Environmental conditions and litter nutrients are key determinants of soluble C, N, and P release during litter mixture decomposition

Plant litter-derived dissolved compounds leaching is an important process for soil carbon (C) sequestration and nutrient cycling. However, knowledge of the biotic and abiotic drivers of dissolved compound release from litter mixture remains limited. Here, we evaluated the loss of soluble C, N, and P during litter mixtures decomposition across an alpine treeline ecotone, and we sought to assess the relative importance of environmental conditions, litter diversity (functional dissimilarity (Rao) and community-weighted mean (CWM) traits), litter chemistry (C quality, nutrients, and stoichiometry) and microbe drive dissolved compound release during the decomposition process. The results showed that dissolved compound release from litter mixtures deviated from predictions based on litter monoculture, with predominantly synergistic effects, and the hierarchical drivers suggested: temperature strongly regulated the release of dissolved compounds and its non-additivity. In particular, freeze thaw cycles and seasonal snow accelerated the synergistic effects on dissolved compound loss. Litter CWM and Rao traits only accelerated soluble C release and the synergistic effects of soluble P at the last stage of dissolved compound loss, respectively. Litter nutrients directly drove the release of soluble C and P at different stages. Litter C quality and microbes regulated the release of soluble C and P via direct effects, and stoichiometry had an indirect impact, which mainly before 40 % of initial mass loss. Yet, litter chemistry showed a minimal effect on soluble N release, so controls established for the release of soluble C and P might not be valid for soluble N during decomposition. Collectively, our findings advocate the decomposition environment and litter nutrients are key factors for controlling the dissolved compounds leaching, then followed by the interactions of litter C quality, stoichiometry, litter functional diversity, and microbe, which is important for understanding soil organic matter pool and soil fertility in alpine ecosystems.