Impacts of soil fauna on lignin and cellulose degradation in litter decomposition across an alpine forest-tundra ecotone

The degradation of lignin and cellulose is the primary ecological process in terrestrial ecosystems; these chemical changes have been associated with the subsequent colonization and activity of decomposer flora and fauna. To evaluate the contribution of soil fauna on lignin and cellulose degradation during litter decomposition, we conducted a field experiment along an elevation gradient: coniferous forest, alpine timberline and alpine meadow, and monitored Abies faxoniana and Rhododendron lapponicum foliar litter decomposition with litterbags of different mesh sizes. We observed soil fauna significantly accelerated litter decay. Soil fauna effect on cellulose degradation rate was significantly accelerated in the snowing period (213-320d), which were 19.3%, 12.36%, 27.96% in A. faxoniana litter and 9.2%, 32.65%, 22.11% in R. lapponicum litter in the coniferous forest, alpine timberline and alpine meadow, respectively. By contrast, lignin degradation rates by soil fauna were higher in the later stages (321-554d). In addition, the average monthly contribution of soil fauna effect on cellulose degradation rate mainly occurred during the first year. However, the contribution of lignin degradation by soil fauna was higher in coniferous forest and alpine meadow, where they were 13.84% and 18.06% in A. faxoniana, and 14.5% and 10.1% in R. lapponicum litter. Elevation gradient and seasonal dynamics will influence on activity of soil fauna, which may modify the impacts of soil fauna on lignin and cellulose degradation during litter decomposition. Elucidating the role of soil fauna in litter decomposition is important for understanding the formation of soil organic matter in alpine ecosystems.