ИСТИНА

Pedogenesis in Siberia occurs in cold environment, and in the past the climate was even colder and permafrost was more common than now that implies the development of cryogenesis both in the present and in the past. The presence of texturally differentiated and practically undifferentiated soils at relatively short distances may be explained by the differences in hydrothermal regimes, which depend on topography, lithology and vegetation of particular sites. We aimed at revealing the dependence of processes leading to the formation of textural differentiation in loamy soils in the Middle taiga zone of Siberia on past and present pedoenvironments. The research was done in Western and Eastern Siberia. Western Siberia is characterized by flat topography. The climate is moderately cold with mean annual temperature -4 -2°C, mean January temperature -20°C and mean June temperature +18°C. The annual precipitation is 580 mm. The area has insular permafrost. Central Yakutia (Eastern Siberia) is located on plateau. Its climate is more continental with mean annual temperature -10.2°C, mean January temperature -38,6°C, and mean June temperature +19,5°C. The annual precipitation is 238 mm. The area has continuous permafrost. Both are covered with taiga forests with larch, pine and Siberian pine. The parent materials of the studied soils are loams, sandy loams, sands of alluvial and ancient alluvial origin. Soil pits on the Severo-Sosvinsk Upland, the Agan Uval, the left bank of the Kiryas’s distributary in Western Siberia and the Prilenskoye plateau in Yakutia were studied. Soils is brownish and pale colors with specific caviar and сryo-platy structures, which are typical for permafrost-affected soils. Micromorphological study of soil thin sections in transmitted and reflected light showed the presence of rounded aggregates. Soil pairs with and without textural differentiation were identified as Cambisol and Alisol in Western Siberia, and Cryosol and Planosol in Eastern Siberia. We hypothesized that as a result of divergent evolution under similar conditions, there was a discrepancy between the types of soils studied. The texturally differentiated loamy soils can be formed in warmer areas and earlier thawing, and are characterized by leaching water regime practically throughout the growing season. In recent decades, global climatic changes have been observed, which have an impact on current soil formation, and can lead to increased differentiation processes in soil.