土壤有机碳库是维持陆地生态系统功能稳定、缓解全球气候变化及其反馈过程的调节者。根际激发效应（rhizosphere priming effect, RPE），由根的活动导致土壤有机碳分解速率的变化，是影响土壤有机碳动态变化重要的驱动力。室内实验表明，RPE最高可使土壤有机碳分解速率加快近4倍，其作用与温度、水分相当，且树木幼苗RPE显著大于作物和草本。然而，目前仍不清楚野外条件下成熟大树RPE的变幅多大？与主控因子的关系如何？这严重限制了我们对森林生态系统根际激发效应的深入认识。基于上述科学问题，本项目采用天然(13)C示踪方法，选取亚热带人工林典型树种杉木和马尾松的成熟大树为研究对象，拟探讨成熟大树RPE的方向与强度，并解析其与根系分泌有机碳速率、胞外酶活性等因子间的关系。结果将为土壤有机碳过程模型的优化提供核心参数，为森林生态系统土壤有机碳的科学管理提供新思路。

Soil organic carbon (SOC) pool determines the functioning of terrestrial ecosystems and regulates the release and sequestration of major greenhouse gases at the global scale. Plant roots can strongly accelerate or suppress SOC mineralization - a phenomenon known as the rhizosphere priming effect (RPE). The RPE has emerged as a chief driving force for changing global SOC pool in response to global environmental change. Laboratory studies have indicated that the RPE can enhance the rate of SOC decomposition up to four-fold, which is as significant as the effects of soil temperature and moisture. Furthermore, it has been reported that the magnitude of the RPE for tree seedlings grown under greenhouse conditions is significantly larger than herbaceous species. However, the magnitude and controls of RPE of mature trees on SOC dynamics in forest ecosystem under realistic field conditions remain largely unknown. In this study, we will quantify the RPE of two mature trees (Cunninghamia lanceolata and Pinus massoniana) under field conditions in a subtropical forest. We will also explore the relationships between RPE and other key variables such as root exudation rates and extracellular enzyme activities by using a (13) C natural abundance method. The results are expected to provide new insights about mechanisms regulating the RPE on SOC decomposition. These mechanisms may improve the performance of the terrestrial ecosystems models. The findings will also inform management of SOC stability in forest ecosystem.