Flood pulse regulation of bacterioplankton community composition in an Amazonian floodplain lake

Abstract

Understanding spatial and temporal dynamics of microbial communities is a central challenge in microbial ecology since microorganisms play a key role in ecosystem functioning and biogeochemical cycles. Amazonian aquatic systems comprise a dynamic mosaic of heterogeneous habits but are understudied and there is limited information about the mechanisms that shape bacterial community composition (BCC). There is a consensus that environmental selection (species sorting) and dispersal processes (source–sink dynamics) act in concert to shape the composition of these communities, but the relative importance of each mechanism may vary dramatically through time and between systems. Applying 16S rRNA gene amplicon high-throughput sequencing, we studied factors and processes that modulate BCC in an Amazonian floodplain lake and used source-tracking models to trace the main dispersal sources of microorganisms in the whole floodplain system during a full hydrological cycle. Our source-tracking models indicated that dispersal processes were predominant, explaining most of the BCC variability throughout the study period. We observed more sources contributing to the sink community during the falling water than rising water period, when contributions from the Solimões River dominated. There was a clear seasonal pattern in BCC, closely related to environmental variables, suggesting that the successful establishment of dispersing bacteria also depends on environmental filtering that is linked to water flow. In summary, source–sink dynamics and species sorting were strongly affected by water exchange and connectivity with the main river that varied throughout the flood pulse cycle. Our results demonstrated the influence of lateral transport and temporal dynamics on BCC in Amazonian floodplain lakes that could ultimately impact regional carbon budgets and biogeochemical cycles. © 2018 John Wiley & Sons Ltd