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United States Department of Agriculture

Agricultural Research Service

Title: Effects of Water Vapor Pressure Difference on Leaf Gas Exchange in a Potato and Sorghum at Ambient and Elevated Carbon Dioxide under Field Conditions

item Bunce, James

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 21, 2002
Publication Date: February 1, 2003
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Citation: Bunce, J.A. 2003. Effects of water vapor pressure difference on leaf gas exchange in a potato and sorghum at ambient and elevated carbon dioxide under field conditions. Field Crops Research. 82:37-47.

Interpretive Summary: Low humidity around the leaves of crop plants often reduces their rates of photosynthesis and slows plant growth rates. The rising concentration of carbon dioxide in the atmosphere could potentially benefit crops by overcoming this inhibitory effect of low humidity, but field-based data are lacking. In this study, effects of low humidity on photosynthesis of potato and sorghum leaves were compared at the current concentration of carbon dioxide, and at twice the current concentration, for plants grown under field conditions. Contrary to expectations, elevated carbon dioxide did not reduce the sensitivity of photosynthesis to low humidity in either species. The results indicate that low humidity may continue to pose a major limitation to photosynthesis in crops even as atmospheric carbon dioxide concentrations continue to increase. This information will be of use to scientists adapting crop plants to future climates.

Technical Abstract: High leaf to air water vapor pressure differences (D) often substantially reduce rates of assimilation of carbon dioxide (A), especially in C3 species. Rising concentrations of carbon dioxide in the atmosphere could reduce the sensitivity of A to partial stomatal closure caused by high D by a variety of mechanisms. However, field data addressing this question are scarce. In this study, we examined day to day variation in midday gas exchange rates of upper canopy leaves of potato and sorghum grown at 350 and 700 ppm carbon dioxide in field plots. Stomatal conductance (g) and A were negatively correlated with D across. A was not less sensitive to D at elevated than at 350 ppm carbon dioxide in either species. For both potato and sorghum short-term increases in D for individual leaves produced significantly smaller responses of A and g to D than did the day to day variation in D, again with no reduced sensitivity of A to D at elevated carbon dioxide. The lack of a carbon dioxide effect on the sensitivity of A to D, and the substantial sensitivity of A to D in the C4 species both resulted from reductions in A at a given internal carbon dioxide concentration at high D. The results suggest that high D may continue to be a major limitation to A in C3 and C4 crop species even at twice the current concentration of carbon dioxide in the atmosphere.

Last Modified: 5/5/2015
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