Deciphering the microbial response and functional potential involving in cadmium-arsenic co-contaminated paddy soil...

To remediate cadmium (Cd)-arsenic (As) co-contaminated paddy soils, a novel silicon-magnetic biochar (SBC) was synthesized. Its microbial remediation mechanisms were investigated through a rice pot experiment combined with metagenomics. Results showed SBC significantly improved soil properties, including increased pH and dissolved organic carbon (DOC). This led to a drastic reduction in the rhizosphere bioavailability of Cd (by 69.9 %) and As (by 29.5 %). Consequently, SBC enhanced rice growth, with mature plant height and dry biomass increasing by 25.0 % and 46.7 %, respectively. Crucially, SBC reduced Cd and As accumulation in grains by 38.4 % and 55.6 %. Metagenomics revealed SBC enhanced microbial diversity, stability, and functional potential in both soil and phyllosphere, particularly in cellular processes and genetic information processing. SBC enriched key soil taxa linked to detoxification, such as Geobacter, Gemmatirosa, and Flaviaesturariibacter, and beneficial phyllosphere microbes like Ensifer adhaerens and Rhizobium rosettiformans. Functionally, SBC up-regulated microbial Cd efflux genes, while strong physicochemical adsorption and precipitation (with OH^-, Fe, and S^2-) further enhanced Cd immobilization. Concurrently, it up-regulated As reduction genes while down-regulating As efflux genes, promoting microbial As(III) sequestration. These findings demonstrate SBC passivates Cd and As through synergistic physicochemical immobilization and microbial pathway modulation, which underscore its significant environmental value for restoring soil health and mitigating contamination.