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Microbiotic Crusts

by Dr. Jeffrey R. Johansen
John Carroll University, Cleveland, Ohio

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To begin Dr. Johansen's talk you can click here or read this brief overview, below, that provides links to the best places in the talk for specific topics.

Microbiotic crusts were initially thought to be soil alga crusts, but are now recognized as having more than just algae. Another current term is "cryptogamic crust" with cyanobacteria, the eukariotic algae and fungi as the dominant microbes. Microbiotic crusts occur in deserts worldwide. The morphology may be different and the species composition also will vary by soil type and region.There are several major players in microbiotic crusts: cyanobacteria, diatoms and fungi.

The ecological importance of crusts are many: soil fertility and nitrification, soil retention, seedling establishment and moisture retention. When the crusts are disturbed through trampling or fire, it may require decades or more to recover. Reclamation efforts have had mixed success .

To increase the rate at which recovery happens, native species have been cultivated in the laboratory and turned into a pellet that can be seeded from an airplane. Not all seeding efforts have produced new crusts and there are questions about cyanobacterial viability. Duplicating widely fluctuation rainfall conditions and other environmental factors are difficult under field study conditions. The success rate, as measured by increasing amounts of biomass and types of organisms as a result of the addition of different amendments, varies from one location to another.

In conclusion, microbiotic crusts are very diverse communities and they probably function differently in different places. Further research will likely center around questions such as identifying what these microbes actually do, how they are different and how they are the same worldwide.

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