Phosphorus-transforming microbes enhance phosphatase catalytic efficiency to alleviate phosphorus limitation under nitrogen and phosphorus additions in subtropical forest soil

Phosphatase catalytic efficiency (Vmax/Km) is a key determinant of soil phosphorus (P) availability and is governed by microbial P-transformations. In subtropical forest soils, low intrinsic P availability is constrained by atmospheric nitrogen (N) deposition, yet the effects of P-transforming microorganisms and microbial food webs on Vmax/Km remain unclear. This study quantifies how P-transforming microorganisms and microbial trophic interactions modulate phosphatase catalytic efficiency under N, P, and NP additions in subtropical Chinese fir plantations. Partial least squares path modelling revealed two dominant microbial pathways contributing to increased Vmax/Km: (i) N-induced acidification upregulated phosphate transporter genes (e.g., pstB), increasing microbial P uptake; P and NP additions alleviated microbial P limitation and downregulated P-starvation response genes (e.g., phoB), indicating a shift from stress-response to uptake-oriented strategies. (ii) P and NP additions increased upper trophic-level protist diversity, triggering a top-down microbial food web cascade that selectively enriched Acidobacteria, increased phosphatase catalytic efficiency, and increased P availability in soil. Overall, these gene-regulatory and trophic pathways explained over 60 % of the variation in phosphatase catalytic efficiency across all nutrient treatments. These findings challenge the traditional focus on phosphatase-encoding genes alone and underscore the importance of (i) phosphate transport systems, like pstB gene, and (ii) keystone taxa, like Acidobacteria, in increasing Vmax/Km. This study provides a mechanistic foundation to raisephosphatase catalytic efficiency and alleviate P limitation through targeted microbial and genetic interventions in P-deficient subtropical forest soils.