Soil and vegetation of asymmetric watersheds of the steppe zone of the Volga-Ural Interfluve

A distinctive feature of the geomorphology of the Volga-Ural interfluve is polar orientation and asymmetry of the watersheds associated with the latitudinal stretch of the valleys of most rivers of the region. The aim of the research was to evaluate the influence of hydrothermal and topographic factors of asymmetric watersheds of the steppe zone of the Volga-Ural region on the formation of vegetation and soils, and also to study the relationship and interdependence between the properties of chernozems and species composition of phytocenoses. The research is based on the results of long-term field studies of soils and vegetation of steppes of the Volga-Ural Interfluve. We carried out our studies during the period of the maximum vegetation growth (late June-early July) in 2010-2012 and 2014. The study area was an asymmetric watershed of the Chagan-Buzuluk rivers (52°2'47''N, 52°29'44''E) with well-preserved natural vegetation, confined to Obshchy Syrt-Pre-Urals steppe province. Research methods included field observations and laboratory tests. We studied physical and chemical properties of soils by conventional methods (Shein EV). The period of soil biological activity was determined according to Orlova and Biryukova. Cellulose-decomposing activity of soils was investigated by the method of application by NS Vostrov and AN Petrova. Species composition of plants was analyzed within partial florae by BA Yurtsev; for this, we used "The identification manual of vascular plants of Orenburg region" by ZN Ryabinina and MS Knyazev. While conducting the research, we laid a number of 10x10 m geobotanical plots in a 10-fold replication in the upper, middle and lower parts of the slopes of the southern and northern expositions, as well as on the watershed. On the plots, we studied soil properties, determined floristic composition of plant communities and carried out their geobotanical description. Differences in the complex of hydrothermal parameters of the slope landscape form a specific mesoclimate at its each fragment (See Table 1) which provides soil cover heterogeneity of the area (See Table 2). A set of mesoclimate and soil cover conditions caused a diversity of phytocenoses limited to various landscape elements. Some parts of the profile differ in species diversity of plants, occurrence of individual species and representation of individual families (See Table 3). Thus, the maximum species diversity is noted at the northern slope, whereas the minimum - at the southern one; the average similarity of partial florae is 62%. During long-term monitoring studies, we established that hydrothermal conditions of the watershed slopes of different steepness and exposition and their flat tops differ in a set of parameters, resulting in the formation of soil and plant communities with considerable differences in properties and composition. Asymmetric watersheds showed the mosaic structure of soil and vegetation cover: a number of ecosystems in composition of phytocenoses and properties of chernozems are close to true steppes, and some other- to dry steppes. In addition, the generalized characteristics of soils and vegetation of the area correspond to the subzone of dry steppes. The data obtained allow classifying the polar asymmetry of watersheds as a condition that increases species and structural diversity of soil and vegetation cover at the present stage of evolution of steppe landscapes. The article contains 3 Tables, 34 References.

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