Microbial diversity in arctic freshwaters is structured by inoculation of microbes from soils

Microbes are transported in hydrological networks through many environments, but the nature and dynamics of underlying microbial metacommunities and the impact of downslope inoculation on patterns of microbial diversity across landscapes are unknown. Pyrosequencing of small subunit ribosomal RNA gene hypervariable regions to characterize microbial communities along a hydrological continuum in arctic tundra showed a pattern of decreasing diversity downslope, with highest species richness in soil waters and headwater streams, and lowest richness in lake water. In a downstream lake, 58% and 43% of the bacterial and archaeal taxa, respectively, were also detected in diverse upslope communities, including most of the numerically dominant lake taxa. In contrast, only 18% of microbial eukaryotic taxa in the lake were detected upslope. We suggest that patterns of diversity in surface waters are structured by initial inoculation from microbial reservoirs in soils followed by a species-sorting process during downslope dispersal of both common and rare microbial taxa. Our results suggest that, unlike for metazoans, a substantial portion of bacterial and archaeal diversity in surface freshwaters may originate in complex soil environments.     

Diet selection by vertebrate herbivores in the high arctic of Greenland

Microhistological analysis of fecal droppings indicates that graminoids (sedges, grasses, and rushes) and the only willow present, Salix arctica , are primary food items of the muskox Ovibos moschatus , arctic hare Lepus arcticus , and collared lemming Dicrostonyx groenlandicus in northern Greenland (79°-83°N). Plant biomass available during the peak growing season varied with vegetation types from < 2 g m⁻² in polar barrens to 34 g m⁻² in sedge fens. The clustered distribution of vegetation minimizes competition among vertebrate herbivores.     

Site-dependent N uptake from N-form mixtures by arctic plants,soil microbes and ectomycorrhizal fungi

Soil microbes constitute an important control on nitrogen (N) turnover and retention in arctic ecosystems where N availability is the main constraint on primary production. Ectomycorrhizal (ECM) symbioses may facilitate plant competition for the specific N pools available in various arctic ecosystems. We report here our study on the N uptake patterns of coexisting plants and microbes at two tundra sites with contrasting dominance of the circumpolar ECM shrub Betula nana. We added equimolar mixtures of glycine-N, NH₄⁺–N and NO₃⁻–N, with one N form labelled with ¹⁵N at a time, and in the case of glycine, also labelled with ¹³C, either directly to the soil or to ECM fungal ingrowth bags. After 2 days, the vegetation contained 5.6, 7.7 and 9.1% (heath tundra) and 7.1, 14.3 and 12.5% (shrub tundra) of the glycine-, NH₄⁺- and NO₃⁻–¹⁵N, respectively, recovered in the plant–soil system, and the major part of ¹⁵N in the soil was immobilized by microbes (chloroform fumigation-extraction). In the subsequent 24 days, microbial N turnover transferred about half of the immobilized ¹⁵N to the non-extractable soil organic N pool, demonstrating that soil microbes played a major role in N turnover and retention in both tundra types. The ECM mycelial communities at the two tundras differed in N-form preferences, with a higher contribution of glycine to total N uptake at the heath tundra; however, the ECM mycelial communities at both sites strongly discriminated against NO₃⁻. Betula nana did not directly reflect ECM mycelial N uptake, and we conclude that N uptake by ECM plants is modulated by the N uptake patterns of both fungal and plant components of the symbiosis and by competitive interactions in the soil. Our field study furthermore showed that intact free amino acids are potentially important N sources for arctic ECM fungi and plants as well as for soil microorganisms. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Zeitgebers for animals in the continuous daylight of high arctic summer

Summary To find out which of daily oscillating environmental factors in the continuous daylight of arctic summer are responsable for synchronization of animal activity period with the rotation of the earth, in Spitsbergen (78° N) a whole summer continuous measurements of temperature (°C), light intensity (lux) and spectral composition of the light (colour temperature in °K) were done. With a daily amplitude of 4–5° C in the air, resp. 10° C at the ground surface, temperature can only act as a Zeitgeber for heterothermic animals. Measurements of light intensity (with a photocell directed vertical upward to the zenith) showed relatively large daily oscillations. But since light intensity depends on the cosine of the angle of incidence of the light (Lambert's cosine law) and in high latitudes the angle of incidence of the sun is always very great, in fact measurements have to be done with the photocell directed to the sun or, as the latter meets with mechanical problems, all dates got with the photocell vertical upward must be converted after Lambert's cosine law. Converted dates of light intensity oscillate not nearly as intense as measured dates. This small daily amplitude of light intensity, which in addition is strongly influenced by sudden changes of the wheather, can hardly come into consideration as a Zeitgeber of animal activity period. Colour temperature however showed large and regular daily oscillations and therefore could be a Zeitgeber of animal activity period in high arctic summer, particularly because in the laboratory the synchroniing effect of an artificial daily alternation of colour temperature is already proved. Nest (feeding) activity of local snowbuntings and perch hopping activity of greenfinches, brought from Germany, were registrated with light traps. Activity period of both bird species was clearly synchronized with the rotation of the earth. In a narrow valley the activity pattern of greenfinches was identical as in open country, in spite of temporarily total other conditions of light intensity (shading by mountains). Apparently even the activity period of non arctic animals can be synchronized by weak Zeitgebers like colour temperature.     

Microbes in high arctic snow and implications for the cold biosphere

We applied molecular, microscopic, and culture techniques to characterize the microbial communities in snow and air at remote sites in the Canadian High Arctic (Ward Hunt Island, Ellesmere Island, and Cornwallis Island, latitudes 74 to 83(o)N). Members of the Bacteria and Eukarya were prevalent in the snow, and their small subunit (SSU) rRNA gene signatures indicated strong local aerial transport within the region over the preceding 8 months of winter snowpack accumulation. Many of the operational taxonomic units (OTUs) were similar to previously reported SSU rRNA gene sequences from the Arctic Ocean, suggesting the importance of local aerial transport processes for marine microbiota. More than 47% of the cyanobacterial OTUs in the snow have been previously found in microbial mats in the region, indicating that this group was also substantially derived from local sources. Viable cyanobacteria isolated from the snow indicated free exchange between the snow and adjacent mat communities. Other sequences were most similar to those found outside the Canadian Arctic but were from snow, lake and sea ice, glaciers and permafrost, alpine regions, Antarctica, and other regions of the Arctic, supporting the concept of global distribution of microbial ecotypes throughout the cold biosphere.     

Carbon fixation and oxygen evolution by phytoplankton in the Canadian high arctic

Summary In the Canadian high arctic, in summer, in situ profiles of oxygen evolution and carbon fixation by phytoplankton showed excellent qualitative and quantitative agreement with an apparent photosynthetic quotient in the range from 1.3 to 1.8. Water column photosynthesis was linear in the available light at the surface. Daily rates photosynthesis exceeded 1 mg C m^-2 d^-1, implying a minimal estimate for annual production in the range from 35 to 70 g C m^-2 y^-1.     

Clonal diversity in high arctic ostracodes

It remains unclear why the majority of parthenogenetic lineages persist for only brief periods of evolutionary time. However, by characterizing their patterns of genetic variation, it is possible to gain insights regarding their evolutionary origin and potential. We examined clonal diversity patterns in high arctic populations of freshwater ostracodes with the goal of clarifying the factors promoting genotypic diversity. Allozyme electrophoresis showed that the three dominant ostracode species in high arctic ponds reproduce via apomictic parthenogenesis that two of these species (Prionocypris glacialis, Candona rectangulata) were both highly clonally diverse, and had allozyme phenotypes suggestive of polyploidy. Scanning microdensitometry confirmed that many clones of P. glacialis at Igloolik were polyploid. In contrast to most other polyploids, clones of P. glacialis seem to be autopolyploids. Although clonal variation in P. glacialis may reflect multiple transitions to parthenogenesis in an undetected sexual population, it seems likely that genomic recombination associated with polyploidy has also played a role in generating local diversity following the transition to parthenogenesis.     

State-dependent incubation behaviour in the high arctic barnacle geese

Energetic trade-offs between time spent on incubation and times spent on foraging for nesting birds give individuals in good body condition the possibility to incubate more continuously. In the present paper, the incubation behaviour of female barnacle geese Branta leucopsis was quantified in a colony in Svalbard. Females were weighted in early incubation and feeding recess lengths and frequencies were recorded. The feeding behaviour during the course of incubation was significantly correlated to by body mass, and heavy females had both fewer and shorter feeding recesses than lighter females. Moreover, there was an increase in the number of feeding recesses and the total feeding time as the incubation period progressed. Neither clutch size nor egg laying date had an effect on incubation behaviour. However, clutch size was positively related to female body mass suggesting that high-quality females produce large clutches but also allocate more body reserves to incubation. Females left the nest to feed at all times of the day, but more frequently during day time. This was not related to their body mass. Females presumably leave their nest at the time of day when the costs to reheat eggs are at a minimum. The diurnal rhythm may also be adjusted to the activity by egg predators. Overall the results support the state-dependent hypothesis for incubation behaviour, suggesting that body condition at the start of incubation is an important factor for incubation behaviour in barnacle geese.     

Immobilized microbes and a high-rate, continuous waste processor for the production of high Btu gas and the reduction of pollutants

Microbes capable of degrading organic wastes (sewage) are densely packed (immobilized) within the pores of controlled-pore ceramics. When the ceramic displays the optimum pore range for the reproduction of these microbes, the minimum volume for a very efficient reactor is required. A two-stage, anaerobic, immobilized microbe reactor has been designed, and laboratoryscale units have been constructed. A few of these units have been operated continuously for two years. These reactors were designed for the efficent conversion of carbon to methane in biodegradable molecules and for the effective transfer of that gas. The reactors were operated at 20, 30, and 40 degrees C at residence times of 2-5.5 h. The total chemical oxygen demand (COD) of the sewage varied from 800-2600 mg/L. The resulting gas contained greater than 90% methane and less than 5% CO(2). Approximately 32-54% of the influent total carbon was recovered as methane. The reduction in COD varied from 63 to 89%.     

Potential cultivation of Hordeum vulgare L. in soils with high mercury background concentrations

Experimental work was carried out under close-to-real conditions to study mercury uptake by Hordeum vulgare L. cultivated in lysimeter experiments. The soil in the lysimeter experiment was obtained from a test plot located near Almadén (Spain) and had a mean mercury content of 22.9 mg kg(-1). A sequence of four crops was sown starting in autumn 2000 and repeated on a yearly basis until 2004. The first crop was grown in the field prior to the extraction of 5 one-cubic-meter lysimeters. The succeeding crops were sown in the lysimeter experiments at the CIEMAT Research Centre (Madrid, Spain). Samples of root and shoot were obtained during the four seasons. Concentrations of mercury at plant maturity in roots vary between I and 3 mg kg(-1) and in straw and grain the concentrations range from 72 to 480 microg kg(-1) and from 5 to 257 microg kg(-1), respectively. In order to assess the potential risk for human health and animal feed, an evaluation of the mercury content in the edible part of the crop has been carried out. According to legislation, there is no human health intoxication risk with a balanced consumption; otherwise, the forage use would have to be controlled.     

Chrysophyte cysts in 36 Canadian high arctic ponds

Chrysophyte stomatocysts were described from the surface sediments and other habitats (moss, rocks, and open water) of 36 ponds located on Cape Herschel, Ellesmere Island in the Canadian high Arctic (78°37'N). Thirty-five distinct stomatocyst types were described using scanning electron microscopy (SEM); 1 other cyst was common, but was not observed with SEM. Our study ponds were diverse limnologically and contained distinct cyst floras, but the cause(s) of the floristic differences are as yet unclear. Two ponds with extreme values of water chemistry (i.e. high salinity and low pH) supported unique cyst floras. Distinctive cyst floras were also observed in ponds with high nutrient input from nesting birds and/or with diverse microhabitats (e.g. moss banks), which may provide substrate for periphytic chrysophytes. Arctic pond cyst floras are typically less diverse than those from temperate regions. Highly ornamented cysts are also less common in arctic waters, but the reason for this is unknown. Stomatocysts could be used to augment paleolimnological research in arctic ponds, if the environmental factors controlling cyst distributions and possibly degree of ornamentation can be elucidated.     

Moisture relationships of the high arctic collembolan Onychiurus arcticus

Abstract. Rates of desiccation, rehydration and survival, under conditions of 0 and 100% relative humidity, were investigated in the high arctic collembolan Onychiurus arcticus (Tullberg) over a range of temperatures from -3 to 10C. Desiccation, measured over 4h in a dry environment, was rapid and highly significantly correlated with saturated vapour pressure deficit (SVPD). At 10C animals lost over 60% of body moisture in under 1h. Under moist conditions body weight remained constant. Survival, measured over 4h under dry conditions, showed a highly significant negative correlation with SVPD across the range of temperatures. Survival in moist controls was 100%. Partially desiccated animals were able to rehydrate using free water or moisture from a saturated atmosphere, but uptake of the former was faster. Rates of water uptake were around 30 times slower than rates of loss through desiccation. Animals given free water regained initial weights in 24-144h, dependent on temperature. Uptake rates of free water, measured over the time necessary fully to rehydrate, were highly significantly correlated with temperature, whereas those for atmospheric moisture were not. Over the time scales used in the experiments, three linear regression equations accurately predict rates of desiccation, rehydration and survival from SVPD or temperature. Ecological adaptation by O.arcticus to the highly contrasting climatic environments of the arctic summer and winter seasons is discussed in the context of climate change.     

Mineralization and distribution of nutrients in plants and microbes in four arctic ecosystems: responses to warming

Mineralization and nutrient distribution in plants and microbes were studied in four arctic ecosystems at Abisko, Northern Sweden and Toolik Lake, Alaska, which have been subjected to long-term warming with plastic greenhouses. Net mineralization and microbial immobilization were studied by the buried bag method and ecosystem pool sizes of C, N and P were determined by harvest methods. The highest amounts of organic N and P were bound in the soil organic matter. Microbial N and P constituted the largest labile pools often equal to (N) or exceeding (P) the amounts stored in the vegetation. Despite large pools of N and P in the soil, net mineralization of N and P was generally low during the growing season, except in the wet sedge tundra, and in most cases lower than the plant uptake requirement. In contrast, the microorganisms immobilized high amounts of nutrients in the buried bags during incubation. The same high immobilization was not observed in the surrounding soil, where the microbial nutrient content in most cases remained constant or decreased over the growing season. This suggests that the low mineralization measured in many arctic ecosystems over the growing season is due to increased immobilization by soil microbes when competition from plant roots is prevented. Furthermore, it suggests that plants compete well with microbes for nutrients in these four ecosystems. Warming increased net mineralization in several cases, which led to increased assimilation of nutrients by plants but not by the microbes.     

Congruent responses to weather variability in high arctic herbivores

Assessing the role of weather in the dynamics of wildlife populations is a pressing task in the face of rapid environmental change. Rodents and ruminants are abundant herbivore species in most Arctic ecosystems, many of which are experiencing particularly rapid climate change. Their different life-history characteristics, with the exception of their trophic position, suggest that they should show different responses to environmental variation. Here we show that the only mammalian herbivores on the Arctic islands of Svalbard, reindeer (Rangifer tarandus) and sibling voles (Microtus levis), exhibit strong synchrony in population parameters. This synchrony is due to rain-on-snow events that cause ground ice and demonstrates that climate impacts can be similarly integrated and expressed in species with highly contrasting life histories. The finding suggests that responses of wildlife populations to climate variability and change might be more consistent in Polar regions than elsewhere owing to the strength of the climate impact and the simplicity of the ecosystem.     

Trophic interactions in a high arctic snow goose colony

We examined the role of trophic interactions in structuringa high arctic tundra community characterized by a large breedingcolony of greater snow geese (Chen caerulescens atlantica).According to the exploitation ecosystem hypothesis of Oksanenet al. (1981), food chains are controlled by top-down interactions.However, because the arctic primary productivity is low, herbivorepopulations are too small to support functional predator populationsand these communities should thus be dominated by the plant/herbivore trophic-level interaction. Since 1990, we have beenmonitoring annual abundance and productivity of geese, the impactof goose grazing, predator abundance (mostly arctic foxes, Alopexlagopus) and the abundance of lemmings, the other significantherbivore in this community, on Bylot Island, Nunavut, Canada.Goose grazing consistently removed a significant proportionof the standing crop (     

In situ patterns of intracellular photosynthate allocation by sea ice algae in the Canadian high arctic

Summary A novel sampling/incubating device was used to determine the in situ patterns of intracellular photosynthate allocation by algae living in the bottom of annual sea ice in the Canadian arctic. During the seasonal decline of the bloom in late May and June, the average allocation pattern after 24 h incubation in the bottom 1 cm of ice (where the bulk of the algae are found) was 30.5% to low molecular weight materials, 10.6% to lipid, 48.8% to polysaccharide and 8.8% to protein. Allocation patterns were vertically stratified and light-dependent within the bottom ice community, with higher allocation to lipid in the upper, better-illuminated, strata. Chlorophyll-specific photosynthesis rates were extremely low (<0.031 gC·g Chl a ^–1·h^–1). Short incubations (ca. 1h) gave similar results to the 24 h incubations. The in situ allocation patterns were atypical of those normally expected for light-limited microalgae, but were consistent with a physiological response to inorganic nutrient limitation in the late stages of the bloom.     

Potential contributions of root decomposition to the nitrogen cycle in arctic forest and tundra

Plant contributions to the nitrogen (N) cycle from decomposition are likely to be altered by vegetation shifts associated with climate change. Roots account for the majority of soil organic matter input from vegetation, but little is known about differences between vegetation types in their root contributions to nutrient cycling. Here, we examine the potential contribution of fine roots to the N cycle in forest and tundra to gain insight into belowground consequences of the widely observed increase in woody vegetation that accompanies climate change in the Arctic. We combined measurements of root production from minirhizotron images with tissue analysis of roots from differing root diameter and color classes to obtain potential N input following decomposition. In addition, we tested for changes in N concentration of roots during early stages of decomposition, and investigated whether vegetation type (forest or tundra) affected changes in tissue N concentration during decomposition. For completeness, we also present respective measurements of leaves. The potential N input from roots was twofold greater in forest than in tundra, mainly due to greater root production in forest. Potential N input varied with root diameter and color, but this variation tended to be similar in forest and tundra. As for roots, the potential N input from leaves was significantly greater in forest than in tundra. Vegetation type had no effect on changes in root or leaf N concentration after 1 year of decomposition. Our results suggest that shifts in vegetation that accompany climate change in the Arctic will likely increase plant‐associated potential N input both belowground and aboveground. In contrast, shifts in vegetation might not alter changes in tissue N concentration during early stages of decomposition. Overall, differences between forest and tundra in potential contribution of decomposing roots to the N cycle reinforce differences between habitats that occur for leaves.     

Potential sexual transmission of environmental microbes in a traumatically inseminating insect

Abstract.  1. Very little attention has been paid to the importance of environmental microbes and how they gain access to potential hosts during host wounding or sexual interactions. Male members of the family Cimicidae (including the haematophagous human pest, the bed bug, Cimex lectularius ) show traumatic insemination: in order to transfer sperm the male punctures the female's cuticle using a needle-like intromittent organ. The microbes from the local environment that gain entry into females during mating have previously been shown to be an important source of mortality. This study aimed to identify these microbes and their natural environmental substrates.
2. Nine different microbe taxa from the surface of the cuticle were identified, five of them (two Penicillium spp., Stenotrophomonas , Enterobacter , Bacillus ) were found in the local environment as well as on the intromittent organ of male bed bugs: these are strong candidates for the causal agents of mating-induced female mortality. Local differences in the microbial communities and their hosts' response to them are discussed as a source of reproductive isolation.
3. Four microbe genera ( Scopulariopsis , Staphylococcus , Arthrobacter , Micrococcus ) were found exclusively on blood agar. One of them, and four grown on regular agar, are classified as human pathogens. However, because no microbes were isolated from the piercing and sucking mouthparts the epidemiological significance of bed bugs carrying externally attached microbes is probably low.     

The importance of bryophytes in the classification of human-disturbed high arctic vegetation

Abstract. Evidence is presented from a variety of tundra cover types under human disturbance at three sites in the Canadian High Arctic to indicate that higher plants may be insufficient to differentiate among the apparently distinct geobotanical signatures of discrete surface disturbances. Unlike in the Low Arctic, woody growth forms are often minimal or lacking on heavily disturbed ground and several prominent species of ruderal herbs and especially graminoids occur on a wide variety of substrates. Therefore, cryptogams, particularly bryophytes, are important indicator taxa. Presence-absence data on bryophytes from minerotrophic and oligotrophic soils, combined with vascular cover-abundance data, enhanced detection of patch-level floristic gradients within and among disjunct coastal lowlands. However, the pool of ruderal bryophytes is limited, and ultimately factors such as frequency and abundance should be considered.