A habitat suitability model developed for soil biotic communities in the McMurdo Sound region, Antarctica predicts that soil moisture, organic carbon, and salinity exert control on the abundance and ...complexity of soil food chains. The model has been intensively tested in dry and carbon-poor soils of the Dry Valleys. To determine the influence of moisture and soil organic mater in wetter soils with high C content, invertebrates (nematodes, rotifers, and tardigrades) from soil samples collected in and near penguin rookeries on Ross Island (Cape Bird, Cape Crozier, and Cape Royds) were examined. Invertebrates were present in less than 50% of all collected soil samples. Although four nematode species were identified (Eudorylaimus antarcticus, Panagrolaimus davidi, Plectus antarcticus, Scottnema lindsayae), only populations of Panagrolaimus davidi were observed in soils collected from within penguin rookeries. Abundances of Panagrolaimus davidi and rotifers differed among rookeries, and year of sampling had a significant effect only on the populations of Panagrolaimus davidi. There were no temporal differences in soil moisture and soil chlorophyll a concentrations within each rookery or across rookeries. No invertebrates were correlated with soil moisture or chlorophyll a at the time of collection. Counter to our expectations, higher nutrient, organic matter, and moisture levels did not result in more abundant and diverse invertebrate communities in the rookery soils. It appears that excessive accumulations of nutrients, creating high soil salinity, may limit soil invertebrate presence within active rookeries.PUBLICATION 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.PUBLICATION ABSTRACT
The aim of this study was to understand the spatial distribution of microbial communities (18S and 16S rRNA genes) across one of the harshest terrestrial landscapes on Earth. We carried out Illumina ...sequencing using samples from two expeditions to the high slopes (up to 6050 m.a.s.l.) of Volcán Socompa and Llullaillaco to describe the microbial communities associated with the extremely dry tephra compared to areas that receive water from fumaroles and ice fields made up of nieves penitentes. There were strong spatial patterns relative to these landscape features with the most diverse (alpha diversity) communities being associated with fumaroles. Penitentes did not significantly increase alpha diversity compared to dry tephra at the same elevation (5825 m.a.s.l.) on Volcán Socompa, but the structure of the 18S community (beta diversity) was significantly affected by the presence of penitentes on both Socompa and Llullaillaco. In addition, the 18S community was significantly different in tephra wetted by penitentes versus dry tephra sites across many elevations on Llullaillaco. Traditional phototrophs (algae and cyanobacteria) were abundant in wetter tephra associated with fumaroles, and algae (but not cyanobacteria) were common in tephra associated with penitentes. Dry tephra had neither algae nor cyanobacteria but did host potential phototrophs in the Rhodospirillales on Volcán Llullaillaco, but not on Socompa. These results provide new insights into the distribution of microbes across one of the most extreme terrestrial environments on Earth and provide the first ever glimpse of life associated with nieves penitentes, spire-shaped ice structures that are widespread across the mostly unexplored high-elevation Andean Central Volcanic Zone.
Patterns of nematode population dynamics in an extreme environment were studies in the McMurdo Dry Valleys of Antarctica. Nematode populations are sensitive to soil disturbance and are useful ...indicators of environmental change. We hypothesized that the pristine soil environments of Antarctica that are suitable for life would support stable both spatially and temporally nematode populations. We established three sampling sites across an elevation gradient in Taylor Valley and sampled each site at larger and smaller spatial scales three-times over a 6-yr period (1993, 1995, and 1999). Nematode variables and soil moisture were significantly different among years. Soil moisture, nematode abundance, and life cycle parameters varied also with elevation, but not spatial scale at the grid size over the 6 yr. Generally, soil moisture declined during the time of the study and was greatest at the lowest elevation. Throughout the 6 yr, Scottnema lindsayae was most abundant at the highest elevation and dominated all sites, while Eudorylaimus antarcticus was most abundant at the lowest elevation. Plectus antarcticus was present only at the lowest elevation. While Scottnema was negatively correlated with soil moisture, Eudorylaimus and Plectus showed a positive relationship. Similarities among nematode species in life cycle characteristics (e.g., long life cycles and low reproductive rates) may indicate adaptive strategy for survival in the Dry Valleys soil environments. The differences, however, may indicate species specific sensitivity to changes in the soil characteristics such as moisture. Temporal variation of variables describing nematode populations in Antarctic soil suggests the nematode species respond to short-term climate variation and, thus, may be affected by long-term climate change.
Here, we review the current state of knowledge concerning high-elevation members of the extremophilic Cryptococcus albidus clade (now classified as the genus Naganishia). These fungi dominate ...eukaryotic microbial communities across the highest elevation, soil-like material (tephra) on volcanoes such as Llullaillaco, Socompa, and Saírecabur in the Atacama region of Chile, Argentina, and Bolivia. Recent studies indicate that Naganishia species are among the most resistant organisms to UV radiation, and a strain of N. friedmannii from Volcán Llullaillaco is the first organism that is known to grow during the extreme, diurnal freeze-thaw cycles that occur on a continuous basis at elevations above 6000 m.a.s.l. in the Atacama region. These and other extremophilic traits discussed in this review may serve a dual purpose of allowing Naganishia species to survive long-distance transport through the atmosphere and to survive the extreme conditions found at high elevations. Current evidence indicates that there are frequent dispersal events between high-elevation volcanoes of Atacama region and the Dry Valleys of Antarctica via "Rossby Wave" merging of the polar and sub-tropical jet streams. This dispersal hypothesis needs further verification, as does the hypothesis that Naganishia species are flexible "opportunitrophs" that can grow during rare periods of water (from melting snow) and nutrient availability (from Aeolian inputs) in one of the most extreme terrestrial habitats on Earth.
High elevation lakes are extreme ecosystems and serve as sentinels of various global changes.
An expedition to Volcán Llullaillaco in 1996 discovered an unstudied high‐elevation lake (6,170 m a.s.l.) ...that probably was formed as a result of the past eruptive events or climatic processes such as glacial retreat in the lake basin.
This article describes an initial physical characterization of the lake and its microbial communities derived from two sampling expeditions in 2013 and 2016.
The microbial community in the lake, with an area between 1.2 and 1.4 ha and a depth of 6.8 m, was dominated by Proteobacteria, Actinobacteria and Haloarchaea. In addition, 26 bacterial isolates were identified within the genera Subtercola, Xylophilus, Rhodanobacter, Mesorhizobium and Pseudomonas.
Lago Llullaillaco is one of the highest recorded lakes in the world, and this study highlights the unique microbial diversity of this aquatic ecosystem and the importance of its preservation to understand the complex biological processes under polyextreme conditions.
Interest in the sustainability of farming practices has increased in response to environmental problems associated with conventional agricultural management often adopted for the production of ...herbaceous, ornamentals, and fruit crops. Availability of measures of the status of the soil ecosystem is of immediate importance for environmental assessment and monitoring programs, as well as for farm managers who could timely modify their farming practices. This study investigated the effects of various agricultural management regimes comparing standard vs. reduced practices (irrigation rates, fertilization rates, and types of ground cover) on the structure of nematode fauna in a citrus orchard in the sandy ridge area of Central Florida. Ecological measures such as community structure indices, diversity indices, and maturity indices were assessed and related to different agricultural regimes. From the various indices of community structure, maturity indices were most effective in distinguishing differences between agricultural regimes. In an irrigation experiment (six irrigation rates), maturity indices could indicate history of water usage. In a multifactorial experiment (two fertilization levels, two irrigation levels, and two type of ground cover), maturity indices, unlike diversity indices, indicated the status and intensity of soil processes (decomposition, mineralization). Maturity indices were also the only measures at the index level responding consistently and significantly to fertilizer rates. Overall, maturity indices can provide sufficient information and thus prove to be efficient tool for quick estimates of the soil condition. Trophic groups might be useful in describing general and overall trends of the soil ecosystem status, however, this level of resolution is not recommended for monitoring purposes. Trophic grouping averages different, sometimes opposite, nematode responses observed at the generic level. Therefore, the most accurate and indicative information about the status and intensity of the soil processes is provided by characterization of the nematode community at the generic if not species level. The effects of farming practices on the status of macro- and micronutrients in the soil and on sustainability measures were also examined, and related to nematode components of the soil citrus ecosystem. Some nematode measures related to several components of sustainability and soil chemical measures.
PDF
