Biogeochemical Cycle of Nutrients in Arid Ecosystems

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 

Ecosystem Pool on biomass, kg/ba Annual uptake, kg/ha Annual litter, kg/ha  

The biomass of arid ecosystems is significantly less than that of Forest ecosystems and changes from 10 to 25 ton/ha, by dry weight, in Steppe, from 4.0 to 4.5 ton/ha in Desert and from 2 to 3 ton/ha in Extra-Desert Ecosystems of Central Asia. The overall biomass of Arid Steppe and Desert ecosystems is an order of magnitude less than that of Forest ecosystems (Rodin and Bazilevich, 1972). 

The ash content of Arid Steppe and Desert ecosystem vegetation is about 2 times higher than that of forest species. Accordingly, the biogeochemical fluxes of elements are similar to those in the forest ecosystems, in spite of the smaller biomass (see above). The compartments of biogeochemical turnover in Steppe and Desert ecosystems are shown in Table 22. 

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. 

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