Darya Fyodorovna Zolovkina

The resistance to mineralization of water soluble organic matter (WSOM) extracted from a litter of Podzol is increased upon the interaction with the mineral horizons. Both the fraction of WSOM susceptible to mineralization and the average rate of decomposition decrease after the passage through E-horizon, by 2-3 times respectively, in comparison with the values obtained for the initial WSOM. Sorption in the BF horizon gives extra stability to the incoming organic matter. The relative content of mineralized carbon is reduced to 2% (by 8 times). In natural soils sorbed organic matter can be even more resistant to the mineralization, due to lower temperatures and less biological activity, so it can be considered as the basis for the formation of a humus storage. Taking into account the calculated rate of mineralization, the accumulation of the organic carbon in the BF horizon due to WSOM sorption, may range up to 13,5/100 g per year, but this value depends on the concentration of organic substances in soil solutions, hydrological regime and other factors.

The composition of water-soluble organic matter (WSOM) of coniferous-deciduous, coniferous and moss litter was studied. Type of decay affects the composition of WSOM. Sphagnum litter contains less N and dissolved organic carbon (DOC), but more carbohydrates, the WSOM is characterized the lowest extinction coefficients Е₂₅₄. WSOM from mixed litter with a predominance of birch litter has a maximum content of N and a small amount of soluble phenolic (SP) substances. WSOM from litter of pine needles differ from the rest with a lower content of carbohydrates, the maximum amount of SP and hydrophobic fraction. All investigated WSOM are characterized by high rates of decomposition: half-decomposition time of their stable fractions is 2-4 months. WSOM from pine litter at pH ~ 6 are absorbed by the BF horizon of Podzol, since the concentration of DOC of 100 mg/l. Substances from birch-spruce litter in similar conditions adsorbed slightly.