MITIGATION OF NICKEL STRESS IN RICE BY EXOGENOUS APPLICATION OF BIOCHAR AND CHITOSAN

Abstract

Nickel (Ni) is considered as an essential micronutrient for plants, but it becomes phytotoxic at supra-optimal level which leads to inhibition of seed germination, growth and yield reduction as a response of physiological and biochemical dysfunction. Therefore, an experiment was conducted at the shed house of the Department of Agronomy, Sher-e-Bangla Agricultural University, Dhaka-1207, Bangladesh from December 2020 to April 2021 in order to investigate the morphological, physiological, and biochemical responses of rice (Oryza sativa L. cv. BRRI dhan96) upon exposure to different levels of Ni and to study the protective role of biochar (BC) and chitosan (CHT) in mitigating Ni stress. Twenty-one days after transplanting (DAT), rice seedlings were exposed to Ni stress by treating with 0.5, 1.0, and 2.0 mM NiSO 4 •6H 2 O for four times. Exogenous supplementation of BC (0.5 g kg −1 soil) was done once before seedling transplantation and the CHT (200 mg L ) was applied at seven-day intervals from 14 DAT to panicle initiation as foliar spray. The experiment was conducted in a completely randomized design with three replications and all the obtained data was subjected to one-way analysis of variance. Exposure to Ni stress exhibited a notable increase in hydrogen peroxide content, lipid peroxidation, and electrolyte leakage indicating Ni-mediated oxidative damages in the rice plants. Consequently, the Ni stressed plants showed a reduction of plant height, tillers hill –1 , leaf area, root fresh weight, shoot fresh weight, root dry weight, shoot dry weight, soil and plant analysis development value, and yield attributes in a dose dependent manner. The relative water content of the Ni treated plants also reduced with a concomitant increase in the proline accumulation. Supplementation with BC and CHT mitigated the deleterious effects of Ni toxicity in plants as reflected in enhanced growth and physiological attributes under different levels of Ni. Increase of ascorbate and glutathione with the concomitant reduction of dehydroascorbate and glutathione disulfide was observed when BC and CHT was supplemented in the Ni stressed plants. Moreover, the yield attributes such as effective tillers hill , panicle length, rachis panicle –1 , filled grains panicle –1 , and 1000-grain weight were also increased when BC and CHT were applied, thus the grain yield hill was increased under Ni stress. These findings indicated a protective role of BC and CHT against Niinduced damages by enhancing physiological and biochemical processes of rice.