极端气候对中国陆地生态系统碳源汇功能的影响

An increase in the frequency and intensity of climate extreme events is an important feature of global change and becomes one of the most serious problems threating human beings. Climate extreme events can affect the carbon cycle of terrestrial ecosystems in a different way than a gradual change in climate. However, the current research on the impact of climate extremes on the carbon cycle is still lacking. It remains unclear whether the current terrestrial carbon sinks will be weakened or even reversed to be carbon sources in a future climate with an increased frequency and density of climate extreme events. This project will bring together controlled field experiments and observations (tree rings, crop yield, eddy covariance flux tower observations, remote sensing and meteorological data) in China’s major ecosystems to analyze the responses of the carbon cycle to climate extreme events (such as drought and extreme rainfall, heat waves and extreme low temperature) and reveal the mechanisms underlying the recovery of the disturbed carbon cycle due to these events. In addition, utilizing the existing process-based carbon cycle model and the support of observations and field experiments, the project will improve the diagnostic and prognostic modeling ability through optimizing the sensitive model parameters based on the model-data fusion technique. Based on this, the project will then quantify the impact of climate extremes on China’s terrestrial carbon balance over the last 50 years and evaluate the vulnerability of China’s carbon cycle to climate extremes. Implementation of this project will enhance our mechanistic understanding of responses of the carbon cycle to climate extremes and provide scientific supports for sustainable management of ecosystems under global change.

极端气候事件发生频率和强度的增加是全球变化的重要特征之一，也是人类面临的最严峻挑战之一。生态系统碳循环对极端气候的响应和对长期气候逐渐变化的响应截然不同，目前关于极端气候对生态系统碳循环的影响研究尚匮乏，还无法回答陆地生态系统碳汇功能在未来极端气候事件增加下是否削弱甚至被转为碳源。本项目拟整合野外控制实验和观测数据(树木年轮、作物产量、碳通量观测、遥感和气象资料)，阐明中国主要陆地生态系统碳循环过程对极端气候(如干旱和极端降雨、热浪和异常低温)响应的敏感性和恢复机制；优化碳循环模型的关键过程参数，实现观测数据和模型的融合，提高模型的模拟精度；基于此，估算过去50年极端气候对中国生态系统碳源汇功能的影响，评估中国生态系统在未来极端气候变化下的脆弱性。本项目的实施有利于提高对碳循环过程对极端气候的响应机理的认识，为全球变化下生态系统可持续管理提供科学依据。

极端气候事件发生频率和强度的增加是全球变化的重要特征之一，也是人类面临的最严峻挑战之一。本项目围绕“极端气候对陆地生态系统碳循环影响”这一重大研究热点开展了系列研究，取得了以下成果：（1）利用中国陆地生态系统碳循环关键过程的观测数据，结合模型数据融合技术优化和改良了基于过程的生态系统碳循环模型ORCHIDEE，提高了ORCHIDEE模型对中国陆地生态系统碳循环的模拟精度；（2）通过集成分析卫星遥感观测数据集、基于碳通量观测得到的生产力和碳汇数据集、大气反演模型和生态系统过程模型模拟得到的生态系统碳源汇估算数据集，系统评估了中国陆地植被生产力和生态系统碳源汇功能对极端干旱的响应特征及其脆弱性；（3）揭示了树木应对干旱胁迫的抵抗力和恢复力的变化规律，发现1950年代以来，裸子植物的树木生长对干旱的抵抗力明显降低，但在干旱后的恢复速率显著增加，挑战了早期发表在Nature上的“过去100年全球植被对干旱的恢复速率下降”的模型模拟结论；（4）系统梳理和综述了极端气候事件的陆地生态系统碳循环的研究进展及其未来重点研究方向。在项目的支持下，在Nature Ecology & Evolution、Nature Communications等SCI杂志上发表第一资助论文24篇。