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Photosynthesis, Productivity, and Yield of Maize Are Not Affected by Open-Air Elevation of CO2 Concentration in the Absence of Drought.

Leakey AD, Uribelarrea M, Ainsworth EA, Naidu SL, Rogers A, Ort DR, Long SP

Institute for Genomic Biology , University of Illinois at Urbana-Champaign, Urbana, Illinois 61801; Photosynthesis Research Unit, United States Department of Agriculture Agricultural Research Service, Urbana, Illinois 61801.

While increasing temperatures and altered soil moisture arising from climate change in the next 50 years are projected to decrease yield of food crops, elevated CO(2) concentration ([CO(2)]) is predicted to enhance yield and offset these detrimental factors. However, C(4) photosynthesis is usually saturated at current [CO(2)] and theoretically should not be stimulated under elevated [CO(2)]. Nevertheless, some controlled environment studies have reported direct stimulation of C(4) photosynthesis and productivity, as well as physiological acclimation, under elevated [CO(2)]. To test if these effects occur in the open air and within the Corn Belt, maize (Zea mays) was grown in ambient [CO(2)] (376 mumol mol(-1)) and elevated [CO(2)] (550 mumol mol(-1)) using Free-Air Concentration Enrichment technology. The 2004 season had ideal growing conditions in which the crop did not experience water stress. In the absence of water stress, growth at elevated [CO(2)] did not stimulate photosynthesis, biomass, or yield. Nor was there any CO(2) effect on the activity of key photosynthetic enzymes, or metabolic markers of carbon and nitrogen status. Stomatal conductance was lower (-34%) and soil moisture was higher (up to 31%), consistent with reduced crop water use. The results provide unique field evidence that photosynthesis and production of maize may be unaffected by rising [CO(2)] in the absence of drought. This suggests that rising [CO(2)] may not provide the full dividend to North American maize production anticipated in projections of future global food supply.

Published 9 February 2006 in Plant Physiol, 140(2): 779-90.
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