Soil-Agrochemical Aspects of Remediation of Copper-Contaminated Soil upon Application of Growth-Promoting Rhizobacteria

The influence of growth-promoting rhizobacteria of the Pseudomonas genus on the growth and chemical composition of spring wheat plants grown on an artificially contaminated with copper nitrate (300 mg/kg) substrate from the humus horizon of an agrogray soil (Luvic Retic Greyzemic Phaeozem (Loamic)) was studied in a pot experiment. The application of P. fluorescens SV20, P. fluorescens SV21, and P. putida SV23 bacteria significantly reduced the toxic effect of copper in the first half of the growing season. An increase in spring wheat resistance to contamination with copper nitrate as a result of bacteria application was due to an enhanced uptake of N, P, K, Ca, Mg, Fe, Mn, and Zn from the contaminated soil by the plants without significant changes in the concentrations of most elements in the plants and in the soil reaction. Positive effect of bacteria was also associated with an increase in copper accumulation by roots, i.e., an increase in the barrier function of the root system towards the metal. Bacteria increased the copper content in the specifically sorbed fraction and in the fractions bound to iron minerals and, partly, organic matter and decreased it in the residual (firmly bound to clay minerals) fraction as determined by the sequential selective extraction method. Bacteria enhanced phytoextraction—purification of contaminated soil via increasing copper uptake by plant shoots. Application of bacteria can be recommended for remediation of copper-contaminated soils based on environmentally friendly technologies.