Abstract
Bacterioplankton communities commonly consist of few highly abundant species and a large number of rare species that play key roles in biogeochemical cycles of aquatic ecosystems. However, little is known about the biogeographic assemblies of these communities, especially in large rivers suffering from cascade dam regulation. Here, we used a 16S rRNA gene amplicon sequencing approach to investigate the biogeographic patterns and underlying assembly mechanisms of abundant and rare bacterioplankton taxa in cascade reservoirs of the Jinsha River in China. The results revealed species loss of bacterioplankton due to dam construction, which was more significant for rare taxa than for abundant ones. The distributions of abundant and rare taxa exhibited similar spatial and temporal patterns, which were significantly distinct between winter and summer and between upstream and downstream reservoirs. Both spatial (dispersal-related process) and environmental (selection process) factors seemed to together govern the assembly and biogeography of abundant and rare taxa, although both factors explained only a small fraction of variation in the rare taxa. More importantly, environmental factors explained more community variation in abundant sub-community than that in rare sub-community. Co-occurrence network analysis revealed that abundant species with closer interactions were more often located in a central position of the network compared with rare species. Nevertheless, half of the keystone species were rare species and may play important roles in maintaining the network stability. Overall, these findings indicate that distinct assembly mechanisms underlie the similar biogeography of rare and abundant bacteria in cascade reservoirs of a large river.
Highlights
Rivers serve as pipes that shuttle water, organic materials, and nutrients from continents to oceans, providing numerous essential ecosystem services (Read et al, 2015; Savio et al, 2015)
We focused on the following questions: (i) If cascade dam construction affects the diversity and community composition of bacterioplankton? (ii) Are the effects of multiple dams cumulative or largely insignificant? (iii) Do abundant and rare bacterioplankton exhibit similar biogeographic patterns in the cascade reservoirs of the Jinsha River? (iv) What are the major factors influencing the assembly of the bacterioplankton community, and do the contributions of these factors differ for abundant and rare taxa? (v) What are the co-occurrence patterns of abundant and rare taxa, and which taxa occupy more important positions in the co-occurrence network?
Bacterioplankton was collected from 52 water samples and subjected to 16S rRNA amplicon sequencing to yield a total of 2,269,162 high-quality reads, which clustered into 10,384 operational taxonomic units (OTUs) based on 97% similarity
Summary
Rivers serve as pipes that shuttle water, organic materials, and nutrients from continents to oceans, providing numerous essential ecosystem services (Read et al, 2015; Savio et al, 2015). Most previous studies have focused on the abundant taxa due to their important roles in carbon cycling and biomass production (Pedrós-Alió, 2012; Liu et al, 2015a). Recent studies have emphasized the critical ecological functions of rare taxa, which include more metabolically active organisms than abundant taxa (Lynch and Neufeld, 2015; Wu et al, 2017). Recent studies have compared the composition and dynamics of abundant and rare bacterioplankton communities in sea waters (Lindh et al, 2015; Zhang et al, 2018), epipelagic waters (Wu et al, 2017), subtropical bays (Mo et al, 2018), and lakes (Liu et al, 2015a). There is a significant knowledge gap in our understanding of the biogeography of abundant and rare bacterioplankton in rivers
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