Soil Bacterial Communities and Diversity in Alpine Grasslands on the Tibetan Plateau Based on 16S rRNA Gene Sequencing

Youchao Chen,Xuyang Lu,Ziwei Wang,Hongmao Jiang,Yang Hu

doi:10.3389/fevo.2021.630722

Abstract

The Tibetan Plateau, widely known as the world’s “Third Pole,” has gained extensive attention due to its susceptibility to climate change. Alpine grasslands are the dominant ecosystem on the Tibetan Plateau, albeit little is known about the microbial community and diversity among different alpine grassland types. Here, soil bacterial composition and diversity in the upper soils of five alpine grassland ecosystems, alpine meadow (AM), alpine steppe (AS), alpine meadow steppe (AMS), alpine desert (AD), and alpine desert steppe (ADS), were investigated based on the 16S rRNA gene sequencing technology. Actinobacteria (46.12%) and Proteobacteria (29.67%) were the two dominant soil bacteria at the phylum level in alpine grasslands. There were significant differences in the relative abundance at the genus level among the five different grassland types, especially for the Rubrobacter, Solirubrobacter, Pseudonocardia, Gaiella, Haliangium, and Geodermatophilus. Six alpha diversity indices were calculated based on the operational taxonomic units (OTUs), including Good’s coverage index, phylogenetic diversity (PD) whole tree index, Chao1 index, observed species index, Shannon index, and Simpson index. The Good’s coverage index value was around 0.97 for all the grassland types in the study area, meaning the soil bacteria samplings sequenced sufficiently. No statistically significant difference was shown in other diversity indices’ value, indicating the similar richness and evenness of soil bacteria in these alpine grasslands. The beta diversity, represented by Bray–Curtis dissimilarity and the non-metric multidimensional scaling (NMDS), showed that OTUs were clustered within alpine grasslands, indicating a clear separation of soil bacterial communities. In addition, soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), pH, and soil water content (SWC) were closely related to the variations in soil bacterial compositions. These results indicated that soil bacterial taxonomic compositions were similar, while soil bacterial community structures were different among the five alpine grassland types. The environmental conditions, including SOM, TN, TP, pH, and SWC, might influence the soil bacterial communities on the Tibetan Plateau.

Highlights

The Tibetan Plateau, which is considered the world’s “Third Pole,” has attracted extensive attention because of its high altitude and harsh environment (Chen et al, 2013)
alpine meadow steppe (AMS) is a transitional type of alpine grassland from the meadow to the steppe and alpine desert steppe (ADS) is a transitional type of alpine grassland from steppe to desert, covering 7.32 and 10.7%, respectively, of the total grassland area in the Tibetan Plateau (Lu et al, 2018)
A total of 48,366–51,566 clean reads with high-quality 16S rRNA sequences were identified from the 21 samples from the Tibetan Plateau

Summary

Introduction

The Tibetan Plateau, which is considered the world’s “Third Pole,” has attracted extensive attention because of its high altitude and harsh environment (Chen et al, 2013). Environmental factors on the plateau, such as altitude (Cui et al, 2019), precipitation (Zhang K. et al, 2016), and topography (Frindte et al, 2019), have a large impact on soils of alpine ecosystems, resulting in marked changes in microbial diversity and function (Donhauser and Frey, 2018). Alpine grasslands are the representative landscape of the Tibetan Plateau, occupying more than 70% of the total area (Lu et al, 2018; Yu et al, 2019). Climatic, and vegetation characteristics, alpine grasslands on the Tibetan Plateau can be classified as alpine meadow (AM), alpine steppe (AS), alpine meadow steppe (AMS), alpine desert (AD), alpine desert steppe (ADS), etc. Soil microbial communities, which are the key drivers of many below-ground processes, remain poorly understood on the Tibetan Plateau

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