Biochar and trehalose synergistically mitigate antimony toxicity in Brassica napus by enhancing physiological functions and stress-responsive gene expression

Antimony (Sb), a toxic metalloid, severely threatens crop productivity and human health. Biochar (BC) and trehalose (Tre) are known individual stress mitigators, but their combined effect against Sb toxicity remains unexplored. This study investigated the synergistic potential of BC (2% w/w) and Tre (30 mM) in alleviating Sb stress (100 mg kg⁻¹) in Brassica napus. Antimony stress significantly inhibited plant growth and yield, increased membrane damage (malondialdehyde) and hydrogen peroxide levels, enhanced Sb accumulation, and impaired chlorophyll synthesis, osmolyte production, and soil nutrient availability. In contrast, the co-application of BC and Tre most effectively reversed these damages. It enhanced growth and yield by significantly reducing malondialdehyde (52%), H₂O₂ (43%), and soil Sb availability, while increasing chlorophyll content (51-70%), osmolytes (total soluble protein: 49%; free amino acids: 37%), and key soil nutrients (total nitrogen: 18%; available phosphorus: 52%; available potassium: 43%, soil organic carbon: 27%). Concurrently, antioxidant enzyme activities (APX, CAT, POD, SOD) were elevated by 31-65%. This biochemical improvement was strongly associated with the upregulation (30-52%) of corresponding stress-responsive genes (BnAPX, BnCAT, BnPOD, BnSOD). Our findings demonstrate that the BC+Tre combination synergistically immobilizes Sb in soil, enhances soil fertility and plant physiological resilience, and upregulates antioxidant defense genes, presenting a sustainable strategy for remediating Sb-contaminated soils and securing crop production.