Use of the response of photosynthesis to oxygen to estimate mesophyll conductance to carbon dioxide in water-stressed soybean leaves

Authors: Bunce, James

Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2009
Publication Date: 8/1/2009
Citation: Bunce, J.A. 2009. Use of the response of photosynthesis to oxygen to estimate mesophyll conductance to carbon dioxide in water-stressed soybean leaves. Plant Cell and Environment. 32:875-881.

Interpretive Summary: The growth rate of plants during drought is limited by the rate at which carbon dioxide can move from the air to the interior of leaves. Efforts to improve crop growth during drought are limited by lack of knowledge about how carbon dioxide moves through leaves. This research developed a new method of determining how carbon dioxide moves through leaves and found that this movement is slowed by drought. This research will be of use to scientists trying to improve crop growth during drought.

Technical Abstract: Several types of evidence indicate that there is a significant resistance to the movement of carbon dioxide from the substomatal air space to the site of fixation in the chloroplasts and that the resistance may vary with temperature, carbon dioxide concentration and water stress. Methods of estimating the magnitude of this internal resistance are expensive and not readily available to most researchers or rely upon numerous assumptions which are difficult to prove. It is proposed that the measurement of the response of photosynthesis to oxygen, combined with a standard biochemical model of photosynthesis, can provide an estimate of the internal resistance. This method was used to determine whether the internal resistance changed with carbon dioxide concentration and with water stress in soybean leaves. Internal resistance was unchanged over the tested range of carbon dioxide concentrations for both unstressed and severely stressed leaves. Moderate water stress did not affect internal resistance in soybean, while severe stress reduced it. It is concluded that the internal resistance to carbon dioxide movement in soybean and presumably other species can be conveniently estimated using the response of photosynthesis to oxygen.