Biological soil crusts (also called microbiotic, microphytic or cryptogamic crusts) are common cryptogamic communities in various arid and semi-arid regions of the world. Apparently only a few soil crusts worldwide are as well investigated as those of the Nizzana/Sinai-Negev sand fields (Galun and Garty 2001; also see Belnap et al. 2001). Concerning their species diversity, ecology and ecophysiology, several studies have been published and the current knowledge, including some new information, will be presented in the following review. Nevertheless, even though these crusts have been the subject of several studies, we are far from knowing their complete inventory of organisms, since almost all investigations dealing with species composition were restricted to oxygenic-photoautotrophic organisms. Fungi and bacteria, important components in soil crusts also in the north-western Negev Desert (unpublished data), have been widely neglected so far.
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