Response of Community Aboveground Parts Carbon and Nitrogen Content to Experimental Warming in An Alpine Meadow at Three Elevations in the Northern Tibet
气候变暖影响着高寒植物的生长及其碳含量和氮含量。为了探讨藏北高原高寒草甸群落地上部分碳含量和氮含量对气候变暖的响应，2008年7月在西藏当雄县草原站沿着海拔梯度（即4300、4500和4700 m）布设了一个模拟增温实验（增温方法采用开顶式生长室，开口和底部直径分别为1.00和1.45 m，高度为0.40 m）。通过统计分析三海拔高度上的高寒草甸的2011年7月和2012年7月的群落地上部分碳含量、氮含量和碳氮比，探讨了藏北高原高寒草甸群落地上部分碳含量、氮含量和碳氮比对模拟增温的响应。结果表明，模拟增温显著降低了海拔4300 m 2011年7月10.5%（2.43 g?kg~(-1)）的氮含量（F=14.95，P=0.018），显著增加了海拔4300 m 2011年7月12.1%（2.27）的碳氮比（F=22.67，P=0.009）；显著增加了海拔4700 m 2012年7月16.3%（4.44 g?kg~(-1)）的氮含量（F=17.03，P=0.015），显著降低了海拔4700 m 2012年7月8.6%（1.24）的碳氮比（F=12.60，P=0.024）；对三海拔2011年7月（4300 m：F=0.89，P=0.400；4500 m：F=0.28，P=0.627；4700 m：F=2.65，P=0.179）和2012年7月（4300 m：F=0.0004，P=0.985；4500 m：F=4.21，P=0.109；4700 m：F=2.40，P=0.196）的碳含量都无显著影响；对海拔4300 m 2012年7月（氮含量：F=0.13，P=0.736；碳氮比：F=0.10，P=0.764）、4500 m 2011年7月（氮含量：F=0.01，P=0.912；碳氮比：F=0.12，P=0.750）和2012年7月（氮含量：F=0.48，P=0.525；碳氮比：F=0.004，P=0.951）以及4700 m 2011年7月（氮含量：F=0.78，P=0.428；碳氮比：F=0.01，P=0.942）的氮含量和碳氮比都无显著影响。因此，模拟增温对高寒草甸群落地上部分碳含量、氮含量和碳氮比的影响随着海拔高度和观测年份发生变化。
英文摘要:
Climatic warming affects the growth of alpine vegetation and its related carbon and nitrogen content. In order to understand the response of community aboveground parts carbon and nitrogen content to climatic warming in the alpine meadow of the Northern Tibet, a field warming experiment using open top chamber (the top and bottom diameter was 1.00 m and 1.45 m, respectively, and the height was 0.40 m) has been conducted in an alpine meadow located at three elevations: 4300 m, 4500 m and 4700 m, in the Damxung county of the Tibet since July, 2008. The carbon and nitrogen contents and the ratio of carbon to nitrogen of the community aboveground parts in the alpine meadow at the three elevations were measured in July, 2011 and 2012. These carbon and nitrogen contents were analyzed to explore the response of community aboveground parts to experimental warming. Our results showed that experimental warming significantly decreased nitrogen content by 10.5% (2.43 g?kg~(-1), F=14.95, P=0.018) at 4300 m in July, 2011 and decreased the ratio of carbon to nitrogen by 8.6% (1.24, F=12.60, P=0.024) at 4700 m in July, 2012, but experimental warming significantly increased the ratio of carbon to nitrogen by 12.1% (2.27, F=22.67, P=0.009) at 4300 m in July, 2011 and increased the nitrogen content by 16.3% (4.44 g?kg~(-1), F=17.03, P=0.015) at 4700 m in July, 2012. Moreover, experimental warming did not significantly affect carbon content in July, 2011 (4300 m: F=0.89, P=0.400; 4500 m: F=0.28, P=0.627; 4700 m: F=2.65, P=0.179) and July, 2012 (4300 m: F=0.0004, P=0.985; 4500 m: F=4.21, P=0.109; 4700 m: F=2.40, P=0.196), neither did significantly affect the nitrogen content at 4300 m in July, 2012 (F=0.13, P=0.736), at 4500 m in July, 2011 (F=0.01, P=0.912) and July, 2012 (F=0.48, P=0.525), or at 4700 m in July, 2011 (F=0.78, P=0.428). In addition, experimental warming did not significantly affect the ratio of carbon to nitrogen content at 4300 m in July, 2012 (F=0.10, P=0.764), at 4500 m in July, 2011 (F=0.12, P=0.750) and July, 2012 (F=0.004, P=0.951), or at 4700 m in July, 2011 (F=0.01, P=0.942). Therefore, the effects of experimental warming on the carbon content, nitrogen content and the ratio of carbon to nitrogen depended on the elevation and the measuring year in this alpine meadow.