中文摘要：

川西亚高山针叶林是青藏高原东部高寒林区的重要组成部分，也是研究全球变化对森林生态系统影响的重要森林类型。开展亚高山针叶林不同树种对气候变暖响应差异的研究，可为预测未来气候变暖背景下亚高山针叶林植被组成和森林动态提供科学依据。我们以川西亚高山针叶林两种主要树种——红桦（Betula albo-sinensis）和岷江冷杉（Abies faxoniana）为研究材料，采用开顶式增温法（Open-top chamber,OTC）模拟气候变暖，研究了增温对全光条件和林下低光环境中（约为全光的10％）生长的红桦和岷江冷杉幼苗生长和生理的影响。在人工林环境下，OTC使增温框内平均气温和地表温度分别升高了0．51和0．33℃；而在林外空地处，OTC使二者分别升高了0．69和0．41℃。研究结果显示，增温总体上促进了两种幼苗的生长和生理过程，并促使幼苗将更多的生物量投入到其同化部位——叶，使幼苗的根冠比（R/S）显著降低。增温通过增加叶片的光合色素含量和表观量子效率等光合参数，促进了幼苗的光合过程和生长。然而，增温对两种幼苗生长和生理的影响效果与植物种类及其所处的光环境有关。增温仅在林外全光条件下显著影响红桦幼苗的生长和生理过程。岷江冷杉幼苗对增温的响应与红桦相反，即增温仅在林下低光环境下对岷江冷杉幼苗的生长和生理过程有明显促进作用。这种响应差异可能赋予这两种植物在未来气候变暖背景下面对外界环境变化时具有不同的适应能力和竞争优势，从而对亚高山针叶林生态系统物种组成和森林动态产生潜在影响。

英文摘要：

Aims The subalpine coniferous forests in eastern Qinghai-Tibet Plateau provide a natural laboratory for studying effects of climate warming on terrestrial ecosystems. Research on differences between tree species in their responses to experimental warming can provide insights into their regeneration behavior and community composition under a future warmer climate. Methods We used open-top chamber （OTC） to determine short-term effects of two levels of air temperature （ambient and warmed） and light （full light and ca. 10% of full light regimes） on the early growth and physiology of Betula albo-sinensis and Abiesfaxoniana seedlings. Important findings The OTC manipulation increased mean air temperature and soil surface temperature by 0.51 ℃ and 0.33 ℃, respectively, under the 60-year plantation and 0.69 ℃ and 0.41 ℃, respectively, under the forest opening. Warming generally increased the growth, biomass accumulation and advanced physiological processes for seedlings of both species. In response to warming, both species allocated relatively more biomass to foliage and had significantly decreased root/shoot ratios （R/S）, which might provide tree species an adaptive advantage when other environmental factors are not limiting. Warming may enhance photosynthesis in the two seedlings by increasing efficiency of PS II in terms of increase in Fv/Fm, photosynthetic pigment concentrations and apparent quantum yield （Ф）. However, the effects of warming on seedling growth and physiological performance varied by light conditions and species. For B. albo-sinensis seedlings, the effects of warming were pronounced only under full-light conditions, while the growth and physiological responses of A. faxoniana seedlings to warming were found only under low-light conditions. Competitive and adaptive relationships between the two species may be altered as a result of response differences to warming manipulation. The short-term beneficial impact of warming on the early growth and development of the two spe