Fe/Mg-LDH modified biochar for heavy metal soil remediation: Effects on microbial community structure and metabolic...

Heavy metal contamination in farmland soils around the Dabao Mountain mining area, with Cu (573.7 mg/kg), Pb (598.2 mg/kg), and As (288.4 mg/kg), poses a serious threat to food safety and the ecological environment. Herein, an acetate‑intercalated Fe/Mg layered double hydroxide‑modified biochar (Ac‑LB) was synthesized to remediate this co‑contaminated soil. The intercalated acetate expanded the LDH interlayer spacing, enhancing the simultaneous immobilization of cationic (Cu, Pb) and anionic (As) metals. At a 1.5% application dosage, Ac‑LB reduced the bioavailability of Pb, Cu, and As by 41.73%, 39.51%, and 40.53%, respectively, and facilitated the transformation of labile metal fractions into more stable forms. Beyond metal immobilization, Ac‑LB amendment improved soil physicochemical properties (increased pH, organic matter, and nitrogen) and alleviated heavy metal stress on soil microbiota, as evidenced by enhanced urease and sucrase activities, increased bacterial diversity, and enrichment of nutrient‑cycling phyla (Proteobacteria, Gemmatimonadetes). Metabolomics analysis further demonstrated that Ac-LB modulated microbial metabolic pathways related to carbon, nitrogen, and phosphorus cycling in a dosage-dependent manner. However, excessive application of Ac-LB (1.5%) introduced new microbial stress, reducing network modularity and altering metabolite profiles. This study will provide new research insights for the remediation of soils co‑contaminated with cationic and anionic heavy metals and also offer a theoretical basis for the rational application of remediation amendments.