The article considers the role of hydromorphism in the soil formation processes on ancient alluvial sandy deposits at the primary succession period. Soil organic matter was given special attention. The studies were carried out in the European north-east of Russia (the Komi Republic) in the middle taiga subzone in the territory of a building-sand quarry (61°57′35″ N, 50°36′22″ E) and background sites near the quarry. The authors analyzed the morphological structure of soil profiles, and the principal physical-chemical properties of mature and young soils forming under pine forests. Formation of forest litter and humus-accumulative horizons, as well as soil organic matter accumulation were thoroughly studied. Already in the fourth–fifth succession decades, the soils in a series of increasing hydromorphism actively demonstrated regularities that are normally characteristic of background soils, for example, increase in acidity, silt fraction, carbon and nitrogen reserves. Against moisture deficiency, the accumulation rate of organic carbon became slow and amounted to 0.07–0.11 t ha⁻¹ year⁻¹. The excessive soil moisture content increased the rate up to 0.38–0.58 t ha⁻¹ year⁻¹ due to the conservation of plant material in the form of peat. The upper 50-cm profile layer of young soil contains Corg stock 3–5 times less than that of background soils. The major soil-forming processes are litter formation and podzolization in drained conditions, litter formation in conditions of high moisture, and peat formation and gleization against excessive moisture.

The study concerned the abundance and species composition of cultivated microfungi from peat soils and hollows of flat-palsa bogs in the mountain landscapes of the sub-Polar Urals (the northern part of National Park Yugyd Va). The number of fungi in the studied peat soils varied from 0.4 to 242 thousand CFUs/g a.d.s. with maximum values in the upper layer of live mosses of Bog I – 242±66.2 thousand CFUs/g a.d.s.. In the bog hollows, the abundance of micromycetes had relatively low values, in hollow of Bog I – 28.6±7.1 thousand CFUs/g a.d.s., in hollow of Bog II – 32.9±25.5 thousand CFUs/g a.d.s. The taxonomic list of cultivated micromycetes included 61 species of fungi from 15 genera, two divisions and Mycelia sterilia. The Mucoromycota division was represented by 17 species from the genera Absidia, Actinomucor, Mucor, Mortierella, and Umbelopsis. The majority if cultivated fungi belonged to the division Ascomycota (43 species from 10 genera). The genus Penicillium dominates by species number (21 species). Reasoning from the frequency of occurrence, the structure of the complex of microfungi included rare and random species by 53%. The share of frequent and dominant fungi accounted for 34 and 13%, respectively. The dominating group consisted of Pseudogymnoascus pannorum and sterile mycelium. Frequent species were Mortierella alpina, Mucor hiemalis, Umbelopsis ramanniana, U. vinacea, Penicillium canescens, P. granulatum, P. lividum, P. simplicissimum, P. spinulosum, P. thomii, P. verrucosum, Talaromyces funiculosus. Most abundant in the layer of live mosses were Penicillium spinulosum (17%), P. thomii (18%), Talaromyces funiculosus (19%). In the seasonally thawed peat layers, the following species were highly abundant as Pseudogymnoascus pannorum (11%), Talaromyces funiculosus (14%), and sterile mycelium (16%). In the gley soil horizons, Pseudogymnoascus pannorum (78%) dominated by abundance. Only single colonies of sterile mycelium were found in frozen peat layers.

Automorphic soils developed from sandy materials (podzolized podburs, (Entic Podzols) and iron-illuvial podzols (Haplic Podzols)) and loamy materials (organic cryometamorphic soils (Gelic Cambisols) and iron-illuvial svetlozems (Spodi-Stagnic Cambisols)) were studied in the northern forest-tundra zone. Podzolized podburs and podzols of tundra cenoses were less podzolized in comparison with the analogous soils developed under forest cenoses. This can be explained by a higher intensity of cryogenic processes favoring the fixation of iron-humus films on skeletal grains in the sandy soils of tundra cenoses. In the organic cryometamorphic soils, the illuviation of Al-Fe-humus compounds with the formation of bleached skeletans in the upper part of the mineral horizon was identified. The eluvial-illuvial differentiation of the soil mass diagnosed by the analyses of intraped mass was weakly pronounced. The features attributed to the activity of cryogenic processes were also described in these soils. Iron-illuvial svetlozems were characterized by the migration of iron compounds within the microprofile of podzol in the topsoil and by the specific well-structured cryometamorphic horizons in the lower part of the profile. The features inherited from the previous stages of soil development were identified in these soils.