Postpyrogenic Changes in the Properties of Organic Matter in Cryosols of Western Siberia forest-tundra

Organic matter of cryogenic soils of the Western Siberia forest-tundra is concentrated mainly in the upper soil horizons. Fires are a powerful factor in the transformation of the soil and plant cover in northern ecosystems, often leading to an increase in the heat flow deep into the soil and can cause accelerated mineralization of plant residues of organic horizons. The aim of the study was to assess the adsorption capacity of mineral horizons of a Reductaquic Turbic Cryosols thixotropic 28 years after the wildfire and to identify parameters that influence this capacity of the soil. Measurements of the soil organic carbon and total nitrogen contents were carried out using the ECS 4024 and METEK-700 express analyzers; soil texture was measured using the laser diffraction method on the Malvern Mastersizer 3000 analyzer; and the relationships between film water potentials and contents was measured using the WP4-T dewpoint potentiometer. The studied soils did not differ in texture, which allowed us to link changes in the adsorption capacity of the soil with the changes occurring in their organic matter. The results of the studies have shown that 28 years after the wildfire, the studied soil differed significantly from its natural analogue in the total organic carbon content. The average total organic carbon content in the 0–5 cm layer of natural soil was 1.11%, and in the 5–30 cm layer – 1.07%. In the soil of the wildfire territory, the content of total organic carbon in both layers was significantly (p < 0.05) lower and amounted, on average, to 0.73 and 0.71%, respectively. The highest mineral soil layer, which is in direct contact with the overlying organogenic horizon, is 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 soils in the range of the film moisture. In terms of its adsorption properties, the upper mineral layer (0–5 cm) of the wildfire territory soil is closer to the underlying (5–30 cm) mineral layer and is significantly (p < 0.05) different from the similar layer (0–5 cm) of the natural soil.