@article {4940, title = {McMurdo Dry Valley lake edge {\textquoteleft}moats{\textquoteright}: The ecological intersection between terrestrial and aquatic polar desert habitat}, journal = {Antarctic Science}, year = {2024}, month = {04/2024}, pages = {1 - 17}, abstract = {

Aquatic ecosystems - lakes, ponds and streams - are hotspots of biodiversity in the cold and arid environment of Continental Antarctica. Environmental change is expected to increasingly alter Antarctic aquatic ecosystems and modify the physical characteristics and interactions within the habitats that they support. Here, we describe physical and biological features of the peripheral \‘moat\’ of a closed-basin Antarctic lake. These moats mediate connectivity amongst streams, lake and soils. We highlight the cyclical moat transition from a frozen winter state to an active open-water summer system, through refreeze as winter returns. Summer melting begins at the lakebed, initially creating an ice-constrained lens of liquid water in November, which swiftly progresses upwards, creating open water in December. Conversely, freezing progresses slowly from the water surface downwards, with water at 1 m bottom depth remaining liquid until May. Moats support productive, diverse benthic communities that are taxonomically distinct from those under the adjacent permanent lake ice. We show how ion ratios suggest that summer exchange occurs amongst moats, streams, soils and sub-ice lake water, perhaps facilitated by within-moat density-driven convection. Moats occupy a small but dynamic area of lake habitat, are disproportionately affected by recent lake-level rises and may thus be particularly vulnerable to hydrological change.

}, keywords = {LTER-MCM, connectivity, ecosystem, ice, microbial mats, transition}, issn = {0954-1020}, doi = {10.1017/S0954102024000087}, url = {https://www.cambridge.org/core/journals/antarctic-science/article/mcmurdo-dry-valley-lake-edge-moats-the-ecological-intersection-between-terrestrial-and-aquatic-polar-desert-habitats/31D94DD51E651603482A3AE6E8A52A57}, author = {Stone, Michael S. and Devlin, Shawn and Ian Hawes and Kathleen A. Welch and Michael N. Gooseff and Cristina D. Takacs-Vesbach and Rachael M. Morgan-Kiss and Byron Adams and John E. Barrett and John C. Priscu and Peter T. Doran} } @article {4928, title = {Remotely characterizing photosynthetic biocrust in snowpack-fed microhabitats of Taylor Valley, Antarctica}, journal = {Science of Remote Sensing}, year = {2024}, month = {02/2024}, pages = {100120}, abstract = {

Microbial communities are the primary drivers of carbon cycling in the McMurdo Dry Valleys of Antarctica. Dense microbial mats, consisting mainly of photosynthetic cyanobacteria, occupy aquatic areas associated with streams and lakes. Other microbial communities also occur at lower densities as patchy surface biological soil crusts (hereafter, biocrusts) across the terrestrial landscape. Multispectral satellite data have been used to model microbial mat abundance in high-density areas like stream and lake margins, but no previous studies have investigated the lower detection limits of biocrusts. Here, we describe remote sensing and field-based survey and sampling approaches to study the detectability and distribution of biocrusts in the McMurdo Dry Valleys. Using a combination of multi- and hyperspectral tools and spectral linear unmixing, we modeled the abundances of biocrust in eastern Taylor Valley. Our spectral approaches can detect low masses of biocrust material in laboratory microcosms down to biocrust concentrations of 1\% by mass. These techniques also distinguish the spectra of biocrust from both surface rock and mineral signatures from orbit. We found that biocrusts are present throughout the soils of eastern Taylor Valley and are associated with diverse underlying soil communities. The densest biocrust communities identified in this study had total organic carbon 5x greater than the content of typical arid soils. The most productive biocrusts were located downslope of melting snowpacks in unique soil ecosystems that are distinct from the surrounding arid landscape. There are similarities between the snowpack and stream sediment communities (high diversity of soil invertebrates) as well as their ecosystem properties (e.g., persistence of liquid water, high transfer of available nutrients, lower salinity from flushing) compared to the typical arid terrestrial ecosystem of the dry valleys. Our approach extends the capability of orbital remote sensing of photosynthetic communities out of the aquatic margins and into the drier soils which comprise most of this landscape. This interdisciplinary work is critical for measuring and monitoring terrestrial carbon stocks and predicting future ecosystem dynamics in this currently water-limited but increasingly dynamic Antarctic landscape, which is particularly climate-sensitive and difficult to access.

}, keywords = {LTER-MCM, Antarctica, biocrust, carbon, reflectance spectroscopy, snow, soil ecology}, issn = {26660172}, doi = {10.1016/j.srs.2024.100120}, url = {https://www.sciencedirect.com/science/article/pii/S266601722400004X}, author = {Power, Sarah N. and Salvatore, Mark R. and Eric R. Sokol and Lee F. Stanish and Borges, Schuyler R. and Byron Adams and John E. Barrett} } @article {4844, title = {Causes and characteristics of electrical resistivity variability in shallow (<4 m) soils in Taylor Valley, East Antarctica}, journal = {Journal of Geophysical Research: Earth Surface}, volume = {128}, year = {2023}, month = {02/2023}, pages = {e2022JF006696}, abstract = {

Airborne electromagnetic surveys collected in December 2011 and November 2018 and three soil sampling transects were used to analyze the spatial heterogeneity of shallow (\<4 m) soil properties in lower Taylor Valley (TV), East Antarctica. Soil resistivities from 2011 to 2018 ranged from \∼33 Ωm to \∼3,500 Ωm with 200 Ωm assigned as an upper boundary for brine-saturated sediments. Elevations below \∼50 m above sea level (masl) typically exhibit the lowest resistivities with resistivity increasing at high elevations on steeper slopes. Soil water content was empirically estimated from electrical resistivities using Archie\&$\#$39;s Law and range from \∼\<1\% to \∼68\% by volume. An increase in silt- and clay-sized particles at low elevations increases soil porosity but decreases hydraulic conductivity, promoting greater residence times of soil water at low elevations near Lake Fryxell. Soil resistivity variability between 2011 and 2018 shows soils at different stages of soil freeze-thaw cycles, which are caused predominantly by solar warming of soils as opposed to air temperature. This study furthers the understanding of the hydrogeologic structure of the shallow subsurface in TV and identifies locations of soils that are potentially prone to greater rates of thaw and resulting ecosystem homogenization of soil properties from projected increases in hydrological connectivity across the region over the coming decades.

}, keywords = {LTER-MCM, active layer, airborne electromagnetic surveys, McMurdo Dry Valleys, permafrost dynamics}, issn = {2169-9003}, doi = {10.1029/2022JF006696}, url = {https://onlinelibrary.wiley.com/doi/10.1029/2022JF006696}, author = {Gutterman, William S. and Peter T. Doran and Ross A. Virginia and John E. Barrett and Myers, Krista F. and Tulaczyk, Slawek M. and Foley, Neil T. and Jill A. Mikucki and Hilary A. Dugan and Grombacher, Denys and Bording, Thue S. and Auken, E.} } @article {4833, title = {Ecological stoichiometry drives the evolution of soil nematode life history traits}, journal = {Soil Biology and Biochemistry}, volume = {177}, year = {2023}, month = {02/2023}, pages = {108891}, abstract = {

Ecological stoichiometry is a useful theoretical framework for understanding the sources and controls on nutrient availability that structure the composition and diversity of biotic communities. One such relationship is that organismal development rate is positively linked to cellular Phosphorus (P). We hypothesized that P availability, relative to other nutrients, e.g., nitrogen and carbon, would drive the evolution of traits associated with organismal growth and development. We examined the effects of P availability both in situ and in vitro, on free-living soil nematodes. We found that P-deficient environments produce predictable changes in the ecology and evolution of important life history traits. Our results identify altered rRNA gene copy number and subsequent changes in gene expression and protein synthesis as mechanisms by which P-deficiency influences these traits. These findings have important implications for explaining soil ecological and evolutionary patterns across multiple levels of organization, including the structure and functioning of organisms, populations, communities, and ecosystems.

}, keywords = {LTER-MCM, elemental stoichiometry, growth rate hypothesis, life history theory, molecular evolution, nematoda, rRNA}, doi = {10.1016/j.soilbio.2022.108891}, url = {https://www.sciencedirect.com/science/article/pii/S0038071722003480}, author = {Xue, Xia and Bishwo N. Adhikari and Ball, Becky and John E. Barrett and Miao, Jinxin and Perkes, Ammon and Martin, Mac and Breana L. Simmons and Diana H. Wall and Byron Adams} } @mastersthesis {4863, title = {Influence of landscape-variation in geochemistry on taxonomic and functional composition of microbial mat communities in the McMurdo Dry Valleys, Antarctica}, volume = {M.S.}, year = {2023}, school = {Virginia Tech}, type = {masters}, address = {Blacksburg, VA}, abstract = {

Microbial communities play critical roles in biogeochemical cycles of aquatic and terrestrial ecosystems, but studies of soil microbial communities have been limited by the diversity and complexity found in most ecosystems. Here we report on work investigating the functional diversity of microbial mat and underlying soil communities in the McMurdo Dry Valleys of Antarctica across a gradient of phosphorus availability on glacial tills of distinct age and mineral composition in Taylor Valley, Antarctica. Microbial mat and soil DNA were extracted and sequenced on an Illumina NextSeq500 in a 150 bp paired end format. Raw sequences were uploaded to the MG-RAST server for processing and annotation. Community taxonomic and functional annotation were determined using the RefSeq and SEED Subsystem databases, respectively. The results revealed significant variation in microbial mat community taxonomic composition between the two tills, strongly associated with visual assessment of mat morphology, e.g., \"black\" and \"orange\" mats, and soil N:P ratios. The underlying soil microbial communities did not exhibit significant differences in diversity between the two tills, but community composition varied significantly across gradients of soil chemistry, particularly extractable-phosphate content even within tills. The relative abundance of biogeochemistry-relevant pathways determined from the SEED database varied amongst soil microbial communities between the two tills. For example, microbial mat communities exhibited significant variation in the relative abundance of key nitrogen and phosphorus metabolism associated genes strongly associated with the underlying soil N:P. These results suggest that spatial variation in geochemistry influences the distribution and activity of microbial mats, but that the microbial mats themselves also exert a significant homogenizing effect on the underlying soil communities and some of the key biogeochemical processes they facilitate.

}, keywords = {LTER-MCM, carbon, microbial community, microbial mat, nitrogen, phosphorus, polar desert, soil}, url = {http://hdl.handle.net/10919/115384}, author = {Risteca, Paul J.}, editor = {John E. Barrett} } @article {4627, title = {Connectivity: Insights from the U.S. Long Term Ecological Research Network}, journal = {Ecosphere}, volume = {12}, year = {2021}, month = {05/2021}, pages = {e03432}, abstract = {

Ecosystems across the United States are changing in complex and surprising ways. Ongoing demand for critical ecosystem services requires an understanding of the populations and communities in these ecosystems in the future. This paper represents a synthesis effort of the U.S. National Science Foundation-funded Long-Term Ecological Research (LTER) network addressing the core research area of \“populations and communities.\” The objective of this effort was to show the importance of long-term data collection and experiments for addressing the hardest questions in scientific ecology that have significant implications for environmental policy and management. Each LTER site developed at least one compelling case study about what their site could look like in 50\–100 yr as human and environmental drivers influencing specific ecosystems change. As the case studies were prepared, five themes emerged, and the studies were grouped into papers in this LTER Futures Special Feature addressing state change, connectivity, resilience, time lags, and cascading effects. This paper addresses the \“connectivity\” theme and has examples from the Phoenix (urban), Niwot Ridge (alpine tundra), McMurdo Dry Valleys (polar desert), Plum Island (coastal), Santa Barbara Coastal (coastal), and Jornada (arid grassland and shrubland) sites. Connectivity has multiple dimensions, ranging from multi-scalar interactions in space to complex interactions over time that govern the transport of materials and the distribution and movement of organisms. The case studies presented here range widely, showing how land-use legacies interact with climate to alter the structure and function of arid ecosystems and flows of resources and organisms in Antarctic polar desert, alpine, urban, and coastal marine ecosystems. Long-term ecological research demonstrates that connectivity can, in some circumstances, sustain valuable ecosystem functions, such as the persistence of foundation species and their associated biodiversity or, it can be an agent of state change, as when it increases wind and water erosion. Increased connectivity due to warming can also lead to species range expansions or contractions and the introduction of undesirable species. Continued long-term studies are essential for addressing the complexities of connectivity. The diversity of ecosystems within the LTER network is a strong platform for these studies.

}, keywords = {LTER-MCM, alpine tundra, Antarctic polar desert, arid grassland, arid shrubland, coastal, estuary, salt marsh, Special Feature: Forecasting Earth{\textquoteright}s Ecosystems with Long-Term Ecological Research, urban ecosystem}, issn = {2150-8925}, doi = {10.1002/ecs2.v12.510.1002/ecs2.3432}, url = {https://onlinelibrary.wiley.com/doi/10.1002/ecs2.3432}, author = {Iwaniec, David M. and Michael N. Gooseff and Suding, Katharine N. and Johnson, David Samuel and Reed, Daniel C. and Debra P. C. Peters and Byron Adams and John E. Barrett and Bestelmeyer, Brandon T. and Castorani, Max C. N. and Cook, Elizabeth M. and Davidson, Melissa J. and Groffman, Peter M. and Hanan, Niall P. and Huenneke, L and Johnson, Pieter T. J. and Diane M. McKnight and Miller, Robert J. and Okin, Gregory S. and Preston, Daniel L. and Rassweiler, Andrew and Ray, Chris and Osvaldo E. Sala and Schooley, Robert and Seastedt, Timothy and Spasojevic, Marko J. and Vivoni, Enrique R.} } @article {4717, title = {Counting carbon: Quantifying biomass in the McMurdo Dry Valleys through orbital and field observations}, journal = {International Journal of Remote Sensing}, volume = {42}, year = {2021}, month = {10/2021}, pages = {8597 - 8623}, abstract = {

We use correlative field studies and high-resolution multispectral remote sensing data from the WorldView-2 instrument to estimate the abundance of photosynthetically active biomass (photoautotrophs consisting primarily of microbial mats and mosses) in Canada Stream in Taylor Valley, McMurdo Dry Valleys (MDV), Antarctica. In situ field investigations were performed to (1) acquire ground validation targets for atmospherically correcting satellite imagery, (2) derive spectra of \“pure\” geologic and biological endmembers, (3) estimate photoautotroph cover from remote sensing data, and (4) convert these coverage estimates to biomass using data collected in the field. Our results suggest that, on the morning of 12 December 2018, the Canada Stream system contained more than 3,800 kg of photosynthetically active carbon. Extrapolating our unmixing results to the entirety of the Fryxell basin of Taylor Valley, Antarctica, we model the presence of more than 750,000 kg of photosynthetically active carbon across the landscape and carbon fixation rates roughly equivalent to five hectares of tropical rainforest. The ability to spatially and temporally quantify the amount of photosynthetically active biomass using remote sensing data in the MDV of Antarctica is a revolutionary development that will help elucidate the ecological drivers and environmental responses in this cold desert landscape.

}, keywords = {LTER-MCM}, doi = {10.1080/01431161.2021.1981559}, url = {https://www.tandfonline.com/doi/full/10.1080/01431161.2021.1981559}, author = {Salvatore, Mark R. and John E. Barrett and Borges, Schuyler R. and Power, Sarah N. and Lee F. Stanish and Eric R. Sokol and Michael N. Gooseff} } @article {4768, title = {Patterns and trends of organic matter processing and transport: Insights from the US Long-term Ecological Research Network}, journal = {Climate Change Ecology}, volume = {2}, year = {2021}, month = {12/2021}, pages = {100025}, abstract = {

Organic matter (OM) dynamics determine how much carbon is stored in ecosystems, a service that modulates climate. We synthesized research from across the US Long-Term Ecological Research (LTER) Network to assemble a conceptual model of OM dynamics that is consistent with inter-disciplinary perspectives and emphasizes vulnerability of OM pools to disturbance. Guided by this conceptual model, we identified unanticipated patterns and long-term trends in processing and transport of OM emerging from terrestrial, freshwater, wetland, and marine ecosystems. Cross-ecosystem synthesis combined with a survey of researchers revealed several themes: 1) strong effects of climate change on OM dynamics, 2) surprising patterns in OM storage and dynamics resulting from coupling with nutrients, 3) characteristic and often complex legacies of land use and disturbance, 4) a significant role of OM transport that is often overlooked in terrestrial ecosystems, and 5) prospects for reducing uncertainty in forecasting OM dynamics by incorporating the chemical composition of OM. Cross-fertilization of perspectives and approaches across LTER sites and other research networks can stimulate the comprehensive understanding required to support large-scale characterizations of OM budgets and the role of ecosystems in regulating global climate.

}, keywords = {LTER-MCM, coupled biogeochemical cycles, cross-site synthesis, organic matter composition, organic matter storage, stabilization, transport}, issn = {26669005}, doi = {10.1016/j.ecochg.2021.100025}, url = {https://www.sciencedirect.com/science/article/pii/S2666900521000253}, author = {Harms, Tamara K. and Groffman, Peter M. and Aluwihare, Lihini and Craft, Christopher and Wieder, William R and Hobbie, S and Baer, Sara G. and J.M. Blair and Frey, Serita D. and Remucal, Christina K. and Rudgers, Jennifer A. and Collins, SL and Kominoski, John S. and Ball, Becky and John C. Priscu and John E. Barrett} } @article {4516, title = {Estimating microbial mat biomass in the McMurdo Dry Valleys, Antarctica using satellite imagery and ground surveys}, journal = {Polar Biology}, year = {2020}, month = {09/2020}, abstract = {

Cyanobacterial mat communities are the main drivers of primary productivity in the McMurdo Dry Valleys, Antarctica. These microbial communities form laminar mats on desert pavement surfaces adjacent to glacial meltwater streams, ponds, and lakes. The low-density nature of these communities and their patchy distribution make assessments of distribution, biomass, and productivity challenging. We used satellite imagery coupled with in situ surveying, imaging, and sampling to systematically estimate microbial mat biomass in selected wetland regions in Taylor Valley, Antarctica. On January 19th, 2018, the WorldView-2 multispectral satellite acquired an image of our study areas, where we surveyed and sampled seven 100 m2 plots of microbial mats for percent ground cover, ash-free dry mass (AFDM), and pigment content (chlorophyll-a, carotenoids, and scytonemin). Multispectral analyses revealed spectral signatures consistent with photosynthetic activity (relatively strong reflection at near-infrared wavelengths and relatively strong absorption at visible wavelengths), with average normalized difference vegetation index (NDVI) values of 0.09 to 0.28. Strong correlations of microbial mat ground cover (R2\ =\ 0.84), biomass (R2\ =\ 0.74), chlorophyll-a content (R2\ =\ 0.65), and scytonemin content (R2\ =\ 0.98) with logit transformed NDVI values demonstrate that satellite imagery can detect both the presence of microbial mats and their key biological properties. Using the NDVI\—biomass correlation we developed, we estimate carbon (C) stocks of 21,715 kg (14.7 g C m\−2) in the Canada Glacier Antarctic Specially Protected Area, with an upper and lower limit of 74,871 and 6312 kg of C, respectively.

}, keywords = {LTER-MCM, Antarctica, microbial mat, multispectral imagery, NDVI, Nostocales, remote sensing}, doi = {10.1007/s00300-020-02742-y}, url = {https://link.springer.com/article/10.1007\%2Fs00300-020-02742-y}, author = {Power, Sarah N. and Salvatore, Mark R. and Eric R. Sokol and Lee F. Stanish and John E. Barrett} } @article {4515, title = {Evaluating alternative metacommunity hypotheses for diatoms in the McMurdo Dry Valleys using simulations and remote sensing data}, journal = {Frontiers in Ecology and Evolution}, volume = {8}, year = {2020}, month = {09/2020}, abstract = {

Diatoms are diverse and widespread freshwater Eukaryotes that make excellent microbial subjects for addressing questions in metacommunity ecology. In the McMurdo Dry Valleys of Antarctica, the simple trophic structure of glacier-fed streams provides an ideal outdoor laboratory where well-described diatom assemblages are found within two cyanobacterial mat types, which occupy different habitats and vary in coverage within and among streams. Specifically, black mats of Nostoc spp. occur in marginal wetted habitats, and orange mats (Oscillatoria spp. and Phormidium spp.) occur in areas of consistent stream flow. Despite their importance as bioindicators for changing environmental conditions, the role of dispersal in structuring dry valley diatom metacommunities remains unclear. Here, we use MCSim, a spatially explicit metacommunity simulation package for R, to test alternative hypotheses about the roles of dispersal and species sorting in maintaining the biodiversity of diatom assemblages residing in black and orange mats. The spatial distribution and patchiness of cyanobacterial mat habitats was characterized by remote imagery of the Lake Fryxell sub-catchment in Taylor Valley. The available species pool for diatom metacommunity simulation scenarios was informed by the Antarctic Freshwater Diatoms Database, maintained by the McMurdo Dry Valleys Long Term Ecological Research program. We used simulation outcomes to test the plausibility of alternative community assembly hypotheses to explain empirically observed patterns of freshwater diatom biodiversity in the long-term record. The most plausible simulation scenarios suggest species sorting by environmental filters, alone, was not sufficient to maintain biodiversity in the Fryxell Basin diatom metacommunity. The most plausible scenarios included either (1) neutral models with different immigration rates for diatoms in orange and black mats or (2) species sorting by a relatively weak environmental filter, such that dispersal dynamics also influenced diatom community assembly, but there was not such a strong disparity\ in immigration rates between mat types. The results point to the importance of dispersal for understanding current and future biodiversity patterns for diatoms in this ecosystem, and more generally, provide further evidence that metacommunity theory is a useful framework for testing hypotheses about microbial community assembly.

}, keywords = {LTER-MCM, Antarctica, Bacillariophyceae, dispersal, Nostoc, stream ecology}, doi = {10.3389/fevo.2020.521668}, url = {https://www.frontiersin.org/article/10.3389/fevo.2020.521668/full}, author = {Eric R. Sokol and John E. Barrett and Tyler J. Kohler and Diane M. McKnight and Salvatore, Mark R. and Lee F. Stanish} } @article {4449, title = {Remote characterization of photosynthetic communities in the Fryxell basin of Taylor Valley, Antarctica}, journal = {Antarctic Science}, year = {2020}, month = {03/2020}, abstract = {

We investigate the spatial distribution, spectral properties and temporal variability of primary producers (e.g. communities of microbial mats and mosses) throughout the Fryxell basin of Taylor Valley, Antarctica, using high-resolution multispectral remote-sensing data. Our results suggest that photosynthetic communities can be readily detected throughout the Fryxell basin based on their unique near-infrared spectral signatures. Observed intra- and inter-annual variability in spectral signatures are consistent with short-term variations in mat distribution, hydration and photosynthetic activity. Spectral unmixing is also implemented in order to estimate mat abundance, with the most densely vegetated regions observed from orbit correlating spatially with some of the most productive regions of the Fryxell basin. Our work establishes remote sensing as a valuable tool in the study of these ecological communities in the McMurdo Dry Valleys and demonstrates how future scientific investigations and the management of specially protected areas could benefit from these tools and techniques.

}, keywords = {LTER-MCM, ecology, hydrology, McMurdo Dry Valleys, microbiology, remote sensing, spectroscopy}, doi = {10.1017/S0954102020000176}, url = {https://www.cambridge.org/core/journals/antarctic-science/article/remote-characterization-of-photosynthetic-communities-in-the-fryxell-basin-of-taylor-valley-antarctica/8576F6BB1BCFDCA8409F5EA96CA00C6F}, author = {Salvatore, Mark R. and Borges, Schuyler R. and John E. Barrett and Eric R. Sokol and Lee F. Stanish and Power, Sarah N. and Morin, Paul} } @article {4153, title = {Biotic interactions are an unexpected yet critical control on the complexity of an abiotically driven polar ecosystem}, journal = {Communications Biology}, volume = {2}, year = {2019}, month = {02/2019}, abstract = {

Abiotic and biotic factors control ecosystem biodiversity, but their relative contributions remain unclear. The ultraoligotrophic ecosystem of the Antarctic Dry Valleys, a simple yet highly heterogeneous ecosystem, is a natural laboratory well-suited for resolving the abiotic and biotic controls of community structure. We undertook a multidisciplinary investigation to capture ecologically relevant biotic and abiotic attributes of more than 500 sites in the Dry Valleys, encompassing observed landscape heterogeneities across more than 200 km2. Using richness of autotrophic and heterotrophic taxa as a proxy for functional complexity, we linked measured variables in a parsimonious yet comprehensive structural equation model that explained significant variations in biological complexity and identified landscape-scale and fine-scale abiotic factors as the primary drivers of diversity. However, the inclusion of linkages among functional groups was essential for constructing the best-fitting model. Our findings support the notion that biotic interactions make crucial contributions even in an extremely simple ecosystem.

}, keywords = {LTER-MCM}, doi = {10.1038/s42003-018-0274-5}, url = {https://www.nature.com/articles/s42003-018-0274-5}, author = {Charles K. Lee and Laughlin, Daniel C. and Bottos, Eric M. and Caruso, Tancredi and Joy, Kurt and John E. Barrett and Brabyn, Lars and Uffe N. Nielsen and Byron Adams and Diana H. Wall and D. W. Hopkins and Pointing, Steve B. and McDonald, Ian R. and Cowan, Don A. and Banks, Jonathan C. and Stichbury, Glen A. and Jones, Irfon and Zawar-Reza, Peyman and Katurji, Marwan and Hogg, Ian D. and Sparrow, Ashley D. and Storey, Bryan C. and Allan Green, T. G. and Craig S Cary} } @article {4164, title = {Nematodes in a polar desert reveal the relative role of biotic interactions in the coexistence of soil animals}, journal = {Communications Biology}, volume = {2}, year = {2019}, month = {02/2019}, abstract = {

Abiotic factors are major determinants of soil animal distributions and their dominant role is pronounced in extreme ecosystems, with biotic interactions seemingly playing a minor role. We modelled co-occurrence and distribution of the three nematode species that dominate the soil food web of the McMurdo Dry Valleys (Antarctica). Abiotic factors, other biotic groups, and autocorrelation all contributed to structuring nematode species distributions. However, after removing their effects, we found that the presence of the most abundant nematode species greatly, and negatively, affected the probability of detecting one of the other two species. We observed similar patterns in relative abundances for two out of three pairs of species. Harsh abiotic conditions alone are insufficient to explain contemporary nematode distributions whereas the role of negative biotic interactions has been largely underestimated in soil. The future challenge is to understand how the effects of global change on biotic interactions will alter species coexistence.

}, keywords = {LTER-MCM}, doi = {10.1038/s42003-018-0260-y}, url = {http://www.nature.com/articles/s42003-018-0260-y}, author = {Caruso, Tancredi and Hogg, Ian D. and Uffe N. Nielsen and Bottos, Eric M. and Charles K. Lee and D. W. Hopkins and Craig S Cary and John E. Barrett and Green, T. G. Allan and Storey, Bryan C. and Diana H. Wall and Byron Adams} } @article {4196, title = {Unimodal productivity{\textendash}diversity relationships among bacterial communities in a simple polar soil ecosystem}, journal = {Environmental Microbiology}, volume = {21}, year = {2019}, month = {07/2019}, abstract = {

Unlike other macroecological principles, relationships between productivity and diversity have not been effectively tested for microbial communities. Here we describe an experiment in which the availability of resources to soil bacterial communities was manipulated in a model system, the McMurdo Dry Valleys of Antarctica. Mannitol additions were used to simulate a productivity gradient such that a response in bacterial biomass production, taxonomic diversity and functioning (e.g., enzyme activity) were induced. Resource amendment induced a positive linear response in microbial productivity (P \< 0.001) but a unimodal (hump-shaped) response in microbial diversity at multiple taxonomic scales (P = 0.035). Putative oligotrophic (e.g., phyla Nitrospirae and Cyanobacteria) and copiotrophic (e.g., phylum Proteobacteria) taxa were apparent through substantial community turnover along the resource gradient. Soil enzyme activity was inversely related to bacterial biomass but positively related to diversity, suggesting the latter may be a stronger control over enzyme-mediated decomposition. The mechanisms behind this pattern are consistent with macroecological theory of a shift from environmental (e.g., stress tolerance) to biotic (e.g., competition) drivers with increasing resource availability. This evidence is among the first of its kind to document a significant unimodal productivity\–diversity relationship for soil bacteria.

}, keywords = {LTER-MCM}, doi = {10.1111/1462-2920.14639}, url = {https://onlinelibrary.wiley.com/doi/full/10.1111/1462-2920.14639}, author = {Kevin M. Geyer and John E. Barrett} } @article {4110, title = {Catch and release: Hyporheic retention and mineralization of N-fixing Nostoc sustains downstream microbial mat biomass in two polar desert streams}, journal = {Limnology and Oceanography Letters}, volume = {3}, year = {2018}, month = {07/2018}, pages = {357 - 364}, abstract = {

Much work has been performed to investigate controls on nitrogen (N) uptake in streams, yet the fate of assimilated N is comparatively poorly resolved. Here, we use in-stream fixed N as an isotopic tracer to study the fate of assimilated N in glacial meltwater streams. We characterized\ d15N signatures of Oscillatorean, Chlorophyte, and N-fixing\ Nostoc\ mats over the lengths of two streams, and transported particulate organic matter (POM) in one. POM was isotopically most similar to\ Nostoc, which always had values near the atmospheric standard, suggesting N-fixation. Other mat types were depleted upstream, and became progressively enriched downstream, indicating a shift in N source. These results collectively show that\ Nostoc-derived N is mobilized, mineralized, and increasingly assimilated downstream as more depleted glacier-derived N is exhausted, demonstrating the importance of organic matter processing to balancing elemental budgets, and improving our understanding of nutrient cycling in lotic environments.

}, keywords = {LTER-MCM}, doi = {10.1002/lol2.10087}, url = {https://aslopubs.onlinelibrary.wiley.com/doi/abs/10.1002/lol2.10087}, author = {Tyler J. Kohler and Lee F. Stanish and Liptzin, D. and John E. Barrett and Diane M. McKnight} } @article {4060, title = {Observed trends of soil fauna in the Antarctic Dry Valleys: early signs of shifts predicted under climate change}, journal = {Ecology}, volume = {99}, year = {2018}, month = {02/2018}, pages = {312 - 321}, abstract = {

Long-term observations of ecological communities are necessary for generating and testing predictions of ecosystem responses to climate change. We investigated temporal trends and spatial patterns of soil fauna along similar environmental gradients in three sites of the McMurdo Dry Valleys, Antarctica, spanning two distinct climatic phases: a decadal cool- ing trend from the early 1990s through the austral summer of February 2001, followed by a shift to the current trend of warming summers and more frequent discrete warming events. After February 2001, we observed a decline in the dominant species (the nematode Scottnema lindsayae) and increased abundance and expanded distribution of less common taxa (rotifers, tardigrades, and other nematode species). Such diverging responses have resulted in slightly greater evenness and spatial homogeneity of taxa. However, total abundance of soil fauna appears to be declining, as positive trends of the less common species so far have not compen- sated for the declining numbers of the dominant species. Interannual variation in the propor- tion of juveniles in the dominant species was consistent across sites, whereas trends in abundance varied more. Structural equation modeling supports the hypothesis that the observed biological trends arose from dissimilar responses by dominant and less common spe- cies to pulses of water availability resulting from enhanced ice melt. No direct effects of mean summer temperature were found, but there is evidence of indirect effects via its weak but signif- icant positive relationship with soil moisture. Our findings show that combining an under- standing of species responses to environmental change with long-term observations in the field can provide a context for validating and refining predictions of ecological trends in the abun- dance and diversity of soil fauna.\ 

}, keywords = {LTER-MCM}, doi = {10.1002/ecy.2090}, url = {http://doi.wiley.com/10.1002/ecy.2090/full}, author = {Andriuzzi, Walter S. and Byron Adams and John E. Barrett and Ross A. Virginia and Diana H. Wall} } @article {4080, title = {Soil biological responses to C, N and P fertilization in a polar desert of Antarctica}, journal = {Soil Biology and Biochemistry}, volume = {122}, year = {2018}, month = {07/2018}, chapter = {7}, abstract = {

In the polar desert ecosystem of the McMurdo Dry Valleys of Antarctica, biology is constrained by available liquid water, low temperatures, as well as the availability of organic matter and nutrient elements. These soil ecosystems are climate-sensitive, where projected future warming may have profound effects on biological communities and biogeochemical cycling. Warmer temperatures will mobilize meltwater from permafrost and glaciers, may increase precipitation and may be accompanied by pulses of nutrient availability. Enhanced water and nutrient availability have the potential to greatly influence desert soil biology and ecosystem processes. The objectives of this 5-year study were to determine which nutrient elements (C, N, P) are most limiting to dry valley soil communities and whether landscape history (i.e.,\ in situ\ soil type and stoichiometry) influences soil community response to nutrient additions. After 3 years of no noticeable response, soil CO2\ flux was significantly higher under addition of C+ N than the other treatments, regardless of\ in situ\ soil stoichiometry, but microbial biomass and invertebrate abundance were variable and not influenced in the same manner. A stable isotope incubation suggests that fertilization increases C and N mineralization from organic matter via stimulating microbial activity, with loss of both the applied treatments as well\ in situ\ C and N. However, these responses are relatively short-lived, suggesting long-term impacts on C and N cycling would only occur if meltwater and nutrient pulses are sustained over time, a scenario that is increasingly likely for the dry valleys.

}, keywords = {LTER-MCM}, issn = {00380717}, doi = {10.1016/j.soilbio.2018.03.025}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0038071718301081}, author = {Ball, Becky and Byron Adams and John E. Barrett and Diana H. Wall and Ross A. Virginia} } @article {4059, title = {Stable C and N isotope ratios reveal soil food web structure and identify the nematode Eudorylaimus antarcticus as an omnivore{\textendash}predator in~Taylor Valley, Antarctica}, journal = {Polar Biology}, volume = {41}, year = {2018}, month = {05/2018}, pages = {1013{\textendash}1018}, abstract = {

Soil food webs of the McMurdo Dry Valleys, Antarctica are simple. These include primary trophic levels of mosses, algae, cyanobacteria, bacteria, archaea, and fungi, and their protozoan and metazoan consumers (including relatively few species of nematodes, tardigrades, rotifers, and microarthropods). These biota are patchily distributed across the landscape, with greatest faunal biodiversity associated with wet soil. Understanding trophic structure is critical to studies of biotic interactions and distribution; yet, McMurdo Dry Valley soil food web structure has been inferred from limited laboratory culturing and micro- scopic observations. To address this, we measured stable isotope natural abundance ratios of C (13C/12C) and N (15N/14N) for di erent metazoan taxa (using whole body biomass) to determine soil food web structure in Taylor Valley, Antarctica. Nitrogen isotopes were most useful in di erentiating trophic levels because they fractionated predictably at higher trophic levels. Using 15N/14N, we found that three trophic levels were present in wet soil habitats. While cyanobacterial mats were the primary trophic level, the nematode Plectus murrayi, tardigrade Acutuncus antarcticus, and rotifers composed a secondary trophic level of grazers. Eudorylaimus antarcticus had a 15N/14N ratio that was 2\–4\‰ higher than that of grazers, indicating that this species is the sole member of a tertiary trophic level. Understanding the trophic positions of soil fauna is critical to predictions of current and future species interactions and their distributions for the McMurdo Dry Valleys, Antarctica.

}, keywords = {LTER-MCM}, doi = {10.1007/s00300-017-2243-8}, url = {http://link.springer.com/10.1007/s00300-017-2243-8}, author = {Shaw, E. Ashley and Byron Adams and John E. Barrett and W. Berry Lyons and Ross A. Virginia and Diana H. Wall} } @article {4139, title = {Stoichiometric Shifts in Soil C:N:P Promote Bacterial Taxa Dominance, Maintain Biodiversity, and Deconstruct Community Assemblages}, journal = {Frontiers in Microbiology}, volume = {9}, year = {2018}, month = {07/2018}, abstract = {

Imbalances in C:N:P supply ratios may cause bacterial resource limitations and constrain biogeochemical processes, but the importance of shifts in soil stoichiometry are complicated by the nearly limitless interactions between an immensely rich species pool and a multiple chemical resource forms. To more clearly identify the impact of soil C:N:P on bacteria, we evaluated the cumulative effects of single and coupled long-term nutrient additions (i.e., C as mannitol, N as equal concentrations NH4 + and NO3 \− , and P as Na3PO4) and water on communities in an Antarctic polar desert, Taylor Valley. Untreated soils possessed relatively low bacterial diversity, simplified organic C sources due to the absence of plants, limited inorganic N, and excess soil P potentially attenuating links between C:N:P. After 6 years of adding resources, an alleviation of C and N colimitation allowed one rare Micrococcaceae, an Arthrobacter species, to dominate, comprising 47\% of the total community abundance and elevating soil respiration by 136\% relative to untreated soils. The addition of N alone reduced C:N ratios, elevated bacterial richness and diversity, and allowed rare taxa relying on ammonium and nitrite for metabolism to become more abundant [e.g., nitrite oxidizing Nitrospira species (Nitrosomonadaceae), denitrifiers utilizing nitrite (Gemmatimonadaceae) and members of Rhodobacteraceae with a high affinity for ammonium]. Based on community co-occurrence networks, lower C:P ratios in soils following P and CP additions created more diffuse and less connected communities by disrupting 73\% of species interactions and selecting for taxa potentially exploiting abundant P. Unlike amended nutrients, water additions alone elicited no lasting impact on communities. Our results suggest that as soils become nutrient rich a wide array of outcomes are possible from species dominance and the deconstruction of species interconnectedness to the maintenance of biodiversity.

}, keywords = {LTER-MCM, ecological stoichiometry, Lake Fryxell Basin, McMurdo Dry Valleys, network community modeling, nutrient colimitation, Solirubrobacteriaceae}, doi = {10.3389/fmicb.2018.01401}, url = {https://www.frontiersin.org/article/10.3389/fmicb.2018.01401/full}, author = {Aanderud, Zachary T. and Saurey, Sabrina D. and Ball, Becky and Diana H. Wall and John E. Barrett and Muscarella, Mario E. and Griffin, Natasha A. and Ross A. Virginia and Byron Adams} } @article {4022, title = {Decadal ecosystem response to an anomalous melt season in a polar desert in Antarctica}, journal = {Nature Ecology \& Evolution}, volume = {1}, year = {2017}, month = {09/2017}, pages = {1334-1338}, keywords = {LTER-MCM}, doi = {10.1038/s41559-017-0253-0}, url = {https://www.nature.com/articles/s41559-017-0253-0}, author = {Michael N. Gooseff and John E. Barrett and Byron Adams and Peter T. Doran and Andrew G Fountain and W. Berry Lyons and Diane M. McKnight and John C. Priscu and Eric R. Sokol and Cristina D. Takacs-Vesbach and Martijn L. Vandegehuchte and Ross A. Virginia and Diana H. Wall} } @article {4021, title = {Primary productivity as a control over soil microbial diversity along environmental gradients in a polar desert ecosystem}, journal = {PeerJ}, volume = {5}, year = {2017}, month = {07/2017}, pages = {e3377}, abstract = {

Primary production is the fundamental source of energy to foodwebs and ecosystems, and is thus an important constraint on soil communities. This coupling is particularly evident in polar terrestrial ecosystems where biological diversity and activity is tightly constrained by edaphic gradients of productivity (e.g., soil moisture, organic carbon availability) and geochemical severity (e.g., pH, electrical conductivity). In the McMurdo Dry Valleys of Antarctica, environmental gradients determine numerous properties of soil communities and yet relatively few estimates of gross or net primary productivity (GPP, NPP) exist for this region. Here we describe a survey utilizing pulse amplitude modulation (PAM) fluorometry to estimate rates of GPP across a broad environmental gradient along with belowground microbial diversity and decomposition. PAM estimates of GPP ranged from an average of 0.27 mmol O2/m2/s in the most arid soils to an average of 6.97 mmol O2/m2/s in the most productive soils, the latter equivalent to 217 g C/m2/y in annual NPP assuming a 60 day growing season. A diversity index of four carbon-acquiring enzyme activities also increased with soil productivity, suggesting that the diversity of organic substrates in mesic environments may be an additional driver of microbial diversity. Overall, soil productivity was a stronger predictor of microbial diversity and enzymatic activity than any estimate of geochemical severity. These results highlight the fundamental role of environmental gradients to control community diversity and the dynamics of ecosystem-scale carbon pools in arid systems.\ 

}, keywords = {LTER-MCM}, doi = {10.7717/peerj.3377}, url = {https://peerj.com/articles/3377/}, author = {Kevin M. Geyer and Cristina D. Takacs-Vesbach and Michael N. Gooseff and John E. Barrett} } @article {3965, title = {A simulation-based approach to understand how metacommunity characteristics influence emergent biodiversity patterns}, journal = {Oikos}, volume = {126}, year = {2017}, month = {05/2017}, pages = {723-737}, abstract = {

To understand controls over biodiversity, it is necessary to take a multi-scale approach to understand how local and regional factors a ect the community assembly processes that drive emergent patterns. \ is need is re ected in the growing use of the metacommunity concept to interpret multi-scale measures of biodiversity, including metrics derived from diversity partitioning (e.g. a, b and g diversity) and variation partitioning (e.g. spatial and environmental components of compositional turnover) techniques. However, studies have shown limited success using these metrics to characterize underlying community assembly dynamics. Here we demonstrate how a metacommunity simulation package (MCSim) can be used to evaluate when and how biodiversity metrics can be used to make inferences about metacommunity characteristics. We examined a wide range of parameter settings representing ecologically relevant scenarios. We used artificial neural networks (ANNs) to assess the sensitivity of diversity and variation partitioning metrics (calculated from simulation outcomes) to metacommunity parameter settings. In the scenarios examined in this study, the niche-neutral gradient strongly in uenced most biodiversity metrics, metacommunity size exhibited a marginal influence over some metrics, and dispersal dynamics only a ected a subset of variation partitioning outcomes. Variation partitioning response curves along the niche-neutral gradient were not monotonic; however, simulation outcomes suggest other biodiversity metrics (e.g. dissimilarity saturation) can be used in combination with variation partitioning metrics to make inferences about metacommunity properties. With the growing availability of archived ecological data, we expect future work will apply simulation-based techniques to better understand links between biodiversity and the metacommunity characteristics that are presumed to control the underlying community assembly processes.

}, keywords = {LTER-MCM}, doi = {10.1111/oik.03690}, url = {http://doi.wiley.com/10.1111/oik.03690}, author = {Eric R. Sokol and Brown, Bryan L. and John E. Barrett} } @article {3714, title = {Evidence for dispersal and habitat controls on pond diatom communities from the McMurdo Sound Region of Antarctica}, journal = {Polar Biology}, year = {2016}, month = {02/2016}, keywords = {LTER-MCM}, issn = {0722-4060}, doi = {10.1007/s00300-016-1901-6}, url = {http://link.springer.com/10.1007/s00300-016-1901-6http://link.springer.com/content/pdf/10.1007/s00300-016-1901-6http://link.springer.com/content/pdf/10.1007/s00300-016-1901-6.pdfhttp://link.springer.com/article/10.1007/s00300-016-1901-6/fulltext.html}, author = {Sakaeva, A. and Eric R. Sokol and Tyler J. Kohler and Lee F. Stanish and Sarah A. Spaulding and Howkins, Adrian and Kathleen A. Welch and W. Berry Lyons and John E. Barrett and Diane M. McKnight} } @article {3952, title = {Microbial Community Responses to Increased Water and Organic Matter in the Arid Soils of the McMurdo Dry Valleys, Antarctica}, journal = {Frontiers in Microbiology}, volume = {7}, year = {2016}, month = {07/2016}, chapter = {1040}, keywords = {LTER-MCM}, doi = {10.3389/fmicb.2016.01040}, url = {http://journal.frontiersin.org/article/10.3389/fmicb.2016.01040}, author = {Heather N. Buelow and Winter, Ara S. and David J. Van Horn and John E. Barrett and Michael N. Gooseff and Schwartz, Egbert and Cristina D. Takacs-Vesbach} } @article {3715, title = {Global environmental change and the nature of aboveground net primary productivity responses: insights from long-term experiments}, journal = {Oecologia}, volume = {177}, year = {2015}, month = {04/2015}, pages = {935 - 947}, keywords = {LTER-MCM}, issn = {0029-8549}, doi = {10.1007/s00442-015-3230-9}, url = {http://link.springer.com/10.1007/s00442-015-3230-9http://link.springer.com/content/pdf/10.1007/s00442-015-3230-9}, author = {Smith, Melinda D. and La Pierre, Kimberly J. and Collins, SL and Knapp, Alan K. and Gross, Katherine L. and John E. Barrett and Frey, Serita D. and Gough, Laura and Miller, Robert J. and Morris, James T. and Rustad, Lindsey E. and Yarie, John} } @article {3720, title = {Linking management to biodiversity in built ponds using metacommunity simulations}, journal = {Ecological Modelling}, volume = {296}, year = {2015}, month = {01/2015}, pages = {36 - 45}, keywords = {LTER-MCM}, issn = {03043800}, doi = {10.1016/j.ecolmodel.2014.10.022}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0304380014004918}, author = {Eric R. Sokol and Brown, Bryan L. and Carey, Cayelan C. and Tornwall, Brett M. and Swan, Christopher M. and John E. Barrett} } @article {3522, title = {Niche and metabolic principles explain patterns of diversity and distribution: theory and a case study with soil bacterial communities}, journal = {Proceedings of the Royal Society B: Biological Sciences}, volume = {282}, year = {2015}, month = {05/2015}, pages = {2630}, abstract = {

The causes of biodiversity patterns are controversial and elusive due to complex environmental variation, covarying changes in communities, and lack of baseline and null theories to differentiate straightforward causes from more complex mechanisms. To address these limitations, we developed general diversity theory integrating metabolic principles with niche-based community assembly. We evaluated this theory by investigating patterns in the diversity and distribution of soil bacteria taxa across four orders of magnitude variation in spatial scale on an Antarctic mountainside in low complexity, highly oligotrophic soils. Our theory predicts that lower temperatures should reduce taxon niche widths along environmental gradients due to decreasing growth rates, and the changing niche widths should lead to contrasting α- and β-diversity patterns. In accord with the predictions, α-diversity, niche widths and occupancies decreased while β-diversity increased with increasing elevation and decreasing temperature. The theory also successfully predicts a hump-shaped relationship between α-diversity and pH and a negative relationship between α-diversity and salinity. Thus, a few simple principles explained systematic microbial diversity variation along multiple gradients. Such general theory can be used to disentangle baseline effects from more complex effects of temperature and other variables on biodiversity patterns in a variety of ecosystems and organisms.

}, keywords = {LTER-MCM}, issn = {0962-8452}, doi = {10.1098/rspb.2014.2630}, url = {http://rspb.royalsocietypublishing.org/lookup/doi/10.1098/rspb.2014.2630}, author = {Okie, Jordan G. and David J. Van Horn and Storch, David and John E. Barrett and Michael N. Gooseff and Kopsova, Lenka and Cristina D. Takacs-Vesbach} } @article {3215, title = {Recovery of Antarctic stream epilithon from simulated scouring events}, journal = {Antarctic Science}, volume = {27}, year = {2015}, month = {Jan-08-2015}, pages = {341 - 354}, abstract = {

Microbial mats are common in polar streams and often dominate benthic biomass. Climate change may be enhancing the variability of stream flows in the Antarctic, but so far studies investigating mat responses to disturbance have been limited in this region. Mat regrowth was evaluated following disturbance by experimentally scouring rocks from an ephemeral McMurdo Dry Valley stream over two summers (2001\–02 and 2012\–13). Mats were sampled at the beginning and resampled at the end of the flow season. In 2012\–13, mats were additionally resampled mid-season along with previously undisturbed controls. In 2001\–02 rocks regained 47\% of chlorophyll\ aand 40\% of ash-free dry mass by the end of the summer, while in 2012\–13 rocks regrew 18\% and 27\%, respectively. Mat stoichiometry differed between summers, and reflected differences in biomass and discharge.\ Oscillatoria\ spp. were greatest on scoured rocks and\ Phormidium\ spp. on undisturbed rocks. Small diatoms\ Humidophila\ andFistulifera\ spp. increased throughout the summer in all mats, with the latter more abundant in scoured communities. Collectively, these data suggest that mats are variable intra-annually, responsive to hydrology and require multiple summers to regrow initial biomass once lost. These results will aid the interpretation of long-term data, as well as inform Antarctic Specially Managed Area protocols.

}, keywords = {LTER-MCM}, issn = {0954-1020}, doi = {10.1017/S0954102015000024}, url = {http://www.journals.cambridge.org/abstract_S0954102015000024}, author = {Tyler J. Kohler and Ethan Chatfield and Michael N. Gooseff and John E. Barrett and Diane M. McKnight} } @article {1054, title = {Bacterial community composition of divergent soil habitats from a polar desert.}, journal = {FEMS Microbiology Ecology}, volume = {89}, year = {2014}, month = {08/2014}, pages = {490-494}, type = {Short Communication}, chapter = {490}, abstract = {Edaphic factors such as pH, organic matter, and salinity are often the most significant drivers of diversity patterns in soil bacterial communities. Desert ecosystems in particular are model locations for examining such relationships as food web complexity is low and the soil environment is biogeochemically heterogeneous. Here, we present the findings from a 16S rRNA gene sequencing approach used to observe the differences in diversity and community composition among three divergent soil habitats of the McMurdo Dry Valleys, Antarctica. Results show that alpha diversity is significantly lowered in high pH soils, which contain higher proportions of the phyla Acidobacteria and Actinobacteria, while mesic soils with higher soil organic carbon (and ammonium) content contain high proportions of Nitrospira, a nitrite-oxidizing bacteria. Taxonomic community resolution also had a significant impact on our conclusions, as pH was the primary predictor of phylum-level diversity, while moisture was the most significant predictor of diversity at the genus level. Predictive power also increased with increasing taxonomic resolution, suggesting a potential increase in nic}, keywords = {LTER-MCM}, doi = {10.1111/1574-6941.12306}, author = {Kevin M. Geyer and Adam E. Altrichter and Cristina D. Takacs-Vesbach and Michael N. Gooseff and John E. Barrett} } @article {1055, title = {Characterization of Growing Bacterial Populations in McMurdo Dry Valley Soils through Stable Isotope Probing with 18O-water.}, journal = {FEMS Microbiology Ecology.}, volume = {89}, year = {2014}, month = {08/2014}, pages = {415-425}, chapter = {415}, abstract = {Soil 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.}, keywords = {LTER-MCM}, doi = {10.1111/1574-6941.12349}, author = {Schwartz, E. and David J. Van Horn and Heather N. Buelow and Michael N. Gooseff and John E. Barrett and Cristina D. Takacs-Vesbach and Okie, J.G.} } @phdthesis {4086, title = {Environmental Controls Over the Distribution and Function of Antarctic Soil Bacterial Communities}, volume = {Ph.D.}, year = {2014}, school = {Virginia Tech}, type = {doctoral}, address = {Blacksburg, VA}, abstract = {

Microbial community composition plays a vital role in soil biogeochemical cycling. Information that explains the biogeography of microorganisms is consequently necessary for predicting the timing and magnitude of important ecosystem services mediated by soil biota, such as decomposition and nutrient cycling. Theory developed to explain patterns in plant and animal distributions such as the prevalent relationship between ecosystem productivity and diversity may be successfully extended to microbial systems and accelerate an emerging ecological understanding of the \"unseen majority.\" These considerations suggest a need to define the important mechanisms which affect microbial biogeography as well as the sensitivity of community structure/function to changing climatic or environmental conditions. To this end, my dissertation covers three data chapters in which I have 1) examined patterns in bacterial biogeography using gradients of environmental severity and productivity to identify changes in community diversity (e.g. taxonomic richness) and structure (e.g. similarity); 2) detected potential bacterial ecotypes associated with distinct soil habitats such as those of high alkalinity or electrical conductivity and; 3) measured environmental controls over the function (e.g. primary production, exoenzyme activity) of soil organisms in an environment of severe environmental limitations. Sampling was performed in the polar desert of Antarctica\&$\#$39;s McMurdo Dry Valleys, a model ecosystem which hosts microbially-dominated soil foodwebs and displays heterogeneously distributed soil properties across the landscape. Results for Chapter 2 indicate differential effects of resource availability and geochemical severity on bacterial communities,\ with a significant productivity-diversity relationship that plateaus near the highest observed concentrations of the limiting resource organic carbon (0.30mg C/g soil). Geochemical severity (e.g. pH, electrical conductivity) primarily affected bacterial community similarity and successfully explained the divergent structure of a subset of samples. 16S rRNA amplicon pyrosequencing further revealed in Chapter 3 the identity of specific phyla that preferentially exist within certain habitats (i.e.\ Acidobacteria\ in alkaline soils,\ Nitrospira\ in mesic soils) suggesting the presence of niche specialists and spatial heterogeneity of taxa-specific functions (i.e. nitrite oxidation). Additionally, environmental parameters had different explanatory power towards predicting bacterial richness at varying taxonomic scales, from 57\% of phylum-level richness with pH to 91\% of order- and genus-level richness with moisture. Finally, Chapter 4 details a simultaneous sampling of soil communities and their associated ecosystem functions (primary productivity, enzymatic decomposition) and indicates that the overall organic substrate diversity may be greater in mesic soils where bacterial diversity is also highest, thus a potentially unforeseen driver of community dynamics. I also quantified annual rates of soil production which range between 0.7 - 18.1g C/m2/yr from the more arid to productive soils, respectively. In conclusion, the extension of biogeographical theory for macroorganisms has proven successful and both environmental severity and resource availability have obvious (although different) effects on the diversity and composition of soil microbial communities.

}, keywords = {LTER-MCM, biogeochemistry, biogeography, McMurdo Dry Valleys, microbial ecology, productivity/diversity theory}, url = {http://hdl.handle.net/10919/64417}, author = {Kevin M. Geyer}, editor = {John E. Barrett} } @article {1064, title = {Soil microbial responses to increased moisture and organic resources along a salinity gradient in a polar desert.}, journal = {Applied and Environmental Microbiology.}, volume = {80}, year = {2014}, month = {05/2014}, pages = {3034-3043}, chapter = {3034}, abstract = {Microbial 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.}, keywords = {LTER-MCM}, doi = {10.1128/AEM.03414-13}, author = {David J. Van Horn and Okie, J.G. and Heather N. Buelow and Michael N. Gooseff and John E. Barrett and Cristina D. Takacs-Vesbach} } @article {1084, title = {Environmental controls over bacterial communities in polar desert soils}, journal = {Ecosphere}, volume = {4}, year = {2013}, month = {10/2013}, pages = {art127}, keywords = {LTER-MCM}, doi = {10.1890/ES13-00048.1}, author = {Kevin M. Geyer and Adam E. Altrichter and David J. Van Horn and Cristina D. Takacs-Vesbach and Michael N. Gooseff and John E. Barrett} } @article {1092, title = {Factors Controlling Soil Microbial Biomass and Bacterial Diversity and Community Composition in a Cold Desert Ecosystem: Role of Geographic Scale}, journal = {PLoS ONE}, volume = {8}, year = {2013}, month = {06/2013}, pages = {e66103}, keywords = {LTER-MCM}, doi = {10.1371/journal.pone.0066103.s003}, url = {http://www.plosone.org/article/info\%3Adoi\%2F10.1371\%2Fjournal.pone.0066103}, author = {David J. Van Horn and Van Horn, M. Lee and John E. Barrett and Michael N. Gooseff and Adam E. Altrichter and Kevin M. Geyer and Lydia H. Zeglin and Cristina D. Takacs-Vesbach} } @article {1083, title = {Local and regional influences over soil microbial metacommunities in the Transantarctic Mountains}, journal = {Ecosphere}, volume = {4}, year = {2013}, month = {11/2013}, pages = {art136}, keywords = {LTER-MCM}, doi = {10.1890/ES13-00136.1}, author = {Eric R. Sokol and Herbold, Craig W. and Charles K. Lee and Craig S Cary and John E. Barrett} } @article {1089, title = {Seasonal controls on snow distribution and aerial ablation at the snow-patch and landscape scales, McMurdo Dry Valleys, Antarctica}, journal = {The Cryosphere}, volume = {7}, year = {2013}, month = {09/2013}, pages = {917 - 931}, keywords = {LTER-MCM}, doi = {10.5194/tc-7-917-2013}, url = {http://www.the-cryosphere.net/7/917/2013/tc-7-917-2013.html}, author = {Eveland, Jeffery and Michael N. Gooseff and Lampkin, Derrick J. and John E. Barrett and Cristina D. Takacs-Vesbach} } @article {1096, title = {Shallow groundwater systems in a polar desert, McMurdo Dry Valleys}, journal = {Hydrogeology Journal}, volume = {21}, year = {2013}, month = {02/2013}, pages = {171 - 183}, keywords = {LTER-MCM}, doi = {10.1007/s10040-012-0926-3}, url = {http://link.springer.com/article/10.1007\%2Fs10040-012-0926-3}, author = {Michael N. Gooseff and John E. Barrett and Joseph S. Levy} } @article {1090, title = {Spatial and temporal patterns of snow accumulation and aerial ablation across the McMurdo Dry Valleys, Antarctica}, journal = {Hydrological Processes}, volume = {27}, year = {2013}, month = {09/2013}, pages = {2864 - 2875}, keywords = {LTER-MCM}, doi = {10.1002/hyp.9407}, url = {http://onlinelibrary.wiley.com/doi/10.1002/hyp.9407/pdf}, author = {Eveland, Jeffery and Michael N. Gooseff and Lampkin, Derrick J. and John E. Barrett and Cristina D. Takacs-Vesbach} } @article {1100, title = {Water track modification of soil ecosystems in the Lake Hoare basin, Taylor Valley, Antarctica}, journal = {Antarctic Science}, year = {2013}, pages = {1 - 10}, keywords = {LTER-MCM}, doi = {10.1017/S095410201300045X}, author = {Joseph S. Levy and Andrew G Fountain and Michael N. Gooseff and John E. Barrett and Robert Vantreese and Kathleen A. Welch and W. Berry Lyons and Uffe N. Nielsen and Diana H. Wall} } @article {1128, title = {Bacterial Community Structure Along Moisture Gradients in the Parafluvial Sediments of Two Ephemeral Desert Streams}, journal = {Microbial Ecology}, volume = {61}, year = {2011}, month = {4/2011}, pages = {543 - 556}, keywords = {LTER-MCM}, doi = {10.1007/s00248-010-9782-7}, url = {http://www.springerlink.com/content/r83j53334v5n505w/}, author = {Lydia H. Zeglin and Clifford N. Dahm and John E. Barrett and Michael N. Gooseff and Shannon K. Fitpatrick and Cristina D. Takacs-Vesbach} } @article {3537, title = {Implications of meltwater pulse events for soil biology and biogeochemical cycling in a polar desert}, journal = {Polar Research}, volume = {3081281030352511340}, year = {2011}, month = {12/2011}, keywords = {LTER-MCM}, issn = {0800-0395}, doi = {10.3402/polar.v30i0.14555}, url = {http://www.polarresearch.net/index.php/polar/article/view/14555}, author = {Ball, Becky and John E. Barrett and Michael N. Gooseff and Ross A. Virginia and Diana H. Wall} } @article {1147, title = {Experimentally increased snow accumulation alters soil moisture and animal community structure in a polar desert}, journal = {Polar Biology}, volume = {33}, year = {2010}, month = {7/2010}, pages = {897 - 907}, keywords = {LTER-MCM}, doi = {10.1007/s00300-010-0766-3}, author = {Edward Ayres and Johnson N. Nkem and Diana H. Wall and Byron Adams and John E. Barrett and Breana L. Simmons and Ross A. Virginia and Andrew G Fountain} } @inbook {1171, title = {Factors promoting microbial diversity in the McMurdo Dry Valleys}, booktitle = {Life in Antarctic Deserts and other Cold Dry Environments: Astrobiological Analogues}, series = {Cambridge Astrobiology}, volume = {5}, year = {2010}, pages = {221-257}, publisher = {Cambridge University Press}, organization = {Cambridge University Press}, keywords = {LTER-MCM}, isbn = {9780521889193}, doi = {10.1017/CBO9780511712258.008}, url = {http://ebooks.cambridge.org/chapter.jsf?bid=CBO9780511712258\&cid=CBO9780511712258A015}, author = {Cristina D. Takacs-Vesbach and Lydia H. Zeglin and Michael N. Gooseff and John E. Barrett and John C. Priscu} } @mastersthesis {4082, title = {Landscape history and contemporary environmental drivers of microbial community structure and function}, volume = {MS}, year = {2010}, school = {Virginia Tech}, type = {masters}, address = {Blacksburg, VA}, abstract = {

Recent work in microbial ecology has focused on elucidating controls over biogeographic patterns and connecting microbial community composition to ecosystem function. My objective was to investigate the relative influences of landscape legacies and contemporary environmental factors on the distribution of soil microbial communities and their contribution to ecosystem processes across a glacial till sequence in Taylor Valley, Antarctica. Within each till unit, I sampled from dry areas and areas with visible evidence of recent surface water movement generated by seasonal melting of ephemeral snow packs and hillslope ground ice. Using T-RFLP 16S rRNA gene profiles of microbial communities, I analyzed the contribution of till and environmental factors to community similarity, and assessed the functional potential of the microbial community using extracellular enzyme activity assays. Microbial communities were influenced by geochemical differences among both tills and local environments, but especially organized by variables associated with water availability as the first axis of an NMDS ordination was strongly related to shifts in soil moisture content. CCA revealed that tills explained only 3.4\% of the variability in community similarity among sites, while geochemical variables explained 18.5\%. Extracellular enzyme activity was correlated with relevant geochemical variables reflecting the influence of nutrient limitation on microbial activity. In addition, enzyme activity was related to changes in community similarity, particularly in wet environments with a partial Mantel correlation of 0.32. These results demonstrate how landscape history and environmental conditions can shape the functional potential of a microbial community mediated through shifts in microbial community composition.

}, keywords = {LTER-MCM, community similarity, extracellular enzyme activity, McMurdo Dry Valleys, microbial biogeography, soil geochemistry, T-RFLP}, url = {http://hdl.handle.net/10919/31883}, author = {Adam E. Altrichter}, editor = {John E. Barrett} } @inbook {1172, title = {The legacy of aqueous environments on soils of the McMurdo Dry Valleys: contexts for future exploration of martian soils}, booktitle = {Life in Antarctic Deserts and other Cold Dry Environments}, volume = {5}, year = {2010}, pages = {78 - 109}, publisher = {Cambridge University Press}, organization = {Cambridge University Press}, address = {Cambridge}, keywords = {LTER-MCM}, isbn = {9780521889193}, doi = {10.1017/CBO9780511712258.003}, url = {http://ebooks.cambridge.org/chapter.jsf?bid=CBO9780511712258\&cid=CBO9780511712258A010}, author = {John E. Barrett and Poage, M and Michael N. Gooseff and Cristina D. Takacs-Vesbach} } @article {1186, title = {Hydrologic characteristics of lake- and stream-side riparian wetted margins in the McMurdo Dry Valleys, Antarctica}, journal = {Hydrological Processes}, volume = {23}, year = {2009}, pages = {1255-1267}, keywords = {LTER-MCM}, doi = {LTER}, author = {Northcott, M and Michael N. Gooseff and John E. Barrett and Lydia H. Zeglin and Cristina D. Takacs-Vesbach and Humphrey, J} } @article {1187, title = {Interactions between physical and biotic factors influence CO_2 flux in Antarctic dry valley soils}, journal = {Soil Biology and Biochemistry}, volume = {41}, year = {2009}, pages = {1510-1517}, keywords = {LTER-MCM}, doi = {LTER}, author = {Ball, Becky and Ross A. Virginia and John E. Barrett and Andrew N. Parsons and Diana H. Wall} } @article {1189, title = {Landscape Distribution of Microbial Activity in the McMurdo Dry Valleys: Linked Biotic Processes, Hydrology, and Geochemistry in a Cold Desert Ecosystem}, journal = {Ecosystems}, volume = {12}, year = {2009}, pages = {562-573}, keywords = {LTER-MCM}, doi = {LTER}, author = {Lydia H. Zeglin and Sinsabaugh, R and John E. Barrett and Michael N. Gooseff and Cristina D. Takacs-Vesbach} } @article {1190, title = {Long-term experimental warming reduces soil nematode populations in the McMurdo Dry Valleys, Antarctica}, journal = {Soil Biology \& Biochemistry}, volume = {41}, year = {2009}, pages = {2052-2060}, keywords = {LTER-MCM}, doi = {10.1016/j.soilbio.2009.07.009}, author = {Breana L. Simmons and Diana H. Wall and Byron Adams and Edward Ayres and John E. Barrett and Ross A. Virginia} } @article {1193, title = {Spatial variation in soil active-layer geochemistry across hydrologic margins in polar desert ecosystems.}, journal = {Hydrology and Earth System Sciences}, volume = {13}, year = {2009}, pages = {2349-2358}, keywords = {LTER-MCM}, doi = {LTER}, author = {John E. Barrett and Michael N. Gooseff and Cristina D. Takacs-Vesbach} } @article {1194, title = {State of the Antarctic and the Southern Ocean climate system,}, journal = {Review of Geophysics}, volume = {47}, year = {2009}, keywords = {LTER-MCM}, doi = {LTER}, author = {Paul A. Mayewski and David Bromwich and Campbell, H and Hamilton, G and W. Berry Lyons and Maasch, K and Aoki, S and Xiao, C and van Ommen, T and Meredith, M and Summerhayes, C and Turner, J and Worby, A and John E. Barrett and Casassa, G and Bertler, N and T Bracegirdle} } @article {1195, title = {Terrestrial mesofauna in above- and below-ground habitats: Taylor Valley, Antarctica}, journal = {Polar Biology}, volume = {32}, year = {2009}, pages = {1549-1558}, keywords = {LTER-MCM}, doi = {LTER}, author = {Breana L. Simmons and Diana H. Wall and Byron Adams and Edward Ayres and John E. Barrett and Ross A. Virginia} } @article {1196, title = {Thermal Characterisation of Active Layer Across a Soil Moisture Gradient in the McMurdo Dry Valleys, Antarctica}, journal = {Permafrost and Periglacial Processes}, volume = {20}, year = {2009}, pages = {27-39}, keywords = {LTER-MCM}, doi = {10.1002/ppp.634}, author = {Ikard, S and Michael N. Gooseff and John E. Barrett and Cristina D. Takacs-Vesbach} } @article {1210, title = {Decline in a dominant invertebrate species contributes to altered carbon cycling in a low-diversity soil ecosystem}, journal = {Global Change Biology}, volume = {14}, year = {2008}, pages = {1734-1744}, keywords = {LTER-MCM}, doi = {LTER}, author = {John E. Barrett and Ross A. Virginia and Diana H. Wall and Byron Adams} } @article {1211, title = {Effects of Human Trampling on Populations of Soil Fauna in the McMurdo Dry Valleys, Antarctica.}, journal = {Conservation Biology}, volume = {22}, year = {2008}, month = {12/2008}, pages = {1544-1551}, abstract = {

Antarctic ecosystems are often considered nearly pristine because levels of anthropogenic disturbance are extremely low there. Nevertheless, over recent decades there has been a rapid increase in the number of people, researchers and tourists, visiting Antarctica. We evaluated, over 10 years, the direct impact of foot traffic on the abundance of soil animals and soil properties in Taylor Valley within the McMurdo Dry Valleys region of Antarctica. We compared soils from minimally disturbed areas with soils from nearby paths that received intermediate and high levels of human foot traffic (i.e., up to approximately 80 passes per year). The nematodes Scottnema lindsayae and Eudorylaimus sp. were the most commonly found animal species, whereas rotifers and tardigrades were found only occasionally. On the highly trampled footpaths, abundance of S. lindsayae and Eudorylaimus sp. was up to 52 and 76\% lower, respectively, than in untrampled areas. Moreover, reduction in S. lindsayae abundance was more pronounced after 10 years than 2 years and in the surface soil than in the deeper soil, presumably because of the longer period of disturbance and the greater level of physical disturbance experienced by the surface soil. The ratio of living to dead Eudorylaimus sp. also declined with increased trampling intensity, which is indicative of increased mortality or reduced fecundity. At one site there was evidence that high levels of trampling reduced soil CO2 fluxes, which is related to total biological activity in the soil. Our results show that even low levels of human traffic can significantly affect soil biota in this ecosystem and may alter ecosystem processes, such as carbon cycling. Consequently, management and conservation plans for Antarctic soils should consider the high sensitivity of soil fauna to physical disturbance as human presence in this ecosystem increases.

}, keywords = {LTER-MCM}, doi = {10.1111/j.1523-1739.2008.01034.x}, author = {Edward Ayres and Johnson N. Nkem and Diana H. Wall and Byron Adams and John E. Barrett and Broos, E and Andrew N. Parsons and Powers, Laura E. and Breana L. Simmons and Ross A. Virginia} } @article {1204, title = {Hydrologic response to extreme warm and cold summers in the McMurdo Dry Valleys, East Antarctica}, journal = {Antarctic Science}, volume = {20}, year = {2008}, month = {05/16/2008}, pages = {499-509}, type = {Journal}, keywords = {LTER-MCM, Climate Response, streams}, doi = {10.1017/S0954102008001272}, author = {Peter T. Doran and Christopher P. McKay and Andrew G Fountain and Thomas H. Nylen and Diane M. McKnight and Chris Jaros and John E. Barrett} } @article {1205, title = {The influence of soil geochemistry on nematode distribution, McMurdo Dry Valleys, Antarctica}, journal = {Arctic, Antarctic, and Alpine Research}, volume = {40}, year = {2008}, month = {02/2008}, pages = {119-128}, keywords = {LTER-MCM}, doi = {10.1657/1523-0430(06-051)[POAGE]2.0.CO;2}, author = {Poage, M and John E. Barrett and Ross A. Virginia and Diana H. Wall} } @article {1232, title = {Microbial community composition in soils of Northern Victoria Land, Antarctica}, journal = {Environmental Microbiology}, volume = {10}, year = {2008}, pages = {1713-1724}, keywords = {LTER-MCM}, doi = {LTER}, author = {Niederberger, T and McDonald, i and Hacker, A and Soo, R and John E. Barrett and Diana H. Wall and Craig S Cary} } @article {1203, title = {Persistent effects of a discrete climate event on a polar desert ecosystem}, journal = {Global Change Biology}, volume = {14}, year = {2008}, month = {06/2008}, pages = {2249-2261}, type = {Journal}, keywords = {LTER-MCM, Climate Response, nematodes}, doi = {10.1111/j.1365-2486.2008.01641.x}, author = {John E. Barrett and Ross A. Virginia and Diana H. Wall} } @article {1233, title = {Soil phosphorus cycling in an Antarctic polar desert}, journal = {Geochimica et Cosmochimica Acta}, volume = {144}, year = {2008}, pages = {21-32}, keywords = {LTER-MCM}, doi = {LTER}, author = {D. Brad Bate and John E. Barrett and Poage, M and Ross A. Virginia} } @article {1236, title = {Biogeochemical stoichiometry of Antarctic Dry Valley ecosystems}, journal = {Journal of Geophysical Research}, volume = {112}, year = {2007}, month = {02/2007}, pages = {G01010+12}, abstract = {

Among aquatic and terrestrial landscapes of the McMurdo Dry Valleys, Antarctica, ecosystem stoichiometry ranges from values near the Redfield ratios for C:N:P to nutrient concentrations in proportions far above or below ratios necessary to support balanced microbial growth. This polar desert provides an opportunity to evaluate stoichiometric approaches to understand nutrient cycling in an ecosystem where biological diversity and activity are low, and controls over the movement and mass balances of nutrients operate over 10\–106\ years. The simple organisms (microbial and metazoan) comprising dry valley foodwebs adhere to strict biochemical requirements in the composition of their biomass, and when activated by availability of liquid water, they influence the chemical composition of their environment according to these ratios. Nitrogen and phosphorus varied significantly in terrestrial and aquatic ecosystems occurring on landscape surfaces across a wide range of exposure ages, indicating strong influences of landscape development and geochemistry on nutrient availability. Biota control the elemental ratio of stream waters, while geochemical stoichiometry (e.g., weathering, atmospheric deposition) evidently limits the distribution of soil invertebrates. We present a conceptual model describing transformations across dry valley landscapes facilitated by exchanges of liquid water and biotic processing of dissolved nutrients. We conclude that contemporary ecosystem stoichiometry of Antarctic Dry Valley soils, glaciers, streams, and lakes results from a combination of extant biological processes superimposed on a legacy of landscape processes and previous climates.

}, keywords = {LTER-MCM, Biggie}, doi = {10.1029/2005JG000141}, author = {John E. Barrett and Ross A. Virginia and W. Berry Lyons and Diane M. McKnight and John C. Priscu and Andrew G Fountain and Diana H. Wall and Daryl L. Moorhead and Peter T. Doran} } @article {1240, title = {Controls on the spatial dimensions of wetted hydrologic margins of two antarctic lakes}, journal = {Vadose Zone Journal}, volume = {6}, year = {2007}, pages = {841-848}, keywords = {LTER-MCM}, doi = {10.2136/​vzj2006.0161}, author = {Michael N. Gooseff and John E. Barrett and Melissa L. Northcott and D. Brad Bate and Kenneth R. Hill and Lydia H. Zeglin and Bobb, M and Cristina D. Takacs-Vesbach} } @article {1252, title = {Unique similarity of faunal communities across aquatic terrestrial interfaces in a polar desert ecosystem}, journal = {Ecosystems}, year = {2007}, keywords = {LTER-MCM}, doi = {LTER}, author = {Edward Ayres and Diana H. Wall and Byron Adams and John E. Barrett and Ross A. Virginia} } @inbook {1261, title = {Biogeochemistry, terrestrial}, booktitle = {Encyclopedia of the Antarctic Vol 1}, volume = {1}, year = {2006}, pages = {154-155}, publisher = {Routledge Press}, organization = {Routledge Press}, address = {New York}, keywords = {LTER-MCM}, doi = {LTER}, author = {John E. Barrett and Ross A. Virginia}, editor = {B. Riffenburgh} } @article {1264, title = {Co-variation in soil biodiversity and biogeochemistry in Northern and Southern Victoria Land, Antarctica}, journal = {Antarctic Science}, volume = {18}, year = {2006}, pages = {535-548}, keywords = {LTER-MCM}, doi = {10.1017/S0954102006000587}, url = {https://www.cambridge.org/core/journals/antarctic-science/article/covariation-in-soil-biodiversity-and-biogeochemistry-in-northern-and-southern-victoria-land-antarctica/C3514C28DB75F3A19DB5F266D4B1B56E}, author = {John E. Barrett and Ross A. Virginia and Diana H. Wall and Craig S Cary and Byron Adams and Hacker, A and Aislabie, J} } @inbook {1273, title = {Pedogenic carbonate distribution within glacial till in Taylor Valley, Southern Victoria Land, Antarctica}, booktitle = {Paleoenvironmental Record and Applications of Calcretes and Palustrine Carbonates}, year = {2006}, pages = {89-103}, publisher = {Geological Society of America}, organization = {Geological Society of America}, keywords = {LTER-MCM}, doi = {10.1130/2006.2416(06)}, author = {Foley, K and W. Berry Lyons and John E. Barrett and Ross A. Virginia} } @article {1281, title = {Phosphorus fractions in soils of Taylor Valley, Antarctica}, journal = {Soil Science Society of America Journal}, volume = {70}, year = {2006}, pages = {806-815}, keywords = {LTER-MCM}, doi = {LTER}, author = {Blecker, S and Ippolito, J and John E. Barrett and Diana H. Wall and Ross A. Virginia and Norvell, K} } @article {1283, title = {Salt tolerance and survival thresholds for two species of Antarctic soil nematodes}, journal = {Polar Biology}, volume = {29}, year = {2006}, pages = {643-651}, keywords = {LTER-MCM}, doi = {LTER}, author = {Johnson N. Nkem and Ross A. Virginia and John E. Barrett and Diana H. Wall and Li, G} } @article {1274, title = {Soil carbon turnover model for the McMurdo Dry Valleys, Antarctica}, journal = {Soil Biology and Biochemistry}, volume = {38}, year = {2006}, pages = {3065-3082}, keywords = {LTER-MCM}, doi = {LTER}, author = {John E. Barrett and Ross A. Virginia and Andrew N. Parsons and Diana H. Wall} } @article {1277, title = {A synthesis of soil biodiversity and ecosystem functioning in Victoria Land, Antarctica}, journal = {Soil Biology and Biochemistry}, volume = {38}, year = {2006}, pages = {3001-3002}, keywords = {LTER-MCM}, doi = {LTER}, author = {Diana H. Wall and Byron Adams and John E. Barrett and D. W. Hopkins} } @article {1278, title = {Terrestrial ecosystem processes of Victoria Land, Antarctica}, journal = {Soil Biology and Biochemistry}, volume = {38}, year = {2006}, pages = {3019-3034}, keywords = {LTER-MCM}, doi = {LTER}, author = {John E. Barrett and Johnson N. Nkem and Sletten, R and Steltzer, H and Diana H. Wall and Wallenstein, M and Ross A. Virginia and D. W. Hopkins and Aislabie, J and Bargagli, R and Bockheim, J and Campbell, I and W. Berry Lyons and Daryl L. Moorhead} } @article {1279, title = {Wind dispersal of soil invertebrates in the McMurdo Dry Valleys, Antarctica}, journal = {Polar Biology}, volume = {29}, year = {2006}, pages = {346-352}, abstract = {

Dispersal of soil organisms is crucial for their spatial distribution and adaptation to the prevailing conditions of the Antarctic Dry Valleys. This study investigated the possibility of wind dispersal of soil invertebrates within the dry valleys. Soil invertebrates were evaluated in (1) pockets of transported sediments to lake ice and glacier surfaces, (2) wind-transported dust particles in collection pans (Bundt pans) 100\ cm above the soil surface, and (3) sediments transported closer to the surface (\<50\ cm) and collected in open top chambers (OTCs). Invertebrates were extracted and identified. Nematodes were identified to species and classified according to life stage and sex. Three species of nematodes were recovered and\ Scottnema lindsayae\ was the most dominant. There were more juveniles (\∼71\%) in the transported sediments than adults (29\%). Tardigrades and rotifers were more abundant in sediments on lake and glacier surfaces while nematodes were more abundant in the dry sediment collections of Bundt pans and OTCs. The abundance of immobile (dead) nematodes in the Bundt pans and OTCs was three times greater than active (live) nematodes. Anhydrobiosis constitutes a survival mechanism that allows wind dispersal of nematodes in the McMurdo Dry Valleys. Our results show that soil invertebrates are dispersed by wind in the Dry Valleys and are viable in ice communities on lake surfaces and glaciers.

}, keywords = {LTER-MCM, Biggie}, doi = {10.1007/s00300-005-0061-x}, url = {http://link.springer.com/content/pdf/10.1007\%2Fs00300-005-0061-x}, author = {Johnson N. Nkem and Diana H. Wall and Ross A. Virginia and John E. Barrett and Broos, E and Porazinska, D and Byron Adams} } @article {1289, title = {Potential soil organic matter turnover in Taylor Valley, Antarctica}, journal = {Arctic, Antarctic, and Alpine Research}, volume = {37}, year = {2005}, month = {02/2005}, pages = {108-117}, type = {Journal}, abstract = {

Antarctic Dry Valley ecosystems are among the most inhospitable soil ecosystems on earth with simple food webs and nearly undetectable fluxes of carbon (C) and nitrogen (N). Due to the lack of vascular plants, soil organic matter concentrations are extremely low, and it is unclear how much of the contemporary soil C budget is actively cycling or a legacy of paleolake production and sedimentation. While recent work indicates multiple sources of organic matter for dry valley soils, the composition and kinetics of organic pools remain poorly characterized. We examined soil organic matter pools and potential C and N turnover in soils from within six sites located across three hydrological basins of Taylor Valley, Antarctica that differed in surface age, microclimate and proximity to legacy (paleolake) sources of organic matter. We estimated potential C and N mineralization, and rate kinetics using gas exchange and repeated leaching techniques during 90-d incubations of surface soils collected from valley basin and valley slope positions in three basins of Taylor Valley. Soil organic C content was negatively correlated with the ages of underlying tills, supporting previous descriptions of legacy organic matter. Carbon and N mineralization generally followed 1st order kinetics and were well described by exponential models. Labile pools of C (90 d) were 10\% of the total organic C in the upper 5 cm of the soil profile. Labile N was 50\% of the total N in surface soils of Taylor Valley. These results show that a large proportion of soil C and particularly N are mineralizable under suitable conditions and suggest that a kinetically defined labile pool of organic matter is potentially active in the field during brief intervals of favorable microclimate. Climate variation changing the duration of these conditions may have potentially large effects on the small pools of C and N in these soils.

}, keywords = {LTER-MCM, Biggie}, doi = {10.1657/1523-0430(2005)037[0108:PSOMTI]2.0.CO;2}, url = {http://instaar.metapress.com/content/e653225425230175/}, author = {John E. Barrett and Ross A. Virginia and Andrew N. Parsons and Diana H. Wall} } @article {1342, title = {Soil carbon dioxide flux from Antarctic Dry Valley soils}, journal = {Ecosystems}, volume = {7}, year = {2004}, pages = {286-295}, keywords = {LTER-MCM}, author = {Andrew N. Parsons and John E. Barrett and Diana H. Wall and Ross A. Virginia} } @article {1347, title = {Variation in biogeochemistry and soil biodiversity across spatial scales in a polar desert}, journal = {Ecology}, volume = {85}, year = {2004}, pages = {3105-3118}, abstract = {
Desert ecosystems are characterized by distinct spatial patterning in soil
biogeochemistry and biodiversity. In the Antarctic Dry Valleys, soil polygons are prominent
features of the landscape and may be key units for scaling local ecological information to
the greater region. We examined polygon soils in each of the three basins of Taylor Valley,
Antarctica. Our objectives were to characterize variability in soil biogeochemistry and
biodiversity at local to regional scales, and to test the influence of soil properties upon
invertebrate communities. We found that soil biogeochemical properties and biodiversity
vary over multiple spatial scales from fine (,10 m) to broad (.10 km) scales. Differences
in biogeochemistry were most pronounced at broad scales among the major lake basins of
Taylor Valley corresponding to differences in geology and microclimate, while variation
in invertebrate biodiversity and abundance occurred at landscape scales of 10\–500 m, and
within individual soil polygons. Variation in biogeochemistry and invertebrate communities
across these scales reflects the influence of physical processes and landscape development
over ecosystem structure in the dry valleys. The development of soil polygons influences
the spatial patterning of soil properties such as soil organic matter, salinity, moisture, and
invertebrate habitat suitability. Nematode abundance and life history data indicate that
polygon interiors are more suitable habitats than soils in the troughs at the edges of polygons.
These data suggest that physical processes (i.e., polygon development) and biogeochemistry
are important influences on the spatial variability of biotic communities in dry valley soil
ecosystems.
}, keywords = {LTER-MCM}, doi = {10.1890/03-0213}, author = {John E. Barrett and Ross A. Virginia and Diana H. Wall and Andrew N. Parsons and Powers, Laura E. and Melody B. Burkins} } @article {1371, title = {Organic matter and soil biota of upland wetlands in Taylor Valley, Antarctica}, journal = {Polar Biology}, volume = {26}, year = {2003}, pages = {1009-1019}, keywords = {LTER-MCM}, author = {Daryl L. Moorhead and John E. Barrett and Ross A. Virginia and Diana H. Wall and Porazinska, D} } @article {1376, title = {Snow patch influence on soil biogeochemical processes and invertebrate distribution in the McMurdo Dry Valleys, Antarctica}, journal = {Arctic, Antarctic, and Alpine Research}, volume = {35}, year = {2002}, month = {02/2003}, pages = {91-99}, type = {Journal}, keywords = {LTER-MCM, Biggie}, doi = {10.1657/1523-0430(2003)035[0091:SPIOSB]2.0.CO;2}, url = {http://instaar.metapress.com/content/r086455ju7213711/}, author = {Michael N. Gooseff and John E. Barrett and Peter T. Doran and Andrew G Fountain and W. Berry Lyons and Andrew N. Parsons and Porazinska, D and Ross A. Virginia and Diana H. Wall} } @article {1396, title = {Trends in resin and KCl-extractable soil nitrogen across landscape gradients in Taylor Valley, Antarctica}, journal = {Ecosystems}, volume = {5}, year = {2002}, pages = {289-299}, keywords = {LTER-MCM}, author = {John E. Barrett and Ross A. Virginia and Diana H. Wall} }