Biochar Application for Alleviating Nickel Stress and Enhancing Growth, Photosynthetic Pigments, and Antioxidant Defense Mechanisms in Sorghum

Increased nickel (Ni) concentrations in plant cells induce physiological, metabolic, and cellular changes, resulting in serious damage to the plants. Among the various strategies to mitigate Ni toxicity in plants, the use of biochar (BC) is highly effective. Biochar enhances soil remediation by immobilizing Ni, reducing its bioavailability, and improving overall soil health. This research aimed to evaluate the effectiveness of BC in alleviating Ni stress in sorghum. The BC was applied at 0, 2.5 and 5 g per kg of soil and Ni concentration was kept at 0, 50 and 100 ppm. The results indicated that the treatment of BC at 5 g enhanced the root and shoot length, fresh weight, and dry weight of both shoot and root, but the application of Ni reduced all assessed growth parameters. Under Ni stress conditions, a concentration of 5 g of biochar enhanced the photosynthetic pigments chlorophyll a , chlorophyll b , total chlorophyll, chlorophyll ratio, and carotenoids. At 5 g, biochar lowered the amounts of malondialdehyde (MDA) and hydrogen peroxide (H ₂ O ₂ ) by increasing the activity of the antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). However, Ni stress increased the amounts of MDA and H ₂ O ₂ . The application of 5 g of BC under Ni stress enhanced the uptake of Ca²⁺ and K⁺ while reducing Na⁺ accumulation. In conclusion, the application of BC at 5g per kg of soil enhanced plant growth, photosynthetic pigments, Ni absorption, antioxidants, ionic contents, and reduced oxidative stress indications, thereby mitigating Ni stress conditions.