Том 52, № 6 (2019)

The relationship between soil formation and sedimentation on the floodplain of the Utyaganka River (the Ural River basin) in the Arkaim Reserve (Chelyabinsk oblast, Southern Ural, Russia) was studied. Pedological, palynological, and mineralogical research methods were applied, and 15 radiocarbon dates of soil humus and sediments were obtained. The thickness of the Holocene sediments on the low floodplain is 4–5 m. Their top 1.5-m-thick layer formed in the recent 2000 yr contains three buried (partially superposed) soils formed at the mean rate of 13.3 cm/100 yr. Alluvial soddy soils with solonetzic and salinity features reflect intensive anthropogenic erosion in the river basin and characterize the Little Ice Age and the dry and warm Viking Age. At the depth of 1.5–5 m, there are up to five buried soils separated from one another by alluvium layers; they were formed in the period of 12 000–2000 BP at the rate of 1.9–3.1 cm/100 yr. Among them, the soils that developed 4200–2000 BP are characterized by varying humus content and solonetzicity; they are enriched with carbonates and reflect sharp fluctuations in atmospheric moistening against the background of dominating arid and continental climate. The soils formed 5500–4200 BP are gleyed, moderately humified, and calcareous; they testify to a more humid and warm climate than now. This period was characterized by the maximal area of forests (the pollen of tree species reaches 67%). The period of 8000–5500 BP was specified by warm and dry climate, which is indicated by soil properties and palynological data (15% of tree pollen). Soils formed 9500–8000 BP on stony proluvium-alluvium are eroded mucky gley soils; they reflect sharp fluctuations of the climate at the end of the glacial epoch. Floods were probably accompanied not only by alluvium accumulation but also by regular erosion of the surface and a decrease in the thickness of the humus horizon. This resulted in the renewal of soils and slowed down the increase in the thickness of humus horizon and in the intensity of alluvium accumulation. The average portion of humified soil layers reaches 26% of the total thickness of alluvial sediments.

Soil-archeological studies were performed in the area of the ancient Russian settlement Sorokino 1 dating back to the 13th century AD and located in the upper reaches of the Orlik River (Khotynets district, Orel oblast) within the natural zone of deciduous forests. Morphological, physical, and chemical properties of soils associated with the archeological monument and with the background area under the forest were analyzed. Phytolith spectra and the radiocarbon age of soil organic matter were determined in the paleosols of the archeological monument and in the background surface soils. A comparative analysis of the soil features—indicators of the environment—allowed us to determine and characterize the main stages of the formation of soils and landscapes under the influence of climate changes and anthropogenic factors. Climate-related alternation of the phases of steppe and forest development in the study area was revealed. Steppe conditions in the Boreal period of the Holocene were replaced by the spreading of deciduous forests in the Holocene Optimum (Middle Atlantic period). At the end of the Atlantic period, steppe landscapes reappeared in the area, which was reflected in the intensification of the activity of steppe burrowers (mole rats) in the soil profiles. Steppe formation in river valleys during the Medieval Climatic Optimum was replaced by the propagation of forests in the subsequent Little Ice Age. The analysis of phytolith complexes of different ages indicated that the forests growing in the studied area in the Late Holocene included both deciduous and coniferous trees and reflected cooler climatic conditions in comparison with the deciduous forests without conifers of the Atlantic Optimum. In the recent centuries of the active agricultural development, forests have been replaced by arable land and hayfields, which has led to the formation of chernozems in the areas previously occupied by dark gray forest soils (Luvic Greyzemic Phaeozems).

Results of the study of humus composition in about 200 modern soils of different genesis and more than 100 buried Pleistocene and Holocene paleosols have been collected and analyzed. The content of the nonhydrolyzable part of soil organic matter (NH OM) in the paleosols is comparable with that in the modern soils (50 ± 15% and 54 ± 21%, respectively). Thus, NH OM does not accumulate in the buried soils during their diagenesis and is not the inert fraction of the soil organic matter (SOM). The NH OM content in the natural organomineral soil complexes–clay fractions of the soils—is lower than that in the whole soil mass. Data on the solid-state ¹³C NMR spectroscopy of the whole soil samples and the NH OM indicate that the latter are enriched in O-alkyls, including C of acetal groups. The whole soil mass is richer in C of aromatic structures and carboxyl groups. The degree of organic matter humification estimated from the alkyls/O-alkyls ratio for the NH OM is considerably lower than that for the whole SOM. The existence of negative correlation between the contents of NH OM and humic acids in the modern soils (R = –0.86) and in the buried paleosols (R = –0.83) has been shown. The NH OM content in the clay fraction in comparison with the whole soil mass is lower (36 ± 21% and 60 ± 15%, respectively). This reflects the accumulation of weakly decomposed plant residues in this part of the SOM. It is argued that the NH OM is heterogeneous and includes at least two groups of substances: clay-bound organic matter of organomineral complexes (nonhydrolyzable because of strong chemical bonds) and weakly decomposed plant residues resistant to acid and alkaline hydrolysis. The absence of definite relationships between the contents of NH OM and fulvic acids indicates that genetic links between the NH OM and humic acids are stronger than those between the NH OM and fulvic acids. ¹³C NMR spectroscopy of kerogen from the Carboniferous shale attests to the principal difference between the NH OM of soils and kerogen, in which C of alkyl groups predominates.

The present study is aimed at examining the impacts of land use and slope gradient on pore space distribution as well as some soil physicochemical properties. Three land uses were considered in this research: natural forest lands, degraded forest lands, and cultivated lands as dry farming. The study area was divided into four slope classes. Furthermore, two types of soil surface (0–10 cm) sampling were performed: a) soil samples for physicochemical analysis and b) intact samples for thin section preparation and image analysis to extract pore equivalent diameter distribution. Pore diameters were divided into three classes, including macropores, mesopores, and micropores. One hundred and eight soil surface samples were collected from the study area. The results revealed that macropores and mesopores are predominant in the natural forest soils, while micropores are dominant in the cultivated soils. Moreover, the highest contents of soil organic matter (SOM) and cation exchangeable capacity and the lowest value of bulk density are observed in the natural forest soils. Regression analysis revealed a positive regression between SOM and macropores and mesopores and a negative regression between organic matter and micropores. These results indicated the importance of SOM in the formation of macropores and mesopores. It appears that plowing cultivated lands has led to the exposure and decay of SOM. In addition, agricultural machinery traffic affects soil compaction, both resulting in the formation of micropores. Overall, soil pore distribution has the essential sensitivity to detect changes in soil quality due to land use changes or other operations.

Microarthropod communities (Oribatida, Mesostigmata, and Collembolans) in postagrogenic and tundra soils of the European Northeast of Russia have been characterized. In the postagrogenic soils, developed in places of former cultivation of perennial and annual crops, Collembolans predominate among microarthropods, while Oribatid mites predominate in the tundra soils. The population density of Mesostigmata has not been subjected to significant changes. In the studied sites, 58 species of Collembolans have been identified, including 33 species in postagrogenic soils and 46 species in tundra soils. A comparison of the species composition of springtails attested to significant differences in the structure of the complexes of dominant species, though no strongly specialized fauna has been found in the postagrogenic soils. No definite relationships between particular soil properties and population densities of different groups of microarthropods have been found, though these groups are definitely differentiated depending on genetic types of studied soils.

Actinomycetic complexes of soils and plant substrates from tundra and taiga zones of Russia and Finland have been studied. A molecular cytogenetic technique—fluorescence in situ hybridization (FISH) method—has been applied to estimate the metabolically active component in the representatives of the Actinobacteria. In the prokaryotic microbial communities of studied plant substrates, the biomass of metabolically active psychrotolerant representatives of Actinobacteria was determined upon incubation at 5°C reached 34% of the total bacterial biomass; at the incubation temperature of 20°C, it increased to 56%. Under conditions of low temperature, psychrotolerant actinomycetes displayed active growth with the development of both substrate and aerial mycelium. The abundance of psychrotolerant actinomycetes reached thousands and tens of thousands CFU/g for taiga mosses in Finland and increased to millions CFU/g for tundra flowering plants in the Taimyr Peninsula of Russia. It decreased in the sequence: peat soil > plants > moss cushions > litter horizons. The length of actinomycetic mycelium in tundra plants varied from 98 m/g at 5°C to 291 m/g at 20°C; in taiga mosses, it varied from 120 to 180 m/g, respectively. The complex of psychrotolerant actinomycetes was mainly composed of colorless species of the Streptomyces genus possessing specific ecophysiological features, such as the change in the color of substrate and aerial mycelium, the appearance of pigmentation, and the increase in the growth rate upon higher incubation temperatures. More than 60% of actinomycetes isolated from taiga mosses of Finland were represented by psychrotolerant species of Micromonospora genus.

Rice-wheat (RW), rice-fallow (RF), and rice-Chinese milk vetch (RM) are the three major rice rotation systems currently used in the Yangtze Delta of China. However, it remains poorly understood how these systems affect microbial communities in soils. Quantitative polymerase chain reaction (qPCR) and denaturing gradient gel electrophoresis (DGGE) were used to analyze the composition, abundance and diversity of diazotrophic community at different depths in soils under RW, RF and RM treatments. The results showed that rice yields were significantly higher in RM as compared to those in RF and RW in all years from 2011 to 2016. Diazotrophic communities at soil depths of 10–20 cm and 40–80 cm under RM were significantly more diverse than those under the other treatments. Sequences affiliated with Geoalkalibacter spp. showed the greatest abundance under RW at all soil depths, while Desulfovibrio and Pseudacidovorax spp. were both more abundant under RM at the 40–80 cm depth. Redundancy analysis (RDA) identified that the diazotrophic community within the 40–80 cm layer of soil under RM was positively associated with soil macro-aggregates. In conclusion, the RM treatment was characterized by significantly higher diversity of diazotrophic community in subsoil and increased rice yields as compared to the other treatments.

Acid–base characteristics and composition of clay minerals were estimated in the rhizospheres of Norway maple (Acer platanoides) and common spruce (Picea abies) and in the corresponding bulk soil samples taken in five replicates from the AELao horizon of podzolic soils. On the plot under spruce forest, both rhizospheric and nonrhizosheric soils were found to be more acid than those on the plot with a considerable part of maple trees in the forest stand. No reliable differences in pH values were found between the maple rhizosphere and corresponding bulk soil, while the rhizospheric soil under spruce forest had significantly lower pH values as compared with the enclosing soil. The rhizospheric soil under both tree species was found to contain reliably more illite minerals in clay-sized fraction, which could be due to the intensification of illitization and physical disintegration of micas and illites in coarse fractions. Under spruce forest stand, the clay fraction in both rhizospheric and nonrhizosheric soils contained more expandable minerals and less kaolinite and illites as compared with those under maple parcel. These differences can be explained partly by the spatial variability of clay composition in the parent material (mantle sandy loam) and, partly, by the dissimilarities in the functioning of different tree species and associated microbial communities causing lower pH values in soils under spruce forest. In the maple rhizospheric soil, pedogenic chlorites were characterized by a higher degree of aluminization in comparison with the enclosing soil owing to more favorable acid–base conditions. A tendency for a deeper transformation of illites into expandable clay minerals was revealed in the spruce rhizospheric soil as compared with the bulk soil, which can be explained by a more acid reaction facilitating the mobilization of aluminum.

Four river basins located in the forest, forest-steppe, and steppe zones of European Russia were evaluated for two time intervals (1960–1985 and 1986–2015) based on the use of the Universal Soil Loss Equation (USLE) and State Hydrological Institute (SHI) models. The obtained results attest to multidirectional tendencies in the mean annual rates of erosion rates in different landscape zones. The rates of soil erosion have decreased in the forest and eastern steppe zones and have slightly increased in the southern steppe zone. The reduction of surface snowmelt runoff is one of the main reasons for the decrease of soil erosion in the investigated river basins. An increase in the rates of soil erosion is related to the growth of rainfall erosivity factor (R-factor), has been partially offset by an increase in the soil-protective coefficient of crops (C-factor).