T. A. Sokolova

The main sources of the low-molecular-weight aliphatic and aromatic organic acids (LMWOAs) in soils are plant residues, root exudates, and microbial metabolites. In the solutions of upper soil layers of forest ecosystems, citric, oxalic, and malic acids predominate among aliphatic LMWOAs, while substituted and unsubstituted benzoic and cinnamic acids predominate among aromatic LMWOAs. The LMWOA concentrations in plant tissues, root exudates, and microbial metabolites vary from several to some tens of millimoles per liter. In soil solutions, these values decrease by one–two orders of magnitude because of LMWOA sorption and biodegradation, their migration downward the profile, and dilution effect. The sorption of LMWOA anions increases with a decrease in pH and an increase in the concentrations of iron oxides/hydroxides and amorphous aluminosilicate clays. Polybasic acids are more tightly bound to solid phase as compared with monobasic acids. The sorption mechanisms vary depending on pH and LMWOA molecular structure and include formation of innersphere and outersphere surface complexes, ligand exchange, and cation bridge bond. Aromatic LMWOAs can be involved in a hydrophobic interaction. LMWOAs are very rapidly decomposed in the upper horizons, their lifespan amounting to several hours. Some important functions of LMWOAs in soils and landscapes are discussed, including their involvement in the global carbon cycle, mineral weathering, Al and Fe mobilization and translocation, mobilization of Fe and P compounds in the soils deficient in these elements, formation of acid–base buffering of natural waters, and detoxication of soils with increased contents of aluminum, heavy metals, and organic pollutants in soil solutions.

An experiment on the transformation of test biotite of the clay fraction (<1 µm) and the medium silt fraction (5–10 µm) immersed into the AELоа horizon of podzolic soil for one or three years...

Acid–base characteristics and composition of clay minerals were estimated in the rhizospheres of Norway maple ( Acer platanoides) and common spruce ( Picea abies) and in the corresponding...

— 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-...

Potassium fixation capacity has been estimated in chernozem samples taken from the variants of a field experiment with a single application of potassium fertilizers (0, 70, 140 and 280 kg/ha) after a...

An experiment on transformation of biotite (fraction <1 μm) particles placed into containers with different permeability in the AEL horizon of podzolic soil was performed in order to estimate the...

X-ray diffraction patterns of clay fractions from the AEL and EL horizons of pale-podzolic soil before and after treatment with 10% H2O2and the Mehra–Jackson reagent in different sequences have been...

The profile distributions of oxalate- and pyrophosphate-soluble Al compounds and oxalate-soluble Si compounds in the main horizons of pale-podzolic soils of the Central Forest Reserve and the fractions 5 μm have been considered. In the clay-eluvial part of soil profile, the content of these compounds is differentiated by the eluvial–illuvial type with a clear accumulation in the EL horizon compared to the AEL horizon. This distribution is largely ensured by their differentiation in the clay and fine silt fractions, while an accumulative distribution of mobile Al compounds is observed in fractions >5 μm. The high correlation between the Al and Si contents in the Tamm extracts from the clay and fine silt fractions with the (Al_ox–Al_py)/Si_ox molar ratios, which are in the range of 1–3 in the EL horizon, confirms that mobile compounds are accumulated in these fractions in the form of amorphous aluminosilicates. In the AEL and EL horizons, an additional amount of Al can pass into the oxalate solution from the fine fractions due to the dissolution of Al hydroxide interlayers of soil chlorites. The eluvial–illuvial distribution of mobile Al and Si compounds typical for Al–Fe–humus podzols within the clay-illuvial part of profiles of the soils under study can be considered as an example of superimposed evolution.