PIXE-electrophoresis shows starving collembolan reallocates protein-bound metals.

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.

Microbial diversity and PAH catabolic genes tracking spatial heterogeneity of PAH concentrations.

We analyzed the within-site spatial heterogeneity of microbial community diversity, polyaromatic hydrocarbon (PAH) catabolic genotypes, and physiochemical soil properties at a creosote contaminated site. Genetic diversity and community structure were evaluated from an analysis of denaturant gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)-amplified sequences of 16S rRNA gene. The potential PAH degradation capability was determined from PCR amplification of a suit of aromatic dioxygenase genes. Microbial diversity, evenness, and PAH genotypes were patchily distributed, and hot and cold spots of their distribution coincided with hot and cold spots of the PAH distribution. The analyses revealed a positive covariation between microbial diversity, biomass, evenness, and PAH concentration, implying that the creosote contamination at this site promotes diversity and abundance. Three patchily distributed PAH-degrading genotypes, NAH, phnA, and pdo1, were identified, and their abundances were positively correlated with the PAH concentration and the fraction of soil organic carbon. The covariation of the PAH concentration with the number and spatial distribution of catabolic genotypes suggests that a field site capacity to degrade PAHs may vary with the extent of contamination.

Temporal and spatial distribution of waterborne mercury in a gold miner's river.

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.

Ecological, groundwater, and human health risk assessment in a mining region of Nicaragua.

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 (BMDLs(0.1)). 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 BMDLs(0.1) 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.

Endemism predicts intrinsic vulnerability to nonindigenous species on islands.

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.

A spatial approach to environmental risk assessment of PAH contamination.

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 x 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 x 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.

Mercury sorption to sediments: dependence on grain size, dissolved organic carbon, and suspended bacteria.

A combination of laboratory scale derived correlations and measurements of grain size distribution, DOC (dissolved organic carbon) concentration, and density of suspended bacteria promises to be useful in estimating Hg(II) sorption in heterogeneous streambeds and groundwater environments. This was found by shaking intact sediment and fractions thereof (<63-2000microm) with solutions of HgCl2 (1.0-10.0ngml(-1)). The intact sediment was also shaken with the Hg(II) solutions separately in presence of DOC (6.5-90.2microgml(-1)) or brought in contact with suspensions of a strain of groundwater bacteria (2x10(4)-2x10(6)cellsml(-1)). Hg(II) sorption was rather weak and positively correlated with the grain size, and the sorption coefficient (Kd) varied between about 300 and 600mlg(-1). By using the relative surface areas of the fractions, Kd for the intact sediment was back calculated with 2% deviation. Kd was negatively correlated with the concentration of DOC and positively correlated with the number of bacteria. A multiple regression showed that Kd was significantly more influenced by the number of bacteria than by the grain size. The findings imply that common DOC concentrations in groundwater and streambeds, 5-20microgml(-1), will halve the Kd obtained from standard sorption assays of Hg(II), and that Kd will almost double when the cell numbers are doubled at densities that are common in aquifers. The findings suggest that simultaneous measurements of surface areas of sediment particles, DOC concentrations, and bacterial numbers are useful to predict spatial variation of Hg(II) sorption in aquifers and sandy sediments.

Spatial covariation of microbial community composition and polycyclic aromatic hydrocarbon concentration in a creosote-polluted soil.

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 (16:1omega7c, 16:1omega7t, 18:1omega7, 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 18:2omega6,9 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.

Rapid turnover of DOC in temperate forests accounts for increased CO2 production at elevated temperatures.

The evidence for the contribution of soil warming to changes in atmospheric CO(2) 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 CO(2) emitted to the atmosphere.

Bacterial immobilization and remineralization of N at different growth rates and N concentrations.

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 NO(3)(-) is controlled by the soil concentration of NH(4)(+). 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 NH(4)(+)and NO(3)(-) concentrations; (3) establish the microbial preference for NH(4)(+)and NO(3)(-) depending on the NH(4)(+)/NO(3)(-) concentration ratio. Remineralization of microbial N occurred mainly at high growth rates and NH(4)(+) concentrations. There was a positive correlation between NH(4)(+) 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 NO(3)(-) immobilization rates, especially at low NH(4)(+) concentrations, but NO(3)(-) was also immobilized at high NH(4) concentrations. The latter can be understood if part of the microbial community has a preference for NO(3)(-) over NH(4)(+).

Interactions between fungi, bacteria and beech leaves in a stream microcosm.

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-1. 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.

Patterns of amino acid utilization by aquatic hyphomycetes.

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.

Influence of fungi on growth and survival of Onychiurus armatus (Collembola) in a metal polluted soil.

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.

Patchiness and compensatory growth in a fungus-Collembola system.

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.

Reduced grazing rates in Daphnia pulex caused by contaminants: implications for trophic cascades.

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 microg/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.

Soil moisture variations affect short-term plant-microbial competition for ammonium, glycine, and glutamate.

We tested whether the presence of plant roots would impair the uptake of ammonium ([Formula: see text]), glycine, and glutamate by microorganisms in a deciduous forest soil exposed to constant or variable moisture in a short-term (24-h) experiment. The uptake of (15)NH4 and dual labeled amino acids by the grass Festuca gigantea L. and soil microorganisms was determined in planted and unplanted soils maintained at 60% WHC (water holding capacity) or subject to drying and rewetting. The experiment used a design by which competition was tested in soils that were primed by plant roots to the same extent in the planted and unplanted treatments. Festuca gigantea had no effect on microbial N uptake in the constant moist soil, but its presence doubled the microbial [Formula: see text] uptake in the dried and rewetted soil compared with the constant moist. The drying and rewetting reduced by half or more the [Formula: see text] uptake by F. gigantea, despite more than 60% increase in the soil concentration of [Formula: see text]. At the same time, the amino acid and [Formula: see text]-N became equally valued in the plant uptake, suggesting that plants used amino acids to compensate for the lower [Formula: see text] acquisition. Our results demonstrate the flexibility in plant-microbial use of different N sources in response to soil moisture fluctuations and emphasize the importance of including transient soil conditions in experiments on resource competition between plants and soil microorganisms. Competition between plants and microorganisms for N is demonstrated by a combination of removal of one of the potential competitors, the plant, and subsequent observations of the uptake of N in the organisms in soils that differ only in the physical presence and absence of the plant during a short assay. Those conditions are necessary to unequivocally test for competition.

Spatial uncoupling of biodegradation, soil respiration, and PAH concentration in a creosote contaminated soil.

Hotspots and coldspots of concentration and biodegradation of polycyclic aromatic hydrocarbons (PAHs) marginally overlapped at the 0.5-100 m scale in a creosote contaminated soil in southern Sweden, suggesting that concentration and biodegradation had little spatial co-variation. Biodegradation was substantial and its spatial variability considerable and highly irregular, but it had no spatial autocorrelation. The soil concentration of PAHs explained only 20-30% of the variance of their biodegradation. Soil respiration was spatially autocorrelated. The spatial uncoupling between biodegradation and soil respiration seemed to be governed by the aging of PAHs in the soil, since biodegradation of added 13C phenanthrene covaried with both soil respiration and microbial biomass. The latter two were also correlated with high concentrations of phospholipid fatty acids (PLFAs) that are common in gram-negative bacteria. However, several of the hotspots of biodegradation coincided with hotspots for the distribution of a PLFA indicative of fungal biomass.

[Spatial variation of microbial properties in a creosote-contaminated soil].

By the methods of geostatistics, this paper studied the spatial variation of microbial biomass, microbial community structure and microbial activity in a creosote-contaminated soil. The microbial biomass was indicated by the total amount of 26 examined phospholipid fatty acids (totPLFA), the microbial community structure was characterized by the first two principal components (PC1 and PC2) of the PLFA patterns through subjecting the PLFAs to principal component analysis, and the total amount of CO2-C respired (C(re)) during incubation was used to describe the soil microbial activity. The results showed that most of the variables exhibited various degrees of spatial autocorrelation, and spherical models with nugget could fit their semivariograms. The estimated spatial dependence distances of the variables varied from 2.50 to 16.60 m. The PLFA PC1, totPLFA and C(re) displayed relatively high spatial dependences, their relative structural variance, i.e., the proportion of total variance that can be attributed to the spatial autocorrelation, being 82.3%, 79.6% and 64.7%, respectively, while PLFA PC2 was not spatially autocorrelated. The kriged maps showed that there were several hot spots with relatively high microbial biomass and high microbial activity located in the study site. Gram- negative bacteria characterized by PLFAs 16:1omega7t, cyl7:0, 18:1omega7 and cyl9:0 were the dominant community in these hot spots. The concentration and spatial distribution of polycyclic aromatic hydrocarbons as the main contaminants in the soil could be one of the important factors affecting the spatial variation of soil microbial properties.

13C incorporation into signature fatty acids as an assay for carbon allocation in arbuscular mycorrhiza.

The ubiquitous arbuscular mycorrhizal fungi consume significant amounts of plant assimilated C, but this C flow has been difficult to quantify. The neutral lipid fatty acid 16:1omega5 is a quantitative signature for most arbuscular mycorrhizal fungi in roots and soil. We measured carbon transfer from four plant species to the arbuscular mycorrhizal fungus Glomus intraradices by estimating (13)C enrichment of 16:1omega5 and compared it with (13)C enrichment of total root and mycelial C. Carbon allocation to mycelia was detected within 1 day in monoxenic arbuscular mycorrhizal root cultures labeled with [(13)C]glucose. The (13)C enrichment of neutral lipid fatty acid 16:1omega5 extracted from roots increased from 0.14% 1 day after labeling to 2.2% 7 days after labeling. The colonized roots usually were more enriched for (13)C in the arbuscular mycorrhizal fungal neutral lipid fatty acid 16:1omega5 than for the root specific neutral lipid fatty acid 18:2omega6,9. We labeled plant assimilates by using (13)CO(2) in whole-plant experiments. The extraradical mycelium often was more enriched for (13)C than was the intraradical mycelium, suggesting rapid translocation of carbon to and more active growth by the extraradical mycelium. Since there was a good correlation between (13)C enrichment in neutral lipid fatty acid 16:1omega5 and total (13)C in extraradical mycelia in different systems (r(2) = 0.94), we propose that the total amount of labeled C in intraradical and extraradical mycelium can be calculated from the (13)C enrichment of 16:1omega5. The method described enables evaluation of C flow from plants to arbuscular mycorrhizal fungi to be made without extraction, purification and identification of fungal mycelia.

Endogenous free fatty acids repel and attract Collembola.

We used video recording of the movement pattern of Protaphorura armata (Collembola) to test whether its avoidance of the odor of dead conspecifics extends to related species. P. armata was repelled by the odor of dead individuals of Onychiurus scotarius and Onychiurus circulans, but not by live individuals. Free palmitic, oleic, and linoleic acids were present in extracts of the three repellent species, but only free palmitic acid was detected in extracts of a fourth nonrepellent species, Folsomia candida. Synthetic palmitic acid was attractive to P. armata, linoleic acid was repellent, and oleic acid gave no response. o. scotarius and O. circulans also contained 2,3-dimethoxy-pyrido[2,3-b]pyrazine, known as a defense substance. We discuss the role of free fatty acids in predator avoidance, conspecifics attraction, and food recognition in P. armata.