Contrasting roles of labile and inert carbon inputs in regulating soil phosphorus pools in acidic paddy soils: roles mediated by acid phosphatase activity and phoC-harboring bacterial communities

Context Soil bacterial communities and their phosphorus (P) mineralization functions in acidic paddy soils are commonly carbon (C) limited. Aims This study investigated the effects of labile (glucose and sucrose) and inert (biochar) C inputs on soil P fractions, acid phosphatase (ACP) activity, and phoC-harboring bacterial communities. Methods Acidic paddy soils were incubated with labile and inert C sources for 35 days. Soil P fractions, ACP activity, and phoC-harboring bacterial community composition and co-occurrence networks were analyzed. Key results Labile C inputs significantly increased plant-available P contents and ACP activity, promoted the labile organic P fraction (Enzyme-P, i.e. organic P susceptible to hydrolysis by ACP), and reduced the diversity of phoC-harboring bacterial communities. Dominant Proteobacteria and Actinobacteria were positively correlated with ACP and Enzyme-P. Inert biochar showed weaker effects. Conclusions Labile C input encourages phoC-harboring bacteria to allocate energy toward ACP synthesis, gradually transforming soil P pools into labile organic P fractions. Implications These findings support the development of C-based microbial strategies to enhance soil P availability and reduce reliance on chemical P fertilizers in acidic paddy ecosystems.