July 20, 2012 Deserts creep outward in various directions across the western United States. The dry wind shuttles clouds of sand across the landscape, leading the charge to take over surrounding land, advancing the growing desertification problem.
The hope for restoring these arid environments and preventing further desertification may exist on the surface of the desert itself, according to new research by American Society of Agronomy and Soil Science Society of America Member Mandy Williams, a lab manager in the school of Life Science at the University of Nevada -- Las Vegas. She describes the complex blend of microorganisms carpeting arid environments as biological soil crusts (BSC). The organisms fuse with soil particles, stabilizing desert crusts and forming fragile peaks in the soil that influence a variety of processes to allocate important resources. Williams says, "These crusts kind of act like a living mulch across a desert, by protecting the surface from erosion. Once you disturb the soil surface, you're more likely to lose what little resources are available there."
Williams, along with two other UNLV researchers, performed an in-depth micromorphological investigation of BSC samples from the Mojave Desert to better understand the formation, structure, and significant role soil crusts play in arid environments. Their findings, being released in the September-October edition of Soil Science Society of America Journal, show complex internal soil structures suggesting a rich genetic history and a variety of formation processes.
The development of BSC begins with cyanobacteria, a phylum of photosynthetic bacteria. These bacteria form smooth crusts on the desert surface and strengthen soil structure by sealing off the surface to effects of erosion. Wet-dry cycles cause this newly formed soil crust to expand and contract, leaving cracks in the crust that trap dust as it blows over the desert surface. Yet, dust is an important source of nutrients in the Mojave Desert, where organic matter is lacking and much-needed nutrients must migrate to the desert from surrounding environments.
Meanwhile, cyanobacteria weave around particles in the soil, forming thick layers of fine grains by trapping sediments in a sticky casing. Over many years, these bacteria-soil mixtures grow into jagged micro-peaks that accrete more dust and continue to evolve. These peaks are extremely fragile and sensitive to physical impacts such as vehicles, foot traffic, and grazing. BSC also impacts water distribution in arid environments. In the Av soil horizon, fine dust particles settle and pockets of air form beneath the soil. These cavities trap water at the surface to be used by soil microbes and desert plants when it's needed most.
But this new research reveals, recovery of valuable BSC after a disturbance, can take years, depending on several environmental factors. Williams.says, "These crusts form important features that must be considered, not only for the restoration of crusts, but entire desert ecosystems in the future."
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- Amanda J. Williams, Brenda J. Buck and Mengesha A. Beyene. Biological Soil Crusts in the Mojave Desert, USA: Micromorphology and Pedogenesis. Soil Science Society of America Journal, 2012 (in press) DOI: 10.2136/sssaj2012.0021
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