Microtopography of microbiotic crusts on the Colorado Plateau, and distribution of component organisms

We analyzed die microtopography of microbiotic soil crusts at 3 sites on di e Colorado Plateau of southern Utah and investigated distributions of cyano bacteria and several lichens iri distinctive microhabitats created by this topography At all 3 sites the long axes of linear soil mounds were oriented nonrandomly in a NNW-SSE direction. The conspicuous and consistent orienta tion of soil mounds may result from a combination of physical and biotic pr ocesses. Subtle differences across sites in mound orientation and organisma l distribution suggest that these variables may be useful in comparing dist urbance histories of crusts retrospectively. Differences in colonization frequencies, abundances, and distributions of m icroorganisms comprising the crusts, as a function of mound aspect or expos ure, suggest that these organisms are associated with particular aspects du e to distinctive and favorable microhabitats on these exposures. Polysaccha ride sheath material, deposited by cyanobacteria, and associated filaments occurred in greater quantities on ENE than WSW mound exposures, and cover b y Collema spp. lichens exhibited the same pattern. Colonization of mounds b y common lichen species occurred significantly more frequently on ENE than WSW mound aspects at 2 of 3 sites. In contrast, tfie 3 most common lichen s pecies, aside from Collema spp., did not exhibit a tendency for greater cov er on ENE than WSW mound aspects. Physiological differences between gelatin ous cyanolichens and green-algal lichens may explain the different distribu tional patients of Collema spp and the 3 other lichens.