Articles

Water-soluble organic substances (WSOM) of sod and humus horizons of Mollic Gleysol artificially saturated to full moisture capacity were isolated by sequential centrifugation from pores with a diameter of more than and less than 30 microns. The total concentration of carbon and phenolic compounds, the absorption and fluorescence spectra of the solutions do not differ significantly, but a strong variation in the parameters (the ratio of maximum and minimum values is 415 times) indicates the heterogeneity of the composition of the extracted substances. The concentration of simple phenolic acids in solutions of large pores of the humus horizon is 48 times higher than in smaller ones, salicylic, benzoic and cinnamic acids predominate (75% of the total amount). In small pores, p-hydroxybenzoic and benzoic acids predominate (67% of the total amount). Dissolved organic matter (DOM) of soil solution of the Podzolic soil (ELBTg horizon, moisture 22%), were obtained by tension lysimeters from pores with a diameter of more and less than 14.7 microns. DOM in solutions from large pores contain more C, N, phenolic compounds and, according to the absorption spectra, have a large molecular weight and a degree of aromaticity. Organic substances from small pores are more hydrophobic and are characterized by a greater C:N ratio; these features potentially promote DOM resistance to decomposition. Predominant localization of phenolic substances in large pores is favourable for the conservation in soil since transport with water flows assist their chemical stabilization in the lower horizons as organo-mineral compounds. 

Under the conditions of a laboratory incubation experiment, the effect of the introduction of crop residues (rye straw) and mineral nitrogen fertilizer on the formation of nitrous oxide by Albic Retisols was studied. It was found that the increase in the carbon content of microbial biomass is linearly related to the mass of introduced plant residues. An important indicator characterizing the system under study is the C:N ratio of microbial biomass and its dynamics both with changes in the amount of crop residues introduced and over time. At the ratio C:N = 40 in plant residues at the early stages of their decomposition in the soil, the predominant process of microbial nitrogen immobilization is replaced by the predominance of the process of mineralization of organic nitrogen compounds. It is shown that the maximum immobilization "capacity" of microbial biomass in relation to nitrogen is achieved at a ratio of C:N in the substrate equal to 20-40. The dependence of the intensity of nitrous oxide emission by soils on the amount of crop residues introduced has been established. It is shown that the maximum values of the emission factor are characteristic of the experimental variants with the introduction of a substrate enriched with nitrogen (C:N = 7,5-10), which may be associated with better decomposition of plant residues under conditions of better nitrogen supply.

The features of the ground cover in connection with the use of care in typical urban plantings in Moscow are determined. The character of plantings care determines the main features of ground cover more than the type of tree species. As a result of planting care, nemoral shade-tolerant species in the grass layer are actively replaced by meadow nitrophilic and ruderal species belonging to annuals and turf grasses, which contributes to an increase the biological cycle intensity.  In urban ecosystems, the indicative role of plants in relation to soil properties is reduced due to the lack of direct long-term relationships between these components.

Within the landscapes of the upper reaches of the Klyazma River, the long-term component composition of natural waters in the system has been studied: snow waters — soil solutions — soil-ground waters — surface waters. It has been determined that the regular excess of the content of the main macro- and microelements in soil solutions in comparison with snow waters at subsequent stages is first replaced by an increase in the concentration of components in soil-ground water, followed by a decrease in the content in surface waters — streams and river waters. It is shown that the relatively high mobility of sodium, magnesium, potassium and calcium, and of the anions chloride and nitrate ions, is accompanied by a significant decrease in the mobility of elements of the family of iron, copper and zinc at the transition from groundwater to surface water. This explains the wide distribution of segregated forms, presented in the form of nodules in soils of semi-hydromorphic landscapes, up to ortsands, and in the boggy conditions of near-terrace depressions on the border with the super-aquatic landscape, the formation of typical bog ores. Thus, the composition of natural waters and its change serves not only as a good, but also a necessary tool for explaining the features of migration of elements in the soil — natural water system.

Methodological problems of the quantitative assessment of pollution of urban soils by benzo(a)pyrene and their bioremediation are considered by the example of the Moscow metropolis. Available materials of scientific publications and official reports of the «Mosecomonitoring» municipal system about pollution of urban soils by benzo(a)pyrene and the patterns of its dynamics were used. The methodological basis of the study was mathematical modeling, including both non-linear regression analysis in the S-Plot-11 program and numerical computer simulation in the Matlab-7 software. Analysis of published materials reveals at least a double excess of the maximum permissible level of pollution of urban soils by benzo(a)pyrene at 70% of the territory of the Moscow metropolis, with a high probability of an extremely high degree of pollution in several dozen MPCs at 10% of the city's area. Unlike known works in this field, the study links such a negative situation not with the resistance of benzo(a)pyrene in soils, but with its high technogenic load. A simple kinetic model, verified for experimental information on biodegradation of benzo(a)pyrene in soils, makes it possible to assess the permissible limits of technogenic load, guaranteeing the self-cleaning of urban soils from this dangerous pollutant in the conditions of Moscow.

It is shown that the cultural layers of urban ecosystems are distinguished by the accumulation of all groups (general, mineral, organic) phosphorus compounds. At the same time, the humus of the horizons of anthropogenic origin is enriched in organic phosphorus in comparison with natural analogues by 3-10 times. Due to the neutral and close to neutral character of soil acidity, the mobility of all groups of phosphorus compounds is reduced, which is the main reason for their fixation in the profile of stratozems. It was found that the group composition of phosphorus in the soils of settlements and settlements does not reflect the zonal patterns of accumulation and profile distribution of phosphorus, but it can serve as a reliable indicator of the presence of anthropogenic activity in the past.

Urban soils contain a substantial pool of organic matter (OM), the decomposition of which leads to intensive CO₂ emission that important in terms of global climate change. The OM decomposition increases in line soil temperature, the magnitude of such effect largely depends on the soil physicochemical properties. At the same time, the contribution of the functional microbial diversity on the temperature sensitivity of OM decomposition (Q₁₀) is still poorly understood, and especially for urban ecosystems. Consequently, our study aimed to assess the effect of the microbial functional diversity on the Q₁₀ value for urban soils considering its physicochemical properties. In the St. Petersburg, Moscow, Voronezh and Krasnodar, located in different bioclimatic zones (southern taiga, mixed forests, forest-steppe and steppe, respectively), four parks were selected. In each park the samples were taken from the topsoil (0-10 cm layer). In soil samples, decomposition of OM was determined at the temperature 10, 20, 30, and 40°C for the subsequent calculation of Q₁₀ value. The soil physicochemical (moisture, texture, pH, content of C, N, P₂O₅, K₂O) and microbial (functional diversity, biomass) properties were determined as possible Q₁₀ index drivers. The Q₁₀ value in humus horizons of urban soils was mainly correlated with its texture, moisture C and N contents, while the microbial functional diversity was correlated with P₂O₅. The regular distribution pattern of Q₁₀ and the studied soil properties of urban parks along the latitudinal gradient has not been found, however a negative relationship between Q₁₀ and the microbial functional diversity has been revealed (R² = 0.50). Apparently, the high microbial functional diversity contributes to a decrease of the temperature sensitivity of OM decomposition.