Submitted to: Photosynthetica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/1/2013
Publication Date: 3/1/2014
Citation: Qu, M., Bunce, J.A. 2014. Does elevated CO2 protect photosynthesis from damage by high temperature via modifying leaf water status in maize seedlings? Photosynthetica. 52:211-216. Interpretive Summary: An increase in the frequency of high temperature events is anticipated and may damage crop plants. In this work we tested whether elevated carbon dioxide reduced the damage to corn leaves caused by acute high temperature stress, by preventing desiccation. It was found that an elevated carbon dioxide concentration, such as may occur in the next few decades, increased the amount of damage to corn leaves caused by high temperature stress. This work will be of interest to crop scientists attempting to adapt crops to global climate change conditions.
Technical Abstract: Because high temperatures under field conditions are associated with high water vapor pressure deficits, often causing leaf desiccation, we hypothesized that decreased stomatal conductance at elevated carbon dioxide may increase leaf water potential and protect photosynthesis in C4 species from damage caused by high temperature stress. This hypothesis was tested using maize grown at both 380 and 560 ppm carbon dioxide under well-water and fertilized conditions. Intact sections of leaves were exposed to gradually increasing leaf temperatures from 35 to 45 C, held at 45 C for 15 minutes and then leaf temperature was decreased again to 35 C. During this cycle of temperature, leaves were kept at either the growth carbon dioxide or the opposite carbon dioxide. Exposure of leaves to 45 C for 15 minutes reduced photosynthesis by 25 to 40%, and rates remained lower by 27 to 40% after leaf temperature was returned to 35 C. Contrary to the hypothesis, the reduction in photosynthesis by this heat treatment was significantly less at the lower than at the higher carbon dioxide, in both relative and absolute terms. Stomatal conductance in all cases increased during the treatment time at 45 C, while photosynthesis was decreasing. Stomatal conductance during the exposure to 45 C leaf temperature did not differ with carbon dioxide, although the usual differences in stomatal conductance with carbon dioxide occurred at 35 and 40 C. Leaf water potentials during the high temperature treatments did not differ with carbon dioxide and were not different from values for control leaves. Decreases of photosynthesis after heat stress were associated with decreased phosphoenolpyruvate carboxylase activity, and damage to membranes, as indicated by electrolyte leakage. Reasons for the differences in response between carbon dioxide are not known, but elevated carbon dioxide did not improve leaf water status nor protect photosynthesis from inhibition by high leaf temperatures in this case.