随着人类活动强度增加，通过大气干湿沉降输入到陆地生态系统中的含氮化合物日益增多。氮沉降对生态系统的结构和功能可产生重要影响，例如造成生物多样性丧失和生态系统稳定性下降等。申请者于2008年在内蒙古典型草原生态系统建立了一个长期模拟氮沉降研究样地，本项目将以该研究样地为依托，系统研究氮沉降对草地生态系统植物、动物（重点是线虫）、微生物多样性和功能过程的影响及调控机制；同时，研究氮沉降胁迫解除后生态系统的恢复过程。重点研究地上和地下生态过程的联结以及生态系统各个组分对氮沉降的响应，阐明这些组分及其相互作用对氮沉降响应的阈值、饱和值和弹性。该项目对于研究人类干扰对陆地生态系统的影响机理、生态系统生物多样性的功能与维持机制、生物多样性保护和草地生态系统的管理将具有重要的理论和实践意义。

Nitrogen input through dry and wet deposition into terrestrial ecosystems is increasing rapidly with ever-increasing anthropogenic activities. The increasing N input will have profound impact on the structure and function of natural ecosystems. For instance, it will result in loss of biodiversity and destablize the ecosystem functioning. The applicant established a long-term N deposition experiment in the typical grassland of Inner Mongolia. Based on this platform, we will explore the fundamental mechanisms of the responsiveness of grassland ecosystems to N deposition in different components of the ecosystem, including plants, soil macrofauna and function genes of the soil microbial organisms. This project aims at revealing the multifaceted effects of N deposition on ecosystem structure and function. More importantly, we will focus on the linkages between below- and above-ground processes as affected by the N deposition. We will also evaluate the ecosystem recovery processes after the cessation of N addition. Specifically, the response thresholds, saturation points and the resilience of grassland ecosystem to N deposition will be elucidated. Overall, our study will provide important information on the response of terrestrial ecosystems to N deposition, on the maintenance and conservation of biodiversity, as well as on the adaptive management of one of the largest contiguous biomes on this planet.