Local Environmental Factors Drive Divergent Grassland Soil Bacterial Communities in the Western Swiss Alps

Abstract

Mountain ecosystems are characterized by a diverse range of climatic and topographic conditions over short distances and are known to shelter a high biodiversity. Despite important progress, still little is known on bacterial diversity in mountain areas. Here, we investigated soil bacterial biogeography at more than 100 sampling sites randomly stratified across a 700-km 2 area with 2,200-m elevation gradient in the western Swiss Alps. Bacterial grassland communities were highly diverse, with 12,741 total operational taxonomic units (OTUs) across 100 sites and an average of 2,918 OTUs per site. Bacterial community structure was correlated with local climatic, topographic, and soil physicochemical parameters with high statistical significance. We found pH (correlated with % CaO and % mineral carbon), hydrogen index (correlated with bulk gravimetric water content), and annual average number of frost days during the growing season to be among the groups of the most important environmental drivers of bacterial community structure. In contrast, bacterial community structure was only weakly stratified as a function of elevation. Contrasting patterns were discovered for individual bacterial taxa. Acidobacteria responded both positively and negatively to pH extremes. Various families within the Bacteroidetes responded to available phosphorus levels. Different verrucomicrobial groups responded to electrical conductivity, total organic carbon, water content, and mineral carbon contents. Alpine grassland bacterial communities are thus highly diverse, which is likely due to the large variety of different environmental conditions. These results shed new light on the biodiversity of mountain ecosystems, which were already identified as potentially fragile to anthropogenic influences and climate change. IMPORTANCEThis article addresses the question of how microbial communities in alpine regions are dependent on local climatic and soil physicochemical variables. We benefit from a unique 700-km 2 study region in the western Swiss Alps region, which has been exhaustively studied for macro-organismal and fungal ecology, and for topoclimatic modeling of future ecological trends, but without taking into account soil bacterial diversity. Here, we present an in-depth biogeographical characterization of the bacterial community diversity in this alpine region across 100 randomly stratified sites, using 56 environmental variables. Our exhaustive sampling ensured the detection of ecological trends with high statistical robustness. Our data both confirm previously observed general trends and show many new detailed trends for a wide range of bacterial taxonomic groups and environmental parameters.

Patterns of Soil Bacterial Richness and Composition Tied to Plant Richness, Soil Nitrogen, and Soil Acidity in Alpine Tundra

“…The range in pH seen at our site was almost half of the range in acidity seen in the 700 km alpine transect conducted by Yashiro et al (2016). As found here, pH was the strongest environmental correlate in their study.…”

Substrate and spatial variables are major determinants of fungal community in karst caves in Southwest China

“…Spatial and environmental variables are critical elements driving microbial diversity and community composition in other environments, such as forests (Gao et al, 2017;Tedersoo et al, 2014), grasslands (LeBlanc, Kinkel, & Kistler, 2015;Yashiro et al, 2016) and oceans (Li et al, 2017;Sunagawa et al, 2015). However, the influence of spatial and environmental variables on cave fungal communities has rarely been studied, except for nutrients or carbon source (Carmichael et al, 2015;Cloutier et al, 2017).…”

Soil protist diversity in the Swiss western Alps is better predicted by topo-climatic than by edaphic variables

“…Nevertheless, a enhanced drainage reduces the likelihood of water-logging which would select for very specialized protists tolerating anoxia and generally would lead to lower diversity. Soil pH is well known as a major driver of microbial diversity, including bacteria (Santoyo, Hernandez-Pacheco, Hernandez-Salmeron, & Hernandez-Leon, 2017; Yashiro et al, 2016), fungi (Noyce et al, 2016; Pellissier et al, 2014; Zhang, Jia, & Yu, 2016) and protists (Bates et al, 2013; Dupont et al, 2016). The relationship between pH and protist diversity was significant only for three groups, being negative for two groups of phagotrophs (Spirotrichea and Sarcomonadida) and positive for Chlorophyceae.…”

“…The C/N ratio was calculated from the total organic carbon and nitrogen percentages measured by ROCK EVAL pyrolysis (Vinci Technologies, Ruell-Malmaison, France) and combustion infrared spectroscopy (Carlo Erba CNS2500 CHN), respectively. See Yashiro et al (2016) and Buri et al (2017) for more details.…”