中文摘要：

采用开项式生长室（Open-top chamber，OTC）模拟增温对植被影响的研究方法，研究了川西亚高山林线交错带糙皮桦（Betula utilis）和岷江冷杉（Abies faxoniana）幼苗物候及生长特性对模拟增温的响应。结果表明，温度升高使岷江冷杉幼苗芽开放时间显著提前（15．2d）；糙皮桦春季芽物候期变化不显著，而落叶时间明显推迟（19．7d），叶寿命延长（22．8d）。与对照（CK）相比，OTC内糙皮桦叶面积和岷江冷杉叶片长度及两者侧枝生长速率都显著加快。模拟增温对两物种基径相对生长速率都表现为正效应，增温对两物种枝叶特性及分布格局表现为不同程度的正效应、负效应或无影响。不同功能型两物种对模拟增温响应方式存在一定程度差异。

英文摘要：

Aims Betula utilis and Abies faxoniana are two typical, important plants in timberline ecotone in subalpine regions of western Sichuan, China. Their responses in phenology, growth and leaf and branch traits to simulated global warming can be studied using the open-top chamber （OTC） method. The main purposes of our experiment are to determine how two species change their phenology, whether shoot growth is enhanced and whether responsive patterns of deciduous and evergreen species are consistent. We reported the second year＇s responses of plants to the OTC treatment. Methods During the 2007 growing season, we observed phenological events （bud break, leaf expansion and defoliation） and measured branch and leaf growth rates, traits and distribution patterns. Micro- climate data between OTCs and control plots （CK） were automatically recorded at 15-minute intervals. We analyzed phenological events, leaf area, branch length, etc. for OTCs and CKs by the Mann-Whitney U-test. Specific leaf area （SLA） was analyzed by the Wilcoxon＇s signed ranks test. Important findings Air temperature at vegetation height （1.2 m） increased by 2.9 ℃ during the growing season, and soil temperature at 5 cm depth did not differ between OTC and CK throughout the growing season. Abiesfaxoniana showed earlier bud break in the OTC, and B. utilis had extended foliage period and individual leaf longevity in the OTC. Elevated temperature resulted in higher leaf and branch growth rates and basal diameter relative growth rates for both species. There were significant differences in SLA and leaf size for B. utilis between the OTC and the CK. Different responses （positive, negative or no effects） were found in branch length, branch number and leaf distribution pattern for both species. Therefore, evergreen conifer and deciduous broad-leaved species differ in their responses to warming.