Asymmetric responses of leaf litter decomposition to precipitation changes in global terrestrial ecosystem

Climate change-induced alterations in precipitation regimes can substantially impact litter decomposition and consequently affect carbon (C) and nutrient cycling in terrestrial ecosystems. However, the response patterns of litter decomposition to precipitation changes and their controlling factors remain ambiguous. We conducted a global meta-analysis to examine the responses of leaf litter decomposition and their sensitivities to increased precipitation (IP) and decreased precipitation (DP) based on 68 publications with 2940 paired observations in field litterbag experiments. We further explored how responses of litter decomposition varied with the intensity and timing of precipitation changes, ecosystem type, climatic conditions, litter traits, decomposition duration, and soil fauna. Litter decomposition showed double-asymmetric responses to precipitation changes. On a global scale, IP enhanced litter decomposition on average by 16%, whereas DP reduced litter decomposition by 21%. Litter decomposition was more sensitive to IP than DP at low precipitation changes but exhibited a greater response to DP than IP at extreme precipitation changes. In addition, litter decomposition in forests showed a stronger response to precipitation changes than that in other ecosystems, and litter decomposition was more sensitive to precipitation change under warm and wet conditions. Compared to precipitation changes in the growing season, litter decomposition showed a stronger response to IP but exhibited no response to DP in the non-growing season. The impacts of precipitation change gradually decreased with ongoing litter decomposition. Moreover, the initial lignin concentration in litter primarily determined the responses of litter decomposition to precipitation changes, with litter mixture and soil fauna partially mitigating the precipitation change effects. Our meta-analysis extends the double asymmetry model regarding the responses of litter decomposition to precipitation changes, which vary with ecosystem type, climatic conditions, litter chemical traits, decomposition duration, and soil fauna. These findings improve our ability to project the responses of terrestrial C and nutrient cycling to global precipitation changes.