Responses of CO 2 emission to external organic carbon input in the drying-rewetting cycles: a meta-analysis

In recent decades, global warming under rising CO significantly influences external organic carbon (EOC) input and drying-rewetting processes in terrestrial ecosystems. However, little is known about how soil CO emissions respond to these perturbations, which provides us with a chance to explore potential factors and variability. In this study, a meta-analysis on the responses of CO emissions with or without EOC input in the soil drying-rewetting cycles (DWC) based on 291 observations (included 33 study sites and 11 variables) has been conducted. The results indicated that i) CO emission with the increase of EOC by 284% relative to without EOC under DWC; ii) The effect size of CO emission was the smallest in the forest (+15%) and the largest in the grassland (+1468%); iii) The CO emission effect sizes were substantially greater in complex substrates (+288%) than in simple substrates (+132%), and iv) longer drought period in a DWC can induce more CO emission. The study suggests that terrestrial CO emission may be multi folds in the long drought-rapid rewetting processes under large input of EOC.