积雪对青藏高原草地生态系统碳源汇功能的影响

The state of the snowpack is very sensitive to climate change. The snow on the Tibetan Plateau, being an important snow-covered region in Eurasia, changed significantly due to dramatic climatic change in recent decades. Because of harsh natural conditions on the Tibetan Plateau, a small fluctuation in its environmental factors can possibly trigger significant changes in grassland carbon sequestration. However, the current research surrounding impacts of snow on the carbon cycle of the Tibetan Plateau is still lacking and the contribution of snow change to the current grassland carbon balance remains unclear. This project will bring together in-situ snow fence experiments, multiple remote sensing data sources and reanalysis products to analyze the responses of the grassland carbon cycle to snow characteristics (such as snow phenology, snow water equivalent and snow depth) and study the mechanisms of these responses on the Tibetan Plateau. In addition, utilizing the support of local observations and collected soil carbon sampling, the project will improve the diagnostic and prognostic modeling ability through optimizing the key model parameters using the model-data fusion technique. Based on this, the project will then quantify the impacts of changes in snow on the carbon balance of Tibetan grasslands over the last 50 years and in the next 100 years. Implementation of this project will enhance our mechanistic understanding of responses of the carbon cycle to snow and provide scientific supports for sustainable management of grasslands on the Tibetan Plateau under global change.

积雪对气候变化十分敏感，青藏高原作为亚欧大陆重要的积雪区域，近几十年里高原气候的变化导致了积雪的显著改变。高原严酷的自然条件使得环境因子的微小波动都可能引发生态系统碳源汇效应的剧烈变化，而目前关于积雪对高原草地生态系统碳循环的影响研究尚匮乏，还无法回答积雪在影响高原草地生态系统碳源汇功能中所起的作用。本项目拟利用野外雪栅栏试验、多源遥感数据以及多种再分析产品揭示青藏高原草地生态系统碳循环过程对积雪（积雪物候、雪水当量和雪深）的响应及其机制；利用青藏高原地面观测资料和土壤碳采样点数据优化具有多层积雪模块的陆地碳循环模式的关键过程参数，实现模型和数据的融合，提高模型的模拟精度；基于此，估算过去50年和未来百尺度年积雪对青藏高原草地生态系统碳源汇功能的影响。本项目的实施有利于提高对草地碳循环过程对积雪的响应机理的认识，为全球变化下青藏高原草地生态系统可持续管理提供科学依据。

积雪是地球系统的重要组分，它敏感地响应于气候变化，也深刻地改变高寒生态系统碳循环。项目围绕“积雪对青藏高原草地生态系统碳源汇功能的影响”这一核心科学问题，充分利用野外调查、控制实验、多源遥感数据和陆地生态系统碳循环模型等多种手段，取得了以下成果：(1)阐明了春季积雪变化特征及其驱动因子,发现过去20年青藏高原积雪持续减少，且这种减少在未来将持续加剧；(2)厘清了青藏高原植被生长对积雪变化的响应及其生态学机制，阐明了模型中考虑积雪变化将显著提升植被变化的解释率；发现了春季积雪可以通过季风环流调整调控亚洲植被生长；(3)通过整合清查法、生态系统模型和大气反演模型三种方法，估算出2000–2015年高原陆地碳汇为33.12–37.84百万吨碳/年，发现高原积雪持续减少不利于碳汇，但尚未抵消气候暖湿化和CO2对植被生长的促进作用，未来高原植被碳汇仍将持续增加。发表SCI论文10篇，含1篇Nature Climate Change，1篇Nature Geoscience，2篇Nature Communications。