中文摘要：

以长白山针阔叶混交林优势树种蒙古栎为实验对象，研究了生长季（6-9月）减少降水30％（人工截留穿透雨30％）对蒙古栎叶光饱和光合速率、气孔导度、蒸腾速率和水分利用效率的影响。结果表明：在叶片生长初期（6月），减少降水使土壤含水量降低26．4％，减少降水条件下与对照条件下叶片的光饱和光合速率无明显差异，但明显下降的蒸腾作用使蒙古栎叶片的水分利用效率增加了40．3％；7-9月，较高的自然降水量导致不同降水处理条件下的土壤含水量无显著差异，因而叶片的光饱和光合速率、气孔导度、蒸腾速率和水分利用效率亦无明显影响；由此可见，无论是低雨量时期（6月）还是高雨量时期（7-9月），长白山地区降水减少30％不会影响成熟蒙古栎的光合能力；8月的高光合速率可能说明，较高的土壤高含水量并未形成对蒙古栎根系吸水的限制。研究结果认为，成熟蒙古栎能适应较广的土壤含水量范围，在未来气候变暖、降水量变化条件下仍能保持较强的生长和适应能力。

英文摘要：

Quercus mongolica is the dominant tree species in the coniferous and broadleaved mixed forests in Changbai Mountains. In this paper, an investigation was made on the effects of decreased rainfall （artificially intercepting 30% of rainfall） on the leaf light-saturated photosynthetic rate, stomatal conductance, transpiration rate, and water use efficiency of Q. mongolica during its growth season （from June to September）. In early growth stage （June） when the rainfall was low, there was no significant difference in light-saturated photosynthetic rate between decreased rainfall and the control, though the decreased rainfall decreased soil moisture content by 26.4%. However, the decreased rainfall increased the water use efficiency of Q. mongolica by d0. 3%, due to the decrease of transpiration rate. In July- September when the rainfall was abundant, the decreased rainfall had no significant effects on the light-saturated photosynthetic rate, stomatal conductance, transpiration rate, and water use efficiency, because no difference was observed in the soil moisture content between decreased rainfall and the control. Thereby, whether in low rainfall period （June） or in abundant rainfall period （July-September）, a 30% decrease of rainfall in Changbai Mountains could less affect the photosynthetic capacity of mature Q. mongolica during its whole growth season. The high photosynthetic rate in Auzust suggested that the relatively high soil moisture content did not limit the water absorption by Q. mongolica. This study showed that Q. mongolica had a wide adaptation to soil moisture content, and could maintain its growth potential in the future climate warming and precipitation fluctuation.