Phenological changes mediated the effects of nitrogen enrichment on reproduction in an alpine meadow on the Tibetan Plateau

Nitrogen (N) enrichment and precipitation regimes changes may influence plant growth by modifying soil nutrient and water availability, yet they could also shift plant phenology and impact reproductive output and success. However, the responses of plant phenology to N enrichment and precipitation changes, as well as their reproductive consequences, remain poorly understood.Based on a field experiment with N addition and altered precipitation conducted in an alpine meadow on the eastern Tibetan Plateau since 2020, we explored their effects on plant reproductive phenology and reproduction from 2023 to 2024.We found that N addition delayed the reproductive period and decreased both flower and fruit production in alpine plants. Notably, the interactive effects of N and precipitation addition significantly enhanced fruit set. Phenological shifts mediated plant reproductive responses to N addition and altered precipitation. Specifically, while N addition directly decreased flower production, it indirectly increased fruit set via phenological changes.These findings demonstrate the critical regulatory role of plant phenology in the response of alpine plant reproductive success to N enrichment and precipitation changes. However, although delayed reproductive phenology enhances fruit set in alpine plants, its capacity to compensate for N-induced reproductive losses remains severely limited.