Transformation of Soil Organic Matter in Connection with the Intensity of Peat Fire (by the Example of the Swamp Spruce Forest of the Kuznetsk Alatau)

Abstract

Specific features of the organic matter transformation in peat eutrophic soils (Hypereutric Sapric Histosols) and peaty gleezems (Eutric Histic Gleysols) 20 years after a forest–peat fire are discussed within the ecological direction of studying humus using traditional methods and terms. The study object is represented by a green-moss–hypnum spruce forest (Picea obovata Ledeb.) on the eastern slope of the Kuznetsk Alatau (at the altitude of 622 m above sea level). The composition of organic matter of pyrogenic soils (0–30 cm) is characterized by high variability (the variation coefficient is 12–92%). According to the factor analysis, the total variance is related to a combination of humic substances (76%) and to polysaccharides (24%). Cluster analysis enables us to identify two groups of objects, and their statistical reliability is confirmed by the discriminant analysis. Soil clusters reflect the peculiarities of pyrogenic processes: underground focal smoldering below the point of ignition and open intensive and moderate fire. Carbon content decreases to 26.5 and 13.4%, respectively, relative to the background (41% in peats not affected by fire). The formation of humification products is almost equal: (∑HA + ∑FA) is 55.4 and 53.7%, mainly due to fulvic acids (C_HA/C_FA = 0.2–0.6). The peculiarity of the thermal effect is mainly seen at the fractional level. The specificity of underground smoldering consists of an increased formation of fulvic acids of the first fraction free and loosely bound to R₂O₃. An open fire is accompanied by the predominating formation of humic and fulvic acids bonded to calcium. According to standardized coefficients of canonical analysis, the first and second fractions of humic and fulvic acids make the greatest cumulative contribution to cluster discrimination, and the maximal personal weight is related to HA-2, FA-1, and FA-2. Based on previously obtained data on the group composition of buried peats and the important role of anaerobiosis in the formation of humic acids, which better correspond to the restored substance when compared to fulvic acids, it may be assumed that peat formation, continuing in the fire area, can cause the transformation of fulvate humus into fulvate-humate and/or humate one. In the case of burial of a pyrogenic peat layer 0–30 cm in thickness, the transformation may occur over about 270 years, taking into account the rate of linear peat growth in spruce forests of the Kuznetsk Alatau: 1.12 mm/year. The research results confirm that the traditional division of humic acids into fractions is reasonable.