Abstract
Understanding microbial community dynamics in the alpine cryosphere is an important step toward assessing climate change impacts on these fragile ecosystems and meltwater-fed environments downstream. In this study, we analyzed microbial community composition, variation in community alpha and beta diversity, and the number of prokaryotic cells and virus-like particles (VLP) in seasonal snowpack from two consecutive years at three high altitude mountain summits along a longitudinal transect across the European Alps. Numbers of prokaryotic cells and VLP both ranged around 104 and 105 per mL of snow meltwater on average, with variation generally within one order of magnitude between sites and years. VLP-to-prokaryotic cell ratios spanned two orders of magnitude, with median values close to 1, and little variation between sites and years in the majority of cases. Estimates of microbial community alpha diversity inferred from Hill numbers revealed low contributions of common and abundant microbial taxa to the total taxon richness, and thus low community evenness. Similar to prokaryotic cell and VLP numbers, differences in alpha diversity between years and sites were generally relatively modest. In contrast, community composition displayed strong variation between sites and especially between years. Analyses of taxonomic and phylogenetic community composition showed that differences between sites within years were mainly characterized by changes in abundances of microbial taxa from similar phylogenetic clades, whereas shifts between years were due to significant phylogenetic turnover. Our findings on the spatiotemporal dynamics and magnitude of variation of microbial abundances, community diversity, and composition in surface snow may help define baseline levels to assess future impacts of climate change on the alpine cryosphere.
Highlights
The alpine cryosphere is among the ecosystems that are the most affected by climate change
We set out to characterize spatiotemporal variation in microbial abundance, community composition, and diversity associated with seasonal surface snow in high altitudes of the European Alps, as a first step toward establishing a baseline for natural variation of microbial communities in these environments
Prokaryotic cells and virus-like particles (VLP) occurred in similar numbers ranging between 104 and 105 per mL of snow meltwater on average, with relatively little—albeit occasionally significant— variation between sites and years within one order of magnitude
Summary
The alpine cryosphere is among the ecosystems that are the most affected by climate change. In regions like the European Alps, surface air temperatures have increased at a faster rate over the past decades compared to the global average (Hock et al, 2019). The total glacier volume in the European Alps is predicted to decrease by 63–94% compared to present-day levels by the end of this century (Zekollari et al, 2019). Snow cover duration and snow mass are projected to decline by 30–80% and 10–40%, respectively, over the same time period, while winter precipitation extremes will occur more frequently Overall, these changes are expected to alter the amount, quality, and seasonality of runoff (Hock et al, 2019). As mountain snow and ice are important sources of freshwater for downstream environments like rivers and lakes, these changes can have far reaching consequences for biogeochemical processes and biodiversity on a larger scale (Boetius et al, 2015; Hotaling et al, 2017; Hock et al, 2019; Ren et al, 2019; Zhou et al, 2019; Elser et al, 2020)
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