Abstract
BackgroundMicroorganisms in rivers and lakes are essential for nutrient recycling in aquatic ecosystems. Understanding the ecological processes shaping microbial communities is of crucial importance for aquatic microbial ecology and biogeography. However, the diversity of microorganisms and the forces that control this diversity are poorly understood. This is particularly true within the framework of the river-lake continuum in arid regions.ResultsUsing a whole catchment-sampling effort, we explored biogeographical patterns and mechanisms of microbial community (bacteria and archaea) assembly within the catchment of the largest inland once freshwater lake (Lake Bosten) in China. Water samples from headstream tributaries, the mainstream of the River Kaidu to downstream Lake Bosten were characterized using amplicon sequencing of 16S rRNA genes. Higher α-diversity was found in mainstream of River Kaidu and in the tributaries compared with Lake Bosten. And the microbial community composition was also significantly different between the lake and its connected river habitats. Canonical correspondence analysis demonstrated that salinity and total suspended solids were the most important environmental factors shaping the community variations. Overall, pure environmental and pure spatial factors explained 13.7 and 5.6% of the community variation, respectively, while 32.0% of the variation was explained by combined environmental and spatial variables. These observations suggested that spatially structured environmental variations mainly shaped the microbial biogeography in this region. Both deterministic and stochastic processes influenced the microbial community assembly in river and lake habitats, and the stochastic pattern was particularly pronounced for microbiome in river habitat. Co-occurrence network analysis revealed more abundant and complicated correlations among frequently occurred taxa in lake habitat compared with the river habitat, implying that ecological multispecies interactions (e.g., competition) shaped lake microbial community structures.ConclusionsOur findings demonstrate an ecological succession along the river-lake continuum of microbial communities across the largest inland once freshwater lake basin in China, and highlight the effects of spatially structured environmental factors on regional microbial β-diversity and species interactions on local community assembly.
Highlights
Microorganisms in rivers and lakes are essential for nutrient recycling in aquatic ecosystems
The rarefaction curves of richness approached an asymptote after 80% reads were calculated, which indicated that our sequencing depth was sufficient (Additional file 2: Fig. S2)
Spearman correlation analysis showed that the four microbial α-diversity indices were significantly positively correlated to total suspended solids (TSS), total phosphorus (TP) and dissolved oxygen (DO), and significantly negatively correlated to total dissolved solids (TDS), water temperature (WT), pH and dissolved organic carbon (DOC) (Additional file 3: Fig. S3)
Summary
Microorganisms in rivers and lakes are essential for nutrient recycling in aquatic ecosystems. Diverse and functionally important organisms on Earth [4], microorganisms in aquatic ecosystems can response to environmental changes quickly, and have a key role in ecological processes including the biodegradation of pollutants that impact water quality [5]. Streams and rivers link terrestrial, lotic and lentic systems with their lake counterparts and supply numerous ecosystem services such as material transport, biogeochemical nutrient cycling and habitats for biota (including microbes) They provide potable water for public consumption and supply water for irrigation and industry, which is important in arid and semi-arid regions (occupying nearly 40% of the Earth’s land surface). How and to what extend do freshwater streams and rivers affect microbial communities in their salinized downstream lakes have still not been comprehensively investigated This limits our understanding of ecosystem structures and functions and hindering effective predicting the responses of lake ecosystems to environmental change
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