Decreased community litter decomposition associated with nitrogen-induced convergence in leaf traits in an alpine meadow

Anthropogenic activities introduce nitrogen (N) into terrestrial ecosystems, inducing changes in quantity and quality of plants. However, little is known about how do nitrogen (N)-mediated such changes alter functional diversity of green leaf traits? How does N-mediated changes in leaf quality contribute to the rate of litter decomposition at intra- or inter-species level? How can such N-mediated changes in quantity and quality be scaled up to explain and predict community-level litter decomposition? A common garden litter decomposition was conducted in an alpine meadow on the Tibetan Plateau, where six litter species and litter mixtures from the communities that had experienced eight-year N addition treatment, were subjected to decomposition for 641 days, with three harvests. For litter mixtures, littles were selected randomly from aboveground shoots collected from 0.5 × 0.5 m² quadrats. We found that N enrichment increased green leaf and litter N concentrations, and caused small and idiosyncratic variations in phosphorus and carbon concentrations. Plasticity in leaf nutrient concentrations induced little variation in litter decomposition in the six species. Meanwhile, N enrichment induced a reduction in leaf trait diversity and community-level litter decomposition. Correspondingly, positive relationship between decomposition rate (k) and leaf trait diversity were observed. N enrichment reduced dissimilarity of leaf traits, which could relate a reduction of litter decomposition at community level. By integrating intra- and interspecific trait variation with the abundances of coexisting species, these findings can help predict ecosystem function with N enrichment.