Том 6, № 1 (2016)

The microbial biomass variability in buried chestnut and light chestnut soils of different ages under burial mounds and their modern background analogs in the Volga and Ergeni uplands were studied. It was shown that almost all microorganisms in chestnut paleosols of the Bronze Age are in the dormant state and provide no respiratory response to the addition of glucose. In the paleosol buried in the most arid period, an increase in the total microbial biomass and the abundance of colony-forming units was revealed. The maxi-mum values of active microbial biomass upon the minimum number of cells were found in soils buried in rel-atively humid periods. The increase in the total microbial biomass and the proportion of microbial cell carbon in the organic carbon of soils buried in extremely dry seasons at the turn of the III–II millennium BC may indicate the adaptation of microbial communities to unfavorable environmental conditions.

The dynamics of moistening indices and biophysical parameters (MODIS data) of arid pastures is examined for the southeast of the European part of Russia in five-year periods over 2000–2014. It was found that the dynamics was heterogeneous both in the temporal and spatial dimensions. The maximal moisture decrease was noted in 2005–2009 in dry-steppe and semidesert pastures. During 2010–2014, the moisture levels continued to decrease, though less intensively compared to the previous five-year period. The dynamics of biophysical parameters is determined by changes in moistening and the degradation of pastures due to overgrazing. The period of 2005–2009 was noted for reduced NDVI, deterioration of the vegetation condi-tions (VCI), and the growth of albedo and surface temperature in dry-steppe and partly semidesert pastures. The following period was marked by a shift of maximal changes in biophysical parameters to the Kalmyk Republic and the right-bank of Astrakhan oblast. This resulted in the appearance of preconditions for new anthropogenic desertification in the territory of Kalmyk Republic, which was detected by the desertification indicator.

A list of species from the family Brassicaceae Burnett was compiled based on the identification of herbarium samples collected in the Betpak-Dala desert in May 2014, a critical revision of the materials of Herbariums (AA and LE), and consideration of the literature data, The inclusion of some species (Matthiola robusta Bunge, Isatis violascens Bunge, I. maxima Pavl., etc.) in this list is discussed in more detail. The gen-eral list of Brassicaceae comprises 80 species. Eight species (10%) grow only in disturbed areas. These species, which are uncommon in the natural flora of the Betpak-Dala desert, were excluded from the analyzed list at the first stage of analysis. The final list for analysis included 72 species combined in 36 genera. The following genera proved to have the largest number of species in accordance with the study of the taxonomical compo-sition of Brassicaceae: Lepidium—13 (18%), Strigosella—6 (8%), and Alyssum—5 (7%). The classification of species into different vital forms revealed the indisputable dominance of annual plants (42 species), which are mostly ephemers (28 species). The analysis of the preference given by Brassicaceae to different edaphic variants showed that the majority of species prefer pelitophytic substrates. Only a few of them prefer hemi-petrophytic substrates. Of the 53 species growing on salinized substrates, 29 were found on alkaline soils and 24 were found on saline soils. It was shown that most species from the family Brassicaceae grow in either nat-ural undisturbed or weakly and moderately disturbed phytocenoses. Among the secondary (anthropophy-lous) habitats of species from the family Brassicaceae, agricultural lands (crops) are most preferred. In these habitats, 25 species of the general list of Brassicaceae in the Betpak-Dala desert were recorded.

The article presents data on the species composition and coenotic structure of the plant commu-nities of 20-year-old fallow grasslands in the system of protective forest plantations. It was found that the speed of successional dynamics depends on the distance from protective forest plantations.

This work implements the analysis of the history of economic development and human-induced transformation of sandy lands in the steppe zone of Orenburg oblast. Stages of the evolution of sandy lands have been distinguished and characterized. They are determined by the dynamics of socioeconomic develop-ment of the study area. It has been found that, with the development of cattle-breeding and farming, the fre-quency of outbreaks of sandy land degradations gradually increased and began to correlate with periods of increased aridity and comply with the stages of the socioeconomic development of the society.

By the end of the XX century, the ravine forests of the Volga–Ural interfluve degraded as a result of anthropogenic impact and turned into polydominant shrubberies, the area of which continues to decrease. In 2013–2014 the current state of such plant communities was studied on the northwestern coast of Lake Elton. The total area of shrubberies has already decreased by 50% because of fires, and their fire resistance declines constantly as a result of grazing.