A Simulation of Diuranal Variations of Photosynthesis of C3 Plant Leaves
C3植物光合作用日变化的模拟

On the basis of earlier studies of coupled stomatal conductance, photosynthesis model, an integrated photosynthesis-transpiration-stomatal conductance model generalizing the interrelation between and regulating mechanisms of the main physiological processes is developed. The midday depression of photosynthesis caused by environmental factors, such as solar radiation, air temperature and humidity, is simulated by numerical method. The results are as follows: (1) When the boundary layer conductance decreases, midday depression of photosynthesis and transpiration will be enhanced, but stomatal conductance will increase as a feedback. (2) Under certain conditions, the optimal temperature for transpiration is higher than that for photosynthesis, and the optimal temperature for stomatal conductance is lower than that for photosynthesis. When midday depression is caused by high temperature, the extent of decrease in stomatal conductance is the largest and that of transpiration the smallest. The duration of midday depression of stomatal conductance is the longest, and that in transpiration the shortest (Fig. 5). (3) V pd and stomatal conductance are two contradicting factors, which determine transpiration. Transpiration increases with increasing V pd initially, but when V pd exceeds a certain value, it will decrease with increasing V pd caused by a rapid decrease in stomatal conductance and concomitant increase in leaf temperature. (4) When air temperature exceeds a certain value, an increase of solar radiation will cause increasing leaf temperature and the deepness in midday depression. (5) The decrease in c i/c s in midday suggests that stomatal closure is a important factor causing midday depression of photosynthesis.