Decomposition time, chemical traits and climatic factors determine litter-mixing effects on decomposition in an alpine steppe ecosystem in Northern Tibet

Aim In the context of rapid species diversity loss, whether and how species diversity affects litter decomposition in alpine ecosystems remain unclear. Here, we aimed to assess the impact of litter mixing on decomposition and the influencing factors of such litter-mixing effects (LMEs). Methods We incubated the litter of four alpine steppe species in monocultures and all possible litter combinations and analysed the mass remaining over three years. Results Litter mixing showed more frequent antagonistic effects than synergistic effects in the early stage of the experiment; however, the LME might change from antagonistic to synergistic at the latter stage of incubation. The magnitude of the LMEs increased as decomposition progressed. The four-species mixture resulted in more antagonistic effects, while the magnitude of the non-additive effects showed no relationship with species richness. Litter chemical traits and climatic factors affected the direction and magnitude of the non-additive effects, but these influences were time-dependent. Additionally, the fast-decomposing and slow-decomposing litter species had negative and positive responses to the litter mixture, respectively. Conclusion Our results demonstrate that the LME was determined by decomposition time, chemical traits and climatic factors and suggest that assessing the relative individual performances of the litter components in a mixture is an important way to examine the mechanisms underlying LMEs.