This award will provide supplementary support to enable Dr. Mark A. Matthews of the University of California, Davis to conduct collaborative research for eight months with Dr. Kenji Omasa of the National Institute for Environmental Studies in Tsukuba, Japan. They will investigate the physiological mechanisms by which water deficits inhibit photosynthesis and by which photosynth- eitic acclimation to dry conditions occurs. At low water status, stomatal closure and inhibition of chloroplast function reduce photosynthesis. Although significant nonstomatal limitation to photosynthesis at low water status is widely accepted, most studies to date have assumed that rates of photosynthesis and transpiration are homogeneous over the experimental leaf area. This project will use state-of-the art instrumentations for localized measurements of leaf physiology to take into account the heterogeneity in stomatal closure that may occur at low leaf water status. This will allow a more rigorous assessment of the relative importance of stomatal and nonstomatal limitation to photosynthesis under dry conditions.
