Multi-trait functional diversity predicts ecosystem multifunctionality under nitrogen addition in a desert steppe

Background and aims Increased atmospheric nitrogen (N) deposition under global climate change is known to reduce plant species richness in terrestrial ecosystems, with potentially important implications for ecosystem function and processes. However, knowledge gaps remain in our understanding of how N deposition affects the different aspects of plant community diversity (e.g., species, functional, and phylogenetic diversity) and how these impacts propagate to affect ecosystem multifunctionality. Methods Here, we investigated plant species, functional and phylogenetic diversity along a nitrogen gradient (0, 0.5, 1, 3, 6, 12, 24, 48 g N m(-2) yr(-1)) in a desert steppe. In addition, ecosystem multifunctionality was determined by eight functions to assess the relationship between plant community diversity and ecosystem multifunctionality. Results We showed that N addition increased plant functional diversity, but not species and phylogenetic diversity. Along the nitrogen addition gradient, the ecosystem multifunctionality increased first and then decreased which peaked at an addition rate of 24 g center dot m(-2)center dot yr(-1). Importantly, functional diversity was positively correlated with ecosystem multifunctionality. Furthermore, the structural equation model showed that N addition increased ecosystem multifunctionality both directly and by increasing functional diversity. Conclusion The positive relationships between MF and functional diversity suggest that the change and distribution of plant functional traits are beneficial for complementary utilization of N, thus maintaining ecosystem multifunctionality. The superiority of functional diversity over species and phylogenetic diversity highlights an important role of functional diversity in regulating ecosystem functioning to N addition.