Abstract
Bacterioplankton communities play a crucial role in freshwater ecosystem functioning, but it is unknown how co-occurrence networks within these communities respond to human activity disturbances. This represents an important knowledge gap because changes in microbial networks could have implications for their functionality and vulnerability to future disturbances. Here, we compare the spatiotemporal and biogeographical patterns of bacterioplankton molecular ecological networks using high-throughput sequencing of Illumina HiSeq and multivariate statistical analyses from a subtropical river during wet and dry seasons. Results demonstrated that the lower reaches (high human activity intensity) network had less of an average degree (10.568/18.363), especially during the dry season, when compared with the upper reaches (low human activity intensity) network (10.685/37.552) during the wet and dry seasons, respectively. The latter formed more complexity networks with more modularity (0.622/0.556) than the lower reaches (high human activity intensity) network (0.505/0.41) during the wet and dry seasons, respectively. Bacterioplankton molecular ecological network under high human activity intensity became significantly less robust, which is mainly caused by altering of the environmental conditions and keystone species. Human activity altered the composition of modules but preserved their ecological roles in the network and environmental factors (dissolved organic carbon, temperature, arsenic, oxidation–reduction potential and Chao1 index) were the best parameters for explaining the variations in bacterioplankton molecular ecological network structure and modules. Proteobacteria, Actinobacteria and Bacteroidetes were the keystone phylum in shaping the structure and niche differentiations in the network. In addition, the lower reaches (high human activity intensity) reduce the bacterioplankton diversity and ecological niche differentiation, which deterministic processes become more important with increased farmland and constructed land area (especially farmland) with only 35% and 40% of the community variation explained by the neutral community model during the wet season and dry season, respectively. Keystone species in high human activity intensity stress habitats yield intense functional potentials and Bacterioplankton communities harbor keystone taxa in different human activity intensity stress habitats, which may exert their influence on microbiome network composition regardless of abundance. Therefore, human activity plays a crucial role in shaping the structure and function of bacterioplankton molecular ecological networks in subtropical rivers and understanding the mechanisms of this process can provide important information about human–water interaction processes, sustainable uses of freshwater as well as watershed management and conservation.
Highlights
River ecosystems provide important support for terrestrial and aquatic ecosystems and provide important services for human health, well-being as well as economic and social benefits [1]
It is well documented that such changes in network structure affect ecosystem functioning and stability, little is known about the link between human activity intensity and the stability of these microbial systems and whether and how the ecological networks, bacterioplankton molecular ecological networks, will change under human activity intensity change scenarios
To identify assemblages that potenconnector during the wet season belonging to Gemmatimonadetes and two connector Operational taxonomic units (OTUs) tially interact or share niches within bacterioplankton, we focused on major modules during the dry season belonging to Proteobacteria and Ignavibacteriae
Summary
River ecosystems provide important support for terrestrial and aquatic ecosystems and provide important services for human health, well-being as well as economic and social benefits [1]. An increased level of nutrient loads and no-point pollutants from domestic sewage, industries, and agriculture can considerably affect the water environment conditions [15], disturb the spatial distributions of bacterioplankton population, communities and habitats [16], reduce microbial diversity [17], and destabilize microbial co-occurrence networks interactions (e.g., through predation and growth competition) [18]. These findings highlight the fact that rivers are among the most vulnerable ecosystems in the context of a growing human population, much of which is often concentrated along the riverside, and increasing anthropogenic pressure. Understanding the response of river bacterioplankton molecular ecological network and functioning to human activity is critical to human well-being and river sustainable management
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