Efficacy of Fe-BC in enhancing growth, photosynthesis, nutrition, and alleviating the toxicity of Cd and Cr in rapeseed (Brassica napus L.): A tool for managing the environment and attaining sustainable agriculture

Soil contamination with cadmium (Cd) and chromium (Cr) pose serious threats to food safety and ecosystem stability. In current study, pristine biochar (BC) and iron-modified biochar (Fe-BC) were prepared, and the potential of BC and Fe-BC to reduce the bioavailability of Cd and Cr in soil, their uptake, toxicity in rapeseed (Brassica napus L) and the mechanisms involved were examined. In a pot experiment varying levels of BC and Fe-BC were applied to Cd and Cr-contaminated soil. The results indicated that soil supplementation with the highest level of Fe-BC (2 %) incremented the dry weights of roots, shoots, and seeds by 65 %, 33 %, and 149 %, respectively. Additionally, Fe-BC (2 %) treated rapeseed plants showed highest increase in photosynthesis, transpiration, stomatal conductance, intercellular CO₂ emissions, and chlorophyll contents by 43.2 %, 39.5 %, 33.5, 36.9 % and 28 %, respectively. Plants treated with Fe-BC (2 %) showed amplified superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) activities. The results regarding saturated and unsaturated fatty acid contents of seeds showed that Fe-BC (2 %) treatment exhibited the greatest increase in linolenic acid, oleic acid, erucic acid, and linoleic acid contents, increasing these acids by 21 %, 6.5 %, 53 %, and 14.5 %, respectively. Moreover, Fe-BC (2 %) treated seeds depicted increased oil and protein contents by 14 % and 29 %, respectively. Soil application of Fe-BC (2 %) dramatically decreased Cd and Cr levels in the roots, shoots, and seeds by 21 %, 44 %, 88 %, 16 %, 38 %, and 57 %, respectively. The addition of Fe-BC significantly lowered the concentration of exchangeable (Exc) and bound to carbonate (B-C) fractions of Cd and Cr in the soil, while increasing that of iron-manganese (B-Fe-Mn) bounded and residual (Res) fractions. In conclusion, soil application of the Fe-BC amendment could be used as a sustainable approach to reduce the ecological and environmental risks associated with soils contaminated with Cd and Cr, and ensure safer crop production.