Organization, Division of Plant Industry, Canberra, Australia (R.M.G., W.S.C.)
Nonnodulated pea (Pisum sativum L. cv Frosty) and soybean (Glycine max [L.]
Merr. cv Wye) plants were grown under artificial lights from germination
with ample nutrients, 600 [mu]mol photons m-2 s-1, and either 34 to 36
(control) or 64 to 68 Pa (enriched) CO2. For soybean, pod removal and
whole-plant shading treatments were used to alter the source-sink balance
and carbohydrate status of the plants. Growth of both species was
substantially increased by CO2 enrichment despite some down-regulation of
photosynthesis rate per unit leaf area ("acclimation"). Acclimation was
observed in young pea leaves but not old and in old soybean leaves but not
young. Acclimation was neither evident in quantum yield nor was it related
to triose phosphate limitation of net photosynthesis. A correlation between
levels of starch and sugars in the leaf and the amount of acclimation was
apparent but was loose and only weakly related to the source-sink balance
of the plant. A consistent feature of acclimation was reduced ribulose
bisphosphate carboxylase (RuBPCase) content, although in vivo RuBPCase
activity was not necessarily diminished by elevated growth CO2 owing to
increased percentage of activation of the enzyme. A proposal is discussed
that the complexity of photosynthetic acclimation responses to elevated CO2
is as an expression of re-optimization of deployment of within-plant
resources at three levels of competition.
