Abstract
The assessment of distribution patterns or zonation of planktonic microbes along the water column is a crucial step to interpret their function in the ecosystem. In lakes without seasonal thermal stratification or polymictic systems such as high elevation tropical lakes, planktonic bacterial taxa are probably homogeneously distributed in the water column in contrast to what is known for thermally stratified lakes. However, we know little about bacterial distribution patterns in polymictic lakes and their relation to environmental gradients other than temperature. Here we assessed the diversity, microdiversity, and bacterial community composition at different discrete depths in three high elevation lakes (4,400–4,550 m above sea level) from the Andean plateau to test whether bacterial zonation patterns exist along the water column. For this objective, we analyzed bulk DNA and the putatively active fraction (cDNA) of the 16S rRNA gene. Although a clear gradient of temperature and oxygen was not detected along the water column, a significant vertical spatial zonation of the bacterial communities was present in two out of the three lakes, with microdiversity contributing to such pattern. Our results provide a reference for understanding how changing environmental conditions could affect high elevation aquatic ecosystems, particularly when warming is amplified with elevation, accelerating changes in hydrological regimes and biodiversity. Finally, our results highlight the importance of incorporating the whole water column in ecological studies of aquatic ecosystems lacking temporal or permanent thermal stratification.
Highlights
The assessment of distribution patterns or zonation of planktonic microbes is crucial to understand the mechanisms shaping microbial communities and their function in the ecosystem (Ladau and Eloe-Fadrosh, 2019)
In general for all lakes, chlorophyll-a showed the largest variation in the water column with the highest value found in PIA followed by COTA and CHUN
CHUN had the largest variation in oxygen concentration, dissolved organic carbon (DOC) and dissolved nitrogen (DN; mean = 4.5 mg L−1, coefficient of variation (CV) = 68.9%; Supplementary Table 1) along the water column
Summary
The assessment of distribution patterns or zonation of planktonic microbes is crucial to understand the mechanisms shaping microbial communities and their function in the ecosystem (Ladau and Eloe-Fadrosh, 2019). The existence of a spatial change in the structure of a microbial community of thermally stratified waters is expected, Bacterioplankton Zonation in Polymictic Lakes because it is well established that microbes respond to gradients of temperature, oxygen, methane, and nutrient concentrations, among other variables (Taipale et al, 2009; Dodds et al, 2019). Climate change is known to alter organisms dispersal and nutrient loads with environmental consequences such as shifts in productivity and food web structure (Cavicchioli et al, 2019) Such changes could be more pronounced in high-elevation lakes since warming is amplified with elevation (Pepin et al, 2015)
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