Differences in bacterial community structure between three types of biological soil crusts and soil below crusts from the Gurbantunggut Desert, China

The scarcity of knowledge on differences in the microbial assemblage between biological soil crusts (BSCs) and soil below crusts (SBCs) limits our understanding of the contribution of different layers of topsoil to desert ecosystems. This study used Illumina MiSeq sequencing to determine whether differences in bacterial communities among different types of BSCs (algae, lichen and moss dominated) are greater than those between BSCs and their corresponding underlying soils (0-5 cm) in the Gurbantunggut Desert, China. Alpha and beta diversity of bacterial communities showed that richness and diversity were greater in SBCs than in BSCs, but the absolute bacterial abundance was larger in BSCs than in soils. Differences were mainly in the phyla Cyanobacteria, Actinobacteria, Chloroflexi and Acidobacteria. Cyanobacteria were concentrated in BSCs, especially in algae-dominated BSCs. The relative abundances of Actinobacteria, Chloroflexi and Acidobacteria in SBCs were more than twice those in BSCs, and they were also abundant in the lichen- and moss-dominant crusts. The number of sample-specific genera was larger in BSCs, but there were more shared genera among SBCs. These results, combined with the principal coordinate analysis and the predicted function profiles, showed that differences in microbial community structure and function in desert ecosystems were greatest between BSCs and the underlying soils, followed by differences among the three types of BSCs, and differences were smallest between the soils below different crusts. These differences might be closely related to the soil chemical properties, especially to pH and fertility. Our study indicated that microbial communities tended to converge in SBCs of different microhabitats. Highlights We studied bacterial community composition in different types of BSCs and SBCs. Differences in bacterial community were greatest between BSCs and SBCs. BSC components contributed to small-scale microbial heterogeneity in SBCs. Surface soil bacterial communities were strongly stratified even at the centimetre scale from BSCs.