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One of multiple functions of metalloproteins is to provide detoxification to excess metal levels in organisms. Here we address the induction and persistence of a range of low to high molecular weight copper- and zinc binding proteins in the collembolan species Tetrodontophora bielanensis exposed to copper- and zinc-enriched food, followed by a period of recovery from metal exposure, in absence and presence of food. After 10 days of feeding copper and zinc contaminated yeast, specimens were either moved to ample of leaf litter material from their woodland stand of origin or starved (no food offered). The molecular weight distribution of metal binding proteins was determined by native polyacryl gel electrophoresis. One gel was stained with Comassie brilliant blue and a duplicate gel dried and scanned for the amount of copper and zinc by particle-induced X-ray emission. Specimens exposed to copper and recovered from it with ample of food had copper bound to two groups of rather low molecular weight proteins (40-50 kDa) and two of intermediate size (70-80 kDa). Most zinc in specimens from the woodland stand was bound to two large proteins of about 104 and 106 kDa. The same proteins were holding some zinc in metal-exposed specimens, but most zinc was found in proteins <40 kDa in size. Specimens recovered from metal exposure in presence of ample of food had the same distribution pattern of zinc binding proteins, whereas starved specimens had zinc as well as copper mainly bound to two proteins of 8 and 10 kDa in size. Thus, the induction and distribution of copper- and zinc-binding proteins depend on exposure conditions, and the presence of low molecular weight binding proteins, characteristic of metallothioneins, was mainly limited to starving conditions. [ABSTRACT FROM AUTHOR]

We tested whether the presence of plant roots would impair the uptake of ammonium ( [ABSTRACT FROM AUTHOR]

Apart from acting synergistically or additively, threats to species may be associated or disassociated. Here we link global data on threatened Chordata species, mainly birds, mammals, and amphibians, with a probabilistic methodology to test whether the impact from invasive alien species co-occurs purely randomly, associated, or disassociated with impact from nine other major threats to biodiversity listed in the International Union for Conservation of Nature Red List database. Impacts from several of the other threats, in particular from natural disasters, are associated with the impact from invasive alien species. Three of the threats of anthropogenic origin, namely habitat loss, harvesting, and human disturbance, co-occur randomly with impact from invaders, and we suggest several explanations to this unexpected relationship, such as ambiguous evidence for associations between them and human-induced disturbances. Impact from invasive alien predators has a strong association with impact from native predators, indicating that similarity in autecology affects co-occurrences between threats. The threat from invasive predators is disassociated from intrinsic factors on islands, probably because species suffering from for instance inbreeding problems have low densities and rarely encounter invasive alien predators. The analysis of co-occurrence of impact from invasive alien species and other threats is a first step to understand and mitigate vulnerability of a community to the simultaneous exposure to invasive alien species and other threats. Association or disassociation between threats may depend on correlations between exposures and sensitivity to the threats or on the presence of one threat increasing or decreasing the sensitivity to another. [ABSTRACT FROM AUTHOR]

In this paper, a numerical model is developed for analyzing the role of species life history and age structure for the optimal management of a commercial resident species that is exposed to an invasive species. It is shown that reproduction and mortality characteristics of both species ands age structure of the invader at the time of invasion are important for the costs of invasions when the invader and resident species compete for scarce resources. Commercially harvested species with low juvenile survival and high reproduction are found to be economically more robust against invasions. Species with these life-history traits are also the most damaging as invaders. Properties of the harvesting cost function and the discount rate are shown to be of importance for the development of the invader population over time. Hence, it is possible to identify specific combinations of life-history characteristics and economic conditions under which invasions cause particularly large economic damage. [ABSTRACT FROM AUTHOR]

We examined the spatial and temporal (hourly) variation of aqueous concentrations of mercury in a gold miner's river to determine factors that control transport, retention, and export of mercury. The mercury flux was estimated to account for episodic inputs of mercury through mining tailings, variations in flow rate, and the partitioning of mercury between dissolved and particulate phases. Water samples were collected upstream and downstream of two gold mining sites in the Artiguas river, Nicaragua. The samples were analyzed for dissolved and suspended mercury, total solids, dissolved organic carbon, and total iron in water. Water velocity was also measured at the sampling sites. We found that mercury was mainly transported in a suspended phase, with a temporal pattern of diurnal peaks corresponding to the amalgamation schedules at the mining plants. The concentrations decreased with distance from the mining sites, suggesting dilution by tributaries or sedimentation of particle-bound mercury. The lowest total mercury concentrations in the water were less than 0.1 μg l−1 and the highest concentration was 5.0 μg l−1. The mercury concentrations are below the present WHO guidelines of 6 μg l−1 but are considered to lead to a higher risk to aquatic bacteria and fish in the stream than to humans. The aqueous concentrations exceed the hazard endpoints for both groups by a probability of about 1%. Particulate mercury accounted for the largest variation of mercury fluxes, whereas dissolved mercury made up most of the long-range transport along the stream. The estimated total mass of mercury retained due to sedimentation of suspended solids was 2.7 kg per year, and the total mass exported downstream from the mining area was 1.6 kg per year. This study demonstrates the importance of the temporal and spatial resolution of observations in describing the occurrence and fate of mercury in a river affected by anthropogenic activities. [ABSTRACT FROM AUTHOR]

1. The signal crayfish Pacifastacus leniusculus is an invasive species in Sweden, threatening the red-listed nobel crayfish Astacus astacus through spreading the crayfish plague. Time-to-event models can handle censored data on such introduced populations for which the state (successful or not) is only partially known at the last observation, but even though data on introduced populations most often are censored, this type of model is usually not used for likelihood-based inference and predictions of the dynamics of establishing populations. 2. We specified and fitted a probabilistic time-to-event model to be used to predict the time to successful establishment of signal crayfish populations introduced into Sweden. Important covariates of establishment success were found by the methods of ‘model averaging’ and ‘hierarchical partitioning’, considering model uncertainty and multi-colinearity, respectively. 3. The hazard function that received the highest evidence based on the empirical data showed that the chances of establishment were highest in the time periods immediately following the first introduction. The model predicts establishment success to be <50% within 5 years after first introduction over the current distributional range of signal crayfish in Sweden today. 4. Among covariates related to temperature, fish species and physical properties of the habitat, the length of the growing season was the most important and consistent covariate of establishment success. We found that establishment success of signal crayfish is expected to increase with the number of days when growth is possible, and decrease with the number of days with extremely high temperatures, which can be seen to approximate conditions of stress. 5. Synthesis and applications. The results demonstrate lower establishment success of signal crayfish further north in Sweden, which may decrease the incentives of additional illegal introductions that may threaten the red-listed noble crayfish Astacus astacus. We provide a fully probabilistic statistical evaluation that quantifies uncertainty in the duration of the establishment stage that is useful for management decisions of invasive species. The combination of model averaging and hierarchical partitioning provides a comprehensive method to address multi-colinearity common to retrospective data on establishment success of invasive species. [ABSTRACT FROM AUTHOR]

The objective of the present study was to integrate the relative risk from mercury exposure to stream biota, groundwater, and humans in the Río Artiguas (Sucio) river basin, Nicaragua, where local gold mining occurs. A hazard quotient was used as a common exchange rate in probabilistic estimations of exposure and effects by means of Monte Carlo simulations. The endpoint for stream organisms was the lethal no-observed-effect concentration ( NOECs), for groundwater the WHO guideline and the inhibitory Hg concentrations in bacteria ( IC), and for humans the tolerable daily intake ( TDI) and the benchmark dose level with an uncertainty factor of 10 ( BMDLs0.1). Macroinvertebrates and fish in the contaminated river are faced with a higher risk to suffer from exposure to Hg than humans eating contaminated fish and bacteria living in the groundwater. The river sediment is the most hazardous source for the macroinvertebrates, and macroinvertebrates make up the highest risk for fish. The distribution of body concentrations of Hg in fish in the mining areas of the basin may exceed the distribution of endpoint values with close to 100% probability. Similarly, the Hg concentration in cord blood of humans feeding on fish from the river was predicted to exceed the BMDLs0.1 with about 10% probability. Most of the risk to the groundwater quality is confined to the vicinity of the gold refining plants and along the river, with a probability of about 20% to exceed the guideline value. [ABSTRACT FROM AUTHOR]

A green house experiment was designed to test the idea that competition for inorganic nitrogen (N) between plants and heterotrophic microorganisms occurs in soils with high C:N ratios, qualifying for N limited microbial activity, but not at low C:N ratios. The short-term (24 h) 15N uptake by the grass Festuca gigantea and microorganisms in planted and unplanted soils was determined, and the bacterial activity was measured by the 3H-thymidine incorporation technique. Two deciduous forest soils, with C:N-ratios of 20 and 31, and the 20 soil amended with litter to a C:N ratio of 34, were used. A novel and important part of the experimental design was the preparation of the unplanted reference soil with plants present until the competition assay started by the addition of 15N labelled ammonium ( ) or nitrate ). The results suggested that plants and soil microorganisms competed for mineral N but under influence of other factors than the soil C:N ratio. The plants reduced the microbial uptake of and in the soil with low C:N ratio, which also had the lowest bacterial activity. The plants had a larger N uptake than microorganisms in the two natural soils but smaller in the litter-amended, and their presence enhanced the bacterial activity, especially in the latter soil. The litter-amended soil with its high C:N ratio and easily decomposable C was the soil that best fulfilled the criteria for competition, including a net consumption of mineral N during the assay, the lowest plant uptake of mineral N due to the high N immobilization by microorganisms, and a reduced microbial 15N uptake-to-bacterial activity in the presence of plants. Thus, other factors, such as the decomposability of the soil C and the bacterial activity, were more important than the soil C:N ratio to the outcome of plant–microbial competition for N. [ABSTRACT FROM AUTHOR]

While numerous efforts have been made to identify and quantify factors controlling invasibility of biological communities, less attention has been given to analyzing the expressions of vulnerability to nonindigenous species (NIS). Using the International Union for the Conservation of Nature and Natural Resources Red List database for birds, mammals, and amphibians and the Invasive Species Specialist Group global invasive species database as sources of information, we developed a new indicator for the relative intrinsic vulnerability of islands to NIS. It was calculated from the residuals to the global relationship between the impact of NIS and their exposure to the islands. The impact of NIS was expressed as the proportion of indigenous species threatened by NIS, and the exposure was the number of invasive NIS per number of native species. The residuals corresponded to the variability in impact, about 60%, that was not explained by exposure. The proportion of endemic species on the islands was positively correlated with the relative intrinsic vulnerability and explained about 60% of its variability. The robust relationship between endemism and intrinsic vulnerability reinforces the role of long-term isolation for the fate of island indigenous species to biological invasions and is useful in identifying vulnerable environments without having a specific invader in mind. [ABSTRACT FROM AUTHOR]

The extent of remediation of contaminated industrial sites depends on spatial heterogeneity of contaminant concentration and spatially explicit risk characterization. We used sequential Gaussian simulation (SGS) and indicator kriging (IK) to describe the spatial distribution of polycyclic aromatic hydrocarbons (PAHs), pH, electric conductivity, particle aggregate distribution, water holding capacity, and total organic carbon, and quantitative relations among them, in a creosote polluted soil in southern Sweden. The geostatistical analyses were combined with risk analyses, in which the total toxic equivalent concentration of the PAH mixture was calculated from the soil concentrations of individual PAHs and compared with ecotoxicological effect concentrations and regulatory threshold values in block sizes of 1.8 × 1.8 m. Most PAHs were spatially autocorrelated and appeared in several hot spots. The risk calculated by SGS was more confined to specific hot spot areas than the risk calculated by IK, and 40–50% of the site had PAH concentrations exceeding the threshold values with a probability of 80% and higher. The toxic equivalent concentration of the PAH mixture was dependent on the spatial distribution of organic carbon, showing the importance of assessing risk by a combination of measurements of PAH and organic carbon concentrations. Essentially, the same risk distribution pattern was maintained when Monte Carlo simulations were used for implementation of risk in larger (5 × 5 m), economically more feasible remediation blocks, but a smaller area became of great concern for remediation when the simulations included PAH partitioning to two separate sources, creosote and natural, of organic matter, rather than one general. [ABSTRACT FROM AUTHOR]

Little is known about the spatial connection between soil microbial community composition and polycyclic aromatic hydrocarbon (PAH) concentration. A spatially explicit survey at a creosote-contaminated site demonstrated that microbial biomass (total concentration of phospholipid fatty acids [PLFAs]) and microbial community composition (PLFA fingerprints) were spatially autocorrelated, mostly within a distance of 25 m, and covaried with PAH concentrations. The concentration of PLFAs indicative of gram-negative bacteria (16:1ω7c, 16:1ω7t, 18:1ω7, cy17:0, and cy19:0) increased in the PAH hot spots, whereas PLFAs representing fungi and gram-positive bacteria (including actinomycetes) were negatively correlated to PAH concentrations. Most PLFAs were spatially autocorrelated, with distances varying between 4 and 25 m. Those PLFAs that increased in PAH-contaminated soil had autocorrelation ranges between 4 and 16 m, whereas the fungal indicator PLFA 18:2ω6,9 had the largest autocorrelation range (25 m). Bacterial strains isolated using a spray-plate technique and with the same PLFA composition as that in contaminated soil samples were capable of degrading phenanthrene, fluoranthene, and pyrene, indicating that the main PAH degraders could be isolated. [ABSTRACT FROM AUTHOR]

The evidence for the contribution of soil warming to changes in atmospheric CO2 concentrations and carbon stocks of temperate forest ecosystems is equivocal. Here, we use data from a beech/oak forest on concentrations and stable isotope ratios of dissolved organic carbon (DOC), phosphate buffer-extractable organic carbon, soil organic carbon (SOC), respiration and microbial gross assimilation of N to show that respired soil carbon originated from DOC. However, the respiration was not dependent on the DOC concentration but exceeded the daily DOC pool three to four times, suggesting that DOC was turned over several times per day. A mass flow model helped to calculate that a maximum of 40% of the daily DOC production was derived from SOC and to demonstrate that degradation of SOC is limiting respiration of DOC. The carbon flow model on SOC, DOC, microbial C mobilization/immobilization and respiration is linked by temperature-dependent microbial and enzyme activity to global warming effects of CO2 emitted to the atmosphere. [ABSTRACT FROM AUTHOR]

1 This work demonstrates that spatial distribution of understorey vegetation and gross N transformation rates in a mixed beach-oak forest is closely correlated within a distance of a few metres. The findings imply that plant diversity and productivity have a major influence on gross rates of N transformation and vice versa. 2 A geostatistical analysis was used to evaluate the spatial relationships between abundance and species composition of the understorey vegetation and in situ gross N mineralization, immobilization and nitrification rates. 3 The gross N transformation rates and the plants spatial variation were correlated within the forest, but plant distribution was more dependent on the fraction of mineralized N that was nitrified than on individual N transformation rates. 4 The total cover of the understorey vegetation varied more in space than the species composition, and was higher in areas with high N transformation rates. 5 Plant species benefiting from high net nitrification rates were more common in areas with a low activity of mineralizing and nitrifying microorganisms, possibly because the net and gross rates were independent of each other. In fact, those species occurred most often in areas in which a large fraction of mineralized N was nitrified. 6 Beech and oak trees also had an effect on the spatial variation of the understorey vegetation. Beech trees provided conditions more suitable for plants benefiting from , whereas the vascular plant cover was greater under oak trees, probably in response to a higher light interception than under beech trees. 7 Oak generally had a positive impact on gross N transformation rates compared with beech, perhaps reflecting differences in litter quality and climate caused by the two species. 8 The influence of trees alone could not explain the full magnitude of the variation of N transformation rates or the presence of overlapping areas with high mineralization and immobilization rates. These were probably caused by other factors, such as soil moisture content. 9 This work sheds new light on the small-scale spatial links between above-ground plant diversity and abundance, and below-ground microbial N transformations. [ABSTRACT FROM AUTHOR]

We conducted stable isotope analyses of nitrogen and carbon on feathers obtained from willow warblers in Africa to find an explanation for a previously observed pattern of different δ15N and δ13C values across a migratory divide in central Scandinavia. A new data set confirms that north Scandinavian birds of the subspecies P. t. acredula have higher δ15N values than south Scandinavian birds of the subspecies P. t. trochilus. In Africa, we found significant differences for both δ15N and δ13C values among feathers collected from major geographical regions as well as between countries within regions. Isotope signatures of δ15N and δ13C in Scandinavian acredula matched well with those of willow warblers sampled in southern parts of Africa, but differed from samples obtained in East and West Africa. Isotope signatures in Scandinavian trochilus did not agree with the pattern in any of the three African regions (West, East or South). However, a more detailed analysis of the isotopic data in feathers from countries within West Africa, which is the wintering region of Swedish trochilus based on ringing recoveries, revealed a correspondence with samples from Liberia, the Ivory Coast and Nigeria. [ABSTRACT FROM AUTHOR]

A field experiment was designed with the objective to reveal the interactions between soil moisture, temperature, total, dissolved, and phosphate buffer extractable C and N, and microbial activity in the control of in situ gross N mineralization and immobilization rates in a deciduous forest. We had three alternative hypotheses to explain variations of the gross N transformations: 1) microorganisms are C limited, 2) microorganisms are N limited, or 3) neither C nor N limit the microorganisms but moisture and temperature conditions. Each hypothesis had specific criteria to be fulfilled for its acceptance. The results demonstrated that gross N transformation rates were more dependent on and variable with soil moisture and temperature than the size of the different C and N pools. The immobilization of N was dependent on the gross mineralization rate, suggesting that the production of enzymes for mineralization of organic N and the immobilization of N from the surrounding soil is disconfirmed when the intracellular N content of the microorganisms is sufficiently high. If the microorganisms are starved for N, enzyme systems involved in both the assimilation and mineralization of N are activated. The mean in situ gross N mineralization rate was two orders of magnitude higher than the natural N deposition in the area and the N addition in the NITREX experiments, meaning that a reduction in the gross N mineralization rate of about 1% would be enough to compensate for the addition of inorganic N. This decrease would hardly be detectable given the great spatial and temporal variability of N transformation rates. [ABSTRACT FROM AUTHOR]

An experiment was designed to resolve two largely unaddressed questions about the turnover of N in soils. One is the influence of microbial growth rate on mobilization and remineralization of cellular N. The other is to what extent heterotrophic immobilization of is controlled by the soil concentration of . Bacteria were extracted from a deciduous forest soil and inoculated into an aqueous medium. Various N pool dilution/enrichment experiments were carried out to: (1) calculate the gross N immobilization and remineralization rates; (2) investigate their dependence on concentrations; (3) establish the microbial preference for depending on the concentration ratio. Remineralization of microbial N occurred mainly at high growth rates and concentrations. There was a positive correlation between immobilization and remineralization rates, and intracellular recycling of N seemed to be an efficient way for bacteria to withstand low inorganic N concentrations. Thus, extensive remineralization of microbial N is likely to occur only when environmental conditions promote high growth rates. The results support previous observations of high immobilization rates, especially at low concentrations, but was also immobilized at high NH4 concentrations. The latter can be understood if part of the microbial community has a preference for . [Copyright &y& Elsevier]

Ecotoxicological endpoints based on behavioral traits (e.g., predator avoidance, feeding, and locomotion) may be more sensitive and give more insights into patterns of sublethal toxicity than survivorship tests. In this study, the density-dependent grazing rate of Daphnia pulex pre-exposed to p,p'-dichlorodiphenyldichloroethylene (DDE) (insecticide metabolite) and glyphosate (herbicide), via water or a vector, Scenedesmus spp., was assayed in laboratory experiments. The phytoplankton biomass was estimated from the chlorophyll content, and the pesticide uptake and turnover pattern in Daphnia and Scenedesmus were determined from parallel experiments with a radiolabeled source. Scenedesmus spp. relative net growth rate was inversely and linearly related to the density of the grazer. Daphnia pulex exhibited significant reductions in grazing rate: 30% for those pre-exposed to p,p'-DDE via water and 40% for D. pulex pre-exposed to glyphosate via Scenedesmus spp. Through the process of trophic cascading, this impaired grazing allowed Scenedesmus spp. to grow at higher rates, 70 and 60%, respectively. The reduced grazing efficiencies were associated with the treatments that gave the highest body burden of p,p'-DDE (70 µg/g dry wt) and the lowest of glyphosate (13 mg/g dry wt). The pattern of results suggests a toxic effect of p,p'-DDE on D. pulex and a growth enhancement of Scenedesmus spp. in response to nitrogen and phosphorus in glyphosate excreted by D. pulex. [ABSTRACT FROM AUTHOR]

A series of experiments were conducted to address the fate of dissolved organic carbon (DOC) in the peat–stream interface zone linking a minerotrophic poor fen and an ombrotrophic mire with surrounding stream water in the drainage area of Lake Örträsket in northern Sweden. Transport and mineralisation of DOC were quantified in peat–stream interface cores in response to variations in pore water velocity, DOC concentration and the molecular size and source of DOC. Mineralisation and CH4 production were positively correlated with pore water velocity at rates between 0.08 and 0.20 cm h-1 and negatively correlated at rates between 0.20 and 0.40 cm h-1. The DOC concentration of the effluent from the peat cores was independent of the pore water velocity but proportional to the DOC concentration of the source water. Higher concentrations of DOC were exported from than imported to the peat cores, and the cores exported DOC molecules of smaller average molecular size than received. Carbon mineralisation in the peat, assessed in a static system, was independent of the concentration of DOC. DOC with a nominal cutoff at 100 Da was mineralised faster by streamwater bacteria than DOC dialysed with a cutoff at 3500 Da, and their mineralisation rate was positively correlated with the DOC concentration. Streamwater bacteria mineralised streamwater DOC at a lower rate than the peat–stream interface zone pore water DOC. The pattern of velocity dependence of mineralisation was the same for both sources of peat DOC but the mineralisation rates, average molecular size, and bioavailability of DOC were different, emphasising the importance of the compositional heterogeneity of the peat–stream interface zone for the DOC budget of streamwater. [ABSTRACT FROM AUTHOR]

Spatial heterogeneity of hydraulic and sorptive processes may have a strong impact on the mobility of bacteria in porous soils. Whereas heterogeneity at the microscopic solid particl/interstitial pore scale has been conceptually addressed by dividing the porous material into two or more coexisting sorbing fractions, field-scale spatial variability has been approached by developing stochastic methodologies for coupling advective flow and sorption reactions. This calls for an elucidation of correlations between certain soil parameters and sorption of bacteria, with the purpose of substituting tedious and labourious sorption measurements with indirect methods allowing more rapid screening of field samples. Sorption of two 3H-labeled strains of groundwater bacteria was examined in test tubes with sandy aquifer material and filter sterilized groundwater from the same aquifer. The aquifer particles were sieved to different size fractions (0-63, 63-106, 106-212, 212-500, 500-1000, and 1000-1500 µm) and mixtures thereof, and their specific surface area, magnetic susceptibility, and mineral composition were determined. Columns filled with the sieved or original aquifer material were saturated with groundwater, and the breakthrough of the labeled bacteria at a flow rate of 0.2 mL min−1 was measured by liquid scintillation. Cell sorption to soil particles in test tube experiments was controlled by magnetic susceptibility, which characterizes the mineral surfaces primarily according to their iron content. In contrast, there was a negative nonlinear regression between the sorption coefficient and the particle size and a positive linear regression with the specific surface area, each with an R2 of ∼0.85 in the column experiments. The work demonstrates that sorption of groundwater bacteria to aquifer material of low organic carbon content can be predicted from the particle size distribution or the specific surface area. [ABSTRACT FROM AUTHOR]

The utilization of amino acids in leaf protein and leaf leachate by aquatic hyphomycetes was studied during decomposition in a combined field and laboratory experiment. Leaves were sampled from a stream which exhibited a seasonal variation in free amino acid concentration in surface water, reaching peaks in autumn and winter. In the leaf drift environment the concentration of amino acids was approximately two orders of magnitude higher than in surface water. Protein amino acid content, which was higher in alder leaves than in beech leaves, decreased exponentially and faster in alder leaves, so that protein amino acid content was similar in the two leaf types after 9-10 weeks decomposition. From 55% to 75% of leaf amino acids were used instantaneously by attached fungi, which grew well, especially on alder leaves, regardless of the presence of a grazing amphipod. If nitrogen was a limiting nutrient source for fungi, it appeared to be more advantageous to colonize alder leaves. Four times more fungal species were found on alder leaves than on beech leaves. The changes in concentration of amino acids in leaves and water was described by a set of differential equations. Rate constants for the transfer of amino acids from leaves and water were estimated from experimental data and the preference in fungi for protein-bound and free amino acids evaluated. The amounts of free amino acids in water absorbed by fungi varied between leaf types and leaves at different stages of decay. Experimental data showed a switching behaviour in fungal absorption of dissolved amino acids so that absorption became superproportional at a certain proportion of free amino acids available in the water. [ABSTRACT FROM AUTHOR]

Dispersal of bacteria in saturated, porous soils can be characterized by the partitioning of cells between the aqueous and solid phases, as a result of the physical and chemical nature of the soil and water and cell surface modifications. The purpose of this work is to understand variations in partitioning as a consequence of the nutrient conditions and to use this information in mathematical models to predict the dispersal rate of bacteria in aquifer material. Two different models were used to describe dispersal: an advective-dispersive-sorptive model with a first order kinetic sink term to account for irreversible cell reactions, such as death and sorption; and a two-site reaction model, in which the retardation was assumed to be determined by two types of sites, one characterized by instantaneous equilibrium sorption reactions and the other by kinetic nonequilibrium reactions. Water-saturated sand columns were used as continuous-flow groundwater microcosms to test the models under different nutrient regimes. Two strains of indigenous groundwater bacteria were isolated from aquifer material and labelled withH-alanine,C-pyruvic acid,H-glucose, andH-adenosine for different measurements of sorption and dispersal, which were estimated from breakthrough curves. Both experimental data and model variables showed that dispersal of bacteria was a dynamic nonequilibrium process, possibly shaped by two subpopulations, one strongly, even irreversibly, adsorbing to the solid particles, and one with very slow adsorption kinetics. The cell surfaces were modified in response to the growth conditions, which was demonstrated by hydrophobic and electrostatic interaction chromatography. Cell surface hydrophobicity was about eight times higher in groundwater than in eutrophic lake water. The partition coefficient varied between 12.6 in the groundwater and 6.4 in the lake water, indicating the prime importance of hydrophobic binding for attachment in low nutrient conditions. The partitioning was also sensitive to the hydrodynamics of the system and the oxygen supply, as demonstrated by comparison of sorption in agitated test tubes, gently shaken vials, and air-flushed bottles. Sorption kinetics were demonstrated in a continuous flow cell. About 45% of a population was associated with sand particles with a continuous flow of pure groundwater and as little as 20% in lake water. However, more than 50% of the bacteria in the aqueous phase were associated with suspended material of less than 60 μm in diameter. This association may enhance dispersal for example, by size exclusion of the colloidal material in the interstitial pores. [ABSTRACT FROM AUTHOR]

Groundwater bacteria isolated from an oligotrophic-saturated soil showed a mixed strategy of economized metabolism and migration when grown in a continuous-flow column system simulating poor or nutrient-amended growth conditions. The cells were generally <0.5 μm in diameter in pure groundwater, but doubled in size when the concentration of dissolved organic carbon and phosphate in groundwater was increased 10-fold. The biomass, estimated from analysis of muramic acid (MuAc) in cell wall peptidoglucans, increased at the same time by a factor of 5 when the solid support in the columns was gravel and by a factor of 10 when it was glass beads. Bacteria in pure groundwater stored 10 times more of the energy-rich polysaccharide, poly- β-hydroxybutyric acid (PHB), than bacteria in enriched groundwater, and those cells that were attached to the gravel stored 10 times as much as cells in the interstitial pore water. Once phosphate was added to groundwater, stored PHB was metabolized. The proportion of free-living to attached bacteria was 2 to 10 times higher in enriched compared with pure groundwater indicating a mass transport of cells as the carrying capacity of their habitat rose. [ABSTRACT FROM AUTHOR]

Two species of aquatic hyphomycetes, Tetracladium marchalianum and Tricladium splendens, were isolated from decaying leaves in a stream. T. marchalianum was abundant on alder leaves but absent on beech leaves, which were dominated by T. splendens. It was hypothesized that differences in some chemical key factors in the leaves would account for differences in the distribution of the 2 species. In the experiment designed to test the hypothesis, combinations of sterilized leaves and isolated fungi were used. Differences in growth of FDA active mycelium were related to differences in leaf weight loss; T. splendens decomposed beech leaves and T. marchalianum decomposed alder leaves. Extracellular protease activity corresponded with these trends but there was no detectable protein loss in the leaves. Both fungi showed a nitrogen demand, and hydrolysis of leaf proteins was complemented with absorption of free amino acids and ammonium. High concentrations of free amino acids modified the pattern for habitat selection so that T. splendens grew substantially on alder leaves and T. marchalianum colonized beech leaves. No protease activity was, however, found from T. marchalianum on beech leaves, and it is concluded that a more general metabolic inhibition prevents extensive growth of this species on beech leaves. The low natural abundance of T. splendens on alder leaves, where it may grow well, may be a consequence of a specific protease inhibition and competition from other species. [ABSTRACT FROM AUTHOR]

Population differentiation was studied in Onychiurus armatus (Tullb.) and lsotoma notabilis Schäffer from a reference site and two highly polluted (Cu, Zn) sites (long-term and short-term exposed, effectively in the Gusum area, SE Sweden. Growth, survival and reproduction were followed in a F1 generation of O. armatus reared on a diet of the fungus Verticillium bulbillosum (W. Gains and Malla ) grown on a series of Cu + Zn amended agar plates, vival and reproduction were observed in a P generation of l. notabilis incubated in soils with enhanced concentrations of Cu and Zn. Metals affected growth rate but not mean maximum length of O. armatus. The growth rotes of both populations decreased significantly with increasing metal concentrations. Animals from the polluted site were less affected by metals and attained reproductive size earlier than those from the reference site. Survival decreased with increasing metal exposure in both species, but there was no significant difference in survival between populations within the species. Reproduction in t s of egg production ( O. armatus) and number of juveniles (1. notabilis) was significantly reduced by metals. Higher overall reproduction rates were recorded for O. armatus and I. hornbills from polluted sites compared with the reference sites. The difference between populations of both species reached a maximum in the most polluted treatments. The rareness of I. notabilis in comparison with O. armatus in the polluted soil could not be explained from a weaker phenotypic response to metals. In neither of the species was the population from the polluted site inferior to the reference population. Selection for metal resistance in O. armatus is suggested m operate on the body growth and rate and for both species on the reproductive rate. [ABSTRACT FROM AUTHOR]

Transport of bacteria in a soil was delayed relative to the mobile pore water by rate-limited rather than instantaneous sorption to soil particles. Desorption rates were found to be faster than adsorption rates, and sorption kinetics were dependent on the density of bacteria and on the flow rate of water. Sorption kinetics were revealed by a combination of model descriptions of the mass balance and sorption kinetics of a groundwater bacterium entering a porous system and laboratory experiments using a stirred flow chamber and a soil column. The flow chamber was designed and operated to (1) distinguish instantaneous equilibrium reactions from time-dependent reactions, (2) estimate sorption rate coefficients at different cell densities and water velocities, and (3) obtain rate coefficients that could be used to predict the breakthrough of bacteria in a soil column under saturated, continuous flow conditions. Sorption rates in the stirred flow chamber were expressed by three rate laws, first order, Langmuir, and second order, and the transport of bacteria through the soil column was described and predicted by a model assuming a mixture of instantaneous and time-dependent sorption reactions and, alternatively, by a kinetic model. The sorption rate was primafly dependent on the density of sorbed bacteria, but the desorption rate was, in addition, influenced by the density of cells in the aqueous phase. Rate coefficients obtained in the flow chamber could be used to accurately predict transport of bacteria in the soil column at the corresponding density and flow rate, but extrapolations are complicated by the nonlinear relationship between density and sorption rate. Timescales for reaching equilibrium estimated from the rate coefficients were in the range from 10-15 hours to several days, longer for low densities and velocities. [ABSTRACT FROM AUTHOR]

The compensatory growth potential of a grazed fungal biomass was mathematically expressed as a function of patchiness in its distribution and demonstrated in an experiment using the fungivorous collembolan Onychiurus armatus and the soil fungi Verticillium bulbillosum and Penicillium spinulosum. The model addresses the regrowth potential in relation to patch fragmentation, travelling time and consumption rate of the collembolan and the mean relative growth rate of the fungus. It suggests that the mean relative growth rate required for regrowth decreases with patch fragmentation and increases with the mean growth rate of the fungus. The experiments were performed with a system of soil-filled vials provided with fungi and collembolans. The size of the vials and the length of the tubes connecting them were varied to give different patch sizes and travelling times. The respiratory activity of fungi after grazing increased as a unit of mycelium was distributed into smaller connected vials. The slow growing species V. bulbillosum showed a greater but delayed response to grazing in comparison with the fast growing P. spinulosum. An increased travelling time delayed the growth response in both species. [ABSTRACT FROM AUTHOR]

Immigration and colonization of isolates of naturally occurring stream bacteria and hyphomycetes on beech leaves were studied in a laboratory stream microcosm. Fungal spores were more successful immigrants, especially on new leaves, than bacteria, which were more repelled than attracted by the substrate. Fewer bacteria immigrated to older leaves than to new, and bacteria multiplied faster in water than on leaves. Fungi and bacteria showed synergistic relationships so that each group grew significantly faster in presence of the other group. If one considers, differences in immigration, colonization and synergism patterns, fungal mycelia doubled about 10 times faster than bacterial cells which might explain the dominance of fungi usually found on leaves in early decay. The individual fungal species could be assigned to one of three colonization groups; one of fugitive species, preceding a second group of species that grew from rarity to dominance, and a third group of very slow colonizers. The leachate was fractionated in different molecular size classes by gel chromatography, and the fraction around 2500D in the new leaf leachate was associated with a high concentration of polyphenols. High-pressure liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) revealed the presence of 16 phenolic acids in the new leaf leachate at concentrations ranging from < 1 to 640 μg l. All fungi except the species with the slowest growth rate grew faster on leachate with the fraction around 2500D removed, and the density of bacteria was significantly reduced when pure stream water was supplemented with compounds from the same fraction. [ABSTRACT FROM AUTHOR]

The influence of food quantity and quality on growth and survival of Onychiurus armatus (Tullb.) in metal polluted environments has been investigated in laboratory experiments. The Collembola was reared on five species of fungi isolated from a metal polluted soil close to a brass mill in SE Sweden. Survival of O. armatus was improved when fungal biomass was continuously added in a polluted mor (1,300 ppm Zn and 200 ppm Cu), and when specimens were fed metal polluted fungi for 1, 3 and 7 days a week, only those that were starved had increased mortality. Allometric growth, on the other hand, was significantly reduced when Collembola was given surplus of metal polluted fungi, whereas growth losses caused by metals were offset by protein rich food. Hence, sufficient food quantities alone could overcome mortality losses but not growth retardation in a metal polluted environment. Feeding preference of O. armatus was not determined by the protein content of the fungi although this was beneficial for growth. Metals changed the relative palatability of fungal species, but one of the metal tolerant species, Paecilomyces farinosus, which was also protein rich, remained reasonably attractive for O. armatus also when it was metal polluted. The mechanisms by which growth and survival of O. armatus were promoted by a combination of protein and Zn/Cu rich fungi seemed to be crucial in understanding the fate of a population of this species in a metal polluted soil. [ABSTRACT FROM AUTHOR]