Intercropping and Green Manure Return Mitigate Arsenic Contamination in Rice via Induced Shifts in Soil Enzymatic Activities and Microbial Communities

Arsenic (As)‐accumulating plants are used in monoculture or intercropping to remediate contaminated soils, but their As‐rich biomass poses environmental risks. Using this biomass as green manure is a promising strategy to improve soil health, crop yield, and microbial diversity. However, its effects on stress tolerance and As accumulation in brown rice remain poorly understood. This study investigates the impact of five green manures derived from monoculture or intercropping of As‐accumulating plants on brown rice physiology and soil microbial communities in As‐contaminated soil under crop rotations. The application of green manure significantly increased brown rice yield (25.42–39.53 g/plant) and alleviated physiological stress. Activities of oxidative stress‐related enzymes (catalase, superoxide dismutase, and peroxidase) were reduced by 38.70%, 40.13%, and 37.30%, respectively, along with a 48.46% decrease in malondialdehyde content. Green manure also improved soil physicochemical properties, including pH, cation exchange capacity (CEC), and soil organic matter (SOM), while reducing available soil As concentration. These improvements were accompanied by enhanced soil enzyme activities (β‐glucosidase, protease, urease, and acid phosphatase) and distinct shifts in microbial community composition. Notably, the relative abundances of Proteobacteria and Chloroflexi decreased, while Nitrospira, Sphingomonas, Acidibacter, Rokubacteriales, Pedomicrobium, Nocardioides, Saccharimonas, Terrimonas, Haliangium, and Flavobacterium increased. These taxa exhibited strong negative correlations with soil As concentrations and positive associations with pH, CEC, SOM, and soil enzyme activities. Green manure from postphytoremediation biomass improved brown rice stress resilience, yield, soil quality, and beneficial microbial populations. This approach offers a sustainable way to reduce As risks and boost productivity in crop rotation systems.