Iron-Doped Biochar Regulated Soil Nickel Adsorption, Wheat Growth, Its Physiology and Elemental Concentration under Contrasting Abiotic Stresses

The prevalence of abiotic stresses hampers soil health and plant growth in most ecosystems. In this study, rice husk iron-enriched biochar (BC) was prepared and its superiority in terms of nutrients enrichment, porosity and different acidic functional group (O-H, C=O) relative to simple biochar was confirmed through scanning electron microscopic, X-ray fluorescence and Fourier transform infrared analysis. To further evaluate its nickel (Ni), salt (NaCl) and carbonate (CaCO3) stress mitigating impact on wheat physiology and biochemical attributes, a pot experiment was conducted using; BC (1%), Ni (0.5 mM NiNO3), Na (100 mM NaCl) and CO3 (100 mM CaCO3) and with twelve treatments; T1; Control, T2; NiNO3, T3; CaCO3, T4; NaCl, T5; BC, T6; Ni + BC, T7; CaCO3 + BC, T8; NaCl + BC, T9; Ni + CaCO3 + BC, T10; Ni + NaCl + BC, T11; CaCO3 + NaCl + BC, T12; Ni + NaCl + CaCO3 + BC. The Langmuir isotherm model revealed the maximum Ni adsorption capacity (2433 mg g−1) in treatments where Ni was applied with BC soil. Maximum soil DTPA-extractable Ni was found in the T9 treatment; however, Ni concentration was not reported in wheat roots while only trace amounts of Ni were found in wheat shoots with the T9 treatment. It was suggested that BC has the capacity to induce the immunization effect in plant roots by providing additional Fe so their ionic homeostasis and redox metabolism worked properly. This argument was further paved by the enhanced adsorption of these toxic ions in the presence of BC-favored wheat growth as indicated by maximum increases in shoot iron and potassium concentrations under Ni + CaCO3 + BC, relative to control. Furthermore, the decrease in shoot hydrogen peroxide (H2O2) (20%) and malondialdehyde (32%) concentrations and increase in shoot ascorbate peroxidase (81%) and catalase (three-fold) activities under Ni + BC relative to Ni + NaCl + CaCO3 + BC controlled the cell membrane damage. In conclusion, BC proved to be an excellent amendment to reduce the toxic effects of Ni, NaCl and CaCO3 stresses and enhance wheat growth and nutrition.