干旱环境下高温对胡杨光合作用的影响

Effect of High Temperature on Photosynthesis in Populus euphratica under Drought Condition

在塔里木河下游3个地下水埋深(4.64 m,6.15 m,7.02 m)环境下,利用LI-6400便携式光合作用测定仪测定了胡杨叶片在适宜温度(27℃)和高温(39℃)下的净光合速率(Pn)、气孔导度(gs)、蒸腾速率(E)及胞间CO2浓度(Ci),比较了不同地下水埋深下胡杨光合作用对高温的响应。结果表明:在3个地下水埋深下高温都使得光合速率和气孔导度明显减少,并且在地下水埋深(7.02 m)较深处,高温使得光合速率和气孔导度的下降幅度也最大,这都说明干旱胁迫加强了高温对胡杨光合作用的负面效应。然而,在同一地下水埋深下,由于高温的影响,胡杨叶片的胞间CO2浓度并未随着净光合速率和气孔导度的下降而减少,其原因很可能是气孔发生了不均匀关闭。而叶片的蒸腾速率和饱和水汽压由于高温作用的影响都明显增加,并且在地下水埋深7.02 m处,高温引起蒸腾速率的增加幅度是最小的,这表明了气孔对干旱高温胁迫下胡杨的光合作用具有一定调节作用。

Under moderate temperature of 27 ℃ and high temperature of 39 ℃, the net photosynthetic rate, stomatal conductance, transpiration rate, intercellular CO2 concentration of Populus euphratica grown at three different groundwater depths （4.64 m, 6.15 m, 7.02 m） in lower reaches of the Tarim River were measured by the Li-6400 portable gas exchange system. The responses of photosynthesis in P. euphratica grown at three different groundwater depths to high temperature were compared. The results showed that the net photosynthetic rate and stomatal conductance in P. euphratica at each groundwater depth decreased significantly due to high temperature. Moreover, the decreasing extents of net photosynthetic rate and stomatal conductance of trees with 7.02 m groundwater depth were higher than those of trees with 4.64 m or 6.15 m. All of these indicated that drought stress might exacerbate the adverse effect of high temperature on photosynthesis in P. euphratica. Under the same groundwater depth, however, the intercellular CO2 concentration did not decrease with decreasing net photosynthetic rate and stomatal conductance, which might be induced by non-uniform stomatal closure. Due to high temperature of 39℃, the transpiration rate and vapor pressure deficit at leaf surface increased markedly, and the increasing extent of transpiration rate of trees with 7.02 m groundwater depth was lower than those of trees with 4.64 m or 6.15 m, which indicated that stoma can adjust the photosynthesis in P. euphratica under drought and high temperature stress.