Global meta-analysis reveals differential effects of climate and litter quality on soil fauna-mediated litter decomposition across size classes

•Meta-analysis is conducted on litterbag studies from global and Chinese databases.•Meso- and macrofauna increase litter decomposition by 12.25% and 22.14%, respectively.•The effects of meso- and macrofauna on decomposition differed significantly.•Temperature and precipitations are the main factors modulating fauna effects.•Litter C:N ratio influence the macrofaunal effect in dry and tropical climates. Litter decomposition is significantly influenced by soil fauna, litter quality, and climate. Effects of soil fauna on litter decomposition are largely dependent on the size classes of the fauna. However, the understanding of how different soil fauna groups affect litter decomposition remains elusive. In this study, we conducted a global meta-analysis of experiments using litterbags with varying mesh sizes to quantify the contributions of mesofauna and macrofauna to litter decomposition by calculating log response ratios. Additionally, we quantitatively assessed how climatic conditions and litter quality influence the effect of these two faunal size classes on litter decomposition. Our findings demonstrated that mesofauna and macrofauna increased litter decomposition by an average of 12.25% and 22.14%, respectively. Furthermore, the relative increase in litter decomposition induced by mesofauna and macrofauna exhibited a significant statistical difference on a global scale. Specifically, in dry and temperate climatics, the effect of soil macrofauna on litter decomposition was significantly greater than that of mesofauna. Climatic conditions, particularly temperature and precipitation, were the primary factors influencing litter decomposition by both mesofauna and macrofauna. In contrast, litter quality significantly influenced decomposition only by macrofauna in dry and tropical climatic conditions. Our findings underscore that the relative increase in litter decomposition rates to mesofauna and macrofauna differed significantly on a global scale and that the climate and litter quality differentially regulate litter decomposition across faunal size classes.