Trait identity and functional diversity co-drive response of ecosystem productivity to nitrogen enrichment

1. Exploring the mechanisms underlying the change in ecosystem productivity under anthropogenic nitrogen (N) inputs is of fundamental ecological interest. It has been proposed that functional traits, environmental factors, and species richness are central drivers linking ecosystem productivity with environmental change. However, few studies have considered the joint effects of functional traits, environmental factors, and species richness on ecosystem productivity under increasing N inputs. 2. We established a N-manipulation experiment in a Tibetan alpine steppe in 2013. Using structural equation models, we assessed the effects of N-induced changes in environmental factors, species richness, and trait metrics (the mean, variance, skewness and kurtosis of trait distribution) on gross ecosystem productivity as well as three resource use efficiencies (water, light, and phosphorus (P) use efficiencies), based on measurements during the peak growing season in 2016. 3. We found that both ligh...