Soil microbial community assemblage and its seasonal variability in alpine treeline ecotone on the eastern Qinghai-Tibet Plateau

Abstract

The alpine treeline ecotone is characterized as the upper limit of the forest in the high-mountain ecosystem. Due to the freeze-thaw cycles, the soil organism community, such as microbial communities are expected to change between seasons. However, there are limited microbial-community studies focused on the high altitude alpine ecosystem. We conducted a study in the alpine treeline ecotone on the eastern Qinghai-Tibet Plateau, China, and investigated the seasonal variability of the soil microbial community. We collected all soil samples within the alpine treeline ecotone, between the treeline and timberline in the high-mountain region. The 16S rRNA genes of the microbial communities (bacterial and archaeal) were analyzed by high-throughput sequencing to the genus level. The results showed that soil microbial community in the alpine treeline ecotone was consistently dominated by eight phyla which consisted of 95% of the total microbial community, including Proteobacteria, Actinobacteria, Acidobacteria, Firmicutes, Planctomycetes, Chloroflexi, Bacteroidetes, and Verrucomicrobia. The overall diversity and evenness of the community were relatively stable, with an average of 0.5% difference between seasons. The highest seasonal variability occurred at the upper boundary of the alpine treeline ecotone, and few or almost no seasonal change was observed at lower elevations, indicating dense forest cover and litter deposition might have created a local microclimate that reduced seasonal variation among the surrounding environmental conditions. Our study was one of the first group that documented the microbial community assemblage in the treeline ecotone on the Qinghai-Tibet Plateau.