Long-term nitrogen addition changes phosphorus availability and reshapes phosphate-solubilizing bacterial community in purple soil of southwest China

Microorganisms play central roles in regulating soil phosphorus (P) cycling and availability retention. However, how long-term nitrogen (N) fertiliser application in intensively managed croplands affects soil microbial P metabolism remains unclear. In this study, we investigated the effects of different N applications on availability P, phosphatase activity, P functional genes, and microbes that participate in organic P mineralisation and inorganic P dissolution in a continuously managed (6 years) maize fields. The results showed that as the rates of N fertiliser increased, soil pH decreased, whereas AP content increased first before decreasing (N180 highest). A similar trend was found in the activities of alkaline and acid phosphatase. Furthermore, an increase in the N fertiliser application rate enhanced the abundance of phoX, pqqC, and gcd genes but decreased that of phoD and phoA genes. Structural equation modelling and random forest analysis revealed that total N and pH were the most important predictors of phoD- and pqqC-harbouring microbial composition, respectively. N180 and N270 treatments harboured higher modularity, nodes, links, and proportion of positive linkages in the phoD- and pqqC-harbouring microbial co-occurrence networks. Overall, different N applications reshaped the phoD- and pqqC-harbouring communities through direct or indirect effects, making it more flexible and efficient in improving the P-utilisation rate. These results have implications for sustainable agricultural management and will be helpful for deepening our understanding of soil microbial interaction and P activation mechanisms.