Solonetz complex of the Northern Caspian Lowland: phyto- and pedodiversity, relationships between soils, microrelief and plant communities, variation under climate changes and grazing impact Текст научной статьи по специальности «Биологические науки»

ЭКОСИСТЕМЫ: ЭКОЛОГИЯ И ДИНАМИКА, 2018, том 2, № 1, с. 34-72

=————— ДИНАМИКА ЭКОСИСТЕМ И ИХ КОМПОНЕНТОВ ======

УДК 630*232:[63.45+581.526.6](470.47)

SOLONETZ COMPLEX OF THE NORTHERN CASPIAN LOWLAND: PHYTO- AND PEDODIVERSITY, RELATIONSHIPS BETWEEN SOILS, MICRORELIEF AND PLANT COMMUNITIES, VARIATION UNDER CLIMATE CHANGES AND GRAZING IMPACT1

© 2018. N.B. Khitrov*, N.M. Novikova**, А.А. Vyshivkin**, N.A. Volkova**

*V.V. Dokuchaev Soil Institut Russia, 119017, Moscow, Pyzhevsky Lane, 7, Building 2. E-mail: [email protected]

**Water Problems Institute RAS Russia, 119333, Moscow, Gubkina Str., 3. E-mail: [email protected]

The spatiotemporal changes of phytodiversity and pedodiversity of the solonetz complex were studied in the virgin dry steppe ecosystems of the Northern Caspian Lowland. The main objects under investigation are located on the territory of the Dzhanybek scientific research station of Forestry Institute of Russian Academy of Sciences. The study was based on the detailed and independent mapping of soils, microrelief and vegetation on several plots which represent different types of microrelief. The gathered data and maps, compiled by the authors in 2000s, were compared to the data and maps, compiled by D.L. Mozeson, I.V. Kamenetskaya and M.N. Polskyi in 19501955. Estimations of relationships between soils, microrelief and plant communities in the solonetz complex are presented. Changes of solonetz complex components and their relationships due to regional climate changes during the last 50 years, ground water rising and grazing are discussed. Keywords: Endosalic Solonetz, Haplic Luvisols (Endoprotosalic, Sodic, Protocalcic), Eutric Cambisols (Protocalcic), Haplic Kastanozems, plant communities. DOI: 10.24411/2542-2006-2017-10003

Solonetz complexes occupy vast territories of Eurasia, America and Australia continents. In Russia they are represented in forest-steppe, steppe (560 thousands hectares), dry-steppe and semi desert zones (9030 thousands hectares) with maximum in the latter two (Soil Cover ..., 2001). In the XX century territories with solonetz complex was used as pastures and after melioration as tilled fields. Natural areas not under intensive anthropogenic impact have remained mainly within preservations, national parks and scientific experimental stations.

Investigations on the preserved areas permit to observe transformation of ecosystems under natural factors and estimates tendencies of "natural background" changes. In its turn comparative analysis of ecosystems' conditions for preserved territories and those under any anthropogenic influence is the main method to explore the peculiarities of ecosystem transformation under anthropogenic impact.

To search the balance between pasture management and optimum for natural and preserved ecosystems functioning is an important scientific and practice problem being the most urgent for Northern Caspian Lowland, where natural vegetation is the main resource for land management. Natural conditions (arid climate, low soil fertility of solonetz complex) determine range management as the main traditional land use for pastures. To study challenge response of grass ecosystems on grazing is an important research and practice problem, which solution permit to arrange sustainable environment management.

It is important to know interrelations between soils and vegetation and their variations according to microrelief, climatic parameters and groundwater table fluctuations for this problem

1 This research was supported by Russian Foundation for Basic Research, project no. 03-04-48299; Program research of IWP RAS at 2018; Program No 19 of the Presidium of RAS 2018-2020.

solution. For the Northern Caspian territory such information could be obtained during complex flora, fauna, soils, groundwater and climate parameters investigations from 1950-th till our days within the territory of Dzhanybek scientific research station of Forestry Institute of Russian Academy of Sciences (Mozeson, 1952, 1955; Kamenetzkaya, 1952; Kamenetzkaya et al., 1955; Rode, Polsky, 1961; Biocoenotic Basis ..., 1974; Sizemskaya, Sapanov, 2010).

The aim of this chapter is the study of solonetz complex of Northern Caspian Lowland, its plant biodiversity, pedodiversity, relationships between soils, microrelief and plant associations, variation under climate changes and grazing impact.

Objects

The object of research is a solonetz complex at the territory of Dzhanybek experimental station of the Forestry Institute, Russian Academy of Sciences. It is situated in the northwestern part of Pre-Caspian lowland, 30 km north from Elton Lake. According to natural zonation the territory under consideration is included into the closed marine accumulative plain of Khvalyn age occupying the major part of Pre-Caspian lowland in the area between Volga and Ural rivers (Doskach, 1979).

According to the map of geochemical subdivision of the Caspian Lowland the research territory is characterized by domination of chloride-sulfate-sodium saline sediments and soils. Soils of the Dzhanybek research station are characterized by significant contrasts in salinity degree, chemistry of salts and the upper boundary of saline horizon.

Ground waters are qualified as stagnant and their total salt concentration is conjugated with relief and soil type: 5-10 g/l under Solonetz and solonetzic soils on the microhighs, and less 1 g/l under Kastanozems in depressions. Ground water level fluctuates from 4.4 to 7.0 m depending on periodical recharge during spring snow melting in the depressions and evapotranspiration of ecosystems (Sizemskaya, Sapanov, 2010).

It should be mentioned that the territory of Caspian Lowland has a specific ecotone character due to its geological origin. This was the ancient ecotone of the Caspian sea bed which at different time has entered subaerial stage of development. Besides the territory of research is also a zonal ecotone because the border between the steppe and the desert which corresponds to value of the climatic geothermic index of G.N. Vysotsky (1928) equal to 0.5 settles down here. V.A. Nikolaev (2003) characterized this territory as landscape ecotone with intensive fluctuation of natural complexes and prevalence of local factors in dynamics of biocomplexes.

The relief of studied area has elevation of 24-27 m and is largely flat slightly inclined to the south. The monotonous relief is sometimes dissected by shallow closed flat-bottomed mesodepressions, the so-called limans and folds, occupying nearly 10-15% of the total area (Biogeocoenotic Basis ..., 1974). The area of limans is from several to thousand hectares, whereas the area of folds is estimated as several shares to tens hectares. Limans are 2-3 m deep and covered by solodic soils. Folds (0.5-1.5 m deep) are occupied by dark-colored chernozem-like soils. The plain between large closed depressions (85-90% of the total area) displays a clearly expressed microrelief, represented by microelevations as a background, scattered microdepressions of 2-3 to 20-30 m in diameter and microslopes (Bolshakov, Borovsky, 1937; Biogeocoenotic Grounds ..., 1974). Following the statement of many researchers, the microrelief was originated due to sinkhole of Khvalyn saline silty clay loam (Bolshakov, Borovsky, 1937; Doskach, 1979; Mozeson, 1952). The activity of burrowing animals plays a significant role in the microrelief development at the territory under study (Abaturov, 1982).

The vegetation and soil covers are represented by a semidesert solonetz complex in the plain between folds (Kamenetskaya, 1952; Polsky, Rode, 1952; Rode, Polsky, 1961). As evidenced by publications of the above authors, the area confined to microelevations (50-60%) is covered by plant communities of desert type consisting of Artemisia sp. and Kochia sp. on solonchakous

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solonetz soils (WRB: Endosalic Solonetz (Loamic)), while the microdepressions (20-25%) - by herbs association of steppe type on meadow-chestnut soils (WRB: Haplic Kastanozems (Loamic)). In the transitional area (20-25%) on microslopes are widespread the plant communities containing Pyrethrum sp. and Carex caespitosa2 of semidesert type on light-chestnut soils (WRB: Eutric Cambisols (Loamic, Protocalcic; Kamenetskaya, 1952; Rode, Polsky, 1961).

Under study was a key site (fig. 1) located within the area investigated in the 1950s (Mozeson, 1952; Kamenetskaya, 1952). The field survey of this site was conducted in 2003-2005; three adjacent microkey sites (0.72, 0.37 and 0.15 ha respectively) were surveyed being represented by microrelief of flat, watershed and radial-domelike type according to suggestion by D.L. Mozeson (1952).

Climate

In the region of Dzhanybek experimental station the mean annual temperature is 7.2°C, in the warm period it is +18.0°C, whereas in the cold period -3.6°C. At the same time annual fluctuations of the air temperature point out to the climate warming. Playing an important ecological role, the climate in the area under study has been thoroughly studied by A.A. Rode (1959) who indicated peculiar features of the climate in the first half of the XX century. A comprehensive analysis of climatic conditions and their changes was made by (Dinesman, 1960; Sotneva, 2004; Sizemskaya, Sapanov, 2010). It becomes evident now that the changes in climatic parameters reveal a trend towards rising the annual temperature for a long period of time from 1951 due to warming in the winter period by 3.6°C and increasing the precipitation amount by 1.2 mm/year (fig. 1).

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Fig. 1. Fluctuation of precipitations in Dzhanybek during the second half of the XX century. Legend: 1 - annual precipitation, 2 - long-term average annual precipitation, 3 - sum of precipitation during the cold period of year, 4 - sum of precipitation during warm period of year. Рис. 1. Колебание осадков в Джаныбеке во второй половине XX века. Условные обозначения: 1 - годовое количество осадков, 2 - средние многолетние годовые осадки, 3 - сумма осадков за холодный период года, 4 - сумма осадков за теплый период года.

2 Latin names of species are given according to the book S.K. Tcherepanov (1995).

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The precipitation became intensive predominantly in the warm period (March-June and September) that is favorable for the plant growth and development. In July and August the rainfall is rather low (Sizemskaya, Sapanov, 2010).

Climatic parameters display periodical fluctuations resulted in increasing and decreasing the water supply of soils and plants.

To give an integral assessment of the climate parameters changing with time, we used a hydrothermic coefficient (HTC) offered by G.T. Selyaninov and calculated through the formula: HTC=10P/ET, where P - precipitation, ET - the sum of active temperatures for the period of mean daily temperature higher than 0°C (fig. 2).

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Fig. 2. Fluctuation of annual hydrothermal coefficient (HTC) in Dzhanybek during 1955-2009. Legend: 1 - annual HTC, 2 - HTC=1.0 (climatic boundary between forest-steppe and steppe), 3 -HTC=0.5 (climatic boundary between steppe and desert), 4 - linear trend of annual HTC. Рис. 2. Колебание годового гидротермического коэффициента (ГТК) в Джаныбеке в течение 1955-2009. Условные обозначения: 1 - ежегодные значения ГТК, 2 - значение ГТК=1.0 (климатическая граница между лесостепной и степной зонами), 3 - значение ГТК=0.5 (климатическая граница между степной и пустынной зонами), 4 - линейный тренд годовых значений ГТК.

The calculations showed that HTC is estimated as 0.47 for the period from 1951 to 2009. It means that HTC well agrees with desert conditions, because the boundary between the steppe and the desert corresponds to HTC equaled to 0.5. It is known that the years with HTC<0.5 (climatic conditions of the desert) are observed more frequently (by 1.5 times) as compared to those characterized by HTC>0.5 (climatic conditions of the steppe). Typical for the drying period low HTC (<0.22) was observed only 6 times during 53 years. Although statistical trend of HTC rising was rather low (r=0.13) during the 1990s and the early 2000s the territory under consideration.

Thus, the climate changes reveal trends towards increasing the temperature in cold period,

intensifying the precipitation in summer and fluctuating of the HTC values were similar to ones identified at the territory of the East-European plain. However, this process assumes a fluctuating character with alternation of intensive water supply and water deficiency and droughts.

The rise in temperature during the cold period showed changes of ecological conditions of solonetz complex. The surface runoff of thawing waters was declined promoting the increase water accumulation in the soil and supply water by plants from solonchakous solonetz at the microelevations, and decrease runoff accumulation in depressions. In the other words, the water accumulation and supply became less contrast in separate relief elements, whereas in the 1950s the microdepressions received about 80% of thawing waters but microelevations - only 20%. The field observations at the territory of this experimental station showed that the water runoff occurred every 5-6 years before 1995, being stopped after this time. It means that the conditions for water supply have been changed due to climate warming in the autumn-winter period.

Methods

To study the solonetz complex, traditional methods of field observation were performed for identifying a great variety of vegetation and soils in combination with detail mapping of microrelief, soils and plant associations. The key sites were chosen at the territory that was mapped 50 years ago.

Geobotanical research. GPS "Garmin-12" was used to fix geographical coordinates of points for geobotanic description in key sites. Herbarium composing of 49 plant species made it possible to create a database of geobotanic descriptions and classify the plant communities by means of ECOL and SPSS-11 programs. The large-scale mapping was based upon a preliminary elaborated legend and coordinate network presented by a measuring tape (band) 50 m long, stationary bands lying parallel every 2 m and a short tape (2 m) for perpendicular measuring. The boundaries between plant communities were determined by usual geobotanic description of the area identified in such a way.

The geobotanical information was comprehensively analyzed as based upon the data obtained in the 2000s and 1950s. 50 years ago there was a list of plant species, their constant amount in three biotopes (microdepression, slope, microelevation) and geobotanic characteristics of plant communities (Kamenetskaya, 1952; Kamenetskaya et al., 1955), the data obtained in 2003-2004 were analyzed by identical methods to be precisely compared. The plant communities were classified on a dominant basis, what permitted to distinguish 3 groups of basic vegetation components in the solonetz complex: plant communities in microelevations, on slopes and in microdepressions. The first component is represented by plant communities, where Kochia prostrata is dominant. The plant communities of the second component are predominated by Tanacetum achilleifolium. In the herbaceous vegetation of microdepressions Festuca valesiaca, Agropyron desertorum, Medicago romanica, Galium ruthenicum and Jurinea multiflora prevail. It allowed comparing the above groups of plant communities according to the composition of plant species (the total amount, the composition of species and their quantity in a geobotanical plot), the structure (total projecting cover, constant plant species and their abundance) as well as the syntaxonomic structure of vegetation confined to relief elements. This method of comparative analysis made it possible to obtain the characteristics of changes in the composition and structure of plant communities, to define a trend of these processes. Special attention was paid to the plant species, their abundance and demographic structure of perennial populations, the projecting cover but the presence of annual plant species, which can be varied in dependence on the weather conditions, were studied to a lesser extent.

The analysis of data obtained in the course of large-scale geobotanical survey in 2000 was made with the aim at identifying the areas occupied by plant communities of different formations

and associations, their neighboring position and location in relief. These characteristics were compared with those obtained in the 1950s in the same key site. The cartographic analysis like as the analysis of ecological-coenotic structure of plant communities and biodiversity allowed judging about the changes taken place in the vegetation cover at the given territory.

The soil mapping was carried out at scale of 1:200. The vegetation and relief as soil indicators were used only at the initial stage of identifying a diversity of soils and tentative estimating the position of area boundaries. Afterwards the soil areas were determined only by interpolation between the observation points provided with morphological description (946 points in the key area of 0.7 ha, 965 points in the key area of 0.37 ha and 523 points in the key area of 0.15 ha) as well as by additional specific observations along the area boundary. The latter included the carbonate effervescence (every 15-25 cm) appeared at a definite depth and the presence of the solonetzic horizon with the help of knife or spade penetrating.

It is worth emphasizing that the field survey was conducted as based upon the principle of minimal adverse effects on the soil and plant cover. In the semidesert of the Northern Caspian region the soil cover remains destructed by pits and transects for a long period of time. To retain the test area for further monitoring, our observations had a sparing character and allowed detecting a required system of diagnostic soil features without any destruction of the soil and vegetation. The specific of the studied soil cover pattern is a possibility to identify major soils using properties of the topsoil at a depth of 20-30 cm. To identify these soils, it is rather sufficient to make a wedge-shaped cut by spade and then hand borer to the required depth. Having described the soil, the hole and the cut were closed again. The meadow-chestnut soils are described to the depth of 70-90 cm where carbonates occur. A simple vertical sequence of soil horizons permits to identify these soils by hand boring.

Based upon the created maps the elementary soil areas were calculated via computer and the statistical processing of the obtained data by Excel.

Evaluation of pedodiversity was carried out using Shannon's Diversity Index (SHDI) and Shannon's Evenness Index (SHEI; Saldana, Ibanez, 2007; Lo Papa et al., 2011). Three soil classifications were used: Classification and diagnostics of soil of the USSR (K-1977; Classification ..., 1977), Russian soil classification system (RSCS; Classification ..., 2004; Field Guide 2008) and World Reference Base for Soil Resources (WRB; IUSS, 2007).

The mapping survey of microrelief was conducted in the following way. The key site was divided into squares (50x100 m) by theodolite and measuring tape. The core rods in some corners were provided with guide marks for base leveling. A mark remained since the 1950s, was used as a constant one. A randomized grid cell mapping with the step of 1-2 m was carried out being accompanied by additional points on hillocks, in a lower position of depressions, in bends of natural and artificial origin. SURFER programs helped to obtain the mapping relief images.

The boundaries of the area mapped by D.L. Mozeson 50 years ago (Mozeson, 1952, 1955) have no bonding with points of the survey grid, that is why three stages were used for overlaying the map created in the 1950s with that compiled in the 2000s.

First, the map by D.L. Mozeson was overlaid with a grid of planned coordinates obtained within the research in 2000s. A transparent film with vertical section of horizontals every 1 cm and variegated images of curved relief elements that characterizes the key site fragment (150x250 m at scale of 1:1000) was taken for this purpose. Having a complicated picture of the relief image, all the existing hillocks and depressions of different configuration were overlaid by hand.

The second stage was correlation of the elevation marks for two periods because Mozeson's map has a height scale with conditional zero. All the intersection points (about 1300) of relief horizontals at Mozeson's map with lines of coordinate grid compiled in 2000s were accounted. The modern elevation of these points was calculated by interpolation method. The statistical mode of the height difference between two maps in every point was used for correction of conditional zero in

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the height coordinate system obtained during the survey in 2003-2005. It was supposed that such correction permits to obtain the most reliable results. One should stress that the maps compiled by D.L. Mozeson and published in different years, revealed different height marks. We used only the original map published in 1952.

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Fig. 3. Histogram of the difference between repeated elevation measurements.

Рис. 3. Гистограмма разницы между повторными измерениями высоты.

At the third stage the mapping relief image was obtained with section of horizontals (10 cm) as a result of surveying in 2000s. The original map compiled by D.L. Mozeson was digitized to calculate spatial distribution of elevation changes.

Since the natural surface displays a nanorelief and its major part is covered with densely tufted grass the deviations could occur in measurements due to differential leveling. In this context, the elevation was repeatedly measured in different days along the lines of adjacent squares. Figure 3 demonstrates a histogram of the difference between repeated elevation measurements. General standard deviation (s) is 0.89 cm, so it was supposed that unchanged or stable positions of microrelief are within ±3s or approximately ±3 cm.

Kriging-method and SURFER programs were used to compile maps of microrelief and their difference.

Microrelief of the Solonetz Complex and its Changing for 50 Years

Microrelief of the solonetz complex is elevated with an amplitude from 0.4 to 1.0 m at a distance of 5-10 to 40-50 m. It is represented by slightly convex microelevations complicated by microhillocks formed due to the burrowing activity of animals, microdepressions with a flat or slightly concave bottom and microslopes (fig. 4).

The microrelief development is affected by such processes as solution subsidence (Bolshakov, 1937; Doskach, 1979; Mozeson, 1952), surface heaving action due to accumulation of soluble salts at the depth of 1-4 m (Rode, Polsky, 1961), and the burrowing activity of animals (Abaturov, 1982).

D.L. Mozeson (1952, 1955) has identified three types of microrelief, such as flat, watershed and radial-domelike to be different in their size, deepness, mutually arranged depressions and other parameters.

The radial-domelike type of microrelief is an elevated slightly contrasting surface with the height in the range of 30-50 cm. The territory of this microrelief is identical to a dome 1-meter-high with radial microridges and hillocks in the sequence of stretching microdepressions.

The radial-domelike type of microrelief is an elevated slightly contrasting surface with the height in the range of 30-50 cm. The territory of this microrelief is identical to a dome 1-meter-high with radial microridges and hillocks in the sequence of stretching microdepressions.

The watershed type of microrelief is an elevated contrasting surface with a height changing from 50 to 100 cm at a distance of 5-25 m. This is a combination of comparatively small convex, roundish and slightly stretching microdepressions surrounded by microhillocks.

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Fig. 4. Microrelief of studied area and its changes during the second half of the XX century. Legend: A - digitized copy of map compiled by D.L. Mozeson (1955), B - map compiled in 2000s, C - elevation difference after 50 years. Рис. 4. Микрорельеф исследуемой территории и его изменение в течение второй половины XX века. Условные обозначения: А - оцифрованные копии карт, составленные Д.Л. Мозесоном (1955), Б - карта, составленная в 2000-х, С -разница высот через 50 лет.

The flat type of microrelief is a lower surface with large microdepressions, the height of which is ranged from 50 to 70 cm at a distance of 15-40 m.

When comparing digital models of relief in the studied solonetz complex using the data obtained in the 1950s and 2000s, it seemed reasonable to notice that for watershed and flat types of microrelief almost a half of the studied area remained unchanged, one third was sagged from 4 to 20 cm and about a sixth part of the area was found to be elevated by 4-25 cm (fig. 4, right).

The unchanged area looks like a continuous network of the main microrelief elements inimitable in its picture of mutually arranged contrasting microdepressions and microelevations. It

allowed identifying this area by means of maps published in 1950s (Mozeson, 1952, 1955) superposed with those compiled in 2000s (Khitrov, 2005; Khitrov, Omelchenko, 2006).

Against a background of areas unchanged for 50 years the sagged area forms an interrupted network, in polygonal cells of which the elevated areas are distributed.

It was possible to observe uneven surface sagging to 10-20 cm in microrelief of radial-domelike type (80-90% of the total area) probably due to rising groundwater table and capillary fringe resulted in moistening of dry salt horizons in the vadose zone (fig. 4, left).

Microrelief changes with positive sign of deviation are different by nature. The elevation (525 cm) is associated with the burrowing activity of animals and gophers (Spermophilus pygmaeus) in particular. As a result, elevated old and new microhillocks occur and the ground thrown out by animals is taken away at a distance of 1.5-4 m, thus elevating the soil surface. Special field testing of elevated position demonstrated clearly dependence between positive changes of microrelief and the carbonate material of subsoil horizons thrown out not long ago by animals on the ground surface. This material is clearly identified as differed from the AJ and SEL horizons by the carbonate content, color and structure. Moreover, it is feasible to see this material accumulated in consecutive order and in different time.

A small heaving action of the surface (to 4-5 cm) is marked in wide elevated microrelief elements and in the upper part of microslopes adjacent to them. It is explained by the recent pedogenic accumulation of the secondary carbonates in surface horizons of some light-chestnut soils (Eutric Cambisols (Protocalcic)) and Endosalic Solonetz. These soils are mentioned in the following section describing the soil diversity at the studied territory.

The other part of elevated areas (5-7 cm), which has being formed for 50 years, is characterized by absent traces of ground accumulation at the soil surface and substance accumulation in the upper soil horizons. Such areas are confined to the bottom of stretching depressions, dissecting it in several microdepressions. In some cases the bottom edges seem elevated in a depression, decreasing its area. These areas are also identified on microslopes and microelevations. As far as the surface horizons reveal no features of recent accumulation of an additional material, one should assume a local rise of the entire soil profile and the underlying parent material. The hypothesis of surface heaving action due to accumulation of soluble salts at a depth of 1-4 m resulted from the rise of the groundwater level to 4-5 m and the capillary fringe to the soil surface (Rode, Polsky, 1961) is hardly applicable, because the accumulated salts remain in the soil solution causing no changes in the soil or ground volume. It is suggested that a plastic deformation of grounds saturated by water is more reliable and correct. Due to such deformation some blocks are locally sagged and compensated by the rise of the other blocks (Khitrov, 2005).

Changes with negative sign of difference taken place for 50 years are also observed in all the microrelief elements.

There exists an ordinary event, where the surface of microelevations is sagged by 10-20 cm and forms new depressions, the latter being covered by solonetz (WRB: Endosalic Solonetz) and chestnut solonetzic soils (WRB: Haplic Luvisols (Loamic, Cutanic, Sodic, Protocalcic)) reveal a new stage of their evolution due to intensive leaching of the soil profile. As a result, the maximum of the salt content is removed into lower horizons (fig. 5) and the local ground water concentration of soluble salts is increased. B.D. Abaturov (1982) suggested a cause for forming such depressions resulted from the burrowing activity of animals. Large closed cavities formed by animals for hibernation become opened to the surface in spring due to animal makes a move as a vertical tube. The cavities are further filled up by water promoting local removal of salts and sagging of the surface; in its turn, it increases the possible input of a new water portion with all the ensuing consequences.

The sagging of microsaddles is also observed between adjacent microdepressions or their disappearance between local microdepressions in bottoms of middle-sized depressions. It is possible

to observe sagging of gentle microslopes (to 5-7 cm) adjacent to large microdepressions, thus expanding the area up to 1.5-4 m. The possible mechanism responsible for this phenomenon is a solution subsidence associated with salt leaching in light-chestnut soils (WRB: Eutric Cambisols (Loamic, Protocalcic)) on microslopes and in small microdepressions.

Fig. 5. Vertical distribution of sodium activity and chloride activity measured in soil saturated paste of Solonetzs located in stable microelevation (A) and in recently sagged microdepression (B). Рис. 5. Распределение активности ионов натрия и хлоридов, измеренных в насыщенной почвенной пасте по профилю солонцов, расположенных на стабильном микроповышении (А) и в недавно возникшем микропонижении (Б).

Phytodiversity

According to modern knowledge the research territory on the north-west of Caspian Lowland located northward to latitude 48° N (geographical coordinates of the research station are 49°24' N and 46°48' E) belongs to the southern subzone of steppe zone, to the area where most xerophytic steppe vegetation is formed (suffruticose - sod tussock grassland desertified communities), with domination of Stipaeta sareptana formations and codomination of suffruticose sages Artemisia pauciflora and A. lerchiana. The only place in Europe where these communities can be found is south-eastern part of the steppe zone on the border of desert zone (Zones and ..., 1999; Safronova, 2002; Map of the Natural Vegetation ..., 2000). Vegetation of the vicinity of the experimental station is represented by trinomial complex: dominated by Kochia prostrata-Artemisia pauciflora communities occupying solonetz soils (Endosalic Solonetz (Albic, Loamic, Cutanic)) on elevations of microrelief; Leymus ramosus-Agropyron desertorum, Tanacetum achilleifolium, Agropyron desertorum communities and Kochia prostrata-Tanacetum achilleifolium communities growing on light-chestnut soils (Eutric Cambisols (Protocalcic)) of microslopes; Mixteherbosa-Gramineae communities with such dominants as Stipa lessingiana, S. sareptana, Festuca valesiaca, Elytrigia repens and co-dominants Galatella villosa and Jurinea multiflora in micro-depressions with dark-colored meadow-chestnut soils (Haplic Kastanozems; Kamenetskaya, 1952).

Comparison of modern vegetation of solonetz complex on the reserved territory with vegetation observed in 1950. In order to reveal changes of vegetation over a period of more than 50 years floristic and phytocoenotic structure of vegetation of the solonetz complex was compared. Natural vegetation and flora of virgin parts of the research station was first studied by I.V. Kamenetskaya

(1952), later by T.K. Gordeeva and I.V. Larin (1965). Modern study of flora was carried out by A.P. Sukhorukov (2005).

Floristic structure and its changes over a period of 50 years. Flora of the research station consists of 108 species of vascular plants (Gordeeva, Larin, 1965). Research of A.P. Sukhorukov (2005) showed that taxonomic structure of vegetation did not change a lot over 50 years.

Comparison of floristic complex for two terms of observations was carried out according to several characteristics: frequency and phytocoenotic role of the most widespread species -dominants of the communities on the main elements of microrelief (microelevations, slopes, microdepressions, table 1); similarity of species composition of the plant communities on basic elements of microrelief within each relief element during the different climatic periods (table 2). Comparison was carried out basing on 150 geobotanical descriptions executed in the same key points in different periods by I.V. Kamenetskaya (1952) in the 1950th and by the authors in 20022004. It appeared that during different periods of observations the general species list differed a little. Families Asteraceae, Poaceae, Brassicaceae, Chenopodiaceae are steadily leading. The main changes are revealed due to change of species distribution at the elements of microrelief (table 1).

The frequency of occurrence for the species overall at this site were calculated as the percentage of meetings of this type from the total number of descriptions (150) as it was done before by I.V. Kamenetskaya (1952). The frequency of occurrence of the species at the element of microrelief was calculated as the percentage of descriptions in which the species was met from the General array of the descriptions made at this element of the microrelief. The abundance of the species in the element of microrelief reflects the full range of values identified in the descriptions.

In the 2000s, compared to 1950s frequency of graminoids, the dominant in communities, earlier confined to microdepressions, increased (table 1, column 0*). For example, frequency of Festuca valesiaca increases from 66 to 77%, Stipa capillata - from 36 to 47%. However, changes in the frequency of occurrence of the species are ambiguous at the different elements of relief. Festuca valesiaca frequency of occurrence increased almost 7 times at microelevation, decreased slightly at microslopes, and remained unchanged at the microdepressions. Phytocoenotic role of this species increased at microslopes. As a result, it became dominant both at microdepressions and at microslopes.

Stipa capillata did not met at microelevations in 1950s, and currently, the frequency of its meetings is 17%, has increased at the microslopes by almost two times, and decreased at the microdepressions by almost a third. In the 2000s phytocoenotic role of Stipa capillata increased at all microrelief elements, and it became one of the dominants in communities at the microdepressions.

The frequency of occurrence of species typical for microslopes (Agropyron desertorum and Tanacetum achilleifolium) changed differently. Frequency of Agropyron desertorum remained approximately the same (54 and 56%) with increasing of meetings in the microdepressions, and one of Tanacetum achilleifolium decreased almost two times due to a decline in meetings at microelevations and microdepressions. Phytocoenotic role of Agropyron desertorum increased for all elements of the microrelief, but it dominates at microslopes. Phytocoenotic role of Tanacetum achilleifolium has not changed. It is dominant in the communities at microslopes.

Dwarf shrubs (Kochia prostrata, Artemisia pauciflora) were dominant on micro-elevations in 1950s and occurred at other elements of microrelief too. Their frequency of occurrence dramatically reduced in 2000th. The number of meetings Kochia prostrata decreased due to decreasing of its occurrence at microslopes and microdepressions, while at microelevations this species is registered in all descriptions and is a dominant as before. Whilst, occurrence and phytocenotic role of Artemisia pauciflora decreased at all elements of the microrelief, and this species ceased to be a dominant.

Frequency of Poa bulbosa decreased which can be explained by the cessation of grazing.

Decreasing of the frequency of occurrence Leymus ramosus is due to the reduction of soil material recovery on the surface by ground squirrels, the number of which is strongly reduced in this area in the 2000s.

Thus, the main trend of vegetation changes during the period from 1950s till 2000s is an expansion of graminea species at the most elements of microrelief and increasing their phytocenotic role in the communities. At the same time, the analogous indicators for species of dwarf shrubs decreased.

Table 1. Frequency and phytocoenotic role of the most widespread species on the preserved plot of the Dzhanybek research station. Таблица 1. Частота встречаемости и фитоценотическая роль наиболее распространенных видов на охраняемом участке научно-исследовательской станции Джаныбек.

Species Years Frequency, % Abundance (phytocoenotic role)

0* 1** 2** 3** 1 2 3

Festuca valesiaca 1950 2000 66 77 9 62 89 71 100 100 rar-sol rar-sol sol sol-cop sp sol-cop

Agropyron desertorum 1950 2000 54 56 63 62 96 89 4 37 rar-sol rar-sp sp sol-cop sol sol-sp

Asrtemisia austríaca 1950 2000 59 54 2 10 75 69 100 75 sol rar-sol sol-sp rar-sp sp sol-sp

Poa bulbosa 1950 2000 99 50 97 72 100 32 99 50 sP sol-cop sp sol sp sol

Stipa capillata 1950 2000 36 49 17 13 28 93 60 rar-sol rar-sol sol-sp sp sol-cop

Leymus ramosus 1950 2000 93 47 92 69 100 63 87 22 sol sol-sp sp sol-cop sol sol-sp

Kochia prostrata 1950 2000 79 41 100 100 89 30 47 17 sp-cop sp-cop sol rar-sol rar rar

Tanacetum achilleifolium 1950 2000 86 40 74 24 94 73 89 27 sol sol-sp sp-cop sp-cop rar-sol rar-sol

Artemisia pauciflora 1950 2000 67 22 100 79 72 11 31 5 sp-cop rar-sp rar-sol rar-sol rar rar-sol

Notes to table 1: * - calculated for the whole key site, ** - calculated for each component of solonetz complex separately (1 - microelevations, 2 - microslopes, 3 - microdepressions), line - no species. Примечания к таблице 1: * - рассчитано для всего участка, ** - рассчитано для каждого элемента солонцового комплекса отдельно (1 - микроповышения, 2 - микросклоны, 3 - микропонижения), прочерк - нет видов.

Species composition of plant communities at basic elements of microrelief had different similarity between each other in each period of observation separately (table 2). In the 1950th the maximum similarity was noted between communities of microelevations and microslopes (43%), and the minimum - between communities of microelevations and microdepressions (19%). In the 2000th similarity of species composition increased at all elements of microrelief and the range of variation of similarity values decreased: minimum - between communities of microelevations and

microdepressions (35%), maximum - between communities of microslopes and microdepressions (46%). The values of similarity changed during the second half of the XX century. Great increasing of similarity was observed between microelevations and microdepressions (from 19 to 35%), the least - between microelevations and microslopes (from 43 to 45%; table 2).

The maximum similarity of species composition of the plant communities at the same elements of microrelief in 1950s and 2000s was registered for the microdepressions and the minimum - for microelevations (table 3). In other words, the greatest changes in species composition of communities happened at microelevations, a bit less great changes - at microslopes, and the least ones - at microdepressions.

Table 2. Similarity of species composition of plant communities on the main elements of microrelief, according to the data, obtained in 1950s and 2000s (%). Таблица 2. Сходство видового состава растительных сообществ на основных элементах микрорельефа, по данным, полученным в 1950-х и 2000-х годах (%).

Compared components of solonetzic complex Similarity (%) of species composition of the plant communities in

1950 2000

1-2 43 45

1-3 19 35

2-3 37 46

Notes to table 2: 1-3 - elements of microrelief of the solonetz complex: 1 - microelevations, 2 -microslopes, 3 - microdepressions. Примечания к таблице 2: 1-3 - элементы микрорельефа солонцового комплекса: 1 - микроповышения, 2 - микросклоны, 3 - микропонижения;

Table 3. Similarity of species composition of plant communities on the same elements of microrelief in 1950s and 2000s (%). Таблица 3. Сходство видового состава растительных сообществ на одинаковых элементах микрорельефа в 1950-х и 2000-х годах (%).

Components of solonetzic complex 1950

1 2 3

1 41 - -

2000 2 - 51 -

3 - - 80

Notes to table 3: 1-3 - elements of microrelief of the solonetz complex: 1 - microelevations, 2 -microslopes, 3 - microdepressions. Примечания к таблице 3: 1-3 - элементы микрорельефа солонцового комплекса: 1 - микроповышения, 2 - микросклоны, 3 - микропонижения;

Change of plant communities. Along with stated above changes of spatial structure and phytocoenotic role of some species of plants, changes of syntaxon structure (plant communities, fig. 6) were marked: communities with domination of a black wormwood (Artemisia pauciflora) which doesn't take out overmoistening disappeared, its place was taken by leban (Kochia prostrata). Communities with domination of steppe lucerne (Medicago romanica) and other species appeared.

Modern characteristics of components of the solonetz complex on the reserved site were established (table 4, fig. 6). These characteristics can be used as a "key" to the territory located out of the reserved area and affected by grazing.

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Artemisia pauciflora Kohia prostrata Leymus ramosum Tanacetum achilleifolium Agropyron desertorum Festuca valesiaca Koeleria cristata Stipa capillata Stipa lessingiana Carex stenophylla Galatella villosa Jurinea multiflora Medicago romanica Gallium ruthenicum Agropyron cristatum Graminea Elytrigia repens Spirea hypericifolia Poa bulbosa Artemisia austriaca Petrosimonia triandra Lepidium perfoliatum Falcaria vulgaris

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Fig. 6. Dominants and subdominants of the plant communities in different observation dates. In vertical list - dominants of communities, in horizontal list - co-dominants. In bold type - numbers of communities that were not met in 1950s. Legend. Community: 1 - elevations, 2 - slopes, 3 -depressions, 4 - deep depressions, 5 - weed. Рис. 6. Доминанты и субдоминанты растительных сообществ в разные даты наблюдений. Жирным шрифтом выделены сообщества, которые не были встречены в 1950-е годы. Условные обозначения. Cообщества.' 1 - повышений, 2 -склонов, 3 - понижений, 4 - глубоких понижений, 5 - сорные.

The intersection of dominant and subdominant on the figure 6 is indicated by the sequence number of their plant community. This number was assigned to communities during creation of the legend to the vegetation map. Italic type of number represents the community that was not described by I.V. Kamenetskaya in 1950s. These communities emerged due to change of the phytocoenotic role of some species: the role of Festuca valesiaca, Stipa capillata, Agropyron desertorum increases and the role of Artemisia pauciflora, Poa bulbosa etc. decreases.

Soil Diversity in the Studied Solonetz Complex

The soil cover pattern of key sites in the area of virgin solonetz complex is represented by meadow-chestnut (Haplic Kastanozem (Loamic) in WRB), light-chestnut non-solonetzic (WRB: Eutric Cambisol (Loamic Protocalcic, Ochric)), light-chestnut solonetzic soils (WRB: Haplic Luvisol (Loamic, Cutanic, Differentic, Hypereutric, Ochric, Sodic, Protocalcic, Endoprotosalic)) and crusty solonetzes (WRB: Gypsic Endosalic Solonetz (Albic, Loamic, Cutanic, Differentic, Magnesic)). Brief description of these soils is the following.

The profile of meadow-chestnut soils (WRB: Haplic Kastanozem (Loamic)) is the following: AU-BM-BCAmc-BCca in terms of RSCS or Ah-B-Bk-BC in terms of FAO (Guidelines for soil description, 2006). The surface dark-humus horizon AU reveals diagnostic features inherent to Mollic horizon in WRB. Its thickness ranges from 20 to 40 cm. It is followed by structural-metamorphic horizon BM that has no carbonates due to its annual leaching in the spring and corresponds to Cambic horizon in WRB. In the central part of area its thickness is 15-25 cm, being declined to 5-7 cm in the periphery. At a depth of 40-70 cm there is an accumulative-carbonate horizon BCAmc enriched with secondary calcium carbonates as pseudomicelia. Being varied from 40 to 70-80 cm, it corresponds to protocalcic properties and very seldom to Calcic horizon in WRB. The profile is completed by BCca horizon as a transitional horizon to the parent material with carbonates. These soils occupy bottom of microdepressions under herb vegetation. After snowmelt in spring the soil profile is completely moistening by thawing water that is why there are no soluble salts along their profile up to the groundwater level at a depth of 5-7 m.

Table 4. Parameters of structure-functional organization of vegetation of the solonetz complex on the reserved area in 2003. Таблица 4. Параметры структурно-функциональной организации растительности солонцового комплекса на заповедной территории в 2003 году.

Characteristics of plant communities Components of the solonetz complex (plant associations and soils)

Communities of Kochia prostrata-Artemisia pauciflora on solonetz soil Communities dominated by Tanacetum achilleifolium on light-chestnut soils Mixteherbosa- Gramineae communities on meadow-chestnut soils

Total number of species 30 40 64

Number of species on the observation plot 12 16 27

Total projective cover, % 30-40 60-70 70-100

Productivity, (air-dry weight), g/m2 112-109 153-148 235-330

The light-chestnut soils (WRB: Eutric Cambisol (Loamic Protocalcic, Ochric)) have a natural type of the profile: AJ-BCAmc-BCca (or A-Bk-BC). The surface light-humus horizon AJ is light gray in color (10YR 6/1 ... 7/2), crumby-granular, it has a neutral or slightly alkaline reaction (pH 7-8.3). Carbonates may occur sometimes in its lower part. The thickness varies from 5 to 2025 cm. In WRB there is no analog to this horizon. Beneath this horizon there exists an accumulative-carbonate horizon BCAmc with carbonate pseudomicelia. The carbonate content is usually varied from 4-5 to 10-14% that is more than in parent material (Protocalcic qualifier of WRB). The major part of the profile has no soluble salts; the latter being appeared only in BCca horizon and the parent material at a depth of 1 to 2-3 m. The light-chestnut soils are common in different positions of the microrelief under plant communities predominated by Pyrethrum sp. and

Carex caespitosa.

The chestnut solonetzic solonchakous soil (WRB: Haplic Luvisol (Laomic, Cutanic, Differentic, Hypereutric, Ochric, Sodic, Protocalcic, Endoprotosalic)) has a more complicated profile: AJ-BMKsn-BCAmc,s-BCca,s,cs (or A-Bt-Bk-BCy). Beneath the light-humus horizon AJ there is a xerometamorphic BMK horizon complicated by features of solonetzic properties (sn). It has prismatic structure, the presence of sporadic humus-clayey cutans on sides of many aggregates and the content of exchangeable sodium about 5-15% from CEC. Carbonates are usually absent in this horizon. It has insufficient features to be identified as Natric horizon in WRB and corresponds more to Argic horizon. The sum of exchangeable Mg and Na equaled to more than 15% from CEC corresponds to Sodic qualifier. This horizon is followed by an accumulative-carbonate ones BCAmc,s with secondary calcium carbonates as pseudomicelia and soluble salts as well. Electrical conductivity of saturation extract (ECse) varies from 4 to 8 dS/m. The underlying BCca,s,cs as a transitional horizon to the parent material reveals the carbonates, soluble salts and gypsum druses. The presence of the rather small amount of salts at a depth of more than 50 cm makes it feasible to consider as Endoprotosalic qualifier in WRB. The chestnut solonetzic soils occur on microslopes and microhillocks under vegetation composing of Artemisia sp. and Kochia sp.

One of significant component of soil cover pattern is Solonetz. These soils have the similar name both in RSCS and in WRB. The full soil name in WRB-2015 is Gypsic Endosalic Solonetz (Albic, Loamic, Cutanic, Differentic, Magnesic). Soil profile of Solonetz is SEL-BSN-BCAmc,s,cs-BCca,s,cs (or E-Bt-Bkyz-BCyz). The solonetzic-eluvial horizon SEL may be a topsoil or underlain by the light-humus horizon AJ. It is light gray or whitish in color (10YR 7/1 ... 8/2) at the surface being more dark when it is wet (10YR 4/1 ... 5/2). Its structure is fine-layered or platy. In the major cases this horizon corresponds to Albic material in WRB. It is followed by the solonetz horizon BSN that corresponds to Natric hotizon in WRB. The BCAmc,s,cs horizon is rich in pseudomicelia and soft nodules of calcium carbonates, soluble salts and gypsum druses, it combines feathers for identification of Gypsic, Salic horizons and protocalcic properties together. Its upper boundary is at a depth of 25-40 cm, the maximum content of salts and gypsum is confined to the depth from 50100 to 200-250 cm. Salt content decreases with depth although ECse remains at a level of 8 dS/m. A gypsum-bearing subtype is recognized by the gypsum content. According to the thickness of eluvial part of the profile (SEL or AL+SEL) Solonetzes in RSCS are divided into crusty (<5 cm), shallow (5-10 cm), medium (10-20 cm) and deep (>20 cm) species. In the research area all the above species occur. Crusty and shallow Solonetzes are predominant. They are solonchakous, because their upper boundary of the first saline horizon (the toxic salt content in water 1:5 extract is above 0.1% and/or ECse>4 dS/m) is at a depth upper than 30 cm. The soluble salts are predominantly represented by sodium chlorides and sulfates. At the territory under study Solonetzes occur in convex microrelief elements covered by plant associations containing Artemisia sp. and Kochia sp., although due to changes in microrelief they may also occur on microslopes and even in newly formed microdepressions.

Soil cover pattern of the studied territory confines small area of soils with calcium carbonates in the surface horizons and effervescence from the surface due to different reasons. One of them is animal borrowing activity by ground squirrels (Spermophilus pygmaeus), field voles, ants. These animals make holes in the soil and borrow carbonate materials from lower soil horizons to the surface creating microhillock (so called butan). As a result every main soil described above can be covered by carbonate material with the thickness from 1-3 to 20-30 cm. In RSCS such soils are identified as stratificated subtypes and in WRB - as Novic qualifier.

There is another group of soils with effervescence from the surface - the light-chestnut solonetzic and non-solonetzic carbonate soils and carbonate solonetz which reveal no features of the soil material filled up at the surface by living organisms. In RSCS these soils are identified as species "carbonate". In WRB this feature has no taxonomic value. Such soils haven't been

ЭКОСHCTЕМBI: ЭКОПОГHM H AHHAMHKA, 2018, tom 2, № 1

described earlier at the territory of Dzhanybek experimental station. Obviously, they may be considered as developed in the last decades. These soils occupy flat microelevations around hillocks formed by ground squirrels or not far from them.

The carbonate profile of soils is almost similar to that occurred in light-chestnut (non-solonetzic), light-chestnut solonetzic and crusty solonetzs. The main difference is that they are highly effervescent at the surface.

The vertical distribution of carbonate effervescence is rather specific in dependence on carbonate accumulation in upper soil horizons. In clearly expressed variants the entire soil profile displays the strongest effervescence. Accumulation of carbonates in the upper horizon becomes a reason for heave of the surface and formation of a small hillock (2 to 5 cm) dissected by a polygonal network of shallow fissures (3-5 cm) with edges turned outside. These broken edges of fissures are light (pale) in color (10YR 7/2 or 8/2), highly effervescent and compacted at the expense of CaCO3 accumulation in visible soil pores. With the depth of 2-4 cm the soil profile remains the form inherent to soils without carbonates, but differs by color of the topsoil that becomes more light due to carbonate accumulation.

In some carbonate soils the process of calcium carbonate accumulation in the upper horizons is found to be at an intermediate stage. Maximum effervescence is observed at the soil surface, being weakened with depth (10-20 cm) and completely disappeared to show the features of initial non-carbonate horizons. Downwards the profile the carbonates occur again at a depth characteristic of every soil. The carbonates are accumulated due to capillary rise of soil solutions to the surface and evaporation.

Two factors can be responsible for the development of carbonate light-chestnut soils and carbonate solonetzs: (1) the rise of groundwater level by 1.5-2 m, i.e. from 6-7 m in the 1950s to 4.5-5 m since the 1980s to the present time (Sokolova et al., 2001) and (2) some changes in the climate for the last 25 years - winters became more warm resulting in snowmelt several times during this season, and the soils are enriched with the thawing water, thus declining the surface runoff into microdepressions.

As a hypothesis it is possible to suggest the mechanism of carbonate accumulation in the topsoil. As it was written above, the carbonate-enriched soils occupy convex positions of microrelief near or not far from (1-2 m) microhillocks formed by ground squirrels. Such microhillocks contain the carbonate material from the lower horizons burrowed by animals. In warm winters the thawing water infiltrates into the soil including these microhillocks, where the soil solutions are enriched with calcium carbonate. Due to a higher water permeability of the lighthumus horizon AJ and solonetzic-eluvial horizon SEL as compared to underlying BMK or BSN horizons a part of soil solutions moves in the lateral direction within surface horizons into adjacent areas to be further evaporated from the surface. As a result of such a repeated process the calcium carbonates are bit by bit accumulated at the soil surface and upper soil horizons.

The obtained results serve as evidence that the studied soils in solonetz complex are highly dependent on the microrelief type (fig. 7-9).

At the radial-domelike type of microrelief the light-chestnut (non-solonetzic and solonetzic) soils and those covered by burrowed layer are dominant in the soil cover pattern, the most contrasting components (meadow-chestnut soils and solonetzes) are found to be at a subordinated level (table 5, fig. 7). Complexity Index calculated as number of elemental soil area per 1 ha is 900 due to a lot of small soil areas.

At the watershed type of microrelief the solonetz complex is most contrasting due to the largest vertical amplitude of elevation (50-80 cm) within small distances (5-25 m) and approximately the same share of the main soil components (table 5, fig. 8). Complexity Index is also very high (832) because elemental soil areas are from 2-3 to 120-400 m2, median 10-20 m2.

ЭКОСHCTЕМBI: ЭКОПОГHM H AHHÄMHKÄ, 2018, tom 2, № 1

Table 5. Distribution of soils in the key sites with different microrelief type.

Таблица 5. Распределение почв на ключевых участках с микрорельефом разного типа.

Soil A share of soils (%) in different microrelief type

radial-domelike watershed flat

Meadow-chestnut (Haplic Kastanozem) 12.4 15.7 36.7

Light-chestnut (Eutric Cambisol (Protocalcic) 38.0 26.8 41.9

Chestnut solonetzic (Haplic Luvisol (Cutanic, Sodic) 25.3 22.8 8.1

Solonetz (Gypsic Endosalic Solonetz (Loamic)) 4.7 12.8 5.4

Carbonate soil that is not covered by burrowed material 4.6 9 0

Soil covered by burrowed layer (supplementary qualifier Novic) 15.0 12.9 7.6

Light-chestnut (non-solonetzic) and meadow-chestnut soils are predominant in the soil cover pattern at the flat type of microrelief (table 5, fig. 9). The largest areas of these soils are up to 23002900 m2 although there are areas with usual dimensions (from 2-3 to 20-30 m2). The share of chestnut solonetzic soils and solonetzes is the smallest in comparison with the other microrelief types. Complexity Index is the smallest (264) too.

At a qualitative level the mentioned tendency is testified by the knowledge acquired in the present time, although it has not been formulated for the territory of the Dzhanybek experimental station.

In earlier publications relating to soils of Dzhanybek experimental station the distribution of such soils has been indicated in the following order: 50% of solonetz soils, 25% of light-chestnut soils (non-solonetzic and solonetzic ones) and 25% of meadow-chestnut soils. The soils have been identified according to distribution of plant communities including Artemisia sp. and Kochia sp. (50%), Pyrethrum sp. and Carex caespitosa (25%) and herb vegetation (25%; Kamenskaya, 1952). So far as it was believed that vegetation reflected soils and the boundaries of soil areas have been identified according to vegetation, these data were used to show the soil distribution in the solonetz complex (Rode, Polsky, 1961).

Evaluation of soil distribution at three types of microrelief identified by Mozeson has not been made. For the first approximation it can be made now using the map of vegetation compiled by I.V. Kamenetskaya in 1952. The boundaries of key sites that have been mapped in 2003-2004 were overlaid to this map and areas of plant associations and related (by legend of this map) soils were calculated. The results are presented in table 6.

When comparing the data given in tables 5 and 6, it seems reasonable to conclude that the soil indication as based upon vegetation is exceeding the estimate of solonetz distribution, whereas the estimation of light-chestnut soils proves to be declined.

It is worth emphasizing that it is not correct to compare the data about the development of the given solonetz complex taken place during 50 years. First, the estimation has been conducted in different time by using different methods.

By this reason the results cannot be comparable to a definite extent. Secondly, the vegetation state is affected not only by soil properties but also the other factors particularly microrelief and human activities (overgrazing and the regime of nature reserve). The data in table 6 is shown only to demonstrate that the studied key sites located at the territory with different types of microrelief

Fig. 7. Soil map of key site at the radial-domelike type of microrelief. Legend: 1 - meadow-chestnut soil (Haplic Kastanozem (Loamic) in WRB); 2, 3 - light-chestnut non-solonetzic soils non-carbonate (2) and carbonate (3) from the surface (WRB: Eutric Cambisol (Loamic, Protocalcic)); 4, 5 - light-chestnut solonetzic soils non-carbonate (4) and carbonate (5) from the surface (WRB: Haplic Luvisol (Loamic, Cutanic, Sodic, Protocalcic, Endoprotosalic)); 6, 7 - solonetzes non-carbonate (6) and carbonate (7) from the surface (WRB: Gypsic Endosalic Solonetz (Albic, Loamic, Cutanic, Differentic, Magnesic)); 8 - different soils covered by burrowed layer (Kastanozems, Cambisols, Luvisols and Solonetz with qualifier Novic). Рис. 7. Почвенная карта ключевого участка на радиально-куполовидном типе микрорельефа. Условные обозначения: 1 - лугово-каштановые почвы (Haplic Kastanozem (Loamic) в WRB); 2, 3 - светло-каштановые несолонцеватые почвы некарбонатные (2) и карбонатные (3) с поверхности (WRB: Eutric Cambisol (Loamic, Protocalcic)); 4, 5 - светло-каштановые солонцеватые почвы некарбонатные (4) и карбонатные (5) с поверхности (WRB: Haplic Luvisol (Loamic, Cutanic, Натровые, Protocalcic, Endoprotosalic)); 6, 7 - солонцы некарбонатные (6) и карбонатные (7) с поверхности (WRB: гипсовые Endosalic Солонца (Albic, Loamic, Cutanic, Differentic, Magnesic)); 8 - разные почвы, покрытые слоем выбросов землероев (Kastanozems, Cambisols, Luvisols и Solonetz с квалификатором Novic).

Fig. 8. Soil map of key site at the watershed type of microrelief. Legend: 1 - meadow-chestnut soil (Haplic Kastanozem (Loamic) in WRB); 2, 3 - light-chestnut non-solonetzic soils non-carbonate (2) and carbonate (3) from the surface (WRB: Eutric Cambisol (Loamic, Protocalcic)); 4, 5 - light-chestnut solonetzic soils non-carbonate (4) and carbonate (5) from the surface (WRB: Haplic Luvisol (Loamic, Cutanic, Sodic, Protocalcic, Endoprotosalic)); 6, 7 - solonetzes non-carbonate (6) and carbonate (7) from the surface (WRB: Gypsic Endosalic Solonetz (Albic, Loamic, Cutanic, Differentic, Magnesic)); 8 - different soils covered by burrowed layer (Kastanozems, Cambisols, Luvisols and Solonetz with qualifier Novic). Рис. 8. Почвенная карта ключевого участка на водораздельном типе микрорельефа. Условные обозначения: 1 - лугово-каштановые почвы (Haplic Kastanozem (Loamic) в WRB); 2, 3 - светло-каштановые несолонцеватые почвы некарбонатные (2) и карбонатные (3) с поверхности (WRB: Eutric Cambisol (Loamic, Protocalcic)); 4, 5 - светло-каштановые солонцеватые почвы некарбонатные (4) и карбонатные (5) с поверхности (WRB: Haplic Luvisol (Loamic, Cutanic, натриевые, Protocalcic, Endoprotosalic)); 6, 7 - солонцы некарбонатные (6) и карбонатные (7) с поверхности (WRB: гипсовые Endosalic Солонца (Albic, Loamic, Cutanic, Differentic, Magnesic)); 8 - разные почвы, покрытые слоем выбросов землероев (Kastanozems, Cambisols, Luvisols и Solonetz с квалификатором Novic).

had differences even 50 years ago, it being known that these differences between the sites were approximately the same as in the present time.

Pedodiversity was estimated according to the total amount of soil taxa and Shannon's indices (SHDI and SHEI) using in RSCS and WRB. Both classification systems revealed common trends towards changing these indices (table 7). The differences consist only in their numerical values. The richness of soil taxa and SHDI recognized in WRB prove to be always lower but SHEI values are frequently higher as compared to those based on RSCS.

Fig. 9. Soil map of key site at the flat type of microrelief. Legend: 1 - meadow-chestnut soil (Haplic Kastanozem (Loamic) in WRB); 2, 3 - light-chestnut non-solonetzic soils non-carbonate (2) and carbonate (3) from the surface (WRB: Eutric Cambisol (Loamic, Protocalcic)); 4, 5 - light-chestnut solonetzic soils non-carbonate (4) and carbonate (5) from the surface (WRB: Haplic Luvisol (Loamic, Cutanic, Sodic, Protocalcic, Endoprotosalic)); 6, 7 - solonetzes non-carbonate (6) and carbonate (7) from the surface (WRB: Gypsic Endosalic Solonetz (Albic, Loamic, Cutanic, Differentic, Magnesic)); 8 - different soils covered by burrowed layer (Kastanozems, Cambisols, Luvisols and Solonetz with qualifier Novic). Рис. 9. Почвенная карта ключевого участка на плоском типе микрорельефа. Условные обозначения: 1 - лугово-каштановые почвы (Haplic Kastanozem (Loamic) в WRB); 2, 3 - светло-каштановые несолонцеватые почвы некарбонатные (2) и карбонатные (3) с поверхности (WRB: Eutric Cambisol (Loamic, Protocalcic)); 4, 5 - светло-каштановые солонцеватые почвы некарбонатные (4) и карбонатные (5) с поверхности (WRB: Haplic Luvisol (Loamic, Cutanic, натриевые, Protocalcic, Endoprotosalic)); 6, 7 - солонцы некарбонатные (6) и карбонатные (7) с поверхности (WRB: гипсовые Endosalic солонцы (Albic, Loamic, Cutanic, Differentic, Magnesic)); 8 - разные почвы, покрытые выбросами землероев (Kastanozems, Cambisols, Luvisols и Solonetz с квалификатором Novic).

Table 6. The areas of plant communities and soils in key sites with different microrelief types at the vegetation map compiled in 1952 (Kamenetskaya, 1952). It was believed according to the map legend, that soils are close related with plant associations being the major object for mapping. Таблица 6. Доля площади растительных сообществ и почв на ключевых участках с различными типами микрорельефа на карте растительности, составленной в 1952 г. (Каменецкая, 1952). Считалось, в соответствии с легендой к карте, что почвы тесно связаны с растительными сообществами, являющимися основным объектом для картографирования.

Plant communities Soils A share of areas (%) with different type of microrelief

Radial-domelike Watershed Flat

Herbs Meadow-chestnut 19.6 9.9 40.7

Pyrethrum sp. and Carex caespitosa Light-chestnut 24.9 19.9 19.5

Artemisia sp. and Kochia prostrata Solonetz 55.5 70.2 39.8

Table 7. Pedodiversity estimation of the solonetz complex in different microrelief types. Таблица 7. Оценка почвенного разнообразия солонцовых комплексов на участках с разным типом микрорельефа.

Classification system Index Measuring unit Values of pedodiversity indices for different types of microrelief

Radial-domelike Watershed Flat

RSCS Richness of soil types piece 4 5 5

Richness of soil subtypes « - » 8 13 11

Richness of soil species « - » 12 19 13

SHDI dimensionless 1.739 2.164 1.438

SHEI « - » " 0.700 0.735 0.561

WRB Richness of Reference Soil Groups (RSG) piece 4 4 4

Richness of RSG+ principal qualifiers « - » 5 5 5

Richness of RSG+ all qualifiers « - » 8 12 9

SHDI dimensionless 1.557 1.809 1.390

SHEI « - » 0.749 0.728 0.633

This is explained by the fact that in WRB there are no soil species, which are distinguished in RSCS according to accumulation of secondary carbonates in the upper horizons without traces of soil materials scattered on the surface. A share of such carbonate soils in radial-domelike and watershed microrelief types accounts for 4.5% and 9% respectively, thus affecting the values of pedodiversity indices.

The highest values of all the indices are inherent to the solonetz complex in watershed type of relief (table 7). The other two microrelief types have unequal and very close values of pedodiversity indices. Such tendency is not accidental.

Obviously, the solonetz complex in watershed microrelief type may be considered as an active stage of its development, characterized by more or less equal share holding of the main soils, the clearly expressed contrast of changes in the soil properties and large amplitude of changes in the surface elevation at small distances.

The radial-domelike microrelief type shows a slightly expressed differentiation of microrelief and soil cover pattern probably conditioned by the entire convex surface. As a result, in winter the snow is blown away and the water input to soils becomes very low, providing favorable conditions for ground squirrels and a higher share of scattered soils. On the contrary, the flat type of microrelief is distributed at a concave surface, where the soils are supplied with water in spring. As a result, in the composition of the soil cover pattern a share of non-saline meadow-chestnut (Haplic Kastanozems) and light-chestnut (Eutric Cambisols (Protocalcic)) soils increases. A share of Endosalic Solonetz and chestnut solonetzic soils (Haplic Luvisols (Sodic, Protocalcic, Endoprotosalic)) decreases against the background of diversity of solonetzic soils.

Interaction Between Microrelief, Soils and Vegetation

In 1950s it was suggested that soils, forms of microrelief and vegetation are close related between each other (Mozeson, 1952; Kamenetskaya, 1952; Rode, Polsky, 1961). In 2003-2005 detail mapping of microrelief, soils and vegetation was carried out independently of one another at the same key plots. As a result it was found that every soil in the soil cover pattern can potentially occupy each microrelief position (table 8) and can be under different vegetation (table 9) with different probability. The traditional view-point on the relationship between soils and microrelief corresponds to probability 0.8-0.9 for meadow-chestnut soils (Haplic Kastanozems), 0.3-0.5 for light-chestnut soils (Eutric Cambisol (Protocalcic)), 0.1-0.4 for chestnut solonetzic soils (Haplic Luvisol (Sodic, Protocalcic)) and 0.1-0.2 for Solonetz.

The meadow-chestnut soils frequently occupy microdepressions covered by Medicago romanica, Festuca sulcata, Stipa capillata, Leymus ramsus plant formations. Although they may be found on microslopes at the higher positions than light-chestnut soils within a microcatena, as well as in microelevations under Kochia prostrata and those enriched with gopher burrows.

Light-chestnut non-solonetzic soils may be found in all the positions including shallow and middle microdepressions covered by herbaceous plant communities, on microslopes and microelevations under different vegetation. Light-chestnut solonetzic soils and solonetzes occupy microslopes and elevations though they may be met in microdepressions, the major part of which has being developed during the last 50 years.

One of the reasons of weak relationship between soils, microrelief and vegetation in 2003 -2005 is changes in microrelief taken place for the last 50 years. Half of the variants, not corresponding to the traditional view-point, are areas with sagging and elevating the positions of microrelief.

However, there are a number of cases included inversions in relationship soil-microrelief or soil-vegetation in relative stable positions for the last 50 years. For example, some parts of areas are occupied by meadow-chestnut soils in microelevations; light-chestnut soils - in microdepressions or in microelevations. Consequently, the territory under consideration has been subject to changes in microrelief not only for the last 50 years but also in the other periods taken place before.

ЭКОСHCTЕМBI: ЭКОПОГHM H AHHAMHKA, 2018, tom 2, № 1

Table 8. Soil distribution in the solonetz complex as confined to different microrelief elements. Таблица 8. Приуроченность почв солонцового комплекса к различным элементам микрорельефа.

Probable distribution of different soils within a microrelief element

Soil Microdepressions, depth>20 cm Microdepressions, depth=3-20 cm Microslope Microelevation

Meadow-chestnut 0.8-0.9 0.1-0.3 -0.1 -0.02

Light-chestnut 0.1-0.15 0.6-0.8 0.3-0.5 0.2-0.4

Chestnut solonetzic <0.01 0.01-0.12 0.1-0.4 0.1-0.6

Solonetz <0.01 0.01-0.04 0.05-0.2 0.05-0.1

Carbonate soil, not

covered with burrowed 0 0 0.1-0.2 0.1-0.15

material

Soil, covered with burrowed layer <0.001 -0.01 0.1-0.2 0.4-0.5

Table 9. Soil distribution in the solonetz complex under different vegetation formations. Таблица 9. Приуроченность почв солонцового комплекса к участкам, занятым различными видами растений.

Soil Proba le distribution of different soils within a different plant sp pecies

Bare areas Areas covered with Kochia prostrata Areas covered with Pyrethrum achilleifolium or Leymus ramosus Areas covered with Festuca valesiaca Areas covered with Festuca sulcata, Stipa capillata, Leymus ramosus Areas covered with Medicago romanica

Meadow-chestnut 0.05-0.1 <0.05 0.05-0.15 0.4-0.5 0.5-0.65 0.8-0.9

Light-chestnut 0.4-0.5 0.3-0.4 0.4-0.5 0.4-0.5 0.2-0.3 0.05-0.08

Chestnut solonetzic 0.1-0.2 0.1-0.2 0.1-0.2 0.05-0.08 <0.04 <0.01

Solonetz 0.1-0.2 0.05-0.1 0.05-0.1 <0.03 <0.02 <0.02

Carbonate soil that is not covered by burrowed material 0.02-0.05 0.05-0.1 0.03-0.05 <0.02 <0.02 <0.002

Soil covered by burrowed layer 0.1-0.2 0.2-0.3 0.1-0.2 <0.04 <0.05 <0.04

The most appreciable change in the environment is the rise of the groundwater table from 6-7 m to 4.5-5 m. According to data summarized by L.G. Dinesman (1960) identical groundwater fluctuations were typical for the territory in the North-Western Caspian Lowland during the last two centuries and probably in Holocene due to a centuries-old fluctuation of the Caspian Sea level. By this reason, one should assume that the territory of virgin solonetz complex located in Northern Caspian region has being subject to periodical fluctuation. As a result, every soil included into this solonetz complex can periodically change its location in microrelief. New conditions for the further stage provoke evolutional development of the soil. Today it is difficult to assume how frequently occurs the elevation or sagging of a definite position in microrelief, in what time interval is it possible and what is the share of this position. Our research permits to conclude that these processes embraced one fourth of the studied territory, the other part of solonetz complex remains unchanged. It means that this virgin solonetz complex displays no quasi-stationary regime of its functioning. It is characterized by inner development processes, which are needed to be additionally studied.

Change of Ecological Conditions and Characteristics of Vegetation of Solonetz Complex under the Influence of Grazing Pressure of Different Intensity

Grazing pressure is the main type of anthropogenous impact on vegetation of Caspian Lowland. Research of B.D. Abaturov (1991, 2001) carried out at the Dzhanybek experimental station is devoted to the problem of vegetation change under grazing pressure as well as other aspects. His long-term research allowed to make a conclusion that the moderate pasture is favorable for maintenance of species wealth and plant productivity of the solonetz complex both on microelevations with solonetz soils and in microdepressions with light-chestnut and dark-colored soils. Vegetation degradation under overgrazing on these elements of relief passes through various stages of succession but finally comes to the stage of similar annual plant coenosis that was earlier described by B.A. Keller (1923). Considering the results received by previous authors the objective of this research became studying of composition and structure of vegetation cover of the solonetz complex in the conditions of different grazing pressure intensity with use of the methods allowing to conduct long-term research in a mode of monitoring and to connect these changes with different intensity of grazing and with climatic parameters, at the same time on a reserved site - with processes of self-development of landscapes.

A transect method was used towards increasing of the grazing pressure - from the area of nature reserve to that subjected to heavy grazing near the daily pathway for 40 head of cattle and 20 sheep. Transects are efficiently used to study pastures, what has been estimated by many researchers (Morozova, 1985; Yunusbaev et al., 2003; Landsberg et al., 1999; Brock, Owensby, 2000; Ward et al., 2000). The studied transect of 2 km in length stretched from south-southwest to north-northeast: from the area of nature reserve located in the southwest from dendropark to Dzhanybek settlement (fig. 10).

The levelling survey along this transect helped to obtain data about vegetation (total projective covering, the species composition, the plant height and number of plant species) and soils (type, depth of the A+B horizon and carbonate effervescence) in every microrelief element (elevation, depression, slope). The characteristic features of vegetation and soils were taken from publications on grazing-induced changes in the main ecosystem components (Keller, 1923; Kamenetskaya et al., 1955; Gordeeva, Larin, 1965; Abaturov, 1991, 2001). When analyzing the changes in characteristics of vegetation and soils along transect, it seemed possible to determine how is changed a definite parameter of the plant community depending on some distance from transect initial point. As it began in the area of nature reserve being finished in that subjected to overgrazing, the degree of grazing pressure was indirectly estimated taking into consideration only the distance. For purposes of our studies it was very important to define available trends and correlation degree

(r) between the parameters characteristic of plant communities, soils and the grazing pressure (its statistically valuable value).

Fig. 10. Relief of a research area along transect in direction from preserved site to heavily transformed territories. Legend: 1-4 sites which are settling down on a gradient of increase of pasture pressure; A-H - mesodepressions. Рис. 10. Рельеф исследуемого участка вдоль трансекты в направлении от заповедного участка к сильно трансформированным территориям. Условные обозначения: 1-4-участки, располагающиеся по градиенту увеличения пастбищной нагрузки; А-Х - понижения мезорельефа.

Based upon the level surveying results a topographic profile was drawn up to reflect the relief changes leaving out of account the absolute altitude (fig. 10). According to the existing map at a scale of 1:25000 at the territory under study the absolute altitude is 26 m a.s.l, because there exists a half-horizontal of 26.5 m there and the surface incline is from southwest to northeast (Konyushkova, Kozlov, 2010). By this reason, the initial altitude point was increased to 30. Having characterized the meso- and microrelief, we used only relative values including the final point exceeded initial one, maximum, minimum, average, median values of relative excess in the depth of micro-depressions.

To obtain detailed characteristics of the vegetation, transect was divided into 4 key sites: 1 -without grazing, 3 other sites with different grazing pressure (2 - low, 3 - moderate, 4 - heavy grazing; fig. 11, 12). The field observations were conducted in every key site for several years 3 times a year - in April, June and September, i.e. under different conditions of ecosystem functioning and vegetation development.

Traditional geobotanical descriptions repeated 10 times, test plots (1x1 m2) for obtaining the data about the terrestrial phytomass by grass cutting near the soil surface (3 times) were applied in micro-elevations, their slopes and in micro-depressions. Thus, each plant community was characterized by 4 indices: microrelief element, total projective covering, number of species and overground phytomass. Every plant species in the test plot was studied using such parameters as projective covering, its abundance according to Drude's scale, height and phenological status. Its vitality was estimated by means of three-dimensional scale. A comprehensive analysis of geobotanical data allowed identifying the similarity degree of the species composition between all the key sites; Jakkar formula in ECOL was applied for these purposes. Plant species and their behavior under grazing pressure, the succession of plant communities affected by grazing in different relief elements and changes in vegetation productivity have been studied as well.

Fig. 11. Location of the key sites and points of observations with distance intervals starting from the reserved area on a synthesized image of satellite data of Landsat 2007, displaying sites with different degree of transformation of vegetation under grazing influence on the studied territory. Legend: 1 - reserved area (0-500 m), 2 - slightly disturbed area (500-800 m), 3 - area of moderate disturbance (800-1150 m), 4 - heavy disturbance and overgrazing (1330m and farther). Рис. 11. Расположение ключевых участков и точек наблюдений, начиная с заповедной зоны на синтезированном изображении спутниковых данных Landsat 2007, отображающих участки с различной степенью трансформации растительности под воздействием выпаса на исследуемой территории. Условные обозначения: 1 - заповедная зона (0-500 м), 2 - слегка нарушенная зона (500-800 м), 3 - зона умеренного нарушения (800-1150 м), 4 - сильное нарушение и перевыпас (1330 м и дальше).

Changes in Vegetation According to the Gradient of Grazing Pressure Increase

Along the Transect

Total projective covering is a very important feature of plant communities permitting to obtain the information about the phytocoenosis status and conditions for the water regime of its biotope. In key sites located on micro-elevations the plant cover is not completely dense during the vegetation period. The highest values (55-58%) are marked for key sites under low and moderate grazing pressure in the mid-summer as the period of intensive plant growth and development. For key sites under moderate and heavy grazing pressure the low values (17-28%) are observed at the end of the vegetation period. The maximum of projective covering (51%) is on micro-elevations within the area of nature reserve. As regards micro-depressions one should notice that the projective covering is considerably higher during the vegetation period being maximum in the area of nature reserve (83-79%). Low values (44-42%) almost equaled to projective covering on micro-elevations are characteristic of the key site under moderate grazing pressure.

Site № 3 - moderate grazing Site № 4 - heavy grazing

Fig. 12. Pictures of vegetation at the key sites (1-4) with different grazing levels.

Рис. 12. Фотографии растительности ключевых участков (1-4) с различной степенью выпаса.

Due to increasing of grazing pressure the total projective covering shows slightly expressed decline (fig. 13); it is testified by low statistically valuable correlation between this feature and the distance along transect. Total projective covering reveals changes from 30 to 60% in the major part of the profile and from 10 to 60% in its last section (fig. 13).

Number of plant species within the test plot is very important to estimate the fodder base. Maximum of plant species (12) is observed in June in depressions of nature reserve, their minimum (2 plant species in the same month) - on micro-elevation suffered from heavy grazing. The average value of this index accounts for 7 in depressions and 4 on micro-elevations during the entire period of observations. This feature displays trend to decreasing its values depending on the grazing pressure. The number of plant species in all the test plots reveals decline due to grazing pressure to a greater extent in comparing with the total projective covering (fig. 14), what is confirmed by average correlation coefficient (r=-0.53; a=0.001). The number of plant species changes from 3 to 18 for the area of nature reserve being fluctuated in the range of 1 -6 for key sites affected by heavy grazing.

Fig. 13. Changes of total vegetation cover in plant communities along transect, which leads from the key site in the preserved area to the area, suffered from overgrazing. Рис. 13. Изменение общего проективного покрытия в сообществах вдоль трансекты от ключевого участка в районе заповедной зоны до участка, пострадавшего от чрезмерного выпаса скота.

0 500 1000 1500 2000 Distance, m

Fig. 14. Correlation between the number of species and the grazing pressure. Рис. 14. Корреляция между числом видов и пастбищной нагрузкой.

The plant height along transect becomes lower due to increasing the grazing pressure. The correlation coefficient (r=-0.5; a=0.001) speaks about statistically valuable negative correlation. In the area of nature reserve the plant height is 0.3 m, reaching 0.5 m in some cases. It doesn't exceed 0.1 m in the last profile section.

The quantitative parameters of correlation between the main features of plant communities including total projective covering, number of plant species and the height are statistically reliable (95%), thus showing trends in vegetation changes along the gradient of grazing pressure (table 10). The obtained data serve as an evidence that there is a tendency to decreasing the values of all the parameters due to increasing the grazing pressure.

Table 10. Change of characteristics of plant communities, influenced by increased grazing. Таблица 10. Изменение характеристик растительных сообществ под влиянием усиления выпаса скота.

Area with different degree of grazing pressure Characteristics of plant communities

Total projective, % Plants height, cm Number of plant species on the plot 10x10 m2 Overground phytomass, g/m2

Reserved area (1)* 20-60 10-30 4-8 130 (60/200)

Low grazing pressure (2) 30-60 5-30 4-12 70 (50/90)

Moderate grazing pressure (3) 20-60 5-10 3-5 50 (40/60)

Overgrazing (4) 10-60 2-10 2-4 35 (30/40)

Notes to table 10: * - plot numbers correspond to the numbers on the figure 11. Примечания к таблице 10: * - номера площадок соответствуют номерам на рисунке 11.

To comprehend the changes taken place in the vegetation along transect the composition of plant species was studied in every key site to be compared and assessed in respect of its similarity by using Jakkar coefficient. As is evident from figure 15 the plant species composition proves to be similar in key sites 1 and 2 (without and low grazing respectively) - 55% and in key sites 3 and 4 (moderate and heavy grazing) - about 45%. In other words, the difference in the species composition of plant communities is constantly increasing along transect, being quite different in the area of nature reserve and in the area suffered from overgrazing.

Fig. 15. Similarity between species composition of vegetation on sites with a different degree of pasture pressure. Notes: 1- no (preserved), 2 - weak, 3 - moderate, 4 - strong. Рис. 15. Сходство видового состава растительности на участках с разной степенью пастбищной нагрузки. Условные обозначения: 1 - нет (под охраной), 2 - слабая, 3 -умеренная, 4 - сильная.

Plant species depending on grazing pressure. The many years standing of geobotanical observations permitted to distinguish 5 groups of plant species, which are frequently met in key sites with different grazing pressure (table 11). The first group includes 3 species of annual and biennial plants, which are absent in the nature reserve but presented at the territory used for grazing. Such plant species should be related to the category of those preferred grazing.

Table 11. Groups of plant species with different response to grazing pressure. Таблица 11. Группы видов растений с различной реакцией на пастбищную нагрузку.

№ Group, plant species Key site

1 2 3 4

Plants, prefered grazing

1 Bassia sedoides - - + +

2 Petrosimonia triandra - + + +

3 Polygonum patulum - + + +

Resistant to heavy grazing

4 Artemisia austríaca + + + +

5 Artemisia lerchiana + + + +

6 Artemisia pauciflora + + + +

7 Carex supina + + + +

8 Ceratocarpus arenarius + + + +

9 Climacoptera brachiata + + + +

10 Festuca valesiaca + + + +

11 Kochia prostrata + + + +

12 Leymus ramosus + + + +

13 Limonium sareptanum + + + +

14 Phlomoides tuberosa + + + +

15 Poa bulbosa + + + +

16 Potentilla bifurca + + + +

17 Salsola laricina + + + +

18 Tanacetum achilleifolium + + + +

Not resistant to heavy grazing

19 Camphorosma monspeliaca + + + -

20 Ferula nuda + + + -

21 Salvia tesquicola + + + -

Resistant to low grazing

22 Agropyron pectinatum + + - -

23 Astragalus brachylobus + + - -

24 Dianthus borbassii + + - -

25 Galatella villosa + + - -

26 Galium humifisum + + - -

27 Galium ruthenicum + + - -

28 Jurinea multiflora + + - -

29 Koeleria cristata + + - -

30 Phlomoides hybrida + + - -

31 Potentilla recta + + - -

32 Serratula erucifolia + + - -

33 Silene wolgensis + + - -

Resistant to low grazing

34 Stipa capillata + + - -

35 Stipa lessingiana + + - -

Continuation of Table 11. Продолжение таблицы 11.

№ Group, plant species Key site

1 2 3 4

Not resistant to any grazing

36 Asparagus officinale + - - -

37 Batrachium trichophyllum + - - -

38 Delphinium puniceum + - - -

39 Gypsophylla paniculata + - - -

40 Lamium amplexicaule + - - -

41 Ornithogalum fisherianum + - - -

42 Spiraea hypericifolia + - - -

43 Tulipa biflora + - - -

44 Veronica spicata + - - -

Notes to the Table 11: 1-4 - key sites, "+" for present plant species, "-" for absent species). Примечания к таблице 11: 1-4-ключевые участки, "+" - вид присутствует, "-" - вид отсутствует).

The second group consisting of 15 plant species is present in all the key sites including the area of nature reserve. They are characteristic of biotopes on micro-elevations and represented by Artemisia vulgaris, Kochia, Leymus ramosus. They should be considered as indifferent to grazing. However, due to the presence of Ceratocarpus arenarius the obtained data are thought to be preliminary, because this plant species appears in pastures highly disturbed by sheep grazing. The third group contains 3 plant species of different ecology including Camphorosma monspeliaca, Ferula nuda, Salvia tesquicola. They are absent in the area suffered from heavy grazing and should be regarded as not resistant to overgrazing. The group 4 includes 14 plant species, which are spread in the area of nature reserve and in that used for low grazing but they are absolutely absent in the area under heavy grazing pressure and should be considered as plants resistant to low grazing. In the composition of such plant communities there are Stipa capillata, Koeleria cristata and the other species confined to biotopes of micro-depressions. The last group 5 consists of 10 plant species, which are distribted only in the area of nature reserve. They reveal no resistance to grazing and take refuge only in preserved areas. Among them are Tulipa biflora, Ornithogalum fisherianum, Delphinium puniceum, Veronica spicata included into this group not only due to their response to grazing, being considered as ornamental plants.

The absence of Spiraea hypericifolia in key sites used for grazing serves as evidence. According to the available literature data that shrubs disappear under the influence of grazing and this plant species should be included into the category of preserved plants. Lamium amplexicaule is a plant species that indicates disturbed communities in depressions. It is not sustainable to grazing. It is interesting that Medicago romanica as a very valuable fodder plant disappears under low and moderate grazing pressure being spread both in the area of nature reserve and in that suffered from heavy grazing. B.D. Abaturov (2001) indicated the peculiar feature of this plant species and showed that its productivity in the area of heavy grazing increased almost 5 times as compared to that in nature reserve.

Plant succession under grazing pressure. When comparing the species abundance and productivity of plant communities in nature reserve and in the adjacent area under low grazing, it is worthy to note that the key site with low grazing reveals an increase in these indices. Due to further increasing the grazing pressure along transect the species composition becomes impoverished and

substituted by few-species communities. Mechanism responsible for this process has been described in many publications being testified by B.D. Abaturov (2001) at the territory of Dzhanybek experimental station. The overgrazing leads to adverse changes in the ecological status of biotopes: the soil surface layer gets compacted, its capillarity is increased promoting higher water evaporation, soil becomes drier. Permanent grazing of the overground phytomass serves as a cause of soil depletion and succession of plant communities.

Based upon the description of plant communities for every key site along transect a summary scheme has been compiled to reflect their succession beginning with the area of nature reserve to that suffered from overgrazing (table 12).

Table 12. Change of the plant communities at different elements of the microrelief under impact of different degree of grazing pressure. Таблица 12. Смена растительных сообществ на разных элементах микрорельефа под влиянием разной пастбищной нагрузки.

Areas with different grazing regime Plant communities on main relief elements

Microelevations Microslopes Microdepressions

Reserved area (1) Kochia prostrata-Artemisia pauciflora Tanacetum achilleifolium-Festuca valesiaca, Leymus ramosus Festuca valesiaca-Agropyron desertorum-Mixteherbosa; Stipa sareptana, etc.

Low grazing (2) Kochia prostrata-Camphorosma monspeliacum Tanacetum achilleifolium-Festuca valesiaca Festuca valesiaca-Mixteherbosa

Moderate grazing (3) Kochia prostrata-Creatocarpus areanarius Festuca valesiaca-Ceratocarpus arenarius Fastuca valesiaca; Artemisia austriaca

Overgrazing (4) Petrosimonia triandra- Kochia prostrata; Ceratocarpus arenarius-Kochia prostrata; areas without vegetation Lepidium ruderale- Ceratocarpus arenarius-Festuca valesiaca; areas without vegetation Artemisia austriaca-Carex supina-Ceratocarpus arenarius

Plant communities composing of dwarf semishrubs Kochia and Camphorosma are widespread within the area of nature reserve and that used for low grazing. Under conditions of moderate and heavy grazing the plant communities contain annual species of salt-tolerant xerophylous plants characterizing disturbed biotopes (Climacoptera brachiata). The plant communities including Festuca valesiaca and Leymus ramosus are dominated on microslopes in the nature reserve and under low grazing, whereas the areas used for moderate and heavy grazing are rather rich in communities composing of annual xerophylous plants of Bassia sedoides and Ceratocarpus arenarius. In depressions of the nature reserve the plant communities containing Spireae hypericifolia and Gramineae are dominant; in key sites under low grazing - Gramineae and S. lessingiana, under moderate grazing - Festuca sulcata and under heavy grazing - Cyperaceae and Ceratocarpus arenarius.

The key sites with moderate and heavy grazing located on micro-elevation slopes reveal a decline in the biodiversity, i.e. the plant species that must be inherent only to slopes are absent. Hence, the plant cover structure gets simplified as affected by grazing.

Conclusions

The main results obtained to study changes in the solonetz complex at the Northern Caspian Lowland in the second half of the XX century.

1. Changes taken place in virgin solonetz complex for 50 years reveal a combination of all-round tends to evolution of its different components on positions closely located in space. Such tends are rather peculiar in dependence on the microrelief type. The half a century of changes in the solonetz complex are mainly induced by the groundwater rise from 6-7 to 4.5-5 m.

2. General pattern of relative spatial position and configuration of the most contrast microrelief elements (convex and concave) remains almost unchanged, what is evidenced by field observations and overlaying of former and newly obtained cartographic materials.

The surface of the virgin solonetz complex shows some changes in microrelief of watershed and flat types. Stable unchanged positions of microrelief occupy about 50% of the total area, thus forming a tracery net-like frame with mosaic inclusion of some areas, which became lower to 420 cm (30-33%) and elevated up to 4-25 cm (14-18%). This is the action of several mechanisms responsible for changing the microrelief, which and functioned simultaneously and/or in consecutive order.

It was possible to observe uneven surface sagging to 10-20 cm in microrelief of radial-domelike type (80-90% of the total area) probably due to rising groundwater table and capillary fringe resulted in moistening of dry salt horizons in the vadose zone.

3. The soil cover of key sites in the area of virgin solonetz complex is represented by meadow-chestnut (Haplic Kastanozem (Loamic) in WRB), light-chestnut non-solonetzic (WRB: Eutric Cambisol (Loamic, Protocalcic, Ochric)), light-chestnut solonetzic soils (WRB: Haplic Luvisol (Loamic, Cutanic, Sodic, Endoprotosalic, Protocalcic)) and crusty or shallow solonetzes (WRB: Gypsic Endosalic Solonetz (Albic, Loamic, Cutanic, Differentic, Magnesic)).

4. As distinct from the widely used opinion about homogeneity parameters of soil distribution in the solonetz complex and homogenous inter-convex watersheds at the studied territory (Rode, Polsky, 1961) the obtained results serve as evidence of its heterogeneity in dependence on the microrelief type. The watershed type of microrelief has the highest pedodiversity due to the highest contrast in elevation within small distances and approximately the same share of the main soil components. The entire convex surface of the radial-domelike microrelief type and a concave surface of the flat type provide the lower pedodiversity indices due to less contrast conditions.

5. It is evident that the surface carbonate light-chestnut (solonetzic and non-solonetzic) soils and crust or shallow solonetzes without features of mixing the soil material by living organisms should be considered as newly formed components of this soil cover pattern. These soils have a convex surface with the fine cracks due to accumulation of calcium carbonate in the initially carbonate-free topsoil.

6. At present, it is feasible to find any soil within the virgin solonetz complex on different spatial positions and under different plant associations with probability of 0.3-0.8.

7. One third of inversions is connected with changes in microrelief taken place for 50 years, while two thirds of inversions are confined to stable unchanged areas, thus testifying their mobility during the former hundred years.

At the territory under study the rate of changes in microrelief seemed higher as that in soil morphology but it is comparable with the changing rate of the salt state in soils.

8. Since the 1950s the solonetz complex at the territory of the Dzhanybek experimental station retains its complexity being represented by such microrelief as elevations occupied by dominant suffruticose plants Kochia prostrata, Artemisia pauciflora, depressions covered by different grass plants and slopes - by Tanacetum achilleifolium, Leymus ramosus and Agropyron desertorum. Under conditions of overgrazing the plant cover structure becomes simplified due to disappearing

ЭКОСHCTЕМBI: ЭКОПОГHM H AHHAMHKÁ, 2018, tom 2, № 1

the plant communities so specific for slopes.

Changes of vegetation on different elements of relief on a reserved site under the influence of climatic changes revealed a tendency to vegetation mesophytization. It means flattening of contrasts between vegetation of different components of solonetz complex. Strengthen of the role the sod grasses (sheep fescue, hobble, wheat grass) means transformation into steppe.

The plant communities along transect display their succession depending on increasing of the grazing pressure on different microrelief elements. In key sites suffered from heavy grazing the dominated annual plant species such as Petrosimonia triandra, Ceratocarpus arenarius, Ceratocarpus testiculata are capable for preventing the soil degradation.

The transect method permitted to obtain data about the quantitative dependence and to show a decrease in the plant height, species abundance and total projective covering along the gradient of grazing pressure. The most favorable status of vegetation is marked in the area used for low grazing.

The plant species distributed only in nature reserve and being absent in the other pastures are referred to the group of those threatened and the nature reserve of Dzhanybek experimental station contributes to their preservation.

9. The virgin solonetz complex in the Northern Caspian Lowland corresponds to a nonstationary, fluctuant regime of its evolutional development. The only possible reason is periodical cycles of groundwater fluctuation (duration from a few ten years to 1-1.5 century). Moreover, the solonetz complex retains its invariant according to a set and relative ratio between the main soil and vegetation components as well as its principal configuration. By this reason, a part of territorial positions is occupied by components corresponding to quasi-stationary regime of functioning or close to it. In the other part of territorial positions the same components are found at different stages of their development. In total, we observe a mosaic picture of spatial arrangement of quasi-stationary soil components and those developed in different trends.

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СОЛОНЦОВЫЙ КОМПЛЕКС НА СЕВЕРЕ ПРИКАСПИЙСКОЙ НИЗМЕННОСТИ: ФИТО-,

ПЕДОРАЗНООБРАЗИЕ, ВЗАИМОСВЯЗИ МЕЖДУ ПОЧВАМИ, МИКРОРЕЛЬЕФОМ И РАСТИТЕЛЬНЫМИ СООБЩЕСТВАМИ, ТРАНСФОРМАЦИЯ В УСЛОВИЯХ ИЗМЕНЕНИЯ

КЛИМАТА И ВЫПАСА

© 2018 г. Н.Б. Хитров*, Н.М. Новикова**, А.А. Вышивкин**, Н.А. Волкова**

*Почвенный институт им. В.В. Докучаева Россия, 119017, г. Москва, Пыжевский пер., 7, стр. 2. Е-mail: [email protected]

**Институт водных проблем РАН Россия, 119333, г. Москва, ул. Губкина, д. 3. E-mail: [email protected]

Пространственно-временное изменение фито- и педоразнообразия солонцового комплекса изучалось в целинных сухостепных экосистемах на севере Прикасписйской низменности. Основные объекты исследований расположены на территории Джаныбекской научно-исследовательской станции Института леса Российской академии наук. Исследования заключались в проведении детального независимого картографирования почв, микрорельефа и растительности на нескольких участках, отличающихся по микрорельефу. Полученные данные и карты, составленные авторами в 2000-х годах, сопоставлялись с аналогичными данными и картами, составленными Д.Л. Мозесоном, И.В. Каменецкой и М.Н. Польским в 1950-1955 гг. Проанализирована и оценена теснота взаимосвязей в солонцовом комплексе между почвами, микрорельефом и растительными сообществами. Обсуждаются изменения компонентов солонцового комплекса в связи с региональными климатическими изменениями за последние полвека, подъемом подземных вод и выпасом.

Ключевые слова: солонцы, светло-каштановые почвы, светло-каштановые солонцеватые почвы, лугово-каштановые почвы, растительные сообщества. DOI: 10.24411/2542-2006-2017-10003