Patterns of Organic Matter Mineralization in Podzolic Soil Solutions

Resumo

The mineralization of organic substances in soil solutions extracted from horizons of a podzolic soil using tension lysimeters was studied. The stability of dissolved organic matter (DOM) varies depending on the horizon. The maximum content of DOM resistant to biodegradation (mineralization degree <50%) was registered in upper organic horizons, and it decreases down the soil profile. The share of mineralized carbon is inversely proportional to the relative content of hydrophobic and phenolic fractions in the DOM. Organic matter extracted from horizon ELhi features the lowest share of mineralizable carbon (23%) amid the highest hydrophobic fraction content (44%). In the course of the oxidative transformation, the DOM aromaticity degree goes up: the extinction coefficient (SUVA280) increases by 2–12 times and the share of phenolic compounds by 2–10 times, while molecular mass decreases down to 5–5.5 kDa. These changes are manifested more intensely in solutions extracted from lower horizons. Therefore, the nondecomposable DOM residue consists of substances most resistant to decomposition.