Ice-free soils in the McMurdo Dry Valleys (MDVs) of Antarctica select for taxa able to cope with the extremely challenging environmental conditions. The MDV soils low biotic complexity makes it an exceptional ecosystem to investigate environmental and spatial influences on bacterial community structure and diversity. Water tracks are annually wetted habitats in the cold-arid soils that form briefly each summer with moisture sourced from snow melt, ground ice thaw, and atmospheric deposition via deliquescence and vapor flow into brines. Water tracks represent a considerable area (~5-10 km2) of the MDV terrestrial ecosystem, an area that is expected to increase with climate-mediated changes. Water tracks are different from “typical” soil environments in the MDV, and their environmental stressors might be different than in dominant dry soils. Previous biological investigations of Dry Valley water tracks are limited in number and have disagreeing conclusions. The goal of this study was to determine how changes in the physical and chemical environment of water tracks change the structure and diversity of microorganisms within them. Twenty perennially dry and transiently wetted soil samples (off,- and on-track, respectively) were collected and analyzed to assess abiotic influences on microbial composition and diversity. Soil bacterial biodiversity was measured through cultivation independent 16S rRNA gene sequencing. Gravimetric water content (GWC) was calculated to obtain soil moisture values for each sample. Electrical conductivity (EC), a proxy of salinity, was also measured for each sample. In order to test the hypotheses of chemical and spatial influences on community structure and diversity, statistical tests of inter- and intra-site relationships and differences using PERMANOVA tests, redundancy analysis with variation partitioning, and Mantel tests of correlation were undertaken.
Results/Conclusions
Multidimensional scaling and PERMANOVA results revealed significant clustering of microbial communities between on and off water track samples and at different locations; however, there were no significant differences in microbial diversity, richness, or evenness. Of the tested variables, we found salinity to be the best predictor of community composition, with Bacteroidetes concentrated at higher levels of salinity and Actinobacteria in low-saline soils. Soil moisture in this study was significantly higher within water track samples, yet it was not meaningfully correlated with community composition. Results from this study suggest water track formation significantly alter the arid soil microbial communities in Antarctica soils, and therefore possibly ecosystem functions.