Biocrusts are mosaics of bacteria, fungi, and algae that perform essential ecological processes in cold deserts, including carbon storage, nitrogen fixation, and soil stabilization. Although biocrusts are distributed across all continents, the global-scale biogeography of biocrust microorganisms is poorly understood. To better understand the distributions of biocrusts, particularly their bacterial components, we collected and characterized the microbial communities in the top 2 mm of soils in three different cold deserts on three continents (i.e., Antarctica’s McMurdo Dry Valleys including Miers, Taylor, and Garwood; USA’s Great Basin Desert; and China’s Junggar Basin). We evaluated biocrust bacterial and eukaryotic communities by extracting genomic DNA from each sample and sequencing the V4 and V9 regions of the 16s and 18s rRNA genes on an Illumina HiSeq 2500, and creating community co-occurrence networks describing species interactions. We also measured soil physiochemical characteristics in each desert to identify potential environmental constraints on biocrust communities.
Continent had a robust effect on the composition of biocrust bacterial communities. Our PCoA results distinctly separated deserts by continent in ordination space along PCoA axis 1, which explained 40.9% of the variation in community composition. PERMANOVA analysis supported the ordination, demonstrating a compositional difference between communities on different continents (PERMANOVA, F = 9.33, R2 = 0.39, P < 0.0001, df = 1), and highlighting differences among biocrusts within continents (PERMANOVA, F = 1.59, R2 = 0.04, P = 0.03, df = 1). Based on Shannon diversity indices, China’s biocrusts were most diverse (mean = 5.67 ± 0.02) followed closely by crusts from the USA (mean = 5.38 ± 0.04). Antarctic biocrusts were least diverse (mean = 4.04 ± 0.18). Biocrust networks were most complex and interconnected in China’s crusts (number of nodes = 967, number of edges = 21135), intermediate in USA crusts (nodes = 792, edges = 14643), and dramatically less complex in Antarctic crusts (nodes = 144, edges = 602). The compositional differences between geographically distant but environmentally similar cold desert communities provide evidence that dispersal limitation plays a role in biocrust biogeography and the extreme environment of Antarctica may limit the formation of complex biocrust mosaics.