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在野外自然环境条件下对水曲柳叶片的光合效率（PE）及其相关的环境因子的测定结果表明：水曲柳的光合效率随叶片生长发育而升高．旺盛生长的叶片光合效率低于成年叶和老叶；生长末期老叶的光合效率高达5．89％。在影响水曲柳光合效率的环境因子中．PE随光合有效辐射（Q）的增大而呈现幂函数式下降：PE与水汽压亏缺（VPD）成负相关．而与CO2浓度（包括周围空气中的CO2浓度（Ca）和细胞间隙的CO2浓度（Ci））成正相关；凡的最适叶面温度为20～32℃。此外．还观测到水曲柳叶片的光合效率日进程在晴天时有明显的“午降”现象．光抑制可能是其重要原因之一。
The photosynthetic efficiency (PE) and its related environmental factors in Manchurian ash leaves under natural conditions in field showed that the photosynthetic efficiency of Manchurian ash rose with leaf growth and development. The photosynthetic efficiency of vigorously growing leaves was lower than that of adult leaves and old leaves. The photosynthetic efficiency of old leaves at the end of growth was as high as 5.89%. Among the environmental factors affecting the photosynthetic efficiency of Fraxinus mandshurica. PE decreased exponentially with increasing photosynthetically active radiation (Q): PE was negatively correlated with vapor pressure deficit (VPD). But positively correlated with the CO2 concentration (including the CO2 concentration in the surrounding air (Ca) and the CO2 concentration in the intercellular space (Ci)); where the optimum leaf surface temperature is 20 ~ 32 ℃. In addition. It was also observed that the daily photosynthetic efficiency of manchurian ash leaves had a clear “noon” phenomenon in sunny days. Photoinhibition may be one of the important reasons.