Iron-Based Nanomaterials Enhance Rice Growth and Limit Grain Arsenic Accumulation via Iron Plaque Formation and Rhizosphere Modulation

Through 40-day short-term pot experiments and 128-day complete life-cycle pot experiments, this study systematically evaluated the effects of three iron-based nanoparticles (NPs)─nZVI, Fe 2 O 3 NPs, and Fe 3 O 4 NPs─and two ionic iron (Fe) fertilizers (FeCl 3 and FeSO 4 ) on rice growth and arsenic (As) accumulation. We further examined the formation, structural characteristics, and physicochemical properties of root-associated Fe plaque, along with As dynamics in the rhizosphere. All Fe amendments increased rice grain yield. Compared with the control, Fe treatments reduced grain As concentrations by 19.8–44.8% while increasing Fe contents by 16.9–52.7%, with nZVI exhibiting the strongest As mitigation effect. Multiscale analyses revealed that Fe NPs altered the pore structure and Fe speciation of Fe plaque, increased the proportion of crystalline iron oxides, and enhanced the spatial colocalization of As and Fe within the Fe plaque. nZVI notably enhanced the As immobilization capacity of Fe plaque. Concurrently, Fe NPs facilitated the transformation of labile As into more stable forms in rhizosphere soils and increased the abundance of functional genes involved in As oxidation, detoxification, and Fe redox. Overall, Fe NPs represent a promising strategy for reducing As exposure risks in As-contaminated paddy soils.