Changes of community composition strengthen the positive effects of nitrogen deposition on litter N:P stoichiometry in a semi-arid grassland

Aims The stoichiometric traits of litter play an important role in driving litter decomposition and ecosystem nutrient cycling. While the impacts of nitrogen (N) deposition on the species-level litter stoichiometric traits have been well addressed, we know little about that at community-level, which is supposed to be driven by both intra-specific variation and changes in community composition. Methods We examined the effects of N deposition on litter phosphorus (P) concentration and N:P ratio at both species- and community-level in a semi-arid grassland of northern China. We further decomposed the community-level variations of litter nutritional traits into intra- and inter-specific variation. Results Nitrogen addition, especially at high rates, substantially changed community composition. Litter P concentrations and N:P ratios significantly varied among different species. Litter P concentrations and N:P ratios at both species- and community-level were positively correlated with N addition rates. Biomass-weighted community-level N:P ratios were more sensitive to N addition than the non-weighted ones, indicating that community composition strengthened the positive impacts of N addition on litter N:P ratios. There was positive co-variation between intra- and inter-specific variation for litter N:P ratio, indicating the consistency of community composition and intra-specific variation in their effects on litter N:P ratio. Conclusions Our results indicated that the imbalance of N and P following N enrichment would be much larger than the expectation based on the findings from species-level, and thus highlight the importance of changes in community composition in driving the responses of community-level litter N:P stoichiometry to N deposition in the semi-arid grassland.