Abstract
In aquatic systems, microbes likely play critical roles in biogeochemical cycling and ecosystem processes, but much remains to be learned regarding microbial biogeography and ecology. The microbial ecology of mountain lakes is particularly understudied. We hypothesized that microbial distribution among lakes is shaped, in part, by aquatic plant communities and the biogeochemistry of the lake. Specifically, we investigated the associations of yellow water lilies (Nuphar polysepala) with the biogeochemistry and microbial assemblages within mountain lakes at two scales: within a single lake and among lakes within a mountain range. We first compared the biogeochemistry of lakes without water lilies to those colonized to varying degrees by water lilies. Lakes with >10% of the surface occupied by water lilies had lower pH and higher dissolved organic carbon than those without water lilies and had a different microbial composition. Notably, cyanobacteria were negatively associated with water lily presence, a result consistent with the past observation that macrophytes outcompete phytoplankton and can suppress cyanobacterial and algal blooms. To examine the influence of macrophytes on microbial distribution within a lake, we characterized microbial assemblages present on abaxial and adaxial water lily leaf surfaces and in the water column. Microbial diversity and composition varied among all three habitats, with the highest diversity of microbes observed on the adaxial side of leaves. Overall, this study suggests that water lilies influence the biogeochemistry and microbiology of mountains lakes.
Highlights
Bacteria play critical roles in mediating ecosystem processes in aquatic systems (Newton et al, 2011), including the cycling of biologically important nutrients (Clark et al, 2018)
To determine whether lakes with and without water lilies exhibited differences in biogeochemistry, we measured temperature, pH, dissolved oxygen (DO), dissolved organic carbon (DOC), and major cations and anions, and used mixed effects models to identify measures that differed based on water lily abundance while considering the nested nature of our sampling design
We found that pH, and to a lesser extent, DO and sulfate, were lower in lakes with many water lilies and DOC was higher in lakes with many water lilies (>10% coverage) as compared to lakes without water lilies
Summary
Bacteria play critical roles in mediating ecosystem processes in aquatic systems (Newton et al, 2011), including the cycling of biologically important nutrients (Clark et al, 2018). Much remains to be studied regarding microbial ecology and biogeography, especially in high elevation lakes. Despite their underrepresentation in the literature, mountain lakes are important targets for study due to their sensitivity to ongoing environmental change Aquatic microbes may be affected by temperature (Lindström et al, 2005), the concentration and source of dissolved organic carbon (DOC) (Kritzberg et al, 2006), and nutrients such as nitrogen and phosphorus (Logue et al, 2012). The effects of these factors on microbial assemblages are not well defined, especially in mountain lakes
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