The reconstruction of vegetation and conditions of soil formation using soils properties and microbiomorfological data
The pedocomplex with modern and 4 buried soils was studied in the southern taiga zone using the soil properties and microbiomorfological analysis. The pedocomplex is located in the wide valley of the brook Kireeva, which separates sandy-loam terrace of river Ob and loamy interfluvial plain. The terrace is occupied by pine forests with herb cover. The plain is overgrown with birch forests with admixture of conifers (pine, and rare spruce) and tall-herb cover. The herb-grass meadow with dominating of meadow grasses ( Elytrigia repens, Phleum pratense, etc.) developes in the valley. Soil texture, soil properties and composition of humus were determined in the horizons of modern and buried soils. Microbiomorfological analysis was carried out for humus horizons. Radiocarbon dating (<sup>14</sup>C) was made using humic acids and calibrated. Investigated modern and buried soils were formed in different landscape-climatic conditions. Each cycle of denudation started with active sedimentation phase, then the burial of the existing soil profile and ended with the phase of quiet sedimentation with low speeds corresponding to the new climatic conditions of soil formation. The main indicator of differentiation between cycles of lithogenesis is soil texture. The composition of humus characterizes the conditions of soil formation, and phytolith complexes - plant communities. The upper (modern) soil (45 cm) is formed in stratified loamy-sandy loam sediment. The age of the humus layer is 840 years. Smooth elongates and trichomes are dominated in phytolith complex with small amount of polylobates. Such a set corresponds to the modern meadow with dicotyledonous herbs and meadow grasses. The phytoliths of conifers in small quantities seem to be imported from the terrace. Also fan-shaped and bulliforms are found together with shells of diatoms and few spicules of sponges, that indicate increased hydration. The soil texture of the first (I) buried soil (45-88 cm) changes on clay-loam. Humus-accumulation is well-developed (the humus content 8.0%). The composition of organic matter is humic (Cha/Cfa 1.8-2.2). The minimum age for burial of this soil amounts to 1170 years. The concentration of phytoliths is several times higher than modern. Bilobates and polylobates share increases, also spiny elongates and rondels appear. All signs are characteristic of more southern meadow with participation of steppe grasses. Found fan-shaped and bulliforms indicate wet conditions. The deposits, and then the second (II) buried soil (88-142 cm, the minimum burial age 3150 years) were also formed in conditions of quiet sedimentation. The soil texture is clay-loam, with a humus content 1.5-2.88%. The composition of organic matter of the whole selected profile is fulvic-humic (C ha/Cfa 1.48-1.55). The phytolith complex is very similar to modern. A slight increase in the share of conifer phytoliths and the trichomes characteristic of forest grasses may indicate greater forest area. Microbiomorfs - indicators of increased moisture are absent. The features of phytoliths comlex, fulvic-humic humus composition and signs of podzol process along with soddy process indicate dry and relatively cold conditions of soil formation. The profile of the third buried soil (142-174 cm) was formed in deposits with different soil texture -sandy-loam bottom, that typical for sediments of high speed flows, and clay-loam above, reflecting conditions of quiet sedimentation. The humus content is high (2.24-2.34%), humus composition is fulvic-humic (Cha/Cfa 1.5-1.7). The soil is gleyed. Radiocarbon age of pedorelicts 5900 years. The microbiomorf content is very low (minimal). Smooth elongates and trichomes are dominated. Grass phytoliths (polylobates) are rare. Fan-shaped, bulliforms and few spicules of sponges are found. The number of conifer phytoliths, considering the small total phytoliths number, is close to the modern and does not allow us to diagnose confidently wood conditions. All signs show that marshy measow (possibly forest) was developed. Soil texture of the fourth paleosoil (IV) at the depth 174 cm is clay; humus content - 3.3%), the soil is also gleyed. The humic acids are dominated in organic matter composition (Cha/Cfa 2.12-2.34). The phytolith complex is similar to the complex of the third buried soil and allows to recognize marshy meadow. The phytoliths of conifers and forest grasses could be brought from the terrace. The soil waterlogging seems to be associated with ground water at the higher than modern basis of erosion. Thus, wetland meadow, forest with herb cover, wet meadow with steppe elements and modern herb-grass meadow were developed in the formation stages of pedocomplex, fixed in buried humic horizons. Each of the plant communities were formed in climate conditions, corresponding to different subzones of the modern vegetative cover of West Siberia - from southern taiga up to forest-steppe.