Synergistic Regulation of Soil Enzymes and Microbial Communities by Biochar‐Supported Nano‐Hydroxyapatite Under Cadmium Stress

ABSTRACT Biochar has been globally recognized as an effective amendment for enhancing soil fertility and mitigating climate change, but its improvement of microbial communities and enzyme activities remains limited. Soil incubation experiments were conducted using nano‐hydroxyapatite (nHAP)‐modified biochars derived from corn straw, sawdust, and rice straw. The objective was to investigate changes in microbial community structure, composition, and soil enzyme dynamics under cadmium‐contaminated conditions. The results showed that all passivation materials significantly increased urease and sucrase activities while decreasing acid phosphatase activity ( p < 0.05), a phenomenon closely related to increased soil pH and decreased Cd bioavailability. Microbial diversity analysis showed distinct phylum‐level differences, with bacteria being more sensitive to the modified materials than fungi. Furthermore, correlation analysis revealed that nHAP@BC not only alleviated Cd‐induced suppression of sensitive microbial taxa but also reshaped the coupling relationships among nutrients, enzymes, and microbial communities, thereby promoting community succession toward functions favorable to ecological restoration. This study reveals a synergistic interaction between nano‐hydroxyapatite and biochar in modulating soil enzymatic functions and reshaping bacterial community dynamics, which provides a scientific basis for enhancing the ecological safety and sustainability of Cd‐contaminated soil remediation.