Bacterial Communities in Stream Biofilms in a Degrading Grassland Watershed on the Qinghai–Tibet Plateau

Abstract

Grassland is among the largest terrestrial biomes and is experiencing serious degradation, especially on the Qinghai-Tibet Plateau (QTP). However, the influences of grassland degradation on microbial communities in stream biofilms are largely unknown. Using 16S rRNA gene sequencing, we investigated the bacterial communities in stream biofilms in sub-basins with different grassland status in the Qinghai Lake watershed. Grassland status in the sub-basins was quantified using the normalized difference vegetation index (NDVI). Proteobacteria, Bacteroidetes, Cyanobacteria, and Verrucomicrobia were the dominant bacterial phyla. OTUs, 7,050, were detected in total, within which 19 were abundant taxa, and 6,922 were rare taxa. Chao 1, the number of observed OTUs, and phylogenetic diversity had positive correlations with carbon (C), nitrogen (N), and/or phosphorus (P) in biofilms per se. The variation of bacterial communities in stream biofilms was closely associated with the rate of change in NDVI, pH, conductivity, as well as C, N, P, contents and C:N ratio of the biofilms. Abundant subcommunities were more influenced by environmental variables relative to the whole community and to rare subcommunities. These results suggest that the history of grassland degradation (indicated as the rate of change in NDVI) influences bacterial communities in stream biofilms. Moreover, the bacterial community network showed high modularity with five major modules (>50 nodes) that responded differently to environmental variables. According to the module structure, only one module connector and 12 module hubs were identified, suggesting high fragmentation of the network and considerable independence of the modules. Most of the keystone taxa were rare taxa, consistent with fragmentation of the network and with adverse consequences for bacterial community integrity and function in the biofilms. By documenting the properties of bacterial communities in stream biofilms in a degrading grassland watershed, our study adds to our knowledge of the potential influences of grassland degradation on aquatic ecosystems.

Abundant and rare bacterial taxa structuring differently in sediment and water in thermokarst lakes in the Yellow River Source area, Qinghai-Tibet Plateau

“…In our studied bacterial communities, only 4% OTUs were abundant taxa which accounted for 40% of sequences, while more than 70% OTUs were rare taxa which only account for 24% of sequences (Figure S2). Moreover, in line with previous studies in many other ecosystems (Wu et al, 2016;Ren et al, 2020;Shu et al, 2021), abundant taxa had significantly lower β-diversity and occupy higher niche width than rare taxa (Figure 3), suggesting that abundant taxa were more ubiquitous distributed and more competitive for limited resources than rare taxa during the adaptation process (Malik et al, 2020).…”

“…For example, abundant taxa contribute predominantly to biomass production and energy flow, whereas rara taxa contribute mostly to species richness and redundant functions (Pedros-Alio, 2012; Debroas et al, 2015). More and more studies have been conducted to unravel the differences between abundant and rare subcommunities in various environments, such as coastal and marine environments (Campbell et al, 2011; Logares et al, 2014), inland waters (Liu et al, 2015; Xue et al, 2018; Ren et al, 2020), and soil (Jiao and Lu, 2019; Xue et al, 2020). These studies indicated that abundant and rare subcommunities present contrasting community patterns and processes and are subject to distinct environmental factors.…”

Short-Term Grazing Exclusion Alters Soil Bacterial Co-occurrence Patterns Rather Than Community Diversity or Composition in Temperate Grasslands

“…Firstly, pH can directly pose selective pressures on bacteria, as specific species poses different tolerance ability to pH—for example, our study found that the relative abundance of Choloflexi was positively correlated with pH, while the relative abundance of Proteobacteria and Verrucomicrobia showed negative correlations. pH can also indirectly affect the composition of bacterial community as it is normally related with multiple soil factors, including nutrient availability, redox state, and salinity ( Lauber et al, 2009 ; Ren et al, 2020 ). Secondly, available carbon and nitrogen are the two key resources supporting the survival of most terrestrial heterotrophic microorganisms.…”

Genomic Features and Molecular Function of a Novel Stress-Tolerant Bacillus halotolerans Strain Isolated from an Extreme Environment

“…The Qinghai-Tibet Plateau (QTP), the largest plateau on earth, with the highest average altitude, is known as the "third pole of the world" [1]. Due to its extreme geographical location and climatic conditions, the QTP has unique extreme ecosystems, characterized by oxygen deficiency, low temperatures, and intense ultraviolet radiation [2]. The rhizosphere of plants growing in the extreme environment could be a rich source of microbes with potential stress resistance and biocontrol properties [3].…”