Aminat Batalbievna Umarova

Abundance and diversity of soil saprotrophic bacteria complexes were monitored for two years on the territory of one of the large industrial cities of the European North of Russia, Syktyvkar. The work was carried out before and after quarantine in connection with the COVID-19 pandemic. The capital of Komi is characterized by a high population, and by tense environmental conditions according to the ecological standard. Studies were conducted in 2019—2020. Topsoils (0—10 cm) of urbanozems, horizon A in the park area in the urban space, as well as zonal undisturbed podzolic soil were analyzed. Comparison of the two)year monitoring results demonstrated a marked increase in the number and diversity of saprotro) phic bacteria complexes in 2020 both in urban and control soils (topsoil, 0—10 cm).

Detailed studies of Enterobacteriaceae demonstrated a decrease in the share of opportunistic (Enterobacter agglomerans, Citrobacter europaeus, Klebsiella oxytoca, Serratia marcescens, etc.) as well as fecal coliforms (Escherichia coli, Enterococcus faecalis) in urbanozems in 2020 — a consequence of a sharp and prolonged decrease in the anthropogenic impact on the environment. It can be viewed as a manifestation of the soil ability to “self-purification” when anthropogenic impact on the environment reduces.

The results of 60-year research on physical properties of soils in the MSU large lysimeters are discussed. The
questions under study were the elements of soil water balance, soil evolution, soil temperature regime, and transport of various substances in soil profile. The long-term changes in soil texture, soil mineralogy, and organic carbon content were observed. It was shown that the horizon sequence in soil profile affects the intensity of drainage flux and its stabilization in the long-term aspect. It was also found that the amount of the transit transfer of substances in different soil profiles depended both on profile structure and upper boundary conditions.

Complexes of cultured saprotrophic bacteria and yeasts from different components of soil constructions (humus soil horizon and peat) were studied simultaneously with the assessment of auxin-producing activity (synthesis of 3-indolylacetic acid, IAA), of some bacteria and yeast strains isolated. The study was conducted at the stage of laying two variants of constructions in Syktyvkar, formed from components of local origin (variant 1) and imported (humus soil horizon, Moscow, peat "Seliger-agro", Tver region) (variant 2).

The taxonomic structure of microbial complexes isolated from the studied substrates had significant features of similarity. At the same time, components of variant 1 revealed a greater diversity of cultivated saprotrophic bacteria (Bacillus species) species resistant to adverse environmental conditions as well as the presence of psychrophilic basidiomycete yeast Leucosporidium scottii, which was not found in the components of variant 2.

The average IAA production by the yeast strains studied was 647.6 µg/L and by saprotrophic bacteria - 741.3 µg/L. The highest values of IAA concentration were found in the culture liquid of the yeast Tausonia pullulans (strain Y-6) - 3362.6 µg/l, isolated from the humus soil layer of variant 1, and of the two saprotrophic bacteria Flavobacterium рsychrophilum (strain B-7 - 2616.8 µg/L and B-5 - 1056.3 µg/L), isolated from the humus soil horizon in variant 1 and from peat of variant 2. For strains of the yeast Leucosporidium scottii and the cultured saprotrophic bacteria Flavobacterium psychrophilum the ability to synthesize IAA was found for the first time. 

The mechanical characteristics of soils of the same genesis and diff erent land use of Syktyvkar are studied: agrodernovo-
podzolic urban-stratifi ed soil within the city, post-frost park soil, podzolic soil of suburban territory. The analysis of their relationship with the content of organic matter and granulometric composition is carried out. In
agrodern-podzolic urban-stratifi ed soil, the strength properties are largely due to the content of large granulometric
fractions (> 0.25 mm), and in podzolic soil — the content of organic matter. Rows of soils were built according
to the values of rheological parameters. The strength of structural bonds, estimated by the parameter of the initial
modulus of elasticity, is greatest in podzolic soil, a wide range of linear viscoelastic state distinguishes the horizons
of agroderno-podzolic urban-stratified soil. Both post-frost and podzolic soil have the same average values of the
starting point of the viscous flow region.

The paper presents the results of experiments to study changes in hydrological properties of soil substrates composing profiles of artificial soils (construktozems) 1-4 years aft er their creation. Constructozems are represented by two variants - layered soils including Ap horizon, lowland peat and quarry sand of the same thickness, and a mixture of these substrates in an identical amount by weight, as for layered constructozems. Water retention curves obtained by capillarimetric method on samples of undisturbed structure were compared. A decrease in the water-holding capacity of the peat layer and an increase in the mixture samples were found a year after their functioning as part of the artificial soils. Laboratory and field experiments showed a statistically significant difference in water filtration rates of the layered constructozems and the mixture. Sharp boundaries between soil horizons contrasting in their properties reduce water migration rates down to zero values. Obtaining breakthrough curves of potassium ions allowed us to establish that the formation of continuous paths of rapid movement of water and dissolved substances is observed after four years of functioning of artificial soils and is most pronounced in constructions with homogeneous soil profile structure.

The thermal diffusivity of the upper plow horizon of the urban soil from the territory of MSU Experimental soil station, lowland packed peat, and their mixtures was studied. The soil from Ap horizon was sieved through a 1 mm sieve and mixed with peat in various proportions; the content of peat in mixtures ranged from 1 to 80% by dry weight. Metal cylinders 10 cm high and 3.8 cm in diameter were filled with soil, peat, and soil-peat mixtures. The thermal diffusivity was measured using the unsteady-state method with a working temperature range of 20–26°C. The heating rate of the packed samples was measured after the samples were placed in a liquid thermostat with a constant water temperature. For each sample, a series of measurements was carried out with a step-by-step change in soil water content from the maximum one after capillary saturation of the sample to the minimum one, corresponding to the air-dry state. Within the studied range of water contents, the thermal diffusivity of different samples changed by a factor of 1.3–3.5; the greatest changes with water content were typical for mineral soil. The thermal diffusivity vs. water content dependence was almost linear for peat, and for soil it was an S-shaped curve with a weakly expressed maximum. The lowest thermal diffusivity was obtained for peat and mixtures with high peat contents; the highest one — for soil without peat additions. The non-linear character of the thermal diffusivity vs. peat content dependence was revealed. Small additions of peat to mineral soil resulted in a noticeable decrease in the thermal diffusivity of the mixture; small additions of soil to peat had practically no effect on thermal diffusivity. The thermal diffusivity of the studied substrates increased with increasing sample bulk density and decreased with increasing organic matter content. It was concluded that the patterns typical for soil-peat mixtures are similar to those earlier obtained for peat-sand mixtures, but in the case of soil-peat mixtures these patterns are less clearly expressed.