Phenological shifts compensated reproductive success due to nitrogen enrichment in an alpine meadow

Although nitrogen (N) enrichment and precipitation changes are known to influence plant phenology and reproduction via altered soil nutrient and water availability, as well as above- and belowground biological processes, how these phenological changes affect reproduction remains unclear. 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, reproductive output, and success from 2023 to 2024. N addition delayed the reproductive period, reduced the flowering asynchrony, 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 and fruit production, it indirectly enhanced fruit set via phenological changes (including the peak flowering and the start of fruiting). These findings highlight the critical role of phenology in mediating alpine plant reproduction responses to N enrichment. Although delayed reproductive phenology enhances fruit set in alpine plants, its compensatory effect on N-induced reproductive losses remains limited under continuous nitrogen enrichment.