Natural forests exhibit higher organic carbon concentrations and recalcitrant carbon proportions in soil than plantations: a global data synthesis

Different chemical compositions of soil organic carbon(SOC) affect its persistence and whether it significantly differs between natural forests and plantations remains unclear. By synthesizing 234 observations of SOC chemical compositions, we evaluated global patterns of concentration, individual chemical composition(alkyl C, O-alkyl C, aromatic C, and carbonyl C), and their distribution evenness. Our results indicate a notably higher SOC, a markedly larger proportion of recalcitrant alkyl C, and lower easily decomposed carbonyl C proportion in natural forests. However, SOC chemical compositions were appreciably more evenly distributed in plantations. Based on the assumed conceptual index of SOC chemical composition evenness, we deduced that, compared to natural forests, plantations may have higher possible resistance to SOC decomposition under disturbances. In tropical regions, SOC levels, recalcitrant SOC chemical composition, and their distributed evenness were significantly higher in natural forests, indicating that SOC has higher chemical stability and possible resistance to decomposition. Climate factors had minor effects on alkyl C in forests globally, while they notably affected SOC chemical composition in tropical forests. This could contribute to the differences in chemical compositions and their distributed evenness between plantations and natural stands.