No 1 (2023)

Gypsiferous soils (gazha soils – loose powdery gypsum) developed underdifferent bioclimatic conditions–forest-steppe, steppe, semidesert, and desertof the subboreal zone – are analyzed. Their morphological, micromorphological, mineralogical, and chemical properties are described. Gazha horizons of these soils may have different geneses: sedimentation, in situ weathering of hard gypsum rocks, and hydrogenic precipitation from groundwater. Despite the different origins of the gazhahorizon of these soils, its morphology and properties have much in common: the gypsum content of >50%, its powdery character with crystal size of <0.25 mm, the presence of calcium carbonates and soluble salts with a predominance of sodium and magnesium sulfates. However, in some cases, the field determination of the gazhahorizon and the chemical determination of gypsum give incorrect information about its presence; mineralogical analysis is necessary to determine the composition of the salts. An analysis of the micromorphological structure clearly demonstrates the genesis of gypsum: under hydrogenous conditions, when gypsum precipitates from groundwater or from lake and river water, the predominantly gypsum material with subparallel microstructure is formed, while in the in situ gazha or gazha originated from the lateral (colluvial) processes, gypsum is deposited together with plasmic material.

The relationships between the rhizosphere effects, allocation in soil horizons and bacterial community structure in the rhizosphere and the bulk soil of Retisol under spruce trees (Tver region, Russia) were studied. The rhizosphere factors (R_f) expressed as ratios of soil characteristics in the rhizosphere to that in the bulk soil were determined for the basic indices of microbial respiration, biomass and available nutrients pools in the top AEL (3–15 cm) and deep EL horizons (15–46 cm). The most prominent rhizosphere effects (R_f > 1.6) were revealed for microbial biomass C, basal respiration, and SOM turnover rate. R_f value for the SOM turnover rate in humus AEL horizon was approximately 1.5, while in the EL horizon it reached 6. The Rhizosphere had higher microbial diversity, with a significant contribution of both Gram-positive and Gram-negative bacteria, including representatives of Acidobacteria, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Solibacteres and Spartobacteria. The Gram-positive orders Bacillales and Clostridiales predominated in the bulk soil, with the relative contributions of more than 80 and 50% for the AEL and EL horizons, respectively. Based on the number of microbial activity indices with high R_f values (three for the lower EL horizon and only one for the upper humus AEL horizon), the rhizosphere of the lower horizon is probably more pronounced “hot spot” of biological activity than that in the top soil layer.

The scale and consequences of the transfer of biophilic elements from pasture ecosystems to sheep farms in the clayey semidesert of the Northern Caspian Sea region under the method of pastoralism accepted in the region (on the example of Stepnovsky settlement of Pallasovsky district of Volgograd region) were estimated. For the calculations, we used data on the chemical composition of dominant plants and sheep faeces, the long-term average productivity of phytocenoses, information on the rate of consumption of pasture forage by animals, etc. Soils of pastures and the reserve area, and soils on the sheep farm (in sheep corrals and in their resting places) were investigated. At least 17 t C, 600 kg Ca, 260 kg N, 100 kg Mg, 50 kg K, 40 kg P and 1 kg S were transferred to farms (0.1% of the area) from 1 ha of pasture (15% of the area) during the 6 months grazing season. The long-term stocks of faeces on farms (more than 1 thousand t in the example under consideration) are practically excluded from the circulation in the landscape. Small areas of farm soils are enriched with C, N, P and K. Compared with soils of the protected area, stocks of water soluble K increase (in the 0–30 cm layer) by two orders of magnitude, exchangeable K increases by 12–16 times, C by 8 times, N by 3 times, mobile P by 2 times. In grassland meadow-chestnut soils a decrease in the content of C (1.3 times) and exchangeable forms of K (1.6 times) relative to soils of the reserve area, in solonets on pastures decrease in the concentration of elements is not noted. The absence of statistically significant differences in the stocks of biophilic elements between the pasture soils and the soils of the protected area is partially explained by an increase in soil density by 0.08 g/cm³ in the 0–50 cm layer of the pasture soils. With the existing farming method, it is necessary to control the balance of biophilic elements in pasture soils.

In order to assess the possible toxic effect of potassium chloride used in conjunction with mineral nitrogen fertilizers the authors studied the structural and functional components of the microbial complex of chernozem, in particular, its prokaryotic component. The object of research was soil samples of typical chernozem, selected from the vegetation experience with variants with the introduction of nitrogen-phosphorus and ni-trogen-phosphorus-potassium fertilizers. To obtain a stable effect of easily soluble salts on the microbial community of the soil, long-term composting of soil samples was carried out with alternating cycles of moistening and drying of the soil. During the first two years of composting, the researches detected the suppression of carbon dioxide emissions; however the suppression leveled out only 5 years later. The initial reduction in carbon dioxide emissions, as well as denitrification activity, reached twofold values. The negative effect was manifested when the content of chlorides and nitrates in the soil was significantly lower than the gradation established for slightly saline soils. Prolonged composting of samples of fertile chernozem under the action of potassium chloride led to a decrease in the number and biomass of the metabolically active prokaryotic complex, which confirms its toxic effect on the microbial community of the soil. The representatives of the prokaryotic complex that are resistant and sensitive to the increased content of chlorides and nitrates in the soil have been identified. Among the representatives of the Bacteria domain, almost all were sensitive, with the exception of two phyllum Firmicutes and Verrucomicrobia. For some representatives of the phylogenetic group Actinobacteria, sensitivity to chlorine ions is confirmed at the generic level (Streptomyces and Micromonospora). For the Archaea domain, representatives of the Euryarchaeota phylum are identified as the most resistant to the presence of chlorides. Thus, the suppression of the microbiological activity of chernozem during the introduction of potassium chloride explains the previously identified decrease in the availability of nutrients for plants.

Soil fauna can serve as an excellent tool for ecological assessment of soil quality. The earthworm Eisenia fetida L. is widely used as a bioindicator organism to assess the toxicity of metals, metalloids, and other pollutants. Many studies have shown that the concentrations of metals and metalloids toxic to earthworms are an order of magnitude lower in artificially contaminated soils than in industrially contaminated soils. The novelty of this study is that toxicity estimates were made using native industrially contaminated soils. The results of the two experiments demonstrate the potential use of earthworms for ecological assessment of soils contaminated with metals and metalloids due to copper mining activities in central Chile. The main contaminant in these soils was copper, but arsenic, commonly found in copper ore, was also present in the contaminated soils. In the short-term bioassay, E. fetida earthworms avoided the soil in response to increasing copper content. However, in long-term experiments, arsenic proved to be more toxic to earthworm reproduction, while copper had little effect. In this study, we present toxicity thresholds for copper and arsenic to E. fetida in industrially contaminated native soils.

In six forest parks of Moscow and four rural forests (5 plots each, n = 50), soil physical, chemical and microbial properties of the upper 10 cm layer were assessed in combination to vegetation properties. The content of carbon (C), nitrogen (N), and phosphorus (P) in soil and microbial biomass was determined. It was revealed that soil density, pH value, content of N–\({\text{NO}}_{3}^{ - },\) Ca and heavy metals (Pb, Cu, Ni, Zn) increase in forest parks compared to rural forests. In the soil of the forest parks, a decrease in the content of microbial biomass C (C_mic), its basal respiration (BR), and microbial C- and N-availability (C_mic/C, N_mic/N, BR/C) was noted. The changes of soil microbial properties are mainly driven by the abundance of leaf litter and the content of available soil C (13–35% of the explained variance). The microbial response to the soil enrichment by low molecular weight organic substrates (carbohydrates, carboxylic and phenolic acids, amino acids, amino sugars) in forest parks and rural forests did not differ significantly. In the soils of forest parks, no changes in microbial mineralization and immobilization of P (P_mic, P_mic/P) were found as well. The impact of urbanization on the forest ecosystems has led mainly to a decrease in the intensity of processes associated with soil C and N cycles. Apparently, such changes are caused by the recreational activity and the management practice of green spaces in the city, which leads, in particular, to a decrease in the amount of forest litter in parks compared to rural forests.