Initial litter quality and climate regulate the negative effects of fauna exclusion on litter decomposition in terrestrial and aquatic ecosystems: A global meta-analysis of enclosure studies

Although the exclusion effects of faunal decomposers on litter decomposition have been extensively studied in different experimental contexts, a thorough comparison of the exclusion effects of faunal decomposers with different body sizes on litter decomposition and its possible regulatory factors in terrestrial and aquatic ecosystems is still lacking. Here, through a meta-analysis of 1207 pairs of observations from 110 studies in terrestrial ecosystems and 473 pairs of observations from 60 studies in aquatic ecosystems, we found that fauna exclusion reduced litter decomposition rates in terrestrial and aquatic ecosystems by 30% and 44% on average, respectively. At the global scale, the exclusion effects of macrofauna and mesofauna on litter decomposition rates (reduced by 38% and 36%, respectively) were greater than that of the combination of macrofauna and mesofauna (reduced by 30%). In terrestrial and aquatic ecosystems, the effects of fauna exclusion on litter decomposition rates were mainly regulated by climate and initial litter quality, but the effects of fauna exclusion with different body sizes were differently regulated by climate, initial litter quality, and abiotic environmental variables. These findings will help us better understand the role of faunal decomposers on litter decomposition, especially for faunal decomposers with different body sizes, and underscore the need to incorporate faunal decomposers with different body sizes into dynamic models of litter decomposition to examine the potential effects and regulatory mechanisms of land-water-atmosphere carbon fluxes.