青藏高原多年冻土区高寒草地生态系统对气候变暖的响应

Alpine meadow and swamp meadow in the permafrost region of Qinghai-Tibetan Plateau is very sensitive to climate warming.But the response pattern of biodiversity to climate warming in the alpine grassland of perfrost region is unclear. Moreover, carbon balance was co-determined by grass productivity and soil carbon pool. However, we donot know which changes have the more contributioin rate to carbon balance of alpine grassland ecosystem. The aim of this study was to assess the contribution rate of grass productivity and soil carbon dynamics of two most widespread ecosystem types, swamp meadow and alpine meadow for alpine grassland carbon balance under climate warming, in the Qinghai-Tibetan Plateau, China. The temperatures of air and active soil were passively increased using open-top chambers (OTCs) in alpine meadow and swamp meadow. Community structure and composition,total biomass，soil respiration rate, micrbial C and organic carbon centents were measured in both warming and control plots.and then the relationship between the grass productivity and soil carbon loss were quantitatively analyzed to understand their contribution rate to ecosystem carbon balance. The present study will be helpful to predict the possible effects of future climate change on regional biodiversity. Moreover, the obtained results will also provide the theoretical base for assessing the source-sink relationship in the terrestrial ecosystem under future climate change.

青藏高原多年冻土区广泛分布的高寒草地对气候变暖十分敏感，但是多年冻土区高寒草地生物多样性对气候变暖的响应模式尚不清楚；植被生产力和土壤碳库变化共同决定着高寒草地生态系统的碳平衡，但不清楚哪一种变化对高寒草地生态系统的碳平衡贡献更大？本项目拟通过野外原位设置开顶式增温小室(OTCs)模拟气候变暖，研究青藏高原多年冻土区高寒草地群落组成、结构与群落生物量、土壤碳动态对气候变暖的响应模式，揭示气候变暖对典型高寒草地生物多样性的影响程度；阐明植被生产力和土壤碳排放的变化过程，定量分析二者对高寒草地生态系统碳平衡的贡献率。研究结果有利于正确预测未来气候变化对区域生物多样性的可能影响，并为准确评估青藏高原对我国整个陆地生态系统的源汇贡献、研究碳库对气候变化的响应研究提供理论基础。

本项目选择青藏高原典型多年冻土区两种植被类型（高寒草甸和高寒沼泽）为研究对象，通过野外原位设置开顶式增温小室(OTCs)模拟气候变暖，对比分析自然状态和模拟增温情景下，植被群落物种组成、结构、生产力，以及土壤碳库变化。阐明了青藏高原多年冻土区高寒草地植物群落多样性随着温度升高而丧失，植被净地上初级生产力增加的趋势；揭示了增温促进生态系统呼吸通量的增加，且非生长季节对增温的响应剧烈于生长季节；明晰了未来增温情景下，植被生产力增加对青藏高原多年冻土区高寒草地生态系统碳平衡的贡献大于系统呼吸通量，即增温后高寒草地生态系统是碳汇。从区域尺度的样地研究结果系统地阐明了降雨量，而不是温度，是影响青藏高原高寒草地地上净初级生产力的主要影响因子；明确了多年冻土的存在影响着未来增温情景下高寒草地生态系统生产力的变化趋势，建议预估气候变化对青藏高原高寒草地生产力影响的模型构建时需考虑多年冻土区存在的影响。