Key Laboratory of Adaptation and Evolution of Plateau Biota, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining 810008 China.
Ecology. 2012 Nov;93(11):2365-76. doi: 10.1890/11-1408.1.
Uncertainty about the effects of warming and grazing on soil nitrogen (N) availability, species composition, and aboveground net primary production (ANPP) limits our ability to predict how global carbon sequestration will vary under future warming with grazing in alpine regions. Through a controlled asymmetrical warming (1.2/1.7 degrees C during daytime/nighttime) with a grazing experiment from 2006 to 2010 in an alpine meadow, we found that warming alone and moderate grazing did not significantly affect soil net N mineralization. Although plant species richness significantly decreased by 10% due to warming after 2008, we caution that this may be due to the transient occurrence or disappearance of some rare plant species in all treatments. Warming significantly increased graminoid cover, except in 2009, and legume cover after 2008, but reduced non-legume forb cover in the community. Grazing significantly decreased cover of graminoids and legumes before 2009 but increased forb cover in 2010. Warming significantly increased ANPP regardless of grazing, whereas grazing reduced the response of ANPP to warming. N addition did not affect ANPP in both warming and grazing treatments. Our findings suggest that soil N availability does not determine ANPP under simulated warming and that heavy grazing rather than warming causes degradation of the alpine meadows.
变暖与放牧对土壤氮（N）有效性、物种组成和地上净初级生产力（ANPP）的影响存在不确定性，这限制了我们预测在未来变暖与放牧情景下，高山地区的全球碳固存将如何变化的能力。通过 2006 年至 2010 年在高山草甸上进行的控制非对称变暖（白天/夜间 1.2/1.7°C）与放牧实验，我们发现，单独的变暖以及适度放牧并没有显著影响土壤净氮矿化。尽管由于 2008 年后变暖，植物物种丰富度显著下降了 10%，但我们提醒注意，这可能是由于所有处理中一些稀有植物物种的短暂出现或消失。变暖显著增加了禾本科植物的盖度，除了 2009 年，以及 2008 年后豆科植物的盖度，但减少了群落中非豆科植物的盖度。放牧在 2009 年之前显著降低了禾本科植物和豆科植物的盖度，但在 2010 年增加了草本植物的盖度。无论是否放牧，变暖都显著增加了 ANPP，而放牧则降低了 ANPP 对变暖的响应。N 添加在变暖和放牧处理中均未影响 ANPP。我们的研究结果表明，在模拟变暖下，土壤 N 有效性并不能决定 ANPP，而重度放牧而不是变暖导致高山草甸退化。
