Warming decreased plant litter decomposition by modulating soil fauna interactions in a Tibetan alpine meadow.

Litter decomposition is a vital process for maintaining ecosystem carbon cycling. It is affected by soil fauna which are predators and decomposers of litter. However, how the interactions of soil fauna communities affect litter decomposition remains unclear under warming. Here, we conducted a five-year in-situ manipulative warming experiment by Open-Top Chamber (OTC) in an alpine meadow on the Tibetan Plateau to reveal how warming affects litter decomposition. The results demonstrated that warming decreased the litter decomposition rate by 29 %, the soil collembola abundance by 25 %, and the nematode abundance by 27 %. Nematode ecological indices remain stable but a shift in the decomposition of litter to the fungivores pathway under warming. The piecewise structural equation modelling result revealed that the combined reduction in soil collembola and nematodes synergistically leads to a massive decline in litter decomposition rate under warming. Our results highlight that the interactions of soil fauna can regulate litter decomposition under warming, and collembola abundance as the "speed-limiter" of litter decomposition. Therefore, the response of changes in soil fauna relationships to warming should be completely considered in future climate change modelling of the grassland carbon cycle.