Abstract
Cyanobacteria are important primary producers in temperate freshwater ecosystems. However, studies on the seasonal and spatial distribution of cyanobacteria in deep lakes based on high-throughput DNA sequencing are still rare. In this study, we combined monthly water sampling and monitoring in 2019, amplicon sequence variants analysis (ASVs; a proxy for different species) and quantitative PCR targeting overall cyanobacteria abundance to describe the seasonal and spatial dynamics of cyanobacteria in the deep hard-water oligo-mesotrophic Lake Tiefer See, NE Germany. We observed significant seasonal variation in the cyanobacterial community composition (p < 0.05) in the epi- and metalimnion layers, but not in the hypolimnion. In winter—when the water column is mixed—picocyanobacteria (Synechococcus and Cyanobium) were dominant. With the onset of stratification in late spring, we observed potential niche specialization and coexistence among the cyanobacteria taxa driven mainly by light and nutrient dynamics. Specifically, ASVs assigned to picocyanobacteria and the genus Planktothrix were the main contributors to the formation of deep chlorophyll maxima along a light gradient. While Synechococcus and different Cyanobium ASVs were abundant in the epilimnion up to the base of the euphotic zone from spring to fall, Planktothrix mainly occurred in the metalimnetic layer below the euphotic zone where also overall cyanobacteria abundance was highest in summer. Our data revealed two potentially psychrotolerant (cold-adapted) Cyanobium species that appear to cope well under conditions of lower hypolimnetic water temperature and light as well as increasing sediment-released phosphate in the deeper waters in summer. The potential cold-adapted Cyanobium species were also dominant throughout the water column in fall and winter. Furthermore, Snowella and Microcystis-related ASVs were abundant in the water column during the onset of fall turnover. Altogether, these findings suggest previously unascertained and considerable spatiotemporal changes in the community of cyanobacteria on the species level especially within the genus Cyanobium in deep hard-water temperate lakes.
Highlights
Photosynthetic microorganisms function as the basis of food chains in aquatic environments and are of importance to the ecosystem and to humans
In Lake Vechten (Netherlands; max. depth 11 m), highthroughput sequencing of every meter in the water column revealed changes in bacteria community composition to be driven by lake oxygenation and sulphidic conditions (Diao et al, 2017)
Temperature and dissolved oxygen (DO) in the water column of Lake Tiefer See (Figures 2A,B) showed that in 2019 thermal stratification began in early April and continued beyond late November
Summary
Photosynthetic microorganisms function as the basis of food chains in aquatic environments and are of importance to the ecosystem and to humans. Advances in sequencing techniques with improved taxonomic resolution have provided additional understanding to the seasonal succession of bacterioplankton communities in the upper waters of lakes (Okazaki and Nakano, 2016; Diao et al, 2017; Salmaso et al, 2018). Except for Salmaso et al (2018) that sequenced bacterial 16S rRNA gene to analyze annual bacterioplankton community composition in the euphotic zone (up to 21 m water depth) of Lake Garda Water depth 350 m), there are, to the best of our knowledge, no spatiotemporal comparative studies of cyanobacterial succession across different water layers and seasons in deep temperate lakes and in combination with cyanobacteria-specific marker gene analysis Except for Salmaso et al (2018) that sequenced bacterial 16S rRNA gene to analyze annual bacterioplankton community composition in the euphotic zone (up to 21 m water depth) of Lake Garda (max. water depth 350 m), there are, to the best of our knowledge, no spatiotemporal comparative studies of cyanobacterial succession across different water layers and seasons in deep temperate lakes and in combination with cyanobacteria-specific marker gene analysis
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
