Root functional traits mediate rhizosphere soil carbon stability in a subtropical forest

Plants can be classified as either resource-acquisitive or resource-conservative strategies based on their root traits. Compared with conservative trees, acquisitive trees produce larger amounts of readily decomposable carbon, owing to their high specific root length and low root C:N ratio, which could reduce the content and stability of soil organic carbon (SOC). In this study, we assessed the content of labile particulate organic carbon (POC) and stable mineral-associated organic carbon (MAOC) in the rhizosphere and bulk soils of acquisitive and conservative trees in a subtropical forest. Contrary to our expectations, we found that SOC content in the rhizosphere soil of acquisitive trees (26 g kg −1 ) was 53% higher than that in the rhizosphere soil of conservative trees (17 g kg −1 ), which was mainly attributed to an approximately 1-fold higher MAOC content. Correlation and structural equation modeling analyses indicated that this rhizosphere MAOC was primarily derived from roots and associated with higher specific root length, rhizosphere soil microbial biomass C, and enzyme C:N ratio, whereas the POC was mainly derived from aboveground litter. We further found that the contrasting plant strategies had no significant influence on the POC content of bulk or rhizosphere soil, which could be ascribed to the similar properties of aboveground litter of acquisitive and conservative trees. These findings indicate that acquisitive trees enhance rhizosphere soil C stability primarily via the mediation of root traits and highlight the necessity of considering plant ecological strategies when assessing the effects of tree species on soil C content and stability. • Stability of rhizosphere soil organic carbon assessed with a trait-based framework. • Particulate organic carbon in rhizosphere and bulk soil was not affected by tree type. • Particulate organic carbon related to aboveground litter properties. • Greater mineral-associated organic carbon around acquisitive than conservative trees. • Mineral-associated organic carbon related to root traits and microbial parameters.