Biochar and Vermicompost Alleviate Cadmium Toxicity in Brassica napus by Regulating Photosynthesis, Antioxidant Defence, and Phytochelatin Detoxification

Cadmium (Cd) toxicity severely impacts crop productivity and human health, necessitating the development of effective remediation techniques. Biochar (BC) and vermicompost (VC) are important amendments for improving crop productivity and stress resistance. Nevertheless, their combined effects in mitigating Cd toxicity are poorly understood. This study evaluated the role of BC and VC individually and in combination in counteracting Cd toxicity in Brassica napus. The study included the following treatments: cadmium (Cd) stress (10 mg kg-1), Cd + BC (2%), Cd + VC (2%), and Cd + BC (1%) + VC (1%). Cadmium toxicity inhibited growth and yield by impairing photosynthetic efficiency, root growth, and nutrient availability and increasing electrolyte leakage (EL), malondialdehyde (MDA), and hydrogen peroxide (H2O2) levels. Biochar and VC alleviated the adverse impacts of Cd and significantly enhanced growth. This treatment increased the chlorophyll content, photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (gs) and decreased the EL, MDA (60.25%), and H2O2 production, contributing to improved growth. Biochar and VC amendments also stimulated antioxidant activity and osmolyte synthesis and upregulated the expression of antioxidant defence genes (BnAPX, BnCAT, BnPOD, and BnSOD), thereby protecting the plants. The combined application of BC and VC increased soil nutrient availability and enzyme activity. It also promoted Cd immobilization by increasing the soil pH and encouraging iron plaque formation, which subsequently reduced cadmium uptake and accumulation in roots by 42.12% and in shoots by 82.49%, respectively. Overall, coapplication of BC and VC is an effective strategy to increase crop productivity and reduce health risks by decreasing Cd accumulation in plants.