LAUSR

BACKGROUND AND AIMS Nitrogen enrichment affects biodiversity, plant functional traits, and ecosystem functions. However, the direct and indirect effects of nitrogen addition and biodiversity on the links of plant traits with ecosystem functions have largely been overlooked, even though multidimensional characteristics of plant functional traits are likely critical predictors of ecosystem functions. METHODS To investigate the mechanism underlying the links of plant trait identity, diversity, network topology with aboveground and belowground biomass along a plant species richness gradient under different nitrogen addition levels, a common garden experiment was conducted in which those driving factors were manipulated. KEY RESULTS Our study found that nitrogen addition increased aboveground biomass but did not change belowground biomass, while species richness was positively associated with aboveground and belowground biomass. Nitrogen addition had minor effects on plant trait identity and diversity, and the connectivity and complexity of the trait networks. However, species richness increased aboveground biomass mainly by increasing leaf trait diversity and network modularity, and enhanced belowground biomass through the increase in root nitrogen concentration and network modularity. CONCLUSIONS Our results demonstrate the mechanistic links between community biomass and plant trait identity, diversity, and network topology, reveal that the trait network architecture could be an indicator of the effects of global changes on ecosystem functions as important as trait identity and diversity.