Characterization of soil bacterial communities in alpine and desert grasslands in the Qilian Mountain range

The Qilian Mountain range is an important ecological zone in western China. Grasslands account for a significant proportion of land area in this mountain range. Understanding the composition of soil microbial communities in different grassland types found in the Qilian Mountains, as well as their relationship with soil factors, is important for sustainable conservation of grassland health. In the present study, we examined the diversity of soil bacterial communities using Illumina MiSeq high-throughput sequencing and investigated the relationship between bacterial composition and soil parameters in an alpine grassland meadow on the northeastern side of the Qilian Mountains and in a desert grassland in the Pingshan Lake desert (Linze County, Hexi Corridor). The beta diversity and community composition analyses revealed a significant difference between the bacterial communities in the two investigated grasslands. The four phyla that dominated both grasslands were Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria. These phyla accounted for 84% and 89% of the total bacterial community in the alpine and desert grassland, respectively. Actinobacteria was the most dominant phylum in both grasslands, accounting for 57% and 29% of the total bacterial community in the desert and alpine grassland, respectively. The relative abundances of Actinobacteria and Chloroflexi were significantly higher in the alpine grassland than in the desert grassland (P < 0.05). The relative abundances of Proteobacteria, Acidobacteria, Bacteroidetes, and Rokubacteria were significantly higher in the alpine grassland than in the desert grassland (P < 0.05). There was no significant difference in the relative abundances of Gemmatimonadetes, Verrucomicrobia, and Planctomycetes between the two grasslands (P > 0.05). Pearson correlation and principal component analysis showed that Actinobacteria had a significant negative correlation with soil nutrients (total nitrogen, total carbon, organic carbon, water content, and carbon:nitrogen ratio) (P < 0.01) and a significant positive correlation with soil bulk density (P < 0.01). Proteobacteria, Acidobacteria, and Rokubacteria were positively correlated with soil nutrients and negatively correlated with soil bulk density (P < 0.05). Our results indicated that total soil nitrogen, total soil carbon, soil pH, organic carbon, water content, soil bulk density, and carbon:nitrogen ratio were the key determinants of soil bacterial community distribution at the depth of 0 – 10 cm in the two investigated grassland types.