Cryoconite is a mixture of mineral and organic material covering glacial ice, playing important roles in biogeochemical cycles and lowering the albedo of a glacier surface. Understanding the ...differences in structure of cryoconite across the globe can be important in recognizing past and future changes in supraglacial environments and ice-organisms-minerals interactions. Despite the worldwide distribution and over a century of studies, the basic characteristics of cryoconite, including its forms and geochemistry, remain poorly studied. The major purpose of our study is the presentation and description of morphological diversity, chemical and photoautotrophs composition, and organic matter content of cryoconite sampled from 33 polar and mountain glaciers around the globe. Observations revealed that cryoconite is represented by various morphologies including loose and granular forms. Granular cryoconite includes smooth, rounded, or irregularly shaped forms; with some having their surfaces covered by cyanobacteria filaments. The occurrence of granules increased with the organic matter content in cryoconite. Moreover, a major driver of cryoconite colouring was the concentration of organic matter and its interplay with minerals. The structure of cyanobacteria and algae communities in cryoconite differs between glaciers, but representatives of cyanobacteria families Pseudanabaenaceae and Phormidiaceae, and algae families Mesotaeniaceae and Ulotrichaceae were the most common. The most of detected cyanobacterial taxa are known to produce polymeric substances (EPS) that may cement granules. Organic matter content in cryoconite varied between glaciers, ranging from 1% to 38%. The geochemistry of all the investigated samples reflected local sediment sources, except of highly concentrated Pb and Hg in cryoconite collected from European glaciers near industrialized regions, corroborating cryoconite as element-specific collector and potential environmental indicator of anthropogenic activity. Our work supports a notion that cryoconite may be more than just simple sediment and instead exhibits complex structure with relevance for biodiversity and the functioning of glacial ecosystems.
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•The morphology of cryoconite varies greatly between regions.•Cryoconite consists of loose mineral material or various types of granules.•Colour of cryoconite depends on organic matter content and its interplay with minerals.•Cryoconite is a complex structure providing various ecological niches for glacial microbes.
A major impact of global climate change is the decline of mosses and lichens and their replacement by vascular plants. Although we assume this decline will greatly affect ecosystem functioning, ...particularly in alpine and arctic areas where cryptogams make a substantial amount of biomass, the effects of this change in vegetation on soil microbial communities remains unknown. We asked whether changes in bacterial community composition and enzyme ratios were consistent across two sites in moss versus vascular plant dominated areas. Using data from treeline and subnival ecosystems, we compared bacterial community composition, enzyme activity, and soil chemistry in moss dominated and vascular plant dominated plots of two unique alpine environments. Further, we used a time series to examine plots that actively transitioned from moss dominated to vascular plant dominated over a seven-year time period. Bacterial community composition in the soils under these two vegetation covers was significantly different in both environments and changed over time due to plant colonization. Microbial activity was limited by carbon and phosphorus in all plots and there were no differences in BG:AP enzyme ratios; however, there were significantly higher NAG:AP and BG:AP ratios in vascular plant plots at one site, suggesting the potential for shifts toward microbial N acquisition in vascular plant dominated areas in the alpine. As vascular plants replace mosses under warming conditions, bacterial community composition and nutrient availability shift in ways that may result in changes to biogeochemical cycling and biotic interactions in these vulnerable ecosystems.
•Across two alpine sites we found differences in bacterial communities associated with moss and vascular plant vegetation.•Time series over 7 years of moss communities that actively transition to vascular plant show defined, predictable shift in bacterial communities.•Soil exoenzyme production demonstrates similar carbon and phosphorus nutrient limitations across all alpine samples.•More highly carbon-constrained soils show little biogeochemical responses to shifts of moss to vascular plant communities and related bacterial shifts.•Less carbon-constrained soils show a slight shift in microbial resource allocation toward nitrogen acquisition.
Invasive species have become a dominant component of native grasslands, leading to a reduction in biodiversity and ecosystem functioning. Grasslands hold the potential to sequester more carbon than ...forests, yet few large-scale intact grasslands remain on Earth. Consequently, the restoration of degraded grasslands is critical to resurrect the ecological and economic services they once provided. Although glyphosate-based herbicide restoration projects are among the most effective strategies to remove invasive plants and allow native species to reestablish, their off-target effects on belowground diversity are unclear. Nematodes are the most abundant and diverse animals on Earth and have been recognized as indicators of soil health due to their positioning at all trophic levels and ability to respond to environmental change such as pollution, disturbance, and climate change. The goal of this study was to examine the response of nematode communities to a glyphosate-based grassland restoration project. We applied different frequencies of Roundup ProMax® to field plots in the first year of the project and characterized the impact on nematode communities over the following four years using morphological counts and 18S rRNA metabarcoding. To test the effects of the herbicide on nematode community diversity, composition, and structure, we utilized a modelling approach with general linear models, PERMANOVAs, distance-based redundancy and co-occurrence network analyses. We show persistent negative effects on nematode diversity across all four years. In addition, compositional shifts and changes in nematode-specific functional indices indicated less healthy soils in herbicide-treated plots. Co-occurrence networks further confirmed less structured and more disturbed communities. No recovery of nematode communities in glyphosate treated plots was observed after four years, demonstrating the longevity of effects. In conclusion, this study reports negative off-target effects of glyphosate herbicide restoration projects on belowground diversity and the need to consider these factors in evaluating the long-term success of herbicide-based grassland restoration.
•Grasslands perform essential functions but are hindered by invasive plants.•Glyphosate-based herbicides (GBH) are used for cost-efficient habitat restoration.•GBHs negatively impact nematodes in vitro, but impacts are unclear in situ.•In a GBH grassland restoration scheme, nematodes were negatively affected.•Effects were persistent 4 years post application, despite major temporal variation.
Glyphosate is a widely used herbicide in agricultural, domestic, and restoration settings to manage weeds and invasive plants and is the active ingredient in the herbicide formulation Roundup. ...Concurrently with its drastic increase in usage, concern over indirect ecosystem effects and effects on non-target species has grown. In restoration, glyphosate is often used to remove invasive plants so native plants may be re-introduced. However, successful reintroductions require soils and microbial communities that support native plant growth, and it is critical that glyphosate applications do not harm soil microbes such as mycorrhizal fungi. Despite previous studies investigating the effects of glyphosate on soils and microbial communities, comprehensive field experiments combining soil chemistry and next generation sequencing technologies to describe both bacterial and eukaryotic responses to glyphosate are limited, especially in the contexts of ecosystem restoration and soil health. We studied the effects of the glyphosate-based herbicide Roundup Promax at frequencies of 0, 2, 4, and 5 applications over the course of 12 months on soil biotic and abiotic soil health indicators in a Colorado prairie dominated by the invasive cool-season grass Bromus inermis. Here we report cascading effects on soil chemistry, with increases in nitrate and acidity and consequent decreases in calcium content and cation exchange capacity. Bacterial and archaeal communities were more affected by Roundup Promax than eukaryotic communities, with decreases in phylogenetic diversity and changes in community structure following Roundup Promax applications, particularly after five applications. More critically, the colonization of plant roots by arbuscular mycorrhizal fungi decreased significantly in plots receiving even just two applications of Roundup Promax, and dark septate endophytes decreased after four applications. Our work shows that Roundup Promax had multiple negative effects on soil biota in this field study due to either direct effects or indirect effects mediated through plant removal. Our results suggest that repeated herbicide applications are especially damaging to soil health and microbe-plant associations. These effects in turn could severely hamper the ability of native plants to establish during ecosystem restoration projects.
•Roundup Promax was applied repeatedly to a Colorado grassland dominated by smooth brome (Bromus inermis).•Soil pH, calcium, and cation exchange capacity declined, while soil nitrate increased.•Soil bacterial communities declined in phylogenetic diversity and shifted in composition.•Soil eukaryotic richness and composition were not as affected by Roundup application.•Mycorrhizal fungi colonization of Bromus inermis decreased with Roundup application.
Soils in Antarctica support simple but unique biological assemblages in one of the most extreme terrestrial habitats on Earth. Among terrestrial fauna, microscopic invertebrates (nematodes, rotifers ...and tardigrades) are the most abundant and diverse, but the paucity of surveys still limits a more thorough understanding of their diversity and distribution patterns. To address this gap in knowledge, we conducted a survey across soil environments with differing biogeochemical characteristics (i.e., fellfields, moss communities, wetlands, and ornithogenic soils) at Edmonson Point. Our primary objective was to identify local diversity and drivers of distribution patterns of soil microfauna assemblages at the species level for all phyla. Presence of a broad range of soil habitats supported abundant and diverse microfauna of 24 species, including 18 rotifers, 4 nematodes, and 2 tardigrades. While nematode and tardigrade fauna were generally consistent with previous reports in the region, rotifers consisted mostly of bdelloids, newly-recorded and likely endemic species. Bdelloid rotifers were generally the most abundant followed by nematodes and tardigrades in similar numbers, with very patchy distributions and only nematodes found across all soil habitats. The type of soil environment was the most significant predictor of species distributions, with the richest and most abundant microfauna found in moist soils associated with cryptogamic vegetation and the poorest in dry fellfields and ornithogenic soils. Species distributions were also highly variable within particular environments and were related primarily to moisture, nutrients and organic matter, but availability and quality of food resources was the major underlying driver. Given the exceptionally wide range of terrestrial environments, Edmonson Point represents one of the most important biodiversity hot-spots for microfauna in the Ross Sea region, emphasizing its outstanding ecological importance and conservation value.
•We investigated diversity and distribution patterns of soil microfauna in Antarctica.•A broad range of soil habitats supported an abundant and diverse microfauna.•Species distributions reflected variability in soil geochemistry and food resources.•Distinct species-specific niche preferences were found across all microfaunal phyla.•Edmonson Point supports the highest microfauna diversity in the Ross Sea region.
Molecular evidence from sequences of three regions of ribosomal DNA (partial SSU, ITS-1, 5.8S and ITS-2, and D2/D3 expansion segments of LSU) is presented to show that the two belonolaimids described ...from turfgrass in Australia (Ibipora lolii and Morulaimus gigas) are identical. Morulaimus gigas is therefore considered a junior synonym of I. lolii. The decision to place the nematode in Ibipora rather than Morulaimus is supported by molecular studies which showed that I. lolii is not closely related to Morulaimus or Carphodorus, two belonolaimid genera that are only found in Australia. Survey data are presented to show that I. lolii is widespread on turfgrass around Newcastle in New South Wales and in Perth, Western Australia, where the infested area is increasing rapidly, largely because the nematode is being spread in planting material. Ibipora lolii damages all turfgrass species but is particularly damaging to kikuyu grass (Pennisetum clandestinum), the main grass used for sporting fields and recreational areas in warm regions of Australia. Data from an experiment in pots also show that the nematode multiplies to damaging levels on sugarcane. Symptoms on grasses are similar to those caused by the sting nematode, Belonolaimus longicaudatus, in south-eastern USA, but because the two nematodes are taxonomically different, I. lolii is referred to as the southern sting nematode. Ibipora lolii was not found in surveys of natural vegetation on the east and west coasts of Australia, suggesting that it is an introduced species, possibly originating in South America or the Caribbean, where other Ibipora species are found.
Pyrosequencing of an artificially assembled nematode community of known nematode species at known densities allowed us to characterize the potential extent of chimera problems in multi-template ...eukaryotic samples. Chimeras were confirmed to be very common, making up to 17% of all high quality pyrosequencing reads and exceeding 40% of all OCTUs (operationally clustered taxonomic units). Typically, chimeric OCTUs were made up of single or double reads, but very well covered OCTUs were also present. As expected, the majority of chimeras were formed between two DNA molecules of nematode origin, but a small proportion involved a nematode and a fragment of another eukaryote origin. In addition, examples of a combination of three or even four different template origins were observed. All chimeras were associated with the presence of conserved regions with 80% of all recombinants following a conserved region of about 25bp. While there was a positive influence of species abundance on the overall number of chimeras, the influence of specific-species identity was less apparent. We also suggest that the problem is not nematode exclusive, but instead applies to other eukaryotes typically accompanying nematodes (e.g. fungi, rotifers, tardigrades). An analysis of real environmental samples revealed the presence of chimeras for all eukaryotic taxa in patterns similar to that observed in artificial nematode communities. This information warrants caution for biodiversity studies utilizing a step of PCR amplification of complex DNA samples. When unrecognized, generated abundant chimeric sequences falsely overestimate eukaryotic biodiversity.
Arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) are two fungal groups that colonize plant roots and can benefit plant growth, but little is known about their landscape ...distributions. We performed sequencing and microscopy on a variety of plants across a high-elevation landscape featuring plant density, snowpack, and nutrient gradients. Percent colonization by both AMF and DSE varied significantly among plant species, and DSE colonized forbs and grasses more than sedges. AMF were more abundant in roots at lower elevation areas with lower snowpack and lower phosphorus and nitrogen content, suggesting increased hyphal recruitment by plants to aid in nutrient uptake. DSE colonization was highest in areas with less snowpack and higher inorganic nitrogen levels, suggesting an important role for these fungi in mineralizing organic nitrogen. Both of these groups of fungi are likely to be important for plant fitness and establishment in areas limited by phosphorus and nitrogen.
•Arbuscular mycorrhizae and dark septate endophytes were widespread in alpine plants.•Colonization levels varied among plant species and functional groups.•AMF increased at lower elevation, snowpack, phosphorus, and nitrogen levels.•DSE increased with inorganic nitrogen and lower snowpack.•AMF and DSE colonization levels were negatively correlated.
The McMurdo Dry Valleys is the largest of the ice-free areas in Antarctica. Precipitation events in excess of 1 cm of snow accumulation are rare. During the winter, snow is transported by strong ...katabatic winds blowing from the polar plateau, and deposited into the lee of topographic features (e.g., stream channels and other topographic depressions). At the start of the austral summer (early October), as much as 10% of the valley soils may be covered by distributed snow patches. Because liquid water is the primary driver of biological, physical, and chemical processes in this polar desert, quantifying fluxes of water from snow patches is important to understanding the influence of hydrology on soil biology and nutrient cycling. During the austral summer of 1999–2000, four snow patches that had developed during the previous winter in Taylor Valley were studied. We measured snow-patch area, depth, and snow water equivalent, as well as subnivian (under snow) and nearby exposed (control) soil temperature, light intensity, soil moisture, invertebrate abundance, soil organic matter content, and 95-d labile pools of C and N. Subnivian soils differed from exposed soils being as much as 26.8°C colder than exposed soils; average soil moisture ranging from 6.9 to 13.6% compared to 0.4% in exposed soils; soil invertebrate populations exceeding 7900 individuals kg−1 dry soil versus less than 1200 individuals kg−1 dry soil in exposed soils; and soil invertebrate species richness values greater than 2 taxa, compared to 1.3 taxa in exposed soils. The results of this study show that these seasonal, sparse snow patches may be an important source of moisture and control habitat of soil ecosystems in this extreme environment.
The tree Melaleuca quinquenervia invades all types of habitats of South Florida leading to up to 80% loss of aboveground diversity. To examine impacts on the belowground ecosystem, we investigated ...the composition and diversity of nematodes from soils dominated by the invasive tree and compared them with soils supporting native plant communities at six locations across the Florida Everglades over three years. Despite the significant differences in soil type, hydrology, and native plant composition of the sites, there were consistent differences in nematode communities between soil environments under the native and invaded plant communities. The total abundance and diversity of nematodes in soils dominated by M. quinquenervia was 60% and 80% of adjacent soils under native plants. Fungal-feeding and plant-parasitic nematodes were twice as abundant under native plants as under M. quinquenervia. Nematode communities under M. quinquenervia were bacterivore-dominated, while under native vegetation plant-parasite dominated. The overall diversity of nematodes was 20% lower under the exotic than under native plants, with plant parasites being 36% and fungivores being 30% less diverse. Soil moisture, % of Ca, Mg, and clay particles and total soil C and N were greater in M. quinquenervia soils, but plant-available concentrations of P, K, Ca, and Mg as well as CEC were reduced. Overall, data suggests that the invasion process may modify soil biotic and abiotic conditions that in turn promote the advancement of the exotic M. quinquenervia and displacement of the native plants.
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