Abstract
Alpine lakes are considered pristine freshwater ecosystems and sensitive to direct and indirect changes in water temperature as induced by climate change. The bacterial plankton constitutes a key component in the water column and bacterial metabolic activity has direct consequences for water quality. In order to understand bacterial response to global temperature rise in five alpine lakes located in the Austrian Alps (1700–2188 m a.S.L.) water temperature was compared within a decadal period. Depth-integrated samples were characterized in community composition by 16S rDNA deep-amplicon sequencing early [56 ± 16 (SD) days after ice break up] and later (88 ± 16 days) in the growing season. Within the 10 years period, temperature rise was observed through reduced ice cover duration and increased average water temperature. During the early growing season, the average water temperature recorded between circulation in spring until sampling date (WAS), and the day of autumn circulation, as well as chemical composition including dissolved organic carbon influenced bacterial community composition. In contrast, only nutrients (such as nitrate) were found influential later in the growing season. Metabolic theory of ecology (MTE) was applied to explain the dependence of taxonomic richness on WAS in mathematical terms. The calculated activation energy exceeded the frequently reported prediction emphasizing the role of WAS during early growing season. Accordingly, the relative abundance of predicted metabolism related genes increased with WAS. Thus, the dominant influence of temperature after ice break up could be explained by overall climate change effects, such as a more intense warming in spring and an overall higher amplitude of temperature variation.
Highlights
Climate change, which is mainly caused by anthropogenic activities, is a global issue
Five alpine lakes in the “Niedere Tauern” region of the eastern Alps, Austria (Weckström et al, 2016) [Unterer Giglachsee (GIG), Moaralmsee (MOA), Oberer Landschitzsee (OLA), Twenger Almsee (TWA), and Wirpitschsee (WIR)], were selected as sampling sites (Figure 1A)
Since multivariate ordination analysis revealed a significant influence of WAS and circulation in autumn (CiA) on operational taxonomic units (OTUs) abundance (Figure 3) and richness and diversity were found significantly related to water temperature (Table 2 and Supplementary Table S4) in the early growing season, we were interested to see to which extent Metabolic theory of ecology (MTE) predicts higher richness and diversity with increasing water temperature
Summary
Climate change, which is mainly caused by anthropogenic activities, is a global issue. Alpine-Lake Microbiome Response to Climate average (Beniston et al, 1997; Sommaruga-Wögrath et al, 1997; Parker et al, 2008). The alpine lake ecosystem is affected by global climate change through thawing of ice, melting of frozen soils, altered snow packing, shortened ice cover duration, and increasing summer water temperatures, thereby affecting biodiversity and functioning of water cycles and the microclimate (Holzapfel and Vinebrooke, 2005; Parker et al, 2008). Mountain lake ecosystems are highly sensitive to global warming, functioning as sentinels of climate change (Kamenik et al, 2001; Adrian et al, 2009; Williamson et al, 2009). Various studies have documented the responses of plant and animal biodiversity to temperature, less studies have examined microbial responses to climate warming (Zhou et al, 2016; Guo et al, 2018)
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