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

摘要： 草原植物通过资源差异化利用实现物种共存，并影响群落结构与稳定性。为探讨氮沉降背景下草地利用方式对群落物种共存机制的影响，在呼伦贝尔辉河流域草甸草原刈割和围封草地设置4个氮添加水平（0，2，5，10 g·m^-2·a^-1），探究植物群落多样性、种间总体关联及生态位特征对草地利用方式和氮沉降的响应规律。结果表明，刈割草地对氮添加响应更为敏感，高氮下物种多样性显著降低（P<0.05），群落总体关联减弱并转为负关联；高度生态位重叠比例由N₂的56.06%降至N₅的31.82%，低重叠比例升至53.03%。围封草地总体关联相对稳定；羊草与贝加尔针茅在中氮阶段生态位宽度分别扩展至2.77和2.67，高氮阶段收缩且重叠比例下降。氮添加通过改变资源可利用性重塑种间关系，而草地利用方式决定群落稳定性与生态位调节能力；草甸草原群落对氮添加呈现低氮促进、高氮抑制的响应。

关键词: 氮添加, 围封草地, 刈割草地, 种间关联, 生态位特征