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Microphytic Soil Crusts and Desert Ecosystems Essay

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Microphytic Soil Crusts and Desert Ecosystems


Communities of micro-organisms create crusts on soils throughout semi-arid and arid regions of the world. These microphytic (also called cryptogamic) crusts are formed when all or some of a diverse array of photosynthetic cyanobacteria (blue-green algae), fungi, bacteria, lichens and mosses, bind together with inorganic particles in the first few millimeters of a soil.

Microphytic crusts are dominant feature in desert soils; they are estimated to represent approximately 70% of desert soil biomass world wide (Belnap 1993). Un-restricted human activity (farming, livestock grazing, recreation) results in the denigration or destruction these prominent crusts. Many claim that soils and soil mechanisms are at the base of other ecosystem functions (Vitousek, Walker, Syers in Gillis 1994). In order to better understand and manage desert ecosystems, it is important to begin to understand how cryptogamic crusts form, what role crusts play in shaping desert soil properties, and further, how crust removal might effect soil quality and ecosystem stability.

Crust Formation

It is generally thought that the formation of microphytic crusts begins with the establishment of cyanobacteria or agal communities on the soil surface (Campbell et. al. 1989). There are many different types of algae and cyanobacteria which exist in the new crusts, however it is difficult to ascertain which types of organisms are responsible for which processes of early crust formation. Johansen postulates that crusts begin to form when filamentous cyanobacteria (as opposed to diatomic and nonfilamentous cyanobacteria or other algae) colonize the surface of soils in a period of moist weather (1993). As cyanobacter...


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...ation and Dehydration. Soil Biology and Biochemistry v. 24:1101-1105.

Johansen, J.R. (1993). Cryptogamic Crusts of Semi-arid and Arid Lands of North America. Journal of hycology v. 29:141-147.

Loope, W. L., Gifford, G. F. (1972). Influence of a Soil Microfloral Crust on Select Properties of Soils Under Pinyon-Juniper in Southeastern Utah. Journal of Soil and Water Conservation v. July-August:164-165.

Metting, B. (1991). Biological Surface Features of Semiarid Lands and Deserts. In Semiarid Lands and Deserts: Soil Resource and Reclamation , Skujins, J.(edt.). Marcel Dekker, Inc, New York. pp. 257-293.

Skujins, J. Microbial Ecology of Desert Soils. :62-85.

West, N. E. (1991). Nutrient Cycling in Soils of Semiarid and Arid Regions. In Semiarid Lands and Deserts: Soil Resource and Reclamation , Skujins, J.(edt.)Marcel Dekker, Inc, New York. pp. 295-327


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