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亚热带红壤丘陵地区水稻叶片净光合速率与蒸腾速率在夏季晴天中午有降低现象 ,其日变化曲线呈双峰型。PAR和温度的日变化是形成光合速率日变化的主要环境因子。较高的温度会导致蒸腾强度降低 ,而水分亏缺引起的气孔导度降低气孔阻力增大则造成光合速率的降低。水稻上部叶片的光补偿点低于下部叶片 ,而光饱和点则是下部叶片低于上部。表观初始光能利用效率第 2片叶为 0 0 4 9～ 0 0 68,第 4片叶为 0 0 4 4～ 0 0 60。光能利用率第 2片叶在 2 6%～ 5 7% ,第 4片叶在 2 0 %～ 5 8%。水稻叶片的最大光合速率早稻和晚稻旗叶、2叶、4叶分别可达到 1 9 5 8μmolCO2 m- 2 、1 7 78μmolCO2 m- 2 、1 4 4 μmolCO2 m- 2s- 1 和 2 6 4 6和 1 7 2 7μmolCO2 m- 2 s- 1 。
The net photosynthetic rate and transpiration rate of rice in subtropical red soil hilly region decreased at noon in summer and the diurnal variation curve showed a bimodal pattern. The daily changes of PAR and temperature are the main environmental factors that form the diurnal variation of photosynthetic rate. Higher temperatures lead to a decrease in transpiration, whereas stomatal conductance decreases and stomatal resistance increases due to water deficit, resulting in a decrease in photosynthetic rate. The light compensation point of rice upper leaves is lower than the lower leaves, while the light saturation point is the lower leaves lower than the upper part. Apparent initial energy use efficiency of the second leaf is 0 0 4 9 ~ 0 0 68, the fourth leaf is 0 0 4 4 ~ 0 0 60. Light energy utilization of the second leaf in 26% ~ 57%, the fourth leaf in 20% ~ 58%. The maximum photosynthetic rate of rice leaves could reach 1 958μmolCO2 m-2, 1778μmolCO2 m-2, 1444μmolCO2 m-2s-1 and 2 6 4 6, respectively 1 7 2 7 μmol CO 2 m-2 s-1.