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Soils are the main component of the urban ecosystem and they perform environment‐forming and protective functions. The dynamics of the organic matter and enzymatic activity is an early diagnostic indicator of negative changes in urban pedogenesis. However, the features of the enzymatic activity of urban soils of the Chernozem zone are poorly studied, and the available research focuses on the upper humus‐accumulative horizons or the urbic horizons. The study aimed to reveal the regularities of the enzymatic activity distribution through 200 cm in the profile of urban soils and to show their relationship with the content of the main soil components. Urbic Technosols Molic, Ekranic Technosols, Urbic Technosols, Technic Chernozems (caChernozems of fallow and virgin areas of the Rostov Agglomeration were studied. Soil samples were taken down to a depth of 200 cm. The activity of extracellular enzymes was determined by the fluorescence method. Soil organic matter content was determined by the high‐temperature combustion method on a TOC analyzer. А number of patterns in the distribution of the enzymatic activity have been identified. Most of the Urbic Technosols were characterized by a low enzymatic activity. Factor analysis showed a negative correlation of oxidative and hydrolytic enzymes in natural soil. A positive correlation of oxidases with hydrolases was shown in urbanized horizons. We found that the longer the time of sealing, the stronger the inhibition of enzymatic activity. We conclude that enzymatic activity can be used as an indicator in biodiagnostics, biomonitoring, and bioindication of the urban soils.

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The research aims to study the content of organic matter in typical chernozem, its distribution in the soil profile under herbaceous and wooden phytocenoses. Organic matter plays a key role in the functioning of soils and their stable performance of ecological functions, including – the protection function. This is particularly relevant in the growing urbanization. The research analysis includes 40 full-profile sections of migration-segregated chernozems (typical carbonate) laid on the upland soil of the Rostov agglomeration. We determined organic matter by high-temperature catalytic combustion on a TOC-L CPN Shimadzu in an SSM-5000A solid sample combustion unit. Based on the data obtained, we calculated the organic carbon reserves. Statistical analysis included the calculation of the Mann-Whitney U-test to consider significant differences in the samples of indicators under wooden and herbaceous phytocenoses and descriptive statistics. The research results showed the influence on the organic carbon content of such a widespread type of anthropogenic impact as planting trees in the steppe zone. Comparison of the total organic carbon content values in similar genetic horizons under herbaceous and wooden phytocenoses indicates the spatial heterogeneity of this indicator, associated primarily with the type of land use. The supply of humus for Rostov chernozems under herbaceous phytocenoses was assessed as low and under wooden phytocenoses – as average. In the one-meter layer of natural chernozems of the Rostov agglomeration, humus reserves are 387 t/ha, which corresponds to the average supply level. Thus, the park and recreational zone, where wooden vegetation grows, plays a special ecological role in the city as a place of accumulation of an increased amount of organic matter of natural origin compared to other soils of the Rostov agglomeration.

The content and distribution of organic and inorganic carbon along the profile in the soils of the Rostov agglomeration are considered. The results obtained on a TOC-L CPN Shimadzu carbon analyzer are evaluated using Student's t-test. The groups of some horizons of native soils AU rz, AU, BCA, C, as well as their buried analogues [AU], [BCA], [C] were compared. The analysis of the urbic horizons was carried out taking into account their particle size distribution, previously dividing into horizons clusters - heavy URh and light URl. In the [AU] horizon of soils buried under the anthropogenic stratum, a statistically significant decrease in the organic carbon content is observed, compared to the AU horizon of natural analogues. The middle part of the profile - the BCA and [BCA] horizons - is characterized by the greatest similarity in carbon content, both organic and inorganic, which suggests the lowest anthropogenic impact on these horizons. Significant differences in the inorganic carbon content in the comparison pair - horizons C and [C] are shown, and its content is higher in natural analogues (horizons C). The data analysis of the urbic diagnostic horizons did not reveal any significant regularities because of the high degree of variation of this indicator due to the genesis peculiarities of the anthropogenically transformed stratum.