Abstract
Serving as “natural laboratories”, altitudinal gradients can be used to study changes in the distribution of microorganisms in response to changing environmental conditions that typically occur over short geographical distances. Besides, rhizosphere zones of plants are known to be hot-spots for microbial diversity and to contain different microbial communities when compared with surrounding bulk soil. To discriminate the effects of altitude and plants, we investigated the microbial communities in the rhizosphere of Ranunculus glacialis and bulk soil along a high-alpine altitudinal gradient (2,600–3,400 m a.s.l.). The research area of this study was Mount (Mt.) “Schrankogel” in the Central Alps of Tyrol (Austria). Our results point to significantly different microbial diversities and community compositions in the different altitudinal belts. In the case of prokaryotes, environmental parameters could explain 41% of the total variation of soil communities, with pH and temperature being the strongest influencing factors. Comparing the effects derived from fraction (bulk vs. rhizosphere soil) and environmental factors, the effects of the roots of R. glacialis accounted for about one third of the explained variation. Fungal communities on the other hand were nearly exclusively influenced by environmental parameters accounting for 37.4% of the total variation. Both, for altitudinal zones as well as for bulk and rhizosphere fractions a couple of very specific biomarker taxa could be identified. Generally, the patterns of abundance of several taxa did not follow a steady increased or decreased trend along the altitudinal gradient but in many cases a maximal or minimal occurrence was established at mid-altitudes (3,000–3,100 m). This mid-altitudinal zone is a transition zone (the so-called alpine-nival ecotone) between the (lower) alpine grassland/tundra zone and the (upper) sparsely vegetated nival zone and was shown to correspond with the summer snow line. Climate change and the associated increase in temperature will shift this transition zone and thus, might also shift the described microbial patterns and biomarkers.
Highlights
Mountain habitats are characterized by altitudinal gradients and dramatic climatic changes over short geographic distances, making them to ideal natural laboratories (Körner, 2007)
Chloroflexi, Proteobacteria and Candidate division WPS-2 decreased at mid-altitudes
Archaea were represented by Nitrososphaera sp. only with a relative abundance of 1.3% and 0.5% in bulk and rhizosphere soils, respectively
Summary
Mountain habitats are characterized by altitudinal gradients and dramatic climatic changes over short geographic distances, making them to ideal natural laboratories (Körner, 2007). The main parameters driving soil development in alpine environments are climate, biological factors, parent material, topography, and time (Donhauser and Frey, 2018). Comparable to arctic regions, low temperatures, which can drop below zero degrees Celsius, and long periods of snow cover limit biological processes and microbial life in mountain soils. Global warming has increased the global mean temperature by up to 0.7◦C in the last 100 years (Jones and Moberg, 2003), while in the Alps warming of 1.5◦C has occurred over the same period (Böhm et al, 2001) This above-average warming, coupled with a high sensitivity of Alpine ecosystems, make the Alpine region one of the most vulnerable regions in Europe
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