A synergistic biochar‑mycorrhizal strategy enhances rapeseed phytoremediation and antioxidant defences under Cd and Cr stress

Cadmium (Cd) and chromium (Cr) pollution severely limit the productivity of rapeseed (Brassica napus L.). A synergistic strategy combining biochar and arbuscular mycorrhizal fungi (AMF), applied with or without humic acid, was evaluated in greenhouse soil spiked with 50 mg kg⁻¹ Cd and Cr. AMF inoculation increased shoot dry weight by 36% and the Cd bioconcentration factor by 11% relative to polluted controls. Adding biochar or humic acid further elevated shoot- and root-BCF for Cd and Cr by 25-80% and raised the transfer factor above 1.2, indicating efficient root-to-shoot metal translocation. Total accumulation concentration doubled compared with AMF alone. The humic-acid + AMF treatment reduced malondialdehyde by 36% and moderated superoxide dismutase, catalase, and ascorbate peroxidase activities, evidencing lower oxidative stress. Overall, integrating AMF with biochar or humic acid enhanced biomass, mitigated oxidative damage, and strengthened phytoremediation capacity, offering a practical solution for Cd/Cr-contaminated, low-organic-matter soils.