Secondary shrubs promoted the priming effect by increasing soil particle organic carbon mineralization

Introduction Inputs of additional organic matter to the soil will accelerate or inhibit the decomposition of soil organic carbon (SOC), resulting in a priming effect (PE), which is a key mechanism affecting soil carbon (C) cycling. The impact mechanism of changes in soil properties on the PE is still unclear after vegetation restoration; in particular, the contribution of C pools with different turnover rates to the PE has not been distinguished and quantified. Methods In this study, the secondary shrub (SB) ( Vitex negundo var. heterophylla ) formed by the enclosure of barren grassland was selected as the research object, and the barren grassland (GL) was taken as the control. Equal amounts of 13 C-labeled glucose were added to the topsoil for a 45-day incubation experiment to measure the PE. Moreover, soil samples were destructively sampled to explore the fate of new C and changes in POC and MAOC fractions during incubation. Results After 45 days of incubation, most of the new C formed by glucose flowed to MAOC, with 95.45% in SB soil and 92.29% in GL soil. In the experiment, all soils showed a positive PE. The PE, POC mineralization and MAOC accumulation were higher in SB soil than in GL soil. During incubation, the mineralization of POC was positively correlated with the PE and made a major contribution to the PE. Partial correlation analysis showed that after vegetation restoration, SB further promoted the mineralization of POC by increasing the soil moisture, fungal diversity and necromass C of bacteria, which led to an increase in PE. Conclusion The SB mainly enhanced PE by increasing soil fungal diversity and mineralization of POC. And increasing PE due to the SB may lead to an increase in soil C emissions. Therefore, we need to adopt forest management and other measures to address the potential risks of increased soil C emissions in the vegetation restoration process.