Photosynthetic acclimation of maize to growth under elevated levels of carbon dioxide

The effects of elevated CO2 concentrations on the photochemistry, biochemis try and physiology of C-4 photosynthesis were studied in maize (Zea mays L. ). Plants were grown at ambient (350 mu L L-1) or ca. 3 times ambient (1100 mu L L-1) CO2 levels under high light conditions in a greenhouse for 30 d. Relative to plants grown at ambient CO2 levels, plants grown under elevate d CO2 accumulated ca. 20% more biomass and 23% more leaf area. When measure d at the CO2 concentration of growth, mature leaves of high-CO2-grown plant s had higher light-saturated rates of photosynthesis (ca. 15%), lower stoma tal conductance (71%), higher water-use efficiency (225%) and higher dark r espiration rates (100%). High-CO2-grown plants had lower carboxylation effi ciencies (23%), measured under limiting CO2, and lower leaf protein content s (22%). Activities of a number of C-3 and C-4 cycle enzymes decreased on a leaf-area basis in the high-CO2-grown plants by 5-30%, with NADP-malate de hydrogenase exhibiting the greatest decrease. In contrast, activities of fr uctose 1,6-bisphosphatase and ADP-glucose pyrophosphorylase increased signi ficantly under elevated CO2 condition (8% and 36%, respectively). These dat a show that the C-4 plant maize may benefit from elevated CO2 through accli mation in the capacities of certain photosynthetic enzymes. The increased c apacity to synthesize sucrose and starch, and to utilize these endproducts of photosynthesis to produce extra energy by respiration, may contribute to the enhanced growth of maize under elevated CO2.