Postpyrogenic Changes in the Properties of Organic Matter in Cryosols of West Siberian Forest-Tundra

Organic matter of cryogenic soils of the forest-tundra of Western Siberia is mainly concentrated in the upper soil horizons. Fires are a powerful factor in the transformation of the soil and plant cover in northern ecosystems. Partial removal of the moss–lichen cover and soil litter leads to an increase in the heat flow deep into the soil and can cause accelerated mineralization of plant residues in organic horizons. The aim of the study was to assess the adsorption capacity of mineral horizons of Reductaquic Turbic Cryosols (Thixotropic) 28 years after the wildfire and to identify parameters that influence the adsorption capacity of these soils predominating on well-drained slopes in the north of the forest-tundra zone of Western Siberia, on the Pur–Taz interfluve (Yamalo-Nenets Autonomous okrug). The studied soils did not differ in texture, and this allowed us to link changes in the adsorption capacity of the soils with changes in the soil organic matter. The results of the study indicate that the organic carbon content in the soils 28 years after the wildfire was significantly (p < 0.05) lower than that in the analogous background soils. In the latter, it averaged 1.11% in the layer of 0–5 cm and 1.07% in the layer of 5–30 cm; in the postpyrogenic soils, it decreased to 0.73 and 0.71%, respectively. The mineral soil layer immediately underlying the organic horizon was characterized by a statistically significant (p < 0.05) decrease in the content of particulate organic matter and a statistically significant increase in the adsorption capacity of the soil in the range of the film moisture. In terms of its adsorption properties, the upper mineral layer (0–5 cm) of the postpyrogenic soil was closer to the underlying (5–30 cm) mineral layer and significantly differed from the analogous layer (0–5 cm) of the background natural soil.