Variations of bacterial and fungal communities along a primary successional chronosequence in the Hailuogou glacier retreat area (Gongga Mountain, SW China)

New terrestrial habitats have emerged and a primary succession has developed in the retreat area (29°34'N, 102°00'E, 2951–2886 m) after the retreat of the Hailuogou glacier. To investigate soil microbial changes along the primary successional chronosequence, mixed soil samples were collected at six sites at different ages (2 young sites, 2 mid-aged sites, and 2 old sites). The RNA was extracted and amplified. Bacterial 16S rRNA and fungal 18S rRNA were analyzed using high-throughput 454 pyrosequencing analysis. Overall, pyrosequencing showed that Proteobacteria, Acidobacteria, Bacteroidetes and Actinobacteria were the main bacterial phyla, and the fungal communities were strongly dominated by the phyla Ascomycota and Basidiomycota in the retreat area. The Shannon diversity index (Hshannon) of bacteria was 6.5–7.9, and that of fungi was 2.2–4.1 in these sites. For the bacterial communities, diversity and evenness values were highest on the mid-age sites and were relatively low on the young and old sites. A similar trend was observed for the fungal communities. In contrast, soil properties showed significant linear distributional trends (increase or decrease) with the age of the site. Combining the linear change patterns of soil properties, the highest values of bacterial and fungal evenness and diversity in the mid-aged sites indicated that there was less environmental stress and more niches for microbial communities in the middle successional stage compare with other stages. In addition, our analysis showed that microbial communities were the main drivers that build a soil organic matter pool to expedite pedogenesis for ecosystem succession. This primary succession in the Hailuogou glacier retreat area is developing rapidly compared with that in other glacier retreats.