The interaction between mycorrhiza and phoD-harbouring bacteria influencing soil available phosphorus in Pinus massoniana plantations

The diversity and interactions of bacteria and fungi regulate phosphorus (P) and carbon (C) fluxes. However, how bacterial–fungal interactions mediate the process of soil P transformation and the coupling of P with organic C cycling to increase P availability and C sequestration remains unknown, mainly with the increasing stand age of Pinus massoniana. This study examined soil physicochemical properties, P fractions, soil organic carbon and the diversity and composition of soil microbial communities in P. massoniana forests of five different stand ages (0, 7, 19, 25, and 34 years). A higher relative abundance of ectomycorrhizal fungi (ECM) was observed in the 7- and 34-year-old forests, accompanied by an increase in available P content and soil organic carbon, while a reduction in the diversity of phoD-harbouring bacteria. Concurrently, a decreased abundance of saprotrophic fungi was detected in these forests compared to forests of other stand ages, suggesting that ECM fungi may inhibit SOC decay by free-living microbes. These findings indicate that the enhancement of soil available P by ECM fungi increases plant reliance on these symbiotic organisms, thereby promoting soil C sequestration through a rise in ECM fungal biomass and plant C allocation to soils.