Ecological networks reveal contrasting patterns of bacterial and fungal communities in glacier-fed streams in Central Asia

Abstract

Bacterial and fungal communities in biofilms are important components in driving biogeochemical processes in stream ecosystems. Previous studies have well documented the patterns of bacterial alpha diversity in stream biofilms in glacier-fed streams, where, however, beta diversity of the microbial communities has received much less attention especially considering both bacterial and fungal communities. A focus on beta diversity can provide insights into the mechanisms driving community changes associated to large environmental fluctuations and disturbances, such as in glacier-fed streams. Moreover, modularity of co-occurrence networks can reveal more ecological and evolutionary properties of microbial communities beyond taxonomic groups. Here, integrating beta diversity and co-occurrence approach, we explored the network topology and modularity of the bacterial and fungal communities with consideration of environmental variation in glacier-fed streams in Central Asia. Combining results from hydrological modeling and normalized difference of vegetation index, this study highlighted that hydrological variables and vegetation status are major variables determining the environmental heterogeneity of glacier-fed streams. Bacterial communities formed a more complex and connected network, while the fungal communities formed a more clustered network. Moreover, the strong interrelations among the taxonomic dissimilarities of bacterial community (BC) and modules suggest they had common processes in driving diversity and taxonomic compositions across the heterogeneous environment. In contrast, fungal community (FC) and modules generally showed distinct driving processes to each other. Moreover, bacterial and fungal communities also had different driving processes. Furthermore, the variation of BC and modules were strongly correlated with hydrological properties and vegetation status but not with nutrients, while FC and modules (except one module) were not associated with environmental variation. Our results suggest that bacterial and fungal communities had distinct mechanisms in structuring microbial networks, and environmental variation had strong influences on bacterial communities but not on fungal communities. The fungal communities have unique assembly mechanisms and physiological properties which might lead to their insensitive responses to environmental variations compared to bacterial communities. Overall, beyond alpha diversity in previous studies, these results add our knowledge that bacterial and fungal communities have contrasting assembly mechanisms and respond differently to environmental variation in glacier-fed streams.

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

“…Microbial communities are typically complex and composed of taxa with potential for strong interactions. In these highly complex systems, co-occurrence patterns are important in understanding microbial community structure by offering new insights into potential biotic interactions and community assembly mechanisms (Fuhrman, 2009;Faust and Raes, 2012;Ren and Gao, 2019). Modularity is a characteristic of most large complex systems, representing the tendency to contain sub-clusters of members in a network (Newman, 2006) and is usually related to habitat heterogeneity and niche diversity across broad scales (Barberan et al, 2012;Ren et al, 2017b).…”

Contrasting Patterns of the Bacterial Communities in Melting Ponds and Periglacial Rivers of the Zhuxi glacier in the Tibet Plateau

“…Remarkably, previous studies have documented that Cyanobacteria commonly dominate in glacial habitats, such as Arctic and Antarctic (e.g., Svalbard Glacier, Lower Wright Glaciers, and Diamond Glacier) and other alpine regions (Tibetan Plateau and high-mountain Asia) [13,19,20,22]. In such sites, the Cyanobacteria accounted for 20% to 40% of the whole bacterial assemblages.…”

“…Additionally, these aforementioned studies are limited to basic inventory descriptions at the sample level, leading to several knowledge gaps remaining, especially about interacting interactions and the role of rare taxa. Although it has long been known that bacterial species interact with each other to form complicated networks capable of community level functions, such interaction in glacial ecosystems have only been studied very recently [22,23]. Furthermore, modern ecology has recognized the over-proportional role of rare species, especially in pristine environments [24,25].…”

Bacterial Communities Present Distinct Co-occurrence Networks in Sediment and Water of the Thermokarst Lakes in the Yellow River Source Area

“…In many biological systems, modularity (the tendency of a network parsed into modules) is an essential ecological feature to reveal more ecological and evolution properties but is easily overlooked (Parter et al, 2007;Centler et al, 2020). The relationships between bacterial environmental variations and microbial modules as well as between microbial modules and the whole community can improve our understanding of direct and indirect influences of environmental variations on microbial communities (Menezes et al, 2015;Toju et al, 2016;Ren and Gao, 2019). Changes in bacterial networks have important implications for their functioning and vulnerability under future disturbance, such as climate change (de Vries et al, 2018).…”