Abstract: Dissolved organic carbon (DOC) could be leached rapidly from soils and assimilated by soil microorganisms, and thus is one of key components of biogeochemical cycles in terrestrial ecosystems. Litter is an important source of soil DOC, but the types and amounts of surface litter vary greatly in different ecosystems due to the divergent vegetation types and coverage. Moreover, chemical composition of different litter types directly affects DOC release during decomposition. Therefore, assessing the changes in soil DOC concentrations under litter inputs is of great significance for understanding soil biogeochemical processes. We compiled 494 paired observations (with and without litter addition or removal) from 47 literature to evaluate the changes in soil DOC concentrations under double litter addition or removal of different litter types (leaf litter, roots and both leaf litter and roots) across ecosystems (forests and grasslands) over different experimental periods (<1, 1-3, 3-6 and >6 months). The results showed that double litter addition significantly increased soil DOC by 28.9%, while soil DOC concentrations were reduced by 23.1%, 6.6% and 16.9% after removal of leaf litter, roots, or both, respectively. Soil DOC concentrations in grasslands and forests were increased by 28.6% and 28.5% under double litter input, but were decreased by 30.4% and 21.2% after litter removal, respectively. Soil DOC concentration increased rapidly by 29.6% within one month of double litter addition, but this increase was gradually slowed down in the later periods, yet soil DOC concentration was then increased rapidly by 34.0% after six months of manipulation. Similarly, litter removal decreased soil DOC concentration by 65.2% within one month of manipulation, but such effect was gradually slowed down in the later periods. These results suggest that litter is an important source of soil DOC, and that the contribution of leaf litter is approximately 3.5 times higher than roots. Our global synthesis figures out the interactions between litter inputs and soil DOC, which improve our mechanistic understanding of biogeochemistry in terrestrial ecosystems.

Key words: litter input, litter addition, litter removal, dissolved organic carbon.