Soil fauna accelerated litter C and N release by improving litter quality across an elevational gradient

Abstract Background Soil fauna is an important driver of carbon (C) and nitrogen (N) release from decomposing litter in forest ecosystems. However, its role in C and N cycling concerning climate and litter traits remains less known. In a 4-year field experiment, we evaluated the effects of soil fauna on litter C and N release across an elevation gradient (453, 945, 3023, and 3582 m) and litter traits (coniferous vs. broadleaf) in southwestern China. Results Our results showed that N was retained by –0.4% to 31.5%, but C was immediately released during the early stage (156–516 days) of decomposition for most litter species. Soil fauna significantly increased the peak N content and N retention across litter species, but reduced the C/N ratio for certain species (i.e., Juniperus saltuaria , Betula albosinensis , Quercus acutissima , and Pinus massoniana litter), leading to more C and N being released from decomposing litter across the elevation gradient. Contributions of soil fauna to C and N release were 3.87–9.90% and 1.10–8.71%, respectively, across litter species after 4 years of decomposition. Soil environment and initial litter quality factors caused by elevation directly affected litter C and N release. Changes in soil fauna resulting from elevation and fauna exclusion factors had a direct or indirect impact on C and N release during litter decomposition. Conclusions Our findings suggest that soil fauna promote C and N release from decomposing litter in different magnitudes, mainly controlled by environmental conditions (i.e., temperature and moisture), litter quality (i.e., lignin and cellulose content, and lignin/cellulose), and its diversity across the elevation gradient.