A 2-DIMENSIONAL MODEL OF LEAF GAS-EXCHANGE WITH SPECIAL REFERENCE TO LEAF ANATOMY

This model of leaf gas exchange includes (1) two-dimensional CO2, O-2 and water vapour diffusion in intercellular space schematized accordin g to leaf anatomy, (2) CO2 assimilation by mesophyll cells as describe d by Farquhar's model of photosynthesis and (3) stomatal movements as a regulating factor. Parameters describing the leaf cross-section and gas diffusion properties replace the empirical parameters of earlier m odels. The model was tested for soybean and performed well in represen ting light, CO2 concentration ([CO2]), and temperature response curves as well as the dependence of transpiration on temperature and water v apour deficit. The model allows the calculation of the steady state di stribution of CO2 and water vapour concentrations in the intercellular space and the boundary layer. The direct calculation of diffusion in leaves showed that stomatal aperture effectively regulates the transpi ration rate but usually has a much smaller effect on the rate of assim ilation.