Elevation and micro-topography determine microbial community composition in an arctic-alpine ecosystem via shifts in long-term temperature and soil moisture regimes

Arctic-alpine ecosystems are a prominent model to study the effects of global warming on the biogeography of organisms, and their functional responses. Only little attention was given to the fact that alpine areas are highly heterogeneous. In this study, we analyzed the influence of micro-environmental variables on the microbial community composition along spatial gradients of micro-topography, elevation, and continentality. Surface soil samples were taken at four elevations in two climate regions of the Norwegian Scandes and from four micro-topographic positions. We used a biogeographic approach to correlate 16S rRNA gene amplicon data with the long-term environmental datasets (moisture and temperature) and found significant differences of the microbial community composition along micro-topographic and the elevational gradients, but not with continentality. Further, our analysis enabled us to identify “ecological fingerprints” for each phylogenetic group and their respective temperature and soil moisture thresholds. Taking together, we found that phylogenetic groups enriched in depressions are mainly impacted by the exact threshold of field capacity. Near-ground temperatures were most expressed to determine phylogenetic groups changing with elevation. Further, our results indicate, that microbes are rather responding to 5-year long-term environmental conditions than to 1 or 2-years conditions, indicating that despite short generation times, microbes do not adapt as quick as often thought to temperature changes. This gives implications that global warming studies should be connected with long-term data, because of a high resilience of microbes to short-term variability in arctic-alpine ecosystems.