Fractional Composition of Soil Nickel Compounds and Its Accumulation in Plants under Application of Growth-Promoting Rhizosphere Bacteria in Heavy Metal Contaminated Soil

The article reports the results of a pot experiment concerning the effect of the genus Pseudomonas bacteria on fractional composition of nickel compounds in artificially contaminated agro-gray soil and on spring wheat yield. The experimental design included the following variants: without the use of nickel and bacteria; with introduction of nickel without bacteria application; and with introduction of nickel and bacterium P. fluorescens strain 20, nickel and bacterium P. fluorescens strain 21, and nickel and bacterium P. putida strain 23. Plants were grown to the booting stage in the presence of NiCl 2 · 6H 2 O contamination at a dose of 300 Ni/kg of soil against NPK fertilization. Nickel distribution in soil was investigated in fractions isolated using a method of the sequential selective extractions. A technique of inductively coupled plasma optical emission spectrometry was used to determine nickel content in plants after digestion in mixture of HNO 3 : HClO 4 (2 : 1) and in soil fractions. Application of the bacteria enhanced plant resistance to elevated nickel concentration and improved yield by significantly reducing heavy metal phytotoxicity. Nickel content also increased in exchangeable and specifically sorbed fractions and, to a lesser extent, in fractions associated with organic matter and ferrous minerals and decreased in residual fraction. Bacteria promoted nickel uptake from soil by plant shoots largely due to the improved yield, without changing or increasing a content of the metal in plants. Thus, application of the bacteria enhanced phytoextraction, that is, cleanup of heavy metal contaminated soil. Nickel uptake by plants was increased due to increase in its bioavailability, in exchangeable and specifically sorbed fractions in particular.