Multi-element amendment reshaped rhizosphere microbiome: A microbially driven Fe/Mn/S synergistic action for Cd immobilization.

Cadmium (Cd) contamination in soils threatens rice safety, necessitating effective remediation strategies. While the silicon-calcium-magnesium amendment (FSY) is known to reduce Cd bioavailability, its precise microbial mechanisms remain underexplored. This study integrated metagenomics and machine learning to investigate FSY's impact on the rice rhizosphere microbiome and to elucidate the biological drivers of Cd immobilization. FSY application and rice growth stage were the core factors that significantly reshaped bacterial and archaeal community structures, shifting archaeal community assembly toward deterministic processes, while the fungal community remained relatively stable. Co-occurrence network analysis revealed that FSY enhanced the complexity and stability of microbial interactions, strengthening the roles of key functional taxa. Crucially, functional profiling showed that FSY significantly upregulated genes related to multi-barrier systems (1) iron/manganese oxidation (e.g., feoB): associated with iron-manganese plaque (IP) formation (2) sulfate reduction (e.g., dsrA); linked to cadmium sulfide (CdS) precipitation; and (3) microbial Cd resistance (e.g., the czcA gene). Machine learning identified 14 core species, including key taxa in Campylobacterota and Thermoproteota, as the pivotal drivers of synergistic Fe/Mn/S-Cd interaction. These findings substantiated the microbially driven Fe/Mn/S synergistic model for Cd immobilization through three interconnected mechanisms: enhanced microbially mediated mineral fixation (IP thickening and CdS precipitation), and strengthened community-level Cd resistance. This research provided a deep mechanistic understanding of how chemical amendments induced microbial functions to mitigate heavy metal risks, thereby offering a scientifically-grounded strategy for remediation and safe use of Cd-contaminated field.