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The McMurdo Dry Valleys of Antarctica are an extreme polar desert. Mineral soils support subsurface microbial communities and translucent rocks support development of hypolithic communities on ventral surfaces in soil contact. Despite significant research attention, relatively little is known about taxonomic and functional diversity or their inter-relationships. Here we report a combined diversity and functional interrogation for soil and hypoliths of the Miers Valley in the McMurdo Dry Valleys of Antarctica. The study employed 16S rRNA fingerprinting and high throughput sequencing combined with the GeoChip functional microarray. The soil community was revealed as a highly diverse reservoir of bacterial diversity dominated by actinobacteria. Hypolithic communities were less diverse and dominated by cyanobacteria. Major differences in putative functionality were that soil communities displayed greater diversity in stress tolerance and recalcitrant substrate utilization pathways, whilst hypolithic communities supported greater diversity of nutrient limitation adaptation pathways. A relatively high level of functional redundancy in both soil and hypoliths may indicate adaptation of these communities to fluctuating environmental conditions.

The climate of maritime Antarctica has altered since the 1950s. However, the effects of increased temperature, precipitation and organic carbon and nitrogen availability on the fungal communities inhabiting the barren and oligotrophic fellfield soils that are widespread across the region are poorly understood. Here, we test how warming with open top chambers (OTCs), irrigation and the organic substrates glucose, glycine and tryptone soy broth (TSB) influence a fungal community inhabiting an oligotrophic maritime Antarctic fellfield soil. In contrast with studies in vegetated soils at lower latitudes, OTCs increased fungal community alpha diversity (Simpson's index and evenness) by 102-142% in unamended soil after 5 years. Conversely, OTCs had few effects on diversity in substrate-amended soils, with their only main effects, in glycine-amended soils, being attributable to an abundance of Pseudogymnoascus. The substrates reduced alpha and beta diversity metrics by 18-63%, altered community composition and elevated soil fungal DNA concentrations by 1-2 orders of magnitude after 5 years. In glycine-amended soil, OTCs decreased DNA concentrations by 57% and increased the relative abundance of the yeast Vishniacozyma by 45-fold. The relative abundance of the yeast Gelidatrema declined by 78% in chambered soil and increased by 1.9-fold in irrigated soil. Fungal DNA concentrations were also halved by irrigation in TSB-amended soils. In support of regional- and continental-scale studies across climatic gradients, the observations indicate that soil fungal alpha diversity in maritime Antarctica will increase as the region warms, but suggest that the accumulation of organic carbon and nitrogen compounds in fellfield soils arising from expanding plant populations are likely, in time, to attenuate the positive effects of warming on diversity. [ABSTRACT FROM AUTHOR]

Temperatures approaching or exceeding 20°C have been measured during summer in polar regions at the surfaces of barren fellfield soils under cloudless skies around solar noon. However, despite the upper temperature limit for the growth of cold‐adapted microbes—which are abundant in polar soils and have pivotal roles in nutrient cycling—typically being close to this temperature, previous studies have not addressed the consequences of climate change for the metabolism of these organisms in the natural environment. Here in a 5‐year field experiment on Alexander Island in the southern maritime Antarctic, we show that the abundance of Pseudogymnoascus roseus, the most widespread decomposer fungus in maritime Antarctic fellfield soils, is reduced by 1–2 orders of magnitude when irrigated and nutrient‐amended soils are warmed to >20°C during summer. Laboratory experiments under conditions mimicking those during midsummer in the natural environment indicated that the hyphal extension rates of P. roseus isolates and the activities of five extracellular enzymes are reduced by 54%–96% at high water availability after exposure to temperatures cycling daily from 2 to 21°C and 2 to 24°C, relative to temperatures cycling from 2 to 18°C. Given that the temperatures of surface soils at the study site already reach 19°C during midsummer, the observations reported here suggest that, at predicted rates of warming arising from moderate greenhouse gas emissions, inhibitory effects of climate change on the metabolism of P. roseus could manifest themselves within the next few decades. Furthermore, with peak temperatures at the surfaces of fellfield soils at other maritime Antarctic locations and in High Arctic and alpine regions already exceeding 20°C during summer, the observations suggest that climate warming has the potential to inhibit the growth of other cold‐adapted microbes, with negative effects on soils as the Earth's climate continues to warm. [ABSTRACT FROM AUTHOR]

The soils of the Maritime and sub‐Antarctic experience extreme environmental conditions but nonetheless host biological communities that can survive low temperatures, limited water availability and short day lengths or even the complete absence of solar radiation during the winter. We determined the soil organic carbon (SOC) and total nitrogen (N), soil microbial biomass (SMB), labile carbon (LC) and respiration rate (RR) in soil samples from the longest latitudinal transect (approximately 2,000 km) ever sampled exclusively in the Maritime and sub‐Antarctic, comprising 69 sites located between South Georgia (54°S) and south‐eastern Alexander Island (72°S). With the exception of the most northerly location (South Georgia), the greatest SMB values occurred at 67–68°S, despite the harsh environmental conditions. This is consistent with the relative nutrient richness of the soils at these latitudes, as indicated by large SOC and total soil N concentrations, which are in turn probably linked to more abundant guano and excreta deposition by sea birds and seals, which have fewer and smaller areas of ice‐free terrain to land or haul out on further south. South of 68°S, SOC values declined with increasing latitude, which is probably due to increasingly extreme environmental conditions. We also found that the SOC and SMB values, the proportion of SOC considered labile (LC/SOC) and the carbon mineralization rates expressed as either RR/SOC or RR/SMB were all small compared with values from less extreme temperate and tropical regions. However, the proportion of the SOC in the microbial biomass (SMB/SOC) was substantially greater than that reported for non‐polar soils. We conclude that although the soils of the Maritime and sub‐Antarctic have small and relatively inactive microbial communities, they are characterized by efficient conversion of organic resources into microbial biomass and large affinities for added substrates. Highlights: Soil carbon parameters are reported from sites along the longest latitudinal transect in Antarctica ever sampled.The soil microbial biomass tended to peak at 67–68°S, coinciding with relative SOC and N abundance in the soil, probably arising from guano and excreta from sea birds and mammals.The soil microbial community was small but highly efficient at converting organic resources into microbial biomass, as indicated by large microbial biomass/soil organic carbon ratios. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the relationships between fungal community composition, latitude and a range of physicochemical parameters in 58 soils sampled from a 2370 km latitudinal gradient between South Georgia (54°S, 38°W) in the sub-Antarctic and Mars Oasis (72°S, 68°W) on Alexander Island in the southern maritime Antarctic. Our study, which is based on approximately ten times the number of samples used in previous similar studies, indicates that latitude and its associated environmental parameters are not related to fungal community composition. Significant changes in the composition of soil fungal communities were observed in relation to gradients of the ratio of total organic carbon to nitrogen, and, to a lesser extent, soil pH. [Copyright &y& Elsevier]

Abstract: We investigated the effects of increased soil temperature, water and nutrient availability on soil bacterial communities at Wynn Knolls on Signy Island (60 °S) in the northern maritime Antarctic and at Mars Oasis (71 °S) in the southern maritime Antarctic. After 10–12 months, analyses of the concentrations of ester linked fatty acids (ELFAs) in soil indicated that bacterial communities responded positively to single applications of substrates at both locations, with 20% and 49% increases in total Gram positive and Gram negative bacterial markers, respectively, in response to the application of tryptic soy broth (TSB; a complex substrate containing organic carbon and nitrogen, plus other nutrient elements) at Wynn Knolls, and 120% and 44% increases in Gram positive bacterial markers at Mars Oasis in response to the application of TSB and the amino acid glycine (a relatively simple source of organic carbon and nitrogen), respectively. Responses to the warming treatment were not detected at Wynn Knolls, where open top chambers (OTCs) increased mean monthly soil temperatures by up to 0.7 °C, but at Mars Oasis, where OTCs increased monthly soil temperatures by up to 2.4 °C, warming led to 41% and 46% reductions in the concentrations of Gram positive bacterial markers in soil to which glycine and TSB had been applied, respectively. Warming also led to 55% and 51% reductions in the ratio of Gram positive to Gram negative markers in soils at Mars Oasis to which glycine and TSB had been applied. These data suggest that warming may constrain the responses of bacterial communities to carbon and nitrogen inputs arising from dead plant matter entering maritime Antarctic soils in future decades. [Copyright &y& Elsevier]