Influence of fertilization strategies on arsenic uptake by rice (Oryza sativa L.): Insights from biotic and abiotic perspectives

Fertilization regulates soil organic matter and microbial communities, which affect arsenic behavior in rice rhizospheres, but the coupled mechanisms remain unclear. This study systematically explored the effects of fertilization strategies on soil properties including dissolved organic matter (DOM) characteristics, microbial communities, and arsenic behavior based on a field experiment conducted over a full rice growth cycle in Ningbo, Zhejiang Province, China. The results showed that the combined application of organic and inorganic fertilizers increased soil pH by up to 33 % and elevated the concentration of DOM by 1.5-fold, but had different effects on microbial community and arsenic-related functional genes. High proportion of sludge-based organic fertilizer maintained neutral soil pH while reducing microbial alpha diversity and altering microbial community composition. Whereas manure-based organic fertilizer application significantly improved the DOM aromaticity, promoting arsenic mobilization and increasing pore water arsenic concentrations. High-throughput qPCR revealed that microbial As(V) reductase genes governed arsenic mobility via As(V)-to-As(III) conversion, while elevated arsenic methylation gene abundance in organic fertilizer treatments enhanced volatilization, reducing grain arsenic accumulation. In general, the application of a high proportion of sludge- and manure-based organic fertilizers increased rice biomass by 1.3 to 2.2-fold, but had no significant effect on grain yield or the arsenic content of brown rice. Nevertheless, the long-term organic fertilizer use showed promising potential for improving soil quality, enhancing crop productivity, and mitigating arsenic accumulation. These findings demonstrate that optimized organic fertilization offers a sustainable strategy to improve soil health and reduce rice arsenic risks, supporting food safety in contaminated areas.