Abstract: 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.

Key words: legume, phosphorus cycling, P-cycling functional genes, phosphatase activity, subtropical karst soils