Seed dispersal and recruitment limitation explain the alpine meadow species diversity loss due to nitrogen enrichment.

Widespread evidence found that nitrogen (N) enrichment reduces grassland plant species diversity through multiple mechanisms. The processes of seed dispersal and recruitment are essential for understanding species diversity maintenance. However, how N enrichment influences species diversity from the process of seed dispersal and recruitment remains unclear. Here, we monitored plant community, seed rain, seed bank, seedling, rodent and litter along an 11-year N addition experiment in an alpine meadow on the Tibetan Plateau to investigate the effects of N enrichment on the plant species diversity. We found that there is a positive feedback loop in the crucial process of post-dispersal seeds after N enrichment. N enrichment significantly decreases the species diversity of seed rain, seed bank and seedlings, ultimately resulting in a decline in plant species diversity. During this process, increased seed dispersal and recruitment limitations constrain species diversity, and an increase in rodent density and litter mass is a crucial reason for the increase in seed dispersal and recruitment limitations. These findings emphasize that N enrichment weakens each phase of the process of post-dispersal seeds and highlight that seed availability and favorable recruitment conditions could be effective management strategies to enhance species diversity in alpine meadows following N enrichment.