Alleviation of Cadmium Stress in Wheat through the Combined Application of Boron and Biochar via Regulating Morpho-Physiological and Antioxidant Defense Mechanisms

Abstract

Cadmium (Cd) contamination in soil adversely affects crop productivity, grain quality, and human health. Applications of boron (B) and biochar are known to impart tolerance to crops against abiotic stresses. A pot experiment was performed to assess the effects of the sole and combined application of B and biochar on growth, physiological and antioxidant defense mechanisms, yield, and grain quality of wheat under Cd toxicity-induced stress. The treatments included control (0 mg kg−1 and 0 g kg−1), only Cd (15 mg kg−1), only B (5 g kg−1), only biochar (50 g kg−1), B plus biochar, Cd plus B, Cd plus biochar, and Cd plus B plus biochar, which were applied at the time of sowing and were arranged using completely randomized design (CRD) with five replications. The individual Cd toxicity (15 mg kg1) significantly reduced chl a, chl b, and chl a+b, as well as primary metabolites (soluble protein, amino acids, total soluble sugar, and phenolic contents), while it increased the activities of enzymatic antioxidants like superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) in the leaves of wheat. In addition, Cd stress (15 mg kg1) increased lipid peroxidation in the form of malondialdehyde (MDA), and it enhanced the hydrogen peroxide (H2O2) content, electrolyte leakage (EL), and proline contents in the leaves. Furthermore, Cd (15 mg kg−1) contamination reduced the grain yield and yield-related attributes relative to respective no-Cd treatments. Soil-applied B and biochar improved wheat grain yield by triggering the activities of enzymatic antioxidants. Individual or combined B and biochar applications improved proline contents and reduced H2O2 and MDA contents in plants. The combined application of B and biochar enhanced soluble sugars and total phenolic as compared to the control and Cd-contaminated plants. In conclusion, the combined application of B and biochar was found to be the best soil amendment strategy to improve the yield of wheat under Cd-contaminated soil.