Steppe ecosystems

Cu deficit, excess of Mo and SO Pre-Caucasian plain, Caspian low plain, West Siberian Steppe ecosystems Meadow-Steppe, Eustric Chernozems, Solonchaks, Arenosols The reducing Cu content in the central nervous systems, depressed function of oxidation ferments and activation of catalase, demielinization of the central nervous systems, disturbance of motion, convulsions. Endemic ataxia. Lamb disease is predominant... 

Cu excess South Ural and Bashkortostan Cu enrichment of Chernozems, Kastanozems of Steppe ecosystems and Podsoluvisols of Forest ecosystems. High Cu content in food and forage stuffs Excessive accumulation of Cu in all organs. Progressive exhaustion. Endemic anemia and hepatitis. Sheep diseases. Human endemic anemia and hepatitis... 

This sub-region is in the central and east part of the Chuvash administrative region. Most of the sub-region is occupied by Steppe ecosystems with some small spots of Broad-Leafed Forest ecosystems. The predominant soils are Phaerozems. The biogeochemical food web of this sub-region is presented in Figure 3. 

The characteristic biogeochemical feature inherent in all Steppe and Desert ecosystems is the most intensive cycling of different chemical species in comparison with forest ecosystems. For a Steppe ecosystem the biogeochemical cycle is 2-3 years and this means that the complete renewal of all ecosystems biomass takes place over this period. Remember that in Forest ecosystems the biogeochemical cycling is about 3->25 years and even about 50 years in Forest Swamp ecosystems. The turnover is the highest in Ephemeral Desert and gradually decreases to the north. 

These properties of soils in Steppe ecosystems are favorable to the formation of uppermost humus barrier, where the accumulation of almost all the chemical species occur. The concentration of chemical elements is slightly decreasing downward in soil profile, in parallel with decreasing soil humus content (Figure 2). 

The significant part of heavy metals in the soils of Steppe ecosystems are bound with highly dispersed mineral-organic particles, to a lesser degree, with only organic matter. We can see that the water-soluble and exchangeable forms are less than 1 % of the total content. Specific forms of heavy metals are bound with carbonate and gypsum in B and C horizons (Table 5). 

The water deficiency in Arid ecosystems is the main restricting factor for biogeochem-ical exposure processes. We know that many links of the biogeochemical food web are connected in Steppe soils with invertebrates. Their population varies very much in Steppe ecosystems depending on the moisture conditions (Table 6). For instance, the wet biomass of soil invertebrates in the Meadow Steppe and Forest Steppe ecosystems exceeds that for the Extra-Dry Rocky Desert ecosystems by 150-300 times. 

Table 5. Distribution of Co in Calcaric Chernozem and Chestnut soil of Meadow Steppe ecosystem in the south part of East European Plain.

Table 6. The influence of water deficiency on invertebrate biomass and humus content in Steppe ecosystems.

The humus content in Steppe ecosystem soils reflects the total biomass production and humidity. 

Table 7. The content of heavy metals in the aerial parts of plant species of South Ural Steppe ecosystems, ppm, by dry weight (after Skarlygina-Ufimtseva et al., 1976 Dobrovolsky, 1994).

Table 8. Biogeochemical exposure to heavy metals in the main botanical groups of Meadow Steppe ecosystems of East European Plain, accumulation, mg/kg by dry weight (after Dobrovolsky, 1994).

With aridity increasing, various plant species of forage crops become gradually less numerous to finally disappear. In Dry Steppe ecosystems xerophylic half-shrubs and salt-tolerant plants replace the grasses. However, the ash content is higher in these species. This is attributed not only to a higher concentration of major ash elements in the plant tissue, but also to the exposure to finely dispersed dust adhered to the plants exterior (Table 9). 

Figure 3. Coefficients of bio geochemical uptake of heavy metals by typical plant species of Meadow Steppe Ecosystems of East European Plain. Aerial parts 1—legumes 2—grasses 3—forage crops roots 4—legumes, 5—grasses, 6—forage crops (Dobrovolsky, 1994).

In Desert ecosystems similar to Steppe ecosystems the plants distinctly exhibit their biogeochemical specificity. We can consider the distribution of heavy metals in Dry Desert ecosystems of the Ustyurt Plateau, Kazakhstan, with predominance of wormwood (Artemisia terrae albae) and saxaul (Anabasis salsa). In rubble stone territories, of common occurrence is the dense shrubbery of Sasola anbuscula. Most elements found in the wormwood occur in their highest concentrations. In the roots of the wormwood and saxaul, higher contents of Mn, Cu, Mo, and Sr have been monitored, whereas the aerial parts contain more Ti, V, and Zr. We can see that the root elements are most biologically active and those in aerial parts, more inert. Possibly their presence was related to the dust exposure and deposition on the plant exterior (see above). 

The general trend towards increase of ash elements in the plants of steppe ecosystems from Dry to Extra-Dry Desert ecosystems does not seem to affect the Cb values appreciably (see Box 2). 

SD of mean listed for cool temperate steppe ecosystems in Post et al. (1982). Estimated from root turnover rates listed for tropical forests in Gill and Jackson (2000). 

On the other hand, the abundant silicon powder formation was monitored in Podsoluvisols and Phaerozems at 0.5-2.0 m depth in Forest Steppe Ecosystems of Central Russian Plain, Sonth Siberia, Amnr River valley, and Manjury region of China. In this case, the most reasonable explanation is connected with the deposition of silicon from glacial melting waters after the glaciation period. 

We will consider both Steppe and Desert ecosystems as deficient in atmospheric humidity (evapotranspiration exceeds precipitation). The Sub-Boreal, Semi-arid and Arid Steppe and Desert ecosystems occupy a significant part of the global area. This territory includes Sub-Boreal zones (Steppe, Arid Steppe, and Desert Steppe ecosystems) with total area of 9.23 x 10 km, as well as subtropical zones (Shrub Steppe and Desert Steppe ecosystems) with total area of 7.04 x 10 km. These areas do not include Subtropical and Tropical Sandy Desert ecosystems (5.77 x 10 km-) and Stony Desert ecosystems (8.96 x 10 km ). Thus the extra-tropical arid area takes about 20% of the World s terrestrial ecosystems. Most of this area goes to the inter-continental regions of Eurasia and, partly, of North and South America. The biogeochemistry of semi-arid and arid ecosystems shows distinctive parameters, which allow us to consider the quantitative features of element turnover and dynamics in natural fluxes. 

Grasses, small shrubs and shrubs, whose number of xerophytic and ephemeral forms increases with aridity, are the chief representatives of Arid ecosystems. At the north and south peripheries of the arid zone, herbaceous ecosystems are predominant. In regions with a well balanced atmospheric humidity prior to human activities, of wide occurrence were Meadow Steppe ecosystems intermixed with Broad-leaved Forests. With an increase in climate continental properties, the Meadow Steppe ecosystems of Eurasia grade into Forb-Fescue-Stipa and Fescue-Stipa Steppe ecosystems. In turn, the natural vegetation has been destroyed by humans and replaced by pastures and... 

The various steppe plant species indicate the individual hiogeochemical peculiarities. Eor example, we can discnss the results from South Ural s region, Russia. Table 24 shows the concentrations of trace elements in typical plant species of Steppe ecosystems. 

Meadow Steppe ecosystems of the East European plain... 

High biotic activity is characteristic for soils of Meadow Steppe ecosystems with relatively high precipitation. An enormous number of invertebrates promptly disintegrate and digest the plant residues and mix them with the mineral soil matter. The presence of the predominant part of plant biomass as the underground material facilitates greatly this process. 

Role of biogeochemical processes in aqueous migration of elements in Steppe ecosystems... 

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