Functional identity rather than functional diversity or species richness controls litter mixture decomposition in a subtropical forest

While growing evidence has shown consistently positive plant diversity effects on primary productivity, diversity effects on litter decomposition remain inconclusive. Our aim was to evaluate the relative importance of functional identity (FI), functional diversity (FD) and species richness (SR) for litter mixture decomposition and litter mixing effects. 32 mixtures of leaf litter from seven tree species were constructed by creating two independent gradients of FD and SR. Decomposition of these mixtures was measured using laboratory microcosms. Moreover, component litter was separated from mixtures to assess species-specific responses to mixing. FI but not FD or SR significantly influenced litter mixture decomposition. Six and nine litter mixtures separately exhibited synergistic and antagonistic non-additive effects with litter mixing effects ranging from -8.97% to 16.82%, which did not significantly relate to FD or SR. Mass loss of two fast-decomposing species was inhibited and that of two out of five slow-decomposing species was accelerated by the presence of other species. Chemical traits of a given component species and trait differences between this species and its neighbors significantly influenced its response to litter mixing. These results suggest that relationship between FD and litter mixing effect is far from generalizable and highlight that analyzing species-specific responses to mixing is useful in exploring mechanisms underlying interactions among component litter.