Based on the mechanism whereby cations loaded onto modified biochar can displace Na? in saline–alkali soils via ion exchange,this study used corn-stover biochar as the carrier and employed ball-milling to composite it with flue-gas desulfurization gypsum(DG),single superphosphate(SSP),and poly-aluminum ferric sulfate(PAFC),thereby preparing three modified biochars(BCDG,BCSSP,and BCPAFC)and systematically evaluating their amelioration effects and underlying mechanisms in soda saline–alkali soil.The results showed that ball-milling modification markedly altered the physicochemical properties of biochar;among the three,BCPAFC exhibited a highly porous structure,abundant amorphous metal hydroxyl complexes,and higher polarity and hydrophilicity.Incubation experiments indicated that BCPAFC effectively regulated soil alkalinity,stabilizing soil pH(initially 8.25) within a near-neutral range (6.49–6.88),while maintaining a relatively high electrical conductivity(0.50–0.55 mS/cm).Meanwhile,it increased Ca2? and Mg2? concentrations in the soil solution,promoted sustained Na? release and leaching,and reduced the sodium adsorption ratio(SAR)to 1.91–5.23.In addition,after 12 days of incubation,BCPAFC decreased exchangeable sodium(ENa?) by 10.2%,increased cation exchange capacity(CEC)by 86.4%,and reduced exchangeable sodium percentage(ESP)by 63.4%,demonstrating a pronounced advantage in reshaping soil exchangeable-ion equilibrium.Microbial community analysis further revealed that BCPAFC enhanced bacterial α-diversity,enriched salt-tolerant taxa such as Actinobacteriota and Pseudomonadota(Proteobacteria),and increased alkaline phosphatase and urease activities.Correlation analysis suggested that soil pH,base cations, and carbon–nitrogen nutrients were the primary environmental drivers governing microbial community succession.Overall,BCPAFC enables rapid amelioration and ecological function recovery of soda saline–alkali soil through the synergistic action of multiple mechanisms,including ion exchange,specific adsorption,structural regulation,and microbial activation,providing important theoretical and technical support for the development of biochar-based soil remediation materials.