Multifaceted aspects of synchrony between freshwater prokaryotes and protists

Abstract

Community composition of freshwater prokaryotes and protists varies through time. Few studies contemporarily investigate temporal variation of these freshwater communities for more than 1 year. We compared the temporal patterns of prokaryotes and protists in three distinct habitats for 4 years (2014–2017) in Lake Tovel, a cold‐water lake. This lake showed a marked temperature increase in 2017 linked to altered precipitation patterns. We investigated whether microbial communities reflected this change across habitats and whether changes occurred at the same time and to the same extent. Furthermore, we tested the concept of hydrological year emphasizing the ecological effect of water renewal on communities for its explanatory power of community changes. Microbe diversity was assessed by Illumina sequencing of the V3–V4 hypervariable region of the 16S rRNA gene and 18S rRNA gene, and we applied co‐inertia analysis and asymmetric eigenvector maps modelling to infer synchrony and temporal patterns of prokaryotes and protists. When considering community composition, microbes were invariable in synchrony across habitats and indicated a temporal gradient linked to decreasing precipitation; however, when looking at temporal patterns, the extent of synchrony was reduced. Small‐scale patterns were similar across habitats and microbes and linked to seasonally varying environmental variables, while large‐scale patterns were different and partially linked to an ecosystem change as indicated by increasing water transparency and temperature and decreasing dissolved oxygen. Our advanced statistical approach outlined the multifaceted aspect of synchrony when linked to community composition and temporal patterns.

Do inferences about freshwater phytoplankton communities change when based on microscopy or high‐throughput sequencing data?

“…We attributed this year effect to a change in the lake’s hydrology. The years from 2014 to 2017 showed a decreasing gradient in precipitation (Obertegger et al, 2019). Furthermore during the year 2017, Lake Tovel experienced a shift from nival to pluvial origin of its waters, leading to whole lake warming and increased stability of the water column (Flaim et al 2019).…”

“…Temperature values taken with a multiparametric probe (Idronaut Ocean Seven 316 Plus) at 1‐m intervals were averaged within the respective profile for the littoral (0–4 m), pelagic (0–20 m), and deep hypolimnion (30–35 m). Precipitation (mm), provided from the onshore meteorological station, and water level change (cm) were averaged for the 10 days before sampling as in Obertegger et al (2019). Total yearly precipitation (mm) at Lake Tovel showed a decreasing gradient from 2014 to 2017 (2014: 1867 mm; 2015: 1027 mm; 2016: 1110 mm; 2017: 978 mm; Obertegger et al, 2018).…”

“…Furthermore, we focused on three distinct habitats within Lake Tovel that reflect a varying degree of hydrological stability, light climate, and community composition; the littoral is the most hydrologically unstable because it receives >80% of the lake’s water inflow through underground springs (Borsato & Ferretti, 2006) while the hypolimnion is considered the most stable because of its sheltered position from the in‐ and outflow, and the pelagic is intermediate (Obertegger et al, 2018). Furthermore, the littoral shows highest, the hypolimnion lowest, and the pelagic intermediate light transparency (Obertegger, Pindo, & Flaim, 2019), an important parameter for phytoplankton (Richardson, Beardall, & Raven, 1983). Planktonic communities respond to hydrological stability (Winder & Hunter, 2008; Shade, Jones, & McMahon, 2008; Obertegger et al, 2018) and changing light climate (Edwards, Thomas, Klausmeier, & Litchman, 2016), and varying community composition in different habitats should be equally indicated by microscopy and HTS data.…”

Multi-annual comparisons of summer and under-ice phytoplankton communities of a mountain lake

“…Phytoplankton and heterotrophic bacteria are linked in multiple ways such as competition for nutrients, use of algal exudates, decomposition of decaying algae, or mixotrophic predation of algae on bacteria (Bižić-Ionescu et al, 2014;Salcher, 2014;Unrein et al, 2014;Ivanova et al, 2018). While prokaryotes and protists are in temporal synchrony in Lake Tovel during the ice-free period (Obertegger et al, 2019), this study indicated temporal differences. Small environmental differences in under-ice conditions can have huge impacts on phytoplankton composition (Vehmaa & Salonen, 2009), and we suggest that year-to-year variability in under-ice environmental conditions and biotic interactions (e.g.…”

Small freshwater ecosystems with dissimilar microbial communities exhibit similar temporal patterns

“…However, longer term studies eventually reflecting seasonal patterns are still very rare (Gilbert et al, 2012; Karl & Church, 2014; Linz et al, 2017). Furthermore, most microbial diversity studies, including temporal surveys, focus on either archaeal, bacterial or eukaryotic communities, but an integrated view of how the two change with time, eventually revealing underlying biotic interactions, are extremely scarce and restricted to large environments such as oceans and lakes (Biller et al, 2018; Obertegger et al, 2019; Steele et al, 2011). Yet, differences in overall metabolic capabilities, physiology, trophic features, generation time and dispersal might be reflected in distinct temporal patterns of bacteria and archaea vs. microbial eukaryotes.…”