C_3植物光合作用日变化的模拟

A Simulation of Diuranal Variations of Photosynthesis of C 3 Plant Leaves

对前人光合作用－气孔导度耦合模型进行了修正，建立了光合作用－蒸腾作用－气孔导度的耦合模型，它概括了叶片上各主要物理过程和生理过程之间的相互联系和制约关系。用数值方法研究了不同环境因子（太阳辐射、温度、湿度和风速等）对光合作用、蒸腾作用和气孔导度的日变化及中午降低（ｍｉｄｄａｙｄｅｐｒｅｓｓｉｏｎ）的影响。主要结果是：（１）当边界层导度减小时，光合“午睡”加剧，蒸腾作用减弱，但作为反馈调节，气孔导度增加。（２）气孔导度的最适温度最低，光合作用次之，蒸腾作用最适温度最高。当光合作用中午受到高温的胁迫时，气孔导度下降的幅度最大，光合作用次之，蒸腾作用的降幅最小。一天中，气孔导度降低的持续时间最长，蒸腾作用降低的持续时间最短。（３）空气绝对湿度越低，气孔导度越低，光合午睡越明显。蒸腾作用则决定于饱和水汽压差（Ｖｐｄ）和气孔导度两个因素的相反的作用。蒸腾作用随Ｖｐｄ增加而增大，但Ｖｐｄ超过一定值后，反而使蒸腾作用下降。（４）当温度在光合最适温度以上时，太阳辐射的增加使叶温增加，引起光合“午睡”的加剧和气孔导度的降低。（５）ｃｉ／ｃｓ在中午的降低表明气孔的关闭是光合作用“午睡”

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.