02223nas a2200205   4500008004100000245012900041210006900170260001200239300001200251490000700263520146400270100001701734700002401751700002401775700002501799700002201824700003301846700001501879856012301894       2014                        eng d00aCharacterization of Growing Bacterial Populations in McMurdo Dry Valley Soils through Stable Isotope Probing with 18O-water.0 aCharacterization of Growing Bacterial Populations in McMurdo Dry  c08/2014  a415-4250 v893 aSoil microbial communities of the McMurdo Dry Valleys, Antarctica (MDV) contain representatives from at least fourteen bacterial phyla. However, given low rates of microbial activity, it is unclear whether this richness represents functioning rather than dormant members of the community. We used stable isotope probing (SIP) with (18) O-water to determine if microbial populations grow in MDV soils. Changes in the microbial community were characterized in soils amended with H2 (18) O and H2 (18) O-organic matter. Sequencing the 16S rRNA genes of the heavy and light fractions of the bacterial community DNA shows that DNA of microbial populations was labeled with (18) O-water, indicating these micro-organisms grew in the MDV soils. Significant differences existed in the community composition of the heavy and light fractions of the H2 (18) O and H2 (18) O-organic matter amended samples (Anosim P < 0.05 of weighted Unifrac distance). Control samples and the light DNA fraction of the H2 (18) O amended samples were dominated by representatives of the phyla Deinococcus-Thermus, Proteobacteria, Planctomyces, Gemmatimonadetes, Actinobacteria and Acidobacteria, whereas Proteobacteria were more prevalent in the heavy DNA fractions from the H2 (18) O-water and the H2 (18) O-water-organic matter treatments. Our results indicate that SIP with H2 (18) O can be used to distinguish active bacterial populations even in this low organic matter environment.1 aSchwartz, E.1 aVan Horn, David, J.1 aBuelow, Heather, N.1 aGooseff, Michael, N.1 aBarrett, John, E.1 aTakacs-Vesbach, Cristina, D.1 aOkie, J.G.  uhttps://mcm.lternet.edu/content/characterization-growing-bacterial-populations-mcmurdo-dry-valley-soils-through-stable02505nas a2200193   4500008004100000245011800041210006900159260001200228300001400240490000700254520178100261100002402042700001502066700002402081700002502105700002202130700003302152856012602185       2014                        eng d00aSoil microbial responses to increased moisture and organic resources along a salinity gradient in a polar desert.0 aSoil microbial responses to increased moisture and organic resou  c05/2014  a3034-30430 v803 aMicrobial communities in extreme environments often have low diversity and specialized physiologies suggesting a limited resistance to change. The McMurdo Dry Valleys (MDV) are a microbially dominated, extreme ecosystem currently undergoing climate change-induced disturbances, including the melting of massive buried ice, cutting through of permafrost by streams, and warming events. These processes are increasing moisture across the landscape, altering conditions for soil communities by mobilizing nutrients and salts and stimulating autotrophic carbon inputs to soils. The goal of this study was to determine the effects of resource addition (water/organic matter) on the composition and function of microbial communities in the MDV along a natural salinity gradient representing an additional gradient of stress in an already extreme environment. Soil respiration and the activity of carbon-acquiring extracellular enzymes increased significantly (P < 0.05) with the addition of resources at the low- and moderate-salinity sites but not the high-salinity site. The bacterial community composition was altered, with an increase in Proteobacteria and Firmicutes with water and organic matter additions at the low- and moderate-salinity sites and a near dominance of Firmicutes at the high-salinity site. Principal coordinate analyses of all samples using a phylogenetically informed distance matrix (UniFrac) demonstrated discrete clustering among sites (analysis of similarity [ANOSIM], P < 0.05 and R > 0.40) and among most treatments within sites. The results from this experimental work suggest that microbial communities in this environment will undergo rapid change in response to the altered resources resulting from climate change impacts occurring in this region.1 aVan Horn, David, J.1 aOkie, J.G.1 aBuelow, Heather, N.1 aGooseff, Michael, N.1 aBarrett, John, E.1 aTakacs-Vesbach, Cristina, D.  uhttps://mcm.lternet.edu/content/soil-microbial-responses-increased-moisture-and-organic-resources-along-salinity-gradient