Community-weighted mean traits play crucial roles in driving ecosystem functioning along long-term grassland restoration gradient on the Loess Plateau of China

The relationship between biodiversity and ecosystem functioning (BEF) is a central issue in ecology. Recent empirical and theoretical studies have shown that ecosystem functioning is strongly affected by the community-weighted mean (CWM) traits and functional traits diversity (FTD). However, little is known about the relative roles of CWM traits and FTD in explaining ecosystem functioning along a grassland restoration gradient on the Loess Plateau of China. We set up a grassland restoration gradient on the Loess Plateau of China applying the chronosequence approach. Using community biomass and soil carbon stock (SCS) as proxies for ecosystem functioning, we measured 13 functional traits on 28 common plant species and identified the dominant functional traits through principal component analysis (PCA). Our results showed that: (1) Specific leaf area (SLA), mature plant height (MPH) and leaf dry matter content (LDMC) loaded on separate principle components, which could be regarded as dominant functional traits to assess ecosystem functioning. (2) The variation of species diversity was not obvious, but FTD changed significantly along the restoration gradient. Following initial increases, FTD, CWM-SLA and SCS then declined, with the threshold occurring at the 18-year restoration. (3) Community biomass increased significantly through more biomass allocation to the below-ground in the latter stage of restoration. Community biomass was significantly correlated with CWM-MPH while SCS was positively correlated with CWM-SLA. We conclude that community-level functional traits are better than species diversity and FTD in predicting ecosystem functioning, and specifically restoration for 18 years could be the turning point for the degraded grassland ecosystem on the Loess Plateau of China.