Variation in Biological Soil Crust Bacterial Abundance and Diversity as a Function of Climate in Cold Steppe Ecosystems in the Intermountain West, USA

Biological soil crust (biocrust) is a composite of mosses, lichens, and bacteria that performs many important soil system functions, including increasing soil stability, protecting against wind erosion, reducing nutrient loss, and mediating carbon and nitrogen fixation cycles. These cold desert and steppe ecosystems are expected to experience directional changes in both climate and disturbance. These include increased temperatures, precipitation phase changes, and increased disturbance from anthropogenic land use. In this study, we assessed how climate and grazing disturbance may affect the abundance and diversity of bacteria in biocrusts in cold steppe ecosystems located in southwestern Idaho, USA. To our knowledge, our study is the first to document how biocrust bacterial composition and diversity change along a cold steppe climatic gradient. Analyses based on 16S small subunit ribosomal RNA gene sequences identified the phylum Actinobacteria as the major bacterial component within study site biocrusts (relative abundance = 36-51%). The abundance of the phyla Actinobacteria and Firmicutes was higher at elevations experiencing cooler, wetter climates, while the abundance of Cyanobacteria, Proteobacteria, and Chloroflexi decreased. The abundance of the phyla Cyanobacteria and Proteobacteria showed no significant evidence of decline in grazed areas. Taken together, results from this study indicate that bacterial communities from rolling biocrusts found in cold steppe ecosystems are affected by climate regime and differ substantially from other cold desert ecosystems, resulting in potential differences in nutrient cycling and ecosystem dynamics.