Effects of tree richness and litter composition affect mixed litter decomposition via structuring fungal decomposers in a subtropical forest of south-east China. Tree richness and litter diversity affect mixed litter decomposition

1. There is increasing evidence that plant diversity drives leaf litter decomposition in forests. However, it remains elusive of how leaf litter decomposition is driven by both the diversity of tree community and the diversity of the leaf litter itself, and how both facets of diversity operates through the decomposer community. To elucidate the underlying mechanisms, a litterbag experiment was conducted for three consecutive years in tree community with different tree diversity. 2. We hypothesized that mixed leaf litter decomposes faster with both increasing the richness of tree community and leaf litter species richness. We expected these diversity effects to depend on time, becoming stronger with concomitant recalcitrant substance accumulated at the later stage of decomposition. We also tested whether the effects were moderated through modification of the fungal decomposer community. 3. Our results revealed a significant effect of tree species richness on leaf litter decomposition, while only leaf litter species composition but not litter species richness affected decomposition rates. In support of our hypothesis, the effects of tree community richness and leaf litter composition became much stronger with time, brought about by indirect effects of concomitant changes in the composition of litter fungal community at the late stage of decomposition.4. Synthesis. Our findings demonstrated that not only leaf litter species composition, but also the richness of tree community play a critical role in regulating litter decomposition, particularly at the later stage. A full understanding underlying mechanisms of litter mixture decomposition requires consideration of the interactions that occur between plant and decomposers communities.