关键词: 氮添加, 围封草地, 刈割草地, 种间关联, 生态位特征

Abstract: Grassland plants achieve species coexistence through differentiated resource utilization， which directly affects the community structure and stability. To explore the impacts of grassland utilization patterns on the coexistence mechanism of community species under the background of nitrogen deposition， four nitrogen addition levels （0，2，5，10 g·m^-2·a^-1） were set up in the moving and fenced grasslands of the Huihe River Basin in Hulun Buir， and the response patterns of plant community diversity， overall interspecific association and niche characteristics to grassland utilization patterns and nitrogen deposition were investigated. The results indicated that mowing grassland was more sensitive to nitrogen addition. Under high nitrogen conditions， species diversity significantly decreased（P<0.05）， and the overall community association weakened and turned negative. The proportion of high niche overlap decreased from 56.06% under N₂ to 31.82% under N₅， while the proportion of low overlap increased to 53.03%. The overall correlation of the fenced grassland was relatively stable； the niche breadth of Leymus chinensis and Stipa baicalensis expanded to 2.77 and 2.67 in the medium nitrogen stage， respectively， but contracted and the overlapping ratio decreased in the high nitrogen stage. Nitrogen addition reshaped interspecific relationships by altering resource availability， while the utilization method of grasslands determined the stability of the community and the ability of ecological niche adjustment； the grassland steppe community exhibited a response of low nitrogen promoting and high nitrogen inhibiting to nitrogen addition.

Key words: Nitrogen addition, Fenced grassland, Mowing grassland, Interspecific association, Niche characteristics