中文摘要：

林线作为高山系统中郁闭林与无林高山植被带间特殊的生态过渡带,对全球气候变化极为敏感.柴达木盆地林线附近的祁连圆柏作为青藏高原东北部高山生态系统中海拔分布最高的单一优势树种,是研究林线植物响应气候变化的理想材料.为明确祁连圆柏重要叶片功能性状对林线附近环境变化的响应模式,分别测定了东、西两个坡向上林线附近（郁闭林、林线和树线）祁连圆柏的叶片干物质含量（LDMC）、单位面积的叶片重量（LMA）、叶片碳稳定同位素（δ^13C）、叶片单位重量的碳氮含量（Cmass,Nmass）、碳氮比（C/N）、叶片自由水含量（FW）和叶片自由水与束缚水比（FW/BW）.结果显示：LMA、δ^13C和Cmass在林线附近无显著变化,但林线和树线的Nmass、FW及FW/BW显著高于郁闭林,而LDMC和C/N则相反;在不同坡向上,西坡LMA显著高于东坡.此外,FW与LDMC、Nmass显著正相关,而FW与FW/BW、LMA与Cmass以及Nmass与C/N显著负相关.以上结果表明,祁连圆柏作为我国西北高山生态系统中耐旱、耐寒的树种在林线附近并未受到明显的水分胁迫,其可能主要通过提高叶片自由水含量、光合能力、含氮渗透调节物含量等策略来适应林线附近的恶劣生境,以保证自身的正常生长发育.

英文摘要：

As the special ecotone from the closed forest line to the tree limit in alpine zone,timberline is highly vulnerable to climate change,and the trees near the timberline are very sensitive to environmental change.Sabina przewalskii is the dominant tree species in alpine ecosystems in the northeast Tibetan Plateau,mainly distributed at dry south-facing and infertile slopes. To test the response patterns of the leaf functional traits in Sabina przewalskii along the environmental gradient near the alpine timberline, the following items were measured： leaf dry matter content（ LDMC）,leaf mass per unit area（ LMA）,leaf stable carbon isotope composition（ δ^13C）,leaf carbon content per unit mass（ Cmass）,leaf nitrogen content per unit mass（ Nmass）,leaf carbon-nitrogen ratio（ C / N）,leaf free water content（ FW） and the ratio of leaf free water content and leaf bound water content（ FW / BW） in Sabina przewalskii on the west-facing and east-facing slopes near timberline of the Qaidam Basin in the northeast Tibetan Plateau. It is found that Nmass,FW and FW /BW of Sabina przewalskii located in the sites of treeline and tree species line were higher than that in the sites of closed forest,while that of LDMC and C / N showed the opposite patterns,even LMA,δ^13C and Cmasshad no remarkable changes in near timberline of both west-facing and east-facing slopes. Meanwhile,LMA only changed significantly near timberline in west-facing slope. In addition,FW was positively related with LDMC and Nmass,and negatively related with FW / BW. Negative relationships between LMA and Cmass,Nmassand C / N were also found. Overall,these results indicated that Sabina przewalskii as a drought and cold tolerant native tree species in the alpine ecosystem mainly accommodates the harsh environment by the way of higher leaf free water content,photosynthetic capacity and some nitrogenous compounds.