Runqiu Feng, Mengxuan He, Lingyue Lv, Ziyue Shi, Wei Zhang, Jie Liu
Biochar is increasingly applied to remediate cadmium (Cd)-contaminated soils, yet the microbial mechanisms by which biochar governs Cd speciation remain insufficiently resolved. Here, we evaluated three structurally and chemically distinct biochars— Juglans regia , Flaveria bidentis , and Spartina alterniflora —applied at 1 %, 3 %, and 5 % to coastal saline–alkali soil to elucidate how biochar-driven microbiome reassembly contributes to Cd immobilization. Biochar amendments significantly reshaped bacterial and fungal diversity, with bacterial communities showing greater sensitivity to salinity- and nutrient-mediated stresses. The low-ash J. regia biochar enhanced α-diversity and microhabitat quality, fostering stable functional guilds that supported predictable Cd biotransformation. In contrast, high-ash, ion-releasing F. bidentis and S. alterniflora biochars intensified osmotic and stoichiometric pressures, promoting deterministic assembly and enriching stress-tolerant, Cd-resistant taxa despite reduced overall diversity. Across treatments, biochar was associated with shifts toward microbial taxa predicted to encode pathways related to extracellular polymeric substance production, siderophore biosynthesis, and biofilm formation, which are potentially linked to Cd chelation and detoxification. KEGG-based predictions further revealed strengthened pathways related to lipid biosynthesis, membrane reinforcement, and stress resilience, indicating functional reprogramming of microbial metabolism under Cd exposure. Cd fractionation analyses confirmed substantial reductions in bioavailable Cd following amendment. Collectively, these results demonstrate that tailored feedstock selection can strategically couple biochar's physicochemical properties with microbiome-mediated detoxification to optimize Cd remediation in saline–alkali soils.