Responses of soil mineral-associated and particulate organic carbon to carbon input: A meta-analysis

A minor change of soil organic carbon (SOC) greatly influences atmospheric carbon dioxide concentration and climate change. Exogenous carbon (C) input into soils can induce SOC decomposition or sequestration. The response of SOC to C input can be better understood when SOC is separated into mineral-associated (MAOC) and particulate (POC) organic carbon. The objective of this study is to explore whether exogenous C input promote MAOC and POC increase or decrease and the controlling factors. We gained 1181 observations from 17 studies for this meta-analysis. The effect sizes of exogenous C input on MAOC and POC content, and MAOC decomposition were calculated. The key factors influencing the effect sizes were explored through subgroup analysis. Potential publication bias was explored by using funnel plots, trim and fill method, and Egger's test. Exogenous C input significantly increased MAOC and POC content, although promoted MAOC decomposition. The effect sizes were larger for MAOC content than for POC content irrespective of soil and substrate properties and experiment methods. The effects of C input on MAOC and POC content were more pronounced in forest soils, and depended on the C and nitrogen (N) content in soil and substrates as well as experiment methods. The effect size of C input on MAOC decomposition were larger with substrate input of below 200 g C kg^-1 in specific soils. The sensitivity analysis carried out by removing one observation indicated our results were robust. In conclusion, exogenous C input increases MAOC and POC content although stimulate MAOC decomposition, and the effect sizes were influenced mainly by ecosystem type, carbon and nitrogen content of substrates and soils, and fractionation methods. The findings indicate the importance of C and N content in substrates and soils in controlling the response of SOC rather than the ratio of C to N.