Speciation of arsenic and its accumulation by plants from rhizosphere soils under the influence of Azotobacter and Bacillus bacteria

Abstract

Our study was aimed at disclosing the effect of rhizosphere bacteria Azotobacter and Bacillus, involved in the composition of biological preparations used in plant cultivation, on arsenic accumulation in plants proceeding with its different phase states in the radical rhizosphere part of soil. The plants like wheat, oats, peas and radish have been grown on the controlled soil with some experimental biopreparations applied. In our experiment we worked on the soils differently contaminated with arsenic. The investigation of arsenic phase state was based on the sequential release of extracts from rhizosphere soils occurring as easily exchangeable, carbonate, organic and Fe hydroxide-associated fractions with As identified. We additionally examined the distribution of As in the extract of ethylenediaminetetraacetic acid (EDTA) and in humic substance: fulvic acids and humic acids. It has been inferred, that As migration in the rhizosphere soil is markedly affected by its forms associated with Fe hydroxides and organic compounds: fulvic acids and extracted EDTA by chelate compounds. The experimental results point out that arsenic associated with Fe hydroxides is basically accumulated in the rhizosphere part of soils in their inoculation by rhizo bacteria. In maximally contaminated soils As can possibly be adsorbed on the cells of Azotobacter and Bacillus soil bacteria capable to create a barrier for its supply into plants. Inoculation of soils by rhizosphere bacteria affected the inter-phase transitions of arsenic in soil of rhizosphere significantly influenced the processes of immobilization and mobilization of arsenic in the system “soil–plant” and its biological availability for plants.