Community structure and elevational distribution pattern of soil Actinobacteria in alpine grasslands

Actinobacteria are widely distributed in various ecological environments and play essential roles in the carbon and nitrogen cycles in natural ecosystems. Understanding the community composition, structure and distribution of Actinobacteria is not only fundamentally important for studying their functions to ecosystem, but also conducive to protecting Actinobacteria resources. Furthermore, studies regarding the distribution of Actinobacteria in specific areas would also help us understand the impact of global environmental changes on the world's microbial communities. In this study, six alpine grassland sites, from 3220 m and 4790 m in elevation, were selected in Sanjiangyuan National Natural Reserve, which is located in the center of Qinghai-Tibetan Plateau. Then, using 16S rDNA high-throughput sequencing, the composition and elevational distribution patterns of soil Actinobacterial communities were analyzed. A total of 5052 OTUs were detected, which could attributed to 230 genera, 52 families, 9 orders and 5 subclasses of Actinobacteria, and the Actinobacterial communities were significantly (P < 0.05) different among the six sites, according to detrended correspondence analysis (DCA) and several dissimilarity tests (MRPP, Anosim and Adonis). The subclasses of Actinobacteridae and Rubrobacteridae were dominant in all six sites, and accounted for > 80% of relative abundances, indicating that Actinobacteridae and Rubrobacteridae were the most important subclasses in the alpine grasslands. Through analysis of Actinobacterial ɑ-diversity of the six samples, the number of OTUs ranged from 447.23 ± 52.83 to 675.00 ± 114.69, and the Shannon index ranged from 5.35 ± 0.15 to 5.78 ± 0.11. Both of the measures exhibited strong negative correlations (P < 0.01) with the elevation, indicating that the environmental conditions of higher elevation may not benefit to the survival of Actinobacterial species. Mantel test was implemented to identify the major environmental factors that impact Actinobacterial communities, and the result indicated that elevation and soil temperature, moisture, organic carbon and nitrogen contents were all significantly (P < 0.05) correlated with Actinobacterial community structure and they could be the key factors in determining the distribution of soil Actinobacteria in the alpine grassland in the Tibetan Plateau.