Ten years of urea fertilization alter the pqqC-harbouring community and increase soil inorganic phosphorus mobilization

The bacterial communities that harbour the pyrroloquinoline quinone gene (pqqC-harbouring bacteria communities) play a pivotal role in the mobilization of inorganic phosphorus (Pi). However, there is limited knowledge regarding the connection between soil pqqC-harbouring bacterial communities and Pi fractions, as well as the factors that can regulate them, particularly under different fertilization strategies in the agricultural soil. High-throughput sequencing was used to investigate the pqqC-harbouring communities from the wheat (Triticum aestivum L.)–sweet potato (Ipomoea batatas L.) season in a 9-year field experiment, including without fertilization (control), nitrogen (N) and potassium (K) fertilization (NK), NPK fertilization (NPK) and the combined application of chemical NPK and organic fertilizer (NPKM), and to explore their relationships with Pi fractions and their regulatory factors. Long-term N fertilization and crop type substantially changed the community composition of pqqC-harbouring bacteria but had no effect on their diversity. In two crop seasons, long-term N fertilization significantly increased the content and proportion of moderately labile Pi (aluminium- and iron-bound P) and available P (AP) and significantly decreased the proportion of recalcitrant Pi (calcium-bound P) compared with the control. Specifically, AP increased by 79%–778%, Fe-P by 64%–88%, and Al-P by 71%–308%, while Ca-P decreased by 10%–59%. N fertilization increased the relative abundance of Micromonospora, which was significantly positively correlated with moderately labile Pi and AP. Moreover, the relative abundance of some Streptomyces increased by 391% in the sweet potato season, and they were positively correlated with AP. Structural equation modelling revealed that the interplay between the pqqC-harbouring community composition and Pi mobilization was mainly governed by pH, underscoring the role of pH in shaping the communities of Pi-mobilizing microbes and their effect on Pi mobilization processes. This study emphasized how N fertilization and crops reshape Pi-mobilizing microbial communities, which in turn affects Pi mobilization and P availability. Overall, these findings offer valuable insights into optimizing P cycles and availability through N fertilization strategies.