Human activities add a large amount of reactive nitrogen (N) to terrestrial ecosystem, which exerts great influence on ecosystem productivity. Although the response of ecosystem productivity to N enrichment are well-described, the underlying causes are still poorly understood. It has been suggested that plant functional trait, both dominant species traits (calculated as community-weighted mean, CWM) and functional diversity (FD), are the keys to predicting ecosystem function under changing environment. However, only few studies associated the variations in productivity along N addition gradient with plant traits and they all focused on CWM trait values, leaving how interaction between CWM and FD affect productivity unaddressed. To fill this knowledge gap, we conducted an N-manipulation experiment and quantized the relative contributions of CWM and FD to gross ecosystem productivity (GEP).
Results/Conclusions
Our results showed that along the N addition gradient, increasing ΔCWM (i.e., CWMNadded – CWMcontrol) values of leaf area and leaf N concentration stimulated plant growth, but declines in the ΔFD of leaf P concentration attenuated the positive responses of ΔGEP to N enrichment through decreasing ΔLUE and ΔPUE. Finally, the trade-off between ΔCWM and ΔFD resulted in the nonlinear response pattern of ΔGEP, which initially increased and then declined with increasing N additions. These results suggest that functional trait are crucial for predicting the responses of ecosystem function to increasing N inputs.