Soil-Agrochemical Aspects of Remediation of Nickel-Contaminated Soil Using Growth-Promoting Rhizosphere Bacteria

Abstract

In pot experiments, the effect of introducing rhizospheric bacteria promoting plant growth on the yield and chemical composition of spring wheat when grown in humus horizon of the Luvic Retic Greyzemic Phaeozems (Loamic) soil artificially contaminated with a water-soluble nickel compound was studied. Application of P. fluorescens 20, P. fluorescens 21, and P. putida 23 bacteria increased plant resistance to elevated nickel concentration and increased yields, significantly reducing or completely eliminating heavy metal phytotoxicity. The resistance of plants to impact of nickel stress when using bacteria is due to: a) stimulation of root growth and an increase in the accumulation of nickel in the root system, b) improvement in the mineral nutrition of plants – an increase in uptake of biophilic elements from contaminated soil due to an increase in yield, in general, without significant changes in the content of the most elements in plants, including grain. Application of bacteria increased uptake of nickel from the soil by above-ground organs of plants, thereby enhancing phytoextraction – purification from heavy metal and, consequently, soil remediation. The distribution of nickel in soil in fractions isolated by the method of consecutive selective extractions has been established. In the first half of the growing season, application of bacteria increased the content of nickel in the soil, mainly in the exchangeable and specifically sorbed fractions and, to a lesser extent, in fractions associated with organic matter and ferruginous minerals, and decreased content of the metal in the residual fraction. Increase of nickel accumulation in plants in application of bacteria corresponded to increased heavy metal content in soil, mainly in the composition of compounds associated with exchangeable and specifically bound fractions. At full maturity of plants, no significant changes were found in fractional composition of Ni in the soil. Application of bacteria can be recommended in the development of strategies for remediation of nickel-contaminated soils based on environmentally friendly technologies.