模拟增温和中度放牧对青藏高原东部高寒草甸生态系统净碳交换及组分的影响

Impacts of experimental warming and moderate grazing on ecosystem carbon exchange and its compositions in an alpine meadow on the eastern Qinghai-Tibetan Plateau

青藏高原高寒生态系统碳循环对气候变暖和放牧等的响应依然存在很大不确定性.采用开顶式温室模拟增温,采用刈割和牲畜粪便归还相结合的方法模拟中度放牧,研究气候变暖和中等强度放牧对青藏高原东部高寒草甸生态系统碳交换、生态系统光合、生态系统呼吸与土壤呼吸的影响.结果显示：模拟气候变暖和中度放牧显著改变青藏高原东部高寒草甸生态系统净碳交换及其组分,并且生态系统碳循环的响应随时间呈现不同的变化.增温显著提高净生态系统碳交换和生态系统光合,增加生态系统净碳固定;中度放牧降低生态系统呼吸和土壤呼吸,而对生态系统净碳交换、生态系统光合的影响存在明显季节动态变化,即在处理初期（8月上旬）明显降低,而后逐渐上升,在生长季后期、末期（9月中下旬-10月份）显著高于对照;增温和中度放牧未表现明显的交互作用,增温＋放牧处理增加了季节性平均净生态系统碳交换和生态系统光合,但没有显著影响季节平均生态系统呼吸.增温和中度放牧的交互作用对碳交换的影响存在时间尺度上的变化.本研究表明,在未来气候变暖和中等强度放牧的背景下,青藏高原东部高寒草甸碳汇功能有可能增强.

How net ecosystem carbon exchange and its composition respond to warming and grazing in the alpine meadow ecosystem is considerably uncertain. We used open top chambers（OTCs） and clipping plus dung application to simulate the effects of warming and moderate grazing on ecosystem carbon exchange, including net ecosystem exchange, ecosystem respiration, gross ecosystem photosynthesis, and soil respiration. Our findings suggested that warming and moderate grazing significantly affected net ecosystem carbon exchange and its compositions, which varied with time. Warming significantly increased the net ecosystem carbon exchange and gross ecosystem photosynthesis, as well as the net carbon fixation. Moderate grazing decreased the ecosystem respiration and soil respiration. The effects of moderate grazing on net ecosystem exchange and gross ecosystem photosynthesis varied with seasonal dynamics： grazing significantly reduced net ecosystem exchange and gross ecosystem photosynthesis in early August; as the growing season continued, they increased in the late growing season and became higher than those in the control. No significant interaction was noted between warming and grazing. Warming with grazing increased the seasonal average net ecosystem exchange and seasonal average gross ecosystem photosynthesis, but no significant impact on seasonal average ecosystem respiration was noted. Interaction of carbon exchange with warming and moderate grazing showed a time-dependent change. Our findings suggest that carbon sequestration might enhance under the future climate warming and moderate grazing in the alpine meadow.