Microbial community structure and function prediction of two typical biocrusts in the Mu Us Sandland, Northwest China

Biocrusts (Biological soil crusts) are a living ground cover widely distributed in arid and semi-arid regions worldwide and provide important ecological functions in ecosystems. As an important part of biocrusts, the microorganisms in the formation and succession of biocrusts should not be underestimated. However, the microbial processes among different types of biocrusts are poorly understood. We used high-throughput sequencing to identify soil bacteria and fungal community in two types of biocrusts, lichen crust and moss crust, in the Mu Us Sandland. The aims were to explore the composition, diversity, and ecological function of the microbial community in two types of biocrusts. Our study found that (1) The diversity of bacterial and fungal communities was significantly different between the two types of biocrusts. The Shannon index (6.18) of fungi in moss crust was higher than that (5.75) in lichen crust, and the operational taxonomic units of bacteria and fungi in moss crust were also higher than those in lichen crust by 3.22% and 30.61%, respectively. The bacteria and fungi community structure in two types of biocrusts were significantly different, while the differences were not significant. (2) In the microbiomes of lichen and moss biocrusts, Actinomycetes, Cyanobacteria, and Proteobacteria, the sum of which accounted for 68.01% in lichen crust and 59.88% in moss crust at operational taxonomic units level, were dominant phylum of bacteria, while the dominant phylum of fungi was mainly Ascomycota. Microcoleus (11.10%) and Exophiala (7.37%) were dominant genera in lichen crust, while the dominant genus in moss crust was RB41 (5.16%). (3) The pH, soil dissolved organic carbon, and soil organic carbon were the top three factors that correlated with both bacterial and fungal community structures. (4) The metabolic function of the bacterial community in two types of biocrusts was quite different. The relative abundances of metabolic pathways in moss crust, such as chemoheterotrophy, ureolysis, aromatic compound degradation, and nitrate reduction, were significantly higher than those in lichen crust, however, the relative abundances of cyanobacteria, oxygenic photoautotrophy, photoautotrophy, and phototrophy were significantly lower (ANOVA, P<0.05). Altogether, our study suggests that the biocrust types have significant effects on the pH, taxonomic, and metabolic diversity, providing a theoretical basis for improving the physicochemical properties of the surface soil in the desertification land ecosystem.