Dryland soil microbial communities display spatial biogeographic patterns associated with soil depth and soil parent material

Biological soil crusts (biocrusts) are common to drylands worldwide. We employed replicated, spatially nested sampling and 16 S r RNA gene sequencing to describe the soil microbial communities in three soils derived from different parent material (sandstone, shale, and gypsum). For each soil type, two depths (biocrusts, 0–1 cm; below‐crust soils, 2–5 cm) and two horizontal spatial scales (15 cm and 5 m) were sampled. In all three soils, C yanobacteria and P roteobacteria demonstrated significantly higher relative abundance in the biocrusts, while C hloroflexi and A rchaea were significantly enriched in the below‐crust soils. Biomass and diversity of the communities in biocrusts or below‐crust soils did not differ with soil type. However, biocrusts on gypsum soil harbored significantly larger populations of A ctinobacteria and P roteobacteria and lower populations of C yanobacteria . Numerically dominant operational taxonomic units ( OTU ; 97% sequence identity) in the biocrusts were conserved across the soil types, whereas two dominant OTU s in the below‐crust sand and shale soils were not identified in the gypsum soil. The uniformity with which small‐scale vertical community differences are maintained across larger horizontal spatial scales and soil types is a feature of dryland ecosystems that should be considered when designing management plans and determining the response of biocrusts to environmental disturbances.