Effects Of Nitrogen Addition On Plant Community Structure Of Alpine Meadow Of Qinghai-Tibetan Plateau

N is the main factor in limiting the primary productivity of most terrestrial ecosystems. But since the 19th century industrial revolution, with the burning of fossil fuels discharged the atmospheric emissions of activated nitrogen compounds increasing rapidly. The excessive emissions of nitrogen not only changed global N cycle model, but also seriously threatened the natural ecosystem productivity, species composition and impacted on the plant community stoichiometry.In this paper, our objective was to investigate the effects of different levels of nitrogen addition on species richness, aboveground productivity and plant community stoichiometry of alpine meadow of the Qinghai-Tibetan Plateau.The results as following: 1) Nitrogen addition changed the soil NO3--N content, reducing vegetation light penetration. Species richness decreased sharply (P< 0.001). Aboveground productivity increased first then decreased. The relationship between aboveground productivity and species richness was negative. 2) Different functional groups, grass biomass increased significantly (P<0.05), while forb and legume biomasses decreased. 3) Nitrogen addition changed the leaf N content significantly (P<0.05). The grass N:P ratio was relatively stable. N addition significantly changed the forb leaf N content and N:P ratio.According to these results, we draw the following conclusions: 1) The short term effects of nitrogen addition on community composition and aboveground productivity were determined by the changed soil available nitrogen content. 2) N addition increased grass biomass significantly. 3) Grass and forb were N limitation while legume mainly limited by soil P.