大气氮沉降增加是全球变化的一个重要方面，其可能导致或加剧森林生态系统磷限制，然而目前该领域研究仍存在许多认识上的不足。作为陆地生态系统的重要组成部分，喀斯特森林生态系统具有“氮饱和”及其它特殊的属性，导致氮沉降背景下喀斯特森林磷限制的变化可能具有特殊的模式和机制。然而目前关于喀斯特森林磷限制对氮沉降响应的研究非常缺乏。本项目首先利用在西南喀斯特森林建立的模拟氮沉降增加试验平台，采用多种磷限制指标（叶片氮磷比、根系磷酸酶、酶化学计量学、底物添加法）研究喀斯特森林植物与微生物磷限制在氮沉降背景下的变化；其次，设置盆栽实验研究氮沉降对植物和微生物磷限制的影响在不同树种类型下的差异。最后，通过监测“植物-凋落物-土壤”各主要磷库对氮添加的响应，揭示氮添加对喀斯特森林磷限制的影响机制。本项目在理论上有助于理解和预测氮沉降背景下喀斯特森林磷循环的变化规律，在实践上可为相关环境保护政策制定提供科技支撑。

Elevated nitrogen (N) deposition is an important part of global change. It has been suggested that increased N deposition may cause or aggravate phosphorus (P) limitation in forest ecosystems. However, there remains considerable uncertainty in this filed. As an important terrestrial ecosystem type, karst forest has unique soil characteristics, resulting in that there may have different responses and mechanisms for karst forest ecosystems in response to increased N deposition. Nevertheless, to date, no study has been conducted to address this issue. To fill this gap, firstly, we will use a simulated N deposition experiment in a karst forest in southwest China, to study how ecosystem P limitation changes after N addition. Four methods, i.e. foliar N: P, ecoenzymatic stoichiometry, root-associated phosphatase, and substrate addition, were used to reflect the changes in P limitation to plant or microbes. Secondly, a pot experiment was conducted to study how tree species influence the effects of N addition on ecosystem P limitation. Thirdly, the changes of the main P pools in the karst ecosystem were measured to explore the mechanisms behind the changed P limitation under N addition. This project will be useful to understand the response of ecosystem P cycle to N deposition in karst forests, and will provide scientific and technological support for policy making on environmental protection.