Fractional Composition of Copper Compounds in Metal–Contaminated Soil and Its Accumulation in Plants in Application of Growth Promoting Rhizosphere Bacteria

Studies were carried out to investigate the effect of application of growth-promoting rhizosphere bacteria of genus Pseudomonas in artificial contamination of agro-gray soil with copper in a concentration above the approximately permissible level on fractional composition of metal compounds in soil, weight of spring wheat plants, and metal uptake by plants in pot experiment. To assess the effect of bacteria on the distribution of copper in soil fractions, inoculation with cultures P. fluorescens 20, P. fluorescens 21, and P. putida 23 was used. Wheat plants were grown up to booting stage in contamination with Cu(NO₃)₂·3H₂O at a rate of 300 mg Cu/kg of soil against background of NPK fertilization. Cu accumulation in fractions associated with organic matter, oxides, and hydroxides of Fe and Mn and, to a lesser extent, with carbonates was established. Content of Cu in shoots and roots after combustion in a mixture of HNO₃ : HClO₄ (2 : 1) and in the soil fraction was determined by inductively coupled plasma emission-optical spectrometry. Bacteria raised plant resistance to a high copper concentration and increased their weight by 13…24%, reducing the phytotoxicity of metal. The positive effect of bacteria in copper contamination is due to an increase in the content of metal in roots (18…19 times relative to variant with copper contamination without bacteria application). Bacteria increased copper content mainly in the specifically sorbed fraction associated with carbonates and in the composition of ferruginous minerals, while to a lesser extent in organic fraction and decreased the content of metal in the residual fraction. Growth in copper uptake by plants from the soil by 19…30% in application of bacteria corresponded to an increase in its presence in soil in relatively mobile forms and decrease in the residual fraction.