Deciphering microbial drivers of soil organic matter mineralization in surface and subsurface soil during long-term vegetation succession

The microbial process of soil organic matter (SOM) mineralization changes with vegetation succession and is influenced by litter input, nutrient acquisition, and microbial communities shifts. However, the mechanisms underlying this process at various depths during long-term vegetation succession remain unknown. In this study, we investigated these mechanisms following a succession chronosequence of approximately 160 years after farmland abandonment by sequencing amplicons and using high-throughput quantitative PCR-based chips. SOM mineralization increased from 580 to 1200 mg C kg(-1) during 42 days in the surface soil (0-20 cm) and from 340 to 760 mg C kg(-1) during 42 days in the subsurface soil (20-40 cm). Long-term vegetation succession decreased mineralization efficiency and abundance of carbon decomposition genes. Keystone modules (ecological clusters) of microorganisms associated with SOM mineralization were identified. Long-term vegetation succession increased the abundance of genes related to carbon metabolism pathways within these clusters. Fungal saprotrophs increased, whereas pathotrophs decreased within these clusters over 160 years of vegetation succession. The relative abundance of keystone ecological clusters directly drives SOM mineralization in the surface soil, whereas microbial carbon use efficiency is the main driving factor below 20 cm. These results elucidated the mechanisms of SOM mineralization along soil profiles at a long-term vegetation succession chronosequence, which can provide a reference for further formulating effective management strategies for ecosystem carbon sequestration.