Dominant plants affect litter decomposition mainly through modifications of the soil microbial community

Litter decomposition is a key step in biogeochemical cycling and energy flow underlying ecosystem function. It is well established that dominant plants influence litter decomposition through their litter quality, and by modifying edaphic properties and soil microbial activity at the local scale. Despite this, the pathways through which dominant plants influence litter decomposition remains insufficiently understood. In an alpine meadow on the Tibetan Plateau, we manipulated vegetation structure by factorial removal of shrubs (Dasiphora fruticosa) and graminoids (mainly Elymus nutans) to elucidate their effects on litter decomposition of D. fruticosa and E. nutans via changes in edaphic properties and microbial assemblages. The decomposition of D. fruticosa litter was lower when graminoids were removed, while the removal of either of the dominant species had a negative effect on E. nutant litter decomposition. These effects were attributed to changes in the relative abundance of microbial groups associated with litter decomposition induced by the dominant plants. Specifically, shifts in a subset of the bacterial community was a good predictor of litter decomposition rates, particular of E. nutans, while shifts in the composition and richness of a subset of fungal explained well D. fruticosa litter decomposition rates. This is likely due to the affinity of bacteria to utilize high quality litter (i.e. greater N content), whereas fungi are considered dominant in decomposing more recalcitrant litter. We conclude that dominant plants moderate litter decomposition through their influences on microbial taxa associated with decomposition processes. Our results provide a better understanding of the relative importance of abiotic and biotic factors in controlling litter decomposition.