Abstract: To verify the effects of different biological soil crusts (biocrusts) succession phases (algal crusts, mixed crusts, moss crusts) on microbial community compositions and diversities in biocrustal layer and subsoils in a desert steppe, Ningxia, China, the biocrusts and subsoils (0-5 cm) were sampled using method of space instead of time series. The highthroughput sequencing of V3-V4 fragment of bacterial 16S rRNA was conducted using the platform of Illumina Miseq. The bacterial α and β diversity, community structure and their relationships with soil physical and chemical factors were analyzed. The results showed that bacterial α diversity showed a consistent trend. The Chao1, ACE and Shannon indices in the subsoil (0-5 cm) were all higher than those of biocrustal layer (P<0.05), while α diversity among biocrusts was not significant (P>0.05). Results of principal coordinate analysis results indicated that 0-5 cm soil beneath different biocrusts had similar bacterial OTUs, and could be categorized as one type. Bacterial community structures of algal crust and mixed crust had some similarity, but that under moss crust was significantly different from algal crust and mixed crust. The dominant bacteria community of three biocrusts and subsoils were consistent. The topfive dominant bacterial community phyla were Actinobacteria, Proteobacteria, Acidobacteria, Gemmatimonadetes, and Planctomycetes. The relative abundance of these dominant bacterial communities in subsoil (0-5 cm) were higher than that in biocrustal layer, and that of the endemic and shared genera was higher in subsoil (0-5 cm) than in biocrustal layer. Results of distance based redundancy analysis (db-RDA) indicated that soil available potassium, total nitrogen and soil available phosphorus concentrations were the main factors affecting soil bacterial community structure in biocrustal layer, and explained 21.4%, 18.9% and 17.4% variances (P<0.05), respectively, whereas EC was the major factor affecting soil bacterial community structure in subsoil (0-5 cm), and explained 20.5% of variance (P<0.05). These results suggested that the development of soil microorganisms and the improvement of soil physical and chemical properties were inter-dependent, and that the changes of bacterial community structure and diversity facilitate the improvement of physical and chemical properties of biocrustal layer during the process of biocrusts succession.

Key words: desert steppe, biological soil crusts, bacterial community structure, high-throughput sequencing.