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ARS Home » Southeast Area » Gainesville, Florida » Center for Medical, Agricultural and Veterinary Entomology » Chemistry Research » Research » Publications at this Location » Publication #260067
Title: Elevated CO2 increases water use efficiency by sustaining photosynthesis of water-limited maize and sorghum

Author
item Allen Jr, Leon
item KAKANI, V - University Of Florida
item Vu, Joseph
item BOOTE, KENNETH - University Of Florida

Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2011
Publication Date: 9/19/2011
Citation: Allen Jr, L.H., Kakani, V.G., Vu, J.C., Boote, K.J. 2011. Elevated CO2 increases water use efficiency by sustaining photosynthesis of water-limited maize and sorghum. Journal of Plant Physiology. 168:1909-1918.

Interpretive Summary: Until recently, research on effects of rising carbon dioxide (CO2) and climate change on C4 photosynthetic pathway crops, such as corn and sorghum, has been limited. USDA-ARS scientists of the Chemistry Research Unit in Gainesville, FL, collaborating with the University of Florida, imposed drought on corn and grain sorghum grown at 360 (ambient) or 720 (elevated) ppm of CO2. Irrigation was withheld from matched pairs of treatments at 27 days after sowing. Canopy photosynthesis and transpiration were measured daily. During the drought period (27 to 35 days after sowing), water use efficiency (moles of photosynthetic CO2 uptake per thousand moles of water transpired) was 3.99, 3.88, 5.50, and 8.65 for corn and 3.75, 4.43, 5.26, and 9.94 for sorghum, for ambient-CO2 well-watered, ambient-CO2 stressed, elevated-CO2 well-watered, and elevated-CO2 stressed plants, respectively. Plant dry weight reductions by drought were 42% and 36% at ambient CO2, but only 18% and 14% at elevated CO2, for corn and sorghum, respectively. Thus, under water stress, there was a relative increase of growth of these C4 plants at elevated CO2 compared to ambient CO2. Functionally, drought stress in C4 plants is ameliorated at elevated CO2 by greater leaf intercellular CO2 coupled with lower stomatal conductance. In a high-CO2 world, perhaps limited supplies of irrigation for C4 crops could be managed by applying reduced rates over larger areas rather than full rates over smaller areas.

Technical Abstract: Limited research has been conducted on responses of C4 crops to rising CO2 and climate change factors such as water stress. In this study, drought was imposed on corn and grain sorghum grown in carbon dioxide (CO2) at 360 (ambient) or 720 (elevated, double-ambient) ppm. Irrigation was withheld from matched pairs of treatments at 27 days after sowing (DAS). Daily canopy net photosynthesis (PS) and transpiration (TR) were measured from 0800 to 1700 h. During the 27-35 DAS drought period, water use efficiency (WUE, mol CO2 uptake per Kmol H2O transpired) was 3.99, 3.88, 5.50, and 8.65 for corn and 3.75, 4.43, 5.26, and 9.94 for sorghum, for ambient-CO2 well-watered, ambient-CO2 stressed, elevated-CO2 well-watered, and elevated-CO2 stressed plants, respectively. Improved WUE at high CO2 for corn was more related to maintaining high PS whereas for sorghum it was more related to lower TR. Biomass reductions by drought were 42 and 36% at ambient CO2, compared to 18 and 14% at elevated CO2, for corn and sorghum, respectively. The WUE results confirm experimental evidence and conceptual models that elevated CO2 increases intercellular CO2 sufficiently to maintain photosynthesis despite decreased stomatal conductance. This results in relative increases of growth of C4 plants at elevated CO2 compared to ambient CO2. In short, drought stress in C4 plants can be ameliorated at elevated CO2 as a result of lower stomatal conductance and greater intercellular CO2.