关键词: 半灌木扩张, 氮添加, 群落稳定性, 物种异步性, 优势度, 群落多样性

Abstract: Increased nitrogen deposition caused by climate change and human activities, coupled with shrub encroachment, has become one of the two major challenges facing semi-arid grassland ecosystems; however, how these two factors jointly influence community stability and their underlying mechanisms remain unclear. This study took the typical grassland of Yunwu Mountain in Ningxia, Loess Plateau, as the study site. Four treatment combinations were established, including subshrub (Artemisia gmelinii) encroachment treatments (no encroachment, encroachment) and nitrogen addition treatments (0, 40 g·m-2·yr-1 urea). with four replicates per combination. We systematically analyzed changes in community biomass, species diversity, community stability, and the stability of different dominance groups (dominant species, common species, and rare species), as well as their underlying mechanisms. Results indicated that both nitrogen addition and subshrub encroachment increased total community biomass by promoting dominant species biomass, significantly raising the Simpson dominance index, but significantly reducing species richness; subshrub encroachment significantly enhanced community stability and dominant species stability, whereas nitrogen addition significantly increased species asynchrony and dominant species stability. Structural equation modeling further indicated that nitrogen addition and subshrub encroachment primarily maintained high community stability by promoting dominant species stability, species asynchrony, and the Simpson dominance index. In summary, subshrub encroachment and nitrogen addition regulate grassland community stability primarily by reshaping community species composition, dominance, and species asynchrony dynamics.

Key words: Subshrub encroachment, Nitrogen addition, Community stability, Species asynchrony, Dominance, Community diversity