The heading stage: A critical period for schwertmannite in reducing arsenic accumulation in rice (Oryza sativa L.).

Schwertmannite, a common iron-derived mineral, is known for its high efficiency in adsorbing As from water and reducing the mobility and availability of As in soils. However, few studies have examined the critical period for the effectiveness of schwertmannite in hindering As uptake by rice plants, particularly its impact on the uptake and transport of As across different growth stages of rice. In this study, hydroponic experiments were performed to explore the absorption and translocation of As (500 µg/L As(III) or As(V)), when combined with schwertmannite, in rice during all growth stages. The results showed that As concentration in roots, stems and leaves increased with rice growth, while the addition of schwertmannite reduced the As concentration in all parts of rice, compared to the control without schwertmannite. Besides, schwertmannite application mitigated the harmful impact of As on rice yield, and reduced As levels in grains by 66 %-90 % compared to treatments with only As(III) or As(V). The heading stage is identified as a critical period for applying schwertmannite to reduce As uptake in rice. Specifically, during the heading stages, the plants uptake 85 %-91 % of the As contents in the absence of schwertmannite. However, adding schwertmannite retained about 84 %-90 % of As content, significantly reducing its absorption by rice plants at this stage. Therefore, maintaining As adsorption by schwertmannite up to the heading stage is beneficial to effectively reduce As uptake in rice and lower As concentration in rice grains.