Enterobacter cloacae-loaded biochar suppresses cadmium accumulation in rice: Dual stabilization via soil immobilization and iron plaque interception

Cadmium (Cd) contamination in paddy soils poses serious risks to environmental quality and human health through rice consumption, necessitating effective amendments to immobilize Cd and reduce its uptake by crops. We conducted a pot experiment to evaluate rice straw derived biochar (BC), Enterobacter cloacae suspension (ET), and Enterobacter cloacae- loaded biochar (BE) applied at 1, 2 and 3% (w/w) on soil properties, microbial communities, Cd immobilization, and Cd accumulation in rice. BE treatments significantly improved soil pH, cation exchange capacity, and organic matter content compared with the control. Amone these, BE3% achieved a greatest reduction in soil available Cd (40.84%) and promoted its conversion into more stable residual fractions. Notably, BE2% induced significant shifts in the soil bacterial community, characterized by enrichment of anaerobic carbon-degrading taxa ( Anaerolineaceae and Clostridiaceae ) and iron reducing functional groups ( Anaeromyxobacteraceae and Xanthobacteraceae ), suggesting functionally oriented microbial reassembly driven by niche modification following amendment application. These microbial changes coincided with enhanced formation of iron plaques on rice root, effectively sequestering Cd and restricting its translocation into plant tissues. Partial least squares structural equation modeling (PLS-SEM) analysis revealed that iron plaque development played a pivotal role in stablizing soil Cd stabilization with rice Cd uptake and internal redistribution. These results highlight the critical role of BE in reducing Cd concentrations in rice root, stem, leaf, and grain while enhancing rice yield, with BE2% showing the most favorable overall performance.