热带和亚热带森林被认为普遍受磷限制，升高的氮沉降会加剧其磷限制状态。因此，磷添加可以作为缓解高氮沉降负面效应的一种手段。但是我们还不清楚磷及氮磷交互作用如何影响该区森林的植物多样性。在前期研究的基础上，本项目利用我国最早建立的长期森林氮、磷添加试验样地，通过野外调查结合植物生理和土壤性质测定来研究南亚热带三个代表性森林（马尾松林、混交林和常绿阔叶林）林下植物多样性对磷及氮磷交互作用的响应，旨在：1）验证“低磷环境”是否对亚热带森林植物多样性维持起作用。2）阐明不同演替阶段和氮状态的森林植物多样性对磷及氮磷交互作用的响应格局；3）揭示磷及氮磷交互作用对南亚热带森林植物多样性影响的机理。本项目实施，一方面可以丰富热带亚热带区域磷循环的知识体系，并为多样性研究做出原创性贡献；另一方面，可以评估未来高氮沉降下磷添加对南亚热带森林植物多样性的影响，为我国制定氮氧化物的减排和森林管理政策提供科学依据。

Elevated nitrogen (N) deposition in tropical or subtropical are considered to exacerbate phosphorus (P) deficiency in forests, which negatively affect the biogeochemistry processes. Accordingly, additional P inputs are regarded as a plausible method to mitigate N-induced negative effects. However, it is not clear how N and P interactively affect plant diversity in tropical and subtropical forests. In this project, combined with our previous results, we will examine responses of understory plant diversity to long-term N and P additions in three typical subtropical forest ecosystems (pine forest, pine-broadleaf mixed forest and monsoon evergreen broadleaf forest) of southern China, with an emphasis on explaining the mechanism in altering plant diversity. Results from this study will theoretically provide new understanding on responses of plant diversity to soil P availability in subtropical forests. The implementation of this project could be better to evaluate effects of P addition on N-deposition-induced disturbance in regional forests, and to provide useful information to sustainable forest management.