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Biological soil crusts (BSCs) cover up to 70% of the sparsely-vegetated open spaces in semiarid and arid regions throughout the world and fulfill a wide range of ecological functions. Previous investigations on BSCs mainly focused on the taxonomic or genetic diversity of their components and physical properties, while little attention was given to the functional diversity of microbial community, which plays crucial roles in carbon cycling. In order to distinguish between microbial functional diversity in BSCs with different developmental levels, MicroResp (TM) plates were used to determine the utilization rate of fifteen added carbon sources. Five types of crusts. A-E, were taken from the western Negev Desert (Israel) during the morning hours of March 2011. Abiotic and biotic variables were measured. The well-developed high-biomass BSCs exhibited pronounced increases in their chlorophyll a and organic-matter content. Higher activity and biomass of microbial communities, as well as higher density of viable microfungi, were also found in the well-developed BSCs. Marked increases in the utilization rates of aromatic acid, carbohydrates and carboxylic acid were consistent with the well-developed crusts. Although the utilization rates of the four carbon groups followed the order: carboxylic acid > amino acid > carbohydrates and aromatic acid, the redundancy analysis revealed that crust A preferred consuming amino acids while crusts C and E preferred carboxylic acids and carbohydrates. No significant differences in functional diversity were observed between BSCs with different developmental levels. More carbon sources, as well as molecular and stable isotopic approaches, should be used in further studies. (C) 2012 Elsevier Ltd. All rights reserved.