Molecular mechanism of flavonoids-inducing iron oxides transformation on phosphorus loss potential in paddy soils

Abstract

Phosphorus (P), a non-renewable resource essential for sustaining life, faces increasing environmental losses from agricultural systems. However, the effects of flavonoid-induced iron oxide on soil P behavior remain poorly understood, particularly in paddy soils. Here, we conducted a 7-year field trial under four fertilization regimes combined with laboratory incubations to reveal how flavonoid-modified iron oxides regulate P at molecular scales. Results showed that manure-applied (NPKM) soils increased by 48.7% higher flavonoids and 8.7% more short-range-order minerals (SROs) than chemically fertilized (NPK) soils. Through interfacial reactions between Fe-P minerals and quercetin, the formation of 2-line ferrihydrite was promoted by quercetin with the interplanar distance of 0.26/0.30 nm at pH 7. 14.25% of the Fe-phosphate group was incorporated at a quercetin concentration of 1 mM and Fe oxides acted as the "core" for retaining P in these complexes. Further, phosphate release was observed during the interfacial reaction with increasing quercetin concentrations, suggesting a potential trade-off between P fixation and release. Despite these benefits, NPKM soils exhibited the highest degree of phosphorus saturation (DPS) (18.61%) and the lowest soil phosphorus storage capacity (1.70 mg kg⁻¹), indicating an elevated risk of P loss. And a significant positive correlation was identified among SROs, flavonoids, and DPS in paddy soils. Collectively, our findings demonstrated that flavonoids could modify the morphology of Fe oxides in paddy soils, thereby enhancing P fixation. This presents a promising approach for mitigating diffuse P pollution and promoting sustainable agriculture.