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Crop Biotech Update

Researcher Measures Leaf Transpiration Efficiency of Drought-resistant Maize Lines

July 30, 2010

Stomatal conductance refers to the speed at which water evaporates from pores in a plant. Field measurements of leaf gas exchange in maize often show that high stomatal conductances supply substomatal carbon dioxide concentrations saturating to photosynthesis. This makes maize leaves to operate at lower transpiration efficiency (TE; the biomass produced per water transpired) than possibly attainable for C4 plants. Thus, James A. Bunce of USDA-ARS Crop Systems and Global Change Laboratory investigated if five drought resistant or drought tolerant maize lines operated with higher leaf TE than three less-adapted local maize lines. Field measurements of leaf TE, photosynthesis, stomatal conductance, and substomatal carbon dioxide concentration were obtained over two planting seasons of maize in Beltsville, Maryland.

Consistent and significant variation among the lines were observed for stomatal conductance, substomatal carbon dioxide concentration, and TE, but not for photosynthesis. One of the drought-tolerant lines exhibited the highest TE, and a local line with the lowest TE. However, not all drought-tolerant lines showed higher TE than the local lines. Bunce concluded that significant genotypic variation in leaf TE is possible in maize, and that TE could be enhanced without reducing photosynthesis.

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