Rhizosphere microbial processes of legume species regulate soil phosphorus dynamics in subtropical karst ecosystems

Legumes are well known for improving soil nitrogen (N) status, yet their role in regulating soil phosphorus (P) cycling, particularly via rhizosphere microbial processes, remains insufficiently understood in P-deficient karst ecosystems. In this study, we compared four dominant legume and non-legume species in a subtropical karst ecosystem in southwest China to investigate how legumes influence soil P transformation through rhizosphere microbial traits. A comprehensive assessment of soil P fractions, microbial biomass, phosphatase activities, and P-cycling microbial communities and key functional genes (pqqC, phoC, phoD, and phnK) was conducted. Results showed that legumes exhibited significantly higher total and available P concentrations in rhizosphere soils compared to non-legumes. Legume species generally increased both labile and non-labile P pools, primarily due to elevated resin-P, NaHCO3-Pi, and residual-P fractions. Increased P availability was strongly linked to higher abundances of pqqC, phoC, phoD, and phnK genes. These genes indirectly influenced soil P dynamics by modifying soil pH and enhancing acid and alkaline phosphatase activities, thereby promoting inorganic P solubilization and NaOH-Po mineralization. In contrast, non-legume species exhibited weaker coupling between microbial processes and soil P transformation. Notably, phoC- and phoD-harboring bacterial community diversity showed no direct association with soil P fractions. Overall, these findings highlight that legumes regulate both immediate and long-term soil P dynamics via rhizosphere microbial mechanisms, underscoring their ecological importance for vegetation restoration in nutrient-limited calcareous soils of karst ecosystems.