Application of Fe-based S-rich material mitigates As and Cd toxicity in rice by alleviating root tip structural damage and improving bacterial community function.

The opposite geochemical behaviors of cadmium (Cd) and arsenic (As) in paddy fields lead to challenges in the simultaneous mitigation of Cd and As accumulation in rice (Oryza sativa L.) grains. In this study, an industrial byproduct Fe-based S-rich material (Fe-S-Mat) was used to mitigate As and Cd accumulation in the soil-rice continuum that conferred toxicity relief in rice seedlings. We found that Fe-S-Mat application reduced root Cd and As contents by 34.0%-59.0% and 75.5%-85.9%, respectively, and shoot Cd and As contents by 29.4%-50.9% and 22.9%-39.3%, compared to the control. Cd and As contents in the soil solution decreased by 39.6%-61.3% and 34.3%-44.7%, as both elements shifted from the active acid-extractable fractions to more stable forms. Moreover, the results of scanning electron microscopy and transmission electron microscopy showed that the adverse effects on root meristem cell wall swelling and incomplete nuclear structure almost disappeared. Importantly, the bacterial community structure and functional prediction in the rhizosphere revealed that Fe-S-Mat treatments increased the chemoheterotrophic pathway microbial populations by an average of 91.7% and enhanced resistance to As, including nitrate reduction, sulfate and iron respiration functions. These findings will shed light on the future selection and development of multipurpose passivators for the safe production of rice in Cd and As co-contaminated paddy soil.