Effects of nitrogen addition on plant community characteristics in Tibetan alpine grassland

A fertilizing experiment was conducted in a fenced enclosure in Bange County, which was a typical alpine grassland in Tibetan from July 2013 to September 2014. The aboveground biomass, group coverage, evenness and important values (IV) were assessed under controlled experiment with different nitrogen(N) application level control, 0(N0); low level, 7.5 g·(m2·a)-1(N1) high level, 15 g·(m2·a)-1(N2) to find out the effects of N fertilization on different vegetation communities characteristic of the degraded alpine steppes in Tibetan. The results showed that Gramineae and the total biomass significantly increased compared with the control group without N fertilization, however, high nitrogen application only increased the aboveground biomass of Compositae without significance. There was no significant influence of short term nitrogen application on the coverage of Gramineae, Compositae, Cyperaceae, Rosaceae, forbs and total coverage, while the proportion of Gramineae in the total coverage gradually improved, which was 58.73%, 61.90% and 63.99%, respectively, with different N level (control, low level and high level). There was no significant difference between evenness, important values and the dominant species of all communities in response of different N level.