Mineralogical influences on phosphorus mobilization under coupled acidification, flooding, and organic ligand inputs in contrasting soils.

Legacy phosphorus (P) accumulated in agricultural soils can be remobilized under changing environmental conditions, increasing the risk of diffuse nutrient losses and eutrophication. However, how multiple environmental disturbances jointly regulate P mobilization across contrasting mineralogical soil systems remains insufficiently understood. Here, four representative soils from the Xiangxi River watershed (Three Gorges Reservoir region, China) were subjected to controlled flooding, simulated acidification, and organic ligand treatments. Mineralogical characterization was integrated with dissolved reactive P release, operational P fractionation, adsorption-desorption experiments, and apparent thermodynamic analyses to identify the mineralogical controls on phosphorus mobilization. Phosphorus mobilization differed consistently among soils with contrasting mineralogical characteristics. Flooding, decreasing pH, and organic ligand inputs all enhanced dissolved reactive P release, although the magnitude and dominant pathways varied with soil mineral composition. Fe/Al-rich soils exhibited greater susceptibility to flooding- and ligand-induced desorption, whereas Ca-rich calcareous soils responded more strongly to acidification through redistribution of Ca-associated phosphorus pools. Low-molecular-weight organic acids promoted substantially greater phosphorus mobilization than humic substances, highlighting the importance of ligand chemistry in regulating phosphorus availability. Apparent thermodynamic analyses further indicated that phosphorus sorption in these heterogeneous soils behaved as an overall endothermic process and that the derived thermodynamic parameters are most appropriately interpreted as comparative descriptors of adsorption affinity. Overall, the results demonstrate that soil mineralogy governs phosphorus mobilization by mediating the response of mineral-phosphate interactions to coupled environmental disturbances. Overall, the findings provide an evidence-based framework for understanding mineralogy-dependent phosphorus mobilization under multiple environmental disturbances and support mineralogy-informed assessment and management of phosphorus loss risk in reservoir-influenced agroecosystems.