Iron and zinc-modified nano-biochar alleviate salinity stress in paddy soil by modulating nutrient availability and microbial communities

Application of nano-modified biochar significantly increased soil organic matter, soil organic carbon, and the availability of macronutrients (N, P, and K). FeBC and ZnBC enhanced microbial biomass carbon and nitrogen as well as urease and β-glycosidase activities in saline soil. Nano-biochar treatments altered microbial community composition, increasing the abundance of salt-tolerant bacterial phyla such as <i>Proteobacteria</i>, <i>Chloroflexi</i>, and <i>Bacteroidota</i> under saline conditions, while modifying fungal community structure, including increased relative abundance of Chytridiomycota under FeBC treatment.