Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/19/2005
Publication Date: 2/1/2006
Citation: Leakey, A.B., Uribelarrea, M., Ainsworth, E.A., Naidu, S.L., Rogers, A., Long, S.P., Ort, D.R. 2006. Photosynthesis, productivity and yield of maize are not affected by open-air elevation of CO2 concentration in the absence of drought. Plant Physiology. 140:779-790. Interpretive Summary: Carbon dioxide in the world’s atmosphere is on the rise. In the last century it has risen 20% and this geologically unprecedented pace will continue resulting in an atmosphere in 2050 containing 50% more CO2 than it did in 1900. While this enrichment of the atmosphere CO2 portends certain hazards of which global warming is the most publicized, it also offers the potential to increase crop yield and water use efficiency. However, in the case of corn, the 3rd most important crop globally, how effects of increasing CO2 will affect water use is not adequately understood to allow accurate predictions of future crop production or allow varietal selection for improved productivity in a changing climate. The results show that in the absence of drought there is no enhancement of yield in corn by elevated CO2 even though there is a substantial improvement in water use efficiency by the crop. This outcome indicates that projections of future global food supply for C4 crops are overly optimistic.
Technical Abstract: 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 [CO2] is predicted to enhance yield and offset these detrimental factors. The models used for such projections include “CO2 fertilization” factors that simulate the enhancements of photosynthesis and yield that were observed in controlled environment studies 20 years ago. However, C4 photosynthesis is saturated at current [CO2], and theoretically should not be stimulated under elevated [CO2]. In this case, projections of future food supply are overly optimistic. However, some controlled environment studies have supported the optimistic outlook, reporting direct stimulation of C4 photosynthesis by elevated [CO2]. To test the response of a major production line in the U.S. Corn Belt, Zea mays was grown in fully open-air field trials at SoyFACE,under ambient [CO2] (376 µmol mol-1) and elevated [CO2] projected for 2050 (550 µmol mol-1). The climate in 2004 was unusually cool and the crop did not experience water stress. Growth at elevated [CO2] did not directly stimulate photosynthesis, biomass or yield. Nor was there acclimation of photosynthesis, carbon or nitrogen metabolism. However, at elevated [CO2] 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 maize is unaffected by rising [CO2] in the absence of drought, suggesting that rising [CO2] may not provide the dividend anticipated in projections of future global food supply.