Effects of biochar and zeolite soil amendments with foliar proline spray on nickel immobilization, nutritional quality and nickel concentrations in wheat

Since Ni-rich soils are a threat to the environment, growing edible crops on Ni-rich soils can pose a serious risk to human, animal, plant and ecosystem health and, hence, is considered as a challenging task for the researchers. Contrarily, limiting the bioavailability of Ni in such soils upon the addition of suitable amendments cum foliar spray of proteinogenic amino acids having an objective to alleviate stress to crop plants can considerably reduce the environmental risk. In this pot trail, we substantiate the effects of biochar (BR) and zeolite (ZL) addition in the soil along with proline (PN) spray on the resistance, and stress responses of wheat against Ni as well as on Ni translocation and accumulation in wheat plants grown on a Ni-rich soil contaminated by electroplating effluent. The treatments, applied with and without PN spray, involved: no amendment; BR; ZL; and a concoction of both amendments (BR50%+ZL50%). We found that BR50%+ZL50% treatment significantly immobilized Ni in the soil, reduced its accumulation in the shoot, root, and grain, blocked membrane lipid peroxidation and showed an improvement in photosynthetic parameters, the status of antioxidant activities, grain biochemistry and grain yield, compared to the control. Interestingly, exogenous PN spray caused a significant additive effect on the aforementioned parameters in the wheat plants grown on BR50%+ZL50% treated soil. Our results involved a reduced Ni bioavailability in wheat rhizosphere due to BR50%+ZL50% in soil and, furthermore, the additive effect of PN spray to scavenging ROS, obstructing peroxidation of lipid membrane and, thus providing resilience to wheat plant against Ni stress. The suggested technique can make Ni-rich soils suitable for cultivation and production of high-quality food by minimizing Ni bioavailability and toxicity to plants.