Abstract
Thermokarst lakes are a ubiquitous and important landscape feature in cold regions and are changing tremendously due to the accelerated climate change. In thermokarst lakes, sediment and water are two distinct but highly interconnected habitats, harboring different bacterial communities in terms of taxonomic composition. However, the co-occurrence networks of these bacterial communities remain unclear. Here, we investigate the co-occurrence ecological networks of sediment and water bacterial communities for thermokarst lakes in the Yellow River Source Area on the Qinghai-Tibet Plateau. The results show that the bacterial communities construct distinct co-occurrence networks in sediment and water. The metacommunity network was parsed into four major modules formed by the operational taxonomic units (OTUs) enriched in sediment or water independently, and water-enriched OTUs exhibited much closer interconnections than sediment-enriched OTUs. When considering the sediment and water bacterial networks separately, different topological properties and modular patterns present: the sediment bacterial network was more clustered while the modules less responded to the environmental variables. On the contrary, the water bacterial network was more complex with the OTUs more interconnected and its modules more responded to the environmental variables. Moreover, the results of the structural equation model suggest that, by the influence of environmental variations on individual modules, the water bacterial communities would be more vulnerable under the fact of accelerating climate change. This study provides insights beyond a conventional taxonomic perspective, adding our knowledge of the potential mechanisms structuring bacterial community assembly and improving our prediction of the responses of this fast-changing ecosystem to future climate change.
Highlights
Thermokarst lakes, known as thaw lakes, are formed as a result of thawing ice-rich permafrost, acting as a ubiquitous landscape feature in the cold region with ecological and biogeochemical importance (Kokelj and Jorgenson, 2013; Chin et al, 2016; In’T Zandt et al, 2020; Manasypov et al, 2021)
30 operational taxonomic units (OTUs) were enriched in sediment (Figure 1B), belonging to Proteobacteria (n = 10), Bacteroidetes (n = 9), Firmicutes (n = 7), and Actinobacteria (n = 4), and 72 OTUs were enriched in water (Figure 1B), belonging to Proteobacteria (n = 44), Actinobacteria (n = 9), Gemmatimonadetes (n = 8), Bacteroidetes (n = 7), Acidobacteria (n = 2), Fusobacteria (n = 1), and Nitrospirae (n = 1)
Bacterial taxa were clustered into four major modules, which were consisted of OTUs from various phylum groups (Supplementary Figure 2A)
Summary
Thermokarst lakes, known as thaw lakes, are formed as a result of thawing ice-rich permafrost, acting as a ubiquitous landscape feature in the cold region with ecological and biogeochemical importance (Kokelj and Jorgenson, 2013; Chin et al, 2016; In’T Zandt et al, 2020; Manasypov et al, 2021). As a consequence of accelerating permafrost degradation, thermokarst lakes are changing tremendously in size and abundance during the evolution process of formation, expansion, shrinkage, and disappearance, causing substantial impacts on regional and global ecosystem structure and biogeochemical processes (Yoshikawa and Hinzman, 2003; Smith et al, 2005; Lantz and Turner, 2015; Pastick et al, 2019). Sediment and water are two distinct but highly interconnected habitats (Carter et al, 2003; Parker et al, 2016), which host diverse but substantially different bacterial communities in taxonomic and functional composition (Lozupone and Knight, 2007; Roeske et al, 2012; Ren et al, 2019a,b). Understanding the structuring mechanisms and distribution patterns of bacterial communities in sediment and water is important to promote our understanding of the connections and distinctions between these two habitats
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