Aims The aim of this study was to investigate the effects of varying nitrogen (N) and carbon (C) levels on soil phosphorus (P) compositions, abiotic factors (pH and moisture content), and biotic factors (dehydrogenase (DHA) and phosphatases). Methods A field experiment was conducted at the Inner Mongolia prairie, where different levels of N (0, 25, 50, 100, 200 kg N ha(-1) yr(-1)) and C (0, 250, 500 kg C ha(-1) yr(-1)) were applied to study their effects on soil P transformations. Results High N levels significantly decreased soil pH, concentrations of diesters, activities of DHA and acid phosphomonoesterase (AcP), phosphodiesterase, and inorganic pyrophosphatase (IPP); whereas, increased concentrations of phosphonate, polyphosphate, and myo-IHP; which could potentially affect nutrient availability, microbial processes and soil fertility. Additionally, C supplementation significantly increased concentrations of diesters and myo-IHP, and activities of DHA and IPP, suggesting C supplementation may improve P stability in contexts of excessive natural and anthropogenic N enrichment. SEM revealed two discrepant nutrition-driven modes in P transformation: i) the N-driven mode, where N addition directly affected phosphonate concentrations and indirectly affected P transformation through both abiotic (pH and moisture content) and biotic (AcP and IPP) factors; ii) the C-driven mode, where C addition directly affected concentrations of monoesters and indirectly affected pyrophosphate concentrations through a biotic (IPP) factor. Conclusion Our findings reveal how biotic and abiotic factors regulate P transformation through C management under N enrichment, enhancing our understanding of environmental influences on P cycling via phosphatase and benefiting sustainable grassland practices.