中文摘要：

以分布于长白山北坡海拔1800～2050m的岳桦林为对象,以叶片碳稳定同位素（δ13C）值作为岳桦长期水分利用效率指示值,探讨海拔梯度对岳桦林水分利用效率的影响.结果表明：随海拔升高,岳桦林土壤体积含水量、比叶质量极显著增加,而叶片含水量和土壤温度显著降低;岳桦叶片δ13C值与海拔呈极显著正相关,增幅为1.013‰·（100m）-1,与土壤体积含水量、比叶质量呈显著正相关,与生长季土壤平均温度、叶片含水量呈显著负相关.温度不是长白山林线的唯一限制性因子,海拔梯度上水热条件的差异及其交互作用可能造成岳桦生长期间的生理干旱.

英文摘要：

Taking Betula ermanii forests distributed at the altitudes 1800-2050 m on the northern slope of Changbai Mountains as test objects, and using leaf carbon isotope content （δ13C） as an indicator of B. ermanii water use efficiency （WUE）, this paper studied the effects of altitudinal gradient on the WUE of B. ermanii forests in the area. With the increase of altitude, the soil volumetric water content （VMC） and the leaf mass per area （LMA） of B. ermanii increased significantly, while the leaf water content （LWC） and soil temperature were in adverse. There was a significant positive correlation between leaf δ13C and altitude, with the increment of leaf δ13C being 1.013‰·（100 m）-1, and the leaf δ13C was positively correlated with soil VWC and LMA but negatively correlated with soil temperature and LWC. Temperature was not the sole limiting factor for the distribution of treeline in Changbai Mountains, whereas the physiological drought of B. ermanii during its growing season caused by the different water and heat conditions and their interactions along the altitudinal gradient could be the other limiting factors.