Influence of Rhizosphere Bacteria on the State of Heavy Metal Compounds in the Soil-Plant System

The results of a greenhouse experiment with the humus horizon of a sandy loamy soddy-podzolic soil are presented. It was contaminated with heavy metals added with sewage sludge before 1990, then fodder grasses were grown for 20 years, after that the soil was left for 10 years under fallow. In the experiment, the influence of rhizosphere bacteria of the Pseudomonas genus on the mobility and fractional composition of the compounds of heavy metals: Cu, Zn, Cd, Ni, and Pb in the soil and their entering into the vegetative organs and root system of spring wheat were studied. Under the influence of inoculation with bacteria, the content and ratio of heavy metals compounds in the experimental soil changed with an increase in the contents of mobile Cd and Cd bound with organic matter; and Cu, Ni, Pb, also Zn to a lesser extent, bound with organic matter and iron compounds. At the same time, the contents of Cd and Zn d in the vegetative mass of wheat decreased, and the ratios between the contents of the elements in roots and vegetative mass became wider, which indicated an increase in the plant tolerance towards toxic effect of heavy metals and in the barrier function of the roots.