Biological Characteristics and Concentrations of Extractable Fe, Al, and Si Compounds in Spruce Rhizosphere in Podzolic Soil

Abstract

Some biological properties and concentrations of extractable Fe, Al, and Si compounds in the samples of the AOEL horizon of podzolic soil taken in five replicates from the rhizosphere of 15- to 20-year-old spruce and from the nonrhizosphere soil are discussed. The soil mass of the rhizosphere is characterized by a significantly higher total number of bacteria, more abundant and diverse saprotrophic bacterial complex, greater length of fungal mycelium, and higher content of benzenecarboxylic acids dominated by benzoic acid in comparison with the nonrhizosphere soil. The soil mass of the rhizosphere and the fraction of 1–5 µm isolated from it are also characterized by significantly higher concentrations of Fe and Al extracted by the Tamm and Bascomb reagents because of the accumulation of Fe-organic and Al-organic complexes. For extractable Al compounds in the rhizosphere, this finding is confirmed by the high coefficient of correlation between the amount of Al in the extracts and the C_org content in the bulk soil mass and in the fraction 1–5 µm. Such a correlation is absent in the nonrhizosphere soil. The content of iron compounds extracted by the Mehra–Jackson reagent from the rhizosphere and nonrhizosphere soils is significantly higher than that extracted by the Tamm and Bascomb reagents; in the nonrhizosphere samples, it is significantly higher than in the rhizosphere. This difference can be explained by the fact that the content of Fe oxides and hydroxides minerals decreased in the soil mass of the rhizosphere due to more active dissolution processes under the conditions of more acid medium and higher concentration of organic ligands, so that the mobilized Fe enters Fe–organic complexes.