大气氮沉降影响草地植物物种多样性机制研究综述

大气氮沉降对草地生态系统结构和功能的影响已成为全球变化生物学研究重点。大气氮沉降导致草地群落物种多样性降低已成为全球普遍现象，但其生物学机制还不清楚，因此有必要系统梳理大气氮沉降对全球不同草地生态系统的研究结果，以便在氮沉降背景下为我国草地生态系统的研究和管理制定科学决策。系统综述了氮沉降降低草地群落物种多样性的可能机制，主要包括资源竞争排斥、群落更新限制、土壤酸化及其离子毒害、养分失衡、氮素本身的毒害、次生胁迫。氮沉降导致草地物种多样性降低是多种机制综合作用的结果，每种机制在不同时空具有不同的相对贡献。同时，与欧洲酸性土壤草地和美国高草草原相比，我国草地土壤类型和植被属性具有明显差异。因此，应根据我国草地生态系统的特征、不同植物功能利用养分策略，从土壤养分变化、根系养分吸收转运、叶片生理过程等方面的整合研究思路，探讨氮沉降影响我国草地群落物种多样性的生物学机制，为我国草地生态系统的科学管理提供理论依据。

Mechanisms underlying loss of plant biodiversity by atmospheric nitrogen deposition in grasslands

The impacts of atmospheric nitrogen (N) deposition on structure and function of grassland ecosystems have been one of the most important issues in the field of global change biology. A marked reduction in species richness by N deposition has been widely observed across different grassland ecosystems worldwide, but the underlying mechanisms remain controversial and elusive. Therefore, systematic analysis of N deposition impacts on grasslands across the globe can provide important information that will contribute to efficient management of grasslands in China under elevated atmospheric N deposition. This review summarized the possible mechanisms by which chronic N enrichment led to a decline in plant species richness in grassland ecosystems. The main mechanisms include competition for resource, re-establishment of the community, metal toxicity due to soil-mediated acidification, direct toxicity of N, nutrient imbalance in soils and secondary stress. Several mechanisms operating at the spatial and temporal levels may collectively underpin the overall N deposition-induced decline in species richness of grassland ecosystems. Different mechanisms may account for the decline in species richness for a given grassland ecosystem depending on the duration and rates of atmospheric N deposition. Moreover, both soil and vegetation traits for grasslands in China are unique and differ markedly from those of European and American grasslands. Accordingly, we propose that future studies on species richness of grasslands under N enrichments should integrate species, functional groups and community, and link the soil processes to root-mediated acquisition of nutrients and leaf physiological processes.