Pavel Evgenyevich Odintsov

The dynamics of mineralization of organic substances in soil solutions sampled by the tension lysimeters from podzolic soil has been studied. The stability of dissolved organic matter (DOM) varies with the horizon. The greatest content of resistant to biodegradation DOM (was mineralized less than 50%) was found in the upper organic horizons, down the profile it is decreased. The fraction of mineralized carbon is inversely proportional to the relative content of hydrophobic and phenolic fractions in DOM. The lowest percentage of mineralized carbon (23%) resides in the upper Elhi-horizon, where DOM is contained maximum of hydrophobic fraction (44%). In the course of oxidative transformation the degree of aromaticity of the DOM and the proportion of phenolic compounds increased (SUVA280 - by 2-12 times; phenols - 2 to 10 fold), while molecular masses decreased up to 5-5,5 kDa. These changes are manifested more intensively in solutions from the lower horizons, thus, the non-decomposable residue of this DOM is represented by substances most resistant to the decomposition.