Abstract: Transpiration element is included in the integrated stomatal conductance-photosynthesis model by considering gaseous transfer processes, so the present model is capable to simulate the influence of boundary layer conductance. Leuning in his revised Ball' s model replaced relative humidity with VPDs(the vapor pressure deficit from stomatal pore to leaf surface) and thereby made the relation with transpiration more straightforward, and made it possible for the regulation of transpiration and the influence of boundary layer conductance to be integrated into the combined model. If the differences in water vapor and CO2 concentration between leaf and ambient air are considered, VPDs, the evaporative demand, is influenced by stomatal and boundary layer conductance. The physiological responses of photosynthesis, transpiration, and stomatal function, and the changes of intercellular CO2 and water use efficiency to environmental factors, such as wind speed, photon flux density, leaf temperature and ambient CO2, are analyzed. It is shown that ff the boundary layer conductance drops to a level comparable with stomatal conductance, the results of simulation by the model presented here differ significantly from those by the previous model, and, in some cases, are more realistic than the latter.

Key words: Photosynthesis, Transpiration, Stomatal conductance, Boundary layer conductance, Integrated model