ARS | Publication request: Leaf photosynthesis and carbohydrates of CO2-enriched maize and grain sorghum exposed to a short period of soil water deficit during vegetative development

Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 20, 2011
Publication Date: December 15, 2011
Citation: Kakani, G., Vu, J.C., Allen Jr, L.H., Boote, K.J. 2011. Leaf photosynthesis and carbohydrates of CO2-enriched maize and grain sorghum exposed to a short period of soil water deficit during vegetative development. Journal of Plant Physiology. 168:5169-2176.

Interpretive Summary: Research on effects of rising carbon dioxide (CO2) and climate change has primarily focused on C3 crops such as rice and soybean. Few tests have been done on C4 crops such as corn and sorghum. USDA-ARS scientists of the Chemistry Research Unit in Gainesville, FL, collaborating with the University of Florida, imposed drought on 26-day old corn and grain sorghum grown at 360 (ambient) or 720 (elevated) ppm of CO2. Midday leaf photosynthesis and afternoon carbohydrate concentrations, as well as activities of two key sucrose and starch enzymes, were determined for leaves of well watered and droughted plants. For well watered plants, there was no difference in photosynthesis between ambient and elevated CO2 for either corn or sorghum. Because of corn plants grew faster with greater water use rates, leaf photosynthesis decreased earlier in the drought period for corn than sorghum. Under drought, increases in leaf soluble sugars and decreases in leaf starch were found for corn and sorghum at both CO2 levels. For droughted corn and sorghum, the decreases in leaf starch occurred earlier and were greater at ambient than elevated CO2. The activities of the two key enzymes behaved differently in corn compared to sorghum. Thus, yield responses might be different among C4 crops in future climates.

Technical Abstract: Drought was imposed on 26-day old corn and grain sorghum grown in carbon dioxide (CO2) at 360 (ambient) or 720 (elevated) ppm. Midday leaf CO2 exchange rates (CER), and afternoon carbohydrate concentrations and activities of sucrose phosphate synthase (SPS) & adenosine 5’-diphosphoglucose pyrophosphorylase (ADGP), sucrose and starch metabolism enzymes, respectively, were determined for fully expanded leaves of well watered and droughted plants. For well watered plants, there was no difference in leaf CER between ambient and elevated CO2 for either corn or sorghum. Because of larger corn plants, leaf CER decreased earlier in the drought period for corn than sorghum. Leaf CER decreased to zero at 8 days for corn and 10 days for sorghum for both CO2 treatments. Under drought, increases in leaf soluble sugars and decreases in leaf starch were observed for corn and sorghum at both CO2 treatments. For droughted corn and sorghum, the decreases in leaf starch occurred earlier and were greater at ambient than elevated CO2. Drought did not affect SPS activity for corn, but SPS activity declined for the stressed sorghum of both CO2 treatments. Under drought, ADGP activity increased in corn but not sorghum. Thus, there might be subtype specific differences among C4 crops in future climates.