Abstract
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.
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