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Well developed crusts on Iron-rich sand
Difference between lichen-dominated and cyanobacteria-dominated crusts
Cyanobacteria-dominated crusts
See more pictures of Biological Soil Crusts
Biological Soil Crust Facts:
- The simple fact that aridlands cover some 35% of the total Earth’s continental surface, speaks for the potential significance of these communities in global ecology, as they usually cover the surface of these areas.
- Typical areas of the US where biological crusts cover large portions of undisturbed soils are the Southwest, the rangelands of California, Oregon, Idaho, Wyoming and Montana.
- Extensive crusts are known from the rangelands and desert areas in Australia, Africa, the Middle East, continental Asia and Southern Europe.
- Recent biomass estimates indicate that the populations of microbial primary producers in desert crusts are about 54 x 1012 g of C globally.
- Biological Soil Crusts have been reported to affect the overall hydrology of arid lands.
- Annual carbon input in crusts range from some 30 to 350 kg C ha-1 per year.
- Estimates for N fixation range from as little as 1 to as much as 100 kg N ha-1 per year.
- The mere presence of well-developed desert crusts, dramatically decreases soil erodibility by consolidating soil surfaces and through the direct binding of soil particles.
- A growing recognition of the their ecological importance and their fragility, in the face of anthropogenic disturbance, together with experimental results, demonstrate the slow rates of at which they recover, and underscore our imperious need for a sensible management of crust-covered rangelands.
- In spite of their geographic extent and ecological importance, many aspects of the biology of BSCs remain unknown, especially those related to basic science.
See also part of our research about C and N cycling, and diversity of BSCs
Arid lands cover some 30% of the Earth’s continents. In these areas, where vegetation is sparse, mm-thin microbial communities dominated by cyanobacteria colonize the topsoils. These little studied communities are exposed to extremes of water stress, temperature, insulation and erosional abrasion. They probably contribute significantly to the biogeochemistry of desert areas, and help stabilize them against erosion. We are studying the nature and identity of the extremophiles that build desert crusts as well as their adaptations. We are also interested in the small scale biogeochemical cycling of Carbon and Nitrogen and their implications for arid land fertility. These communities are also of interest because they are the modern analogs of the original land biota before the advent of higher plants.
Biological Soil Crusts of North America
Here, the rough texture of the soil is due to microbial communities. Note the sparse vegetation and arid conditions that allow these crusts to form.
The cyanobacteria in soil crusts quickly turn the surface green once exposed to water.
Crusting is initiated by growth of filamentous cyanobacteria (e.g. Microcoleus sp.) during episodic events of available moisture, with the subsequent entrapment of mineral particles by the network of cyanobacterial filaments and their matrix of extracellular slime (EPS).
Surface-bound assemblages of microorganisms consolidate soils into mm to cm-thick crusts that occur on aridlands wherever the lack of water restricts the settlement and developement of higher plant cover. These microbial communities, variously known as cryptogamic, cryptobiotic, microbbiotic, cyanobacterial, or simply, biological soil crusts (BSCs), are dependent on the primary production of cyanobacteria. Once this first colonizers have stabilized the soil surface, other organisms, such as lichens, eukaryotic microalgae, and mosses, may be integrated as dwellers of the crust.
