Biochar Mitigates Cadmium Stress on Alfalfa Seeds During Germination

Cadmium (Cd +2 ) is a ubiquitous toxic heavy metal (HMs) in the environment. Cadmium chloride was used in three concentrations (0.001, 1, and 5 mM) in presence and absence of Biochar (BC) to evaluate the efficiency of BC in remediation of the Cd toxicity on seed germination. Germination percentage, radicle length, fresh and dry weight gradually decreased with increasing Cd concentration and completely inhibited at 5 mM CdCl 2 . Seedling vigor index (SVI) and metal tolerance index (MTI) decreased, while phyto-toxicity (%) increased with increasing Cd concentration to become 100% at 5 mM CdCl 2 . Cd-stress increased malondialdehyde (MDA), hydrogen peroxide (H 2 O 2 ) and proline content, whereas the total soluble sugars, total soluble proteins, DNA and RNA content decreased. Activity of catalase (CAT), peroxidase (POX) ascorbic acid oxidase (ASAO), polyphenol oxidase (PPO) increased under Cd-stress conditions. On the other hands, Cd negatively affected α-, and β-amylases and protease enzymes. Cd application also caused a great alteration in the permeability of membranes through increasing ion leakage and lipid peroxidation. Application of BC significantly alleviated the inhibitory effects of Cd and consequently, increased germination percentage, SVI and MTI. Phytotoxicity and inhibition value of radicle decreased by BC treatment to become 50% at 5 mM CdCl 2 . Increasing the germination percentage by BC treatment was associated with increasing the activity of the antioxidants and the hydrolytic enzymes under Cd stress.