Effects of Cd and Pb on the survival and juvenile production of Sinella coeca and Folsomia candida

Degradation factors can cause both quantitative and qualitative changes in fauna and thus affect soil functioning. The use of bio-indicators may help to detect environmental changes. The aim of this study was to evaluate the effects of lead and cadmium on the biology (mortality, reproduction, egg hatching) of two euedaphic collembolans, Sinella coeca and Folsomia candida and to evaluate sensitivity differences between the two species. The results showed that low concentrations of lead did not cause dramatic effects on the survival and reproduction of both species. Reproduction of both species was reduced when the soil contained a nominal concentration of Pb at 1000 μg g^–1. S. coeca and F. candida showed a high sensitivity to cadmium and both their reproduction and survival were significantly reduced on exposure to 50 μg g^–1. Moreover, egg hatching of F. candida was affected by the cadmium concentrations in the soil, and by the amount of time that the eggs stayed in contact with cadmium. This study showed that the inhibition determined by Cd on F. candida juvenile production was caused in part by inhibition of deposition and, in part, by reduction of egg viability.     

Interactive effects of pyrimethanil,soil moisture and temperature on Folsomia candida and Sinella curviseta (Collembola)

The aim of the presented investigation was to study effects resulting from specific aspects of climate change and chemical stress (individually or in interaction) on soil organisms. In detail, the interaction of different temperatures (20 °C and 26 °C) and soil moisture levels (30%, 50% and 70% of the water holding capacity) were examined in combination with the fungicide pyrimethanil on the reproduction of two Collembola species (Folsomia candida and Sinella curviseta). Testing was based on the standard collembolan reproduction test (OECD-Guideline 232), following an EC_X design. Low soil moisture led to a significant reduction of the juveniles in the control groups in contrast to medium or high soil moisture. Furthermore, the results showed a significant influence of both climatic factors on the toxicity of the fungicide. In general, both species reacted more sensitive when exposure was conducted in dry soil or at enhanced temperature.     

What causes variability in the Folsomia candida reproduction test?

Large variability is often observed in results of the Folsomia candida reproduction test [ISO 11267, Soil quality—inhibition of reproduction of Collembola (Folsomia candida) by soil pollutants. Inter. Stand. Org. Ed. Genève. (1998) 1–16] and can be detrimental to the test sensitivity. So, we investigated the effects of certain parameters (small differences of ambient temperature and age of the animals) on the variability of reproduction of F. candida. We show that a 1 °C difference has no perceptible effect but that a 1 day difference in age has. Studying the reproduction of isolated individuals shows that a strong apparent interindividual variability exists. Lastly, we compared the variability of reproduction in two tests differing from one another in duration; variability was clearly decreased by lengthening the test.     

Food choice and reproductive success of Folsomia candida feeding on copper-contaminated mycelium of the soil fungus Alternaria alternata

We examined collembolan food preference for fungal mycelium grown on copper-contaminated medium, and the relationship between copper content, food selectivity and collembolan fitness when fed contaminated mycelium.To clarify whether collembolan food selectivity is related to fitness parameters, Folsomia candida were fed mycelium of the dark-pigmented fungus Alternaria alternata grown on medium with different copper concentrations. Copper-contaminated food (fungus grown on 50, 125, 250 and 500 μg Cu g⁻¹ medium, fresh wt.) was offered together with untreated food for 4 weeks. F. candida fed selectively on the provided mycelium and discriminated clearly between mycelium grown on high and low levels of contamination, distinctly preferring fungus grown on medium with a total copper concentration of 50 and 125 μg g⁻¹. In contrast, fungus grown on highly contaminated medium (250 and 500 μg g⁻¹) was avoided. Collembolan food preference generally matched fitness parameters. Reproduction was significantly affected by the total copper concentration of the fungal growth medium. When fed their preferred mycelium, collembolan reproduction was enhanced, whereas a diet of highly contaminated mycelium (250 or 500 μg g⁻¹) resulted in a strong decrease in reproduction. Adult survival was affected only marginally. Even though heavy metal contamination is a potential stress factor for many soil microarthropods, F. candida is able to discriminate between high and low quality food sources, and even benefits from moderately elevated copper concentrations.     

Soil biophysical controls over rice straw decomposition and sequestration in soil: The effects of drying intensity and frequency of drying and wetting cycles

Although it is well known that fluctuations in soil moisture affect the decomposition of organic matter, few studies have provided direct evidence of the underlying biophysical mechanisms. Cycles of wetting and drying (W/D) may not only alter soil pore structure, but also stimulate a proliferation of fungi, since these organisms are typically less affected by drought stress than bacteria, and hence the development of fungal-induced soil water repellency. The biophysical interaction between these processes is likely to influence the decomposition of organic matter amendments to soil and carbon sequestration. By using soil cores amended with rice straw, the objectives of this study were to determine the effects of drying intensity and frequency of W/D cycles on decomposition rate after rewetting, soil pore-size distribution, soil microbial biomass (SMB) and soil water repellency, and to assess their biophysical interaction. One W/D cycle consisted of wetting a soil core from the bottom for 1.5-days at −0.03 kPa followed by 1.5, 3.5 or 6.5 days of drying in open air at 25 ± 2.5 °C. This resulted in different intensities of drying and frequencies of W/D cycles over a 120-d incubation period. The decomposition rate decreased with repeated W/D cycles and increasing drying intensity, particularly between the 3rd and 9th W/D cycles. The SMB-C concentration and soil water repellency peaked at the 3rd W/D cycle. The peak size of the SMB-C concentration was larger in the drier soils and soil water repellency was significantly related to SMB-C concentration (R = 0.57, P = 0.025). The soil with the strongest drying treatment had a greater concentration of particulate organic carbon (POC) and the lowest C:N ratio in POC. Although the decomposition rate was significantly correlated to the concentration of soil organic carbon (SOC) (P < 0.01), POC (P < 0.01) and SMB-C (P < 0.05), stepwise regression analysis further identified that it was largely correlated to soil pore characteristics. The decrease in the decomposition rate in the drier soil was largely explained by the increase in macropores >300 μm in diameter (R = 0.98). The results suggest that an increased drying intensity or a longer duration of drying after rainfall or irrigation may favour SOC sequestration through inhibiting decomposition of amended residue. This may be due to the formation of macropores and their subsequent stabilization via fungal growth and fungal-induced soil water repellency.     

Effects of cadmium,mercury and lead on the survival and instantaneous rate of increase of Paronychiurus kimi (Lee) (Collembola)

The invertebrate springtail species Paronychiurus kimi (Lee) was selected for use in toxicity testing because it is more ecologically relevant to Korean soils than Folsomia candida Willem, which is the standard animal for toxicity tests. Responses of P. kimi to cadmium, mercury and lead were evaluated in artificial soils following the standardized ISO protocol. Although, reproduction of P. kimi was not as high as that of F. candida, 30 adults produced at least 200 juveniles over 28 days. For each of the three heavy metals, LC₅₀ and EC₅₀ for reproduction and NOEC and LOEC for the effect on reproduction and instantaneous rate of population increase (r_i) were also estimated. The 7 days LC₅₀ was 532, 3.9 and 1322 mg/kg dry soil for cadmium, mercury and lead, respectively. As exposure time increased from 7 to 28 days, the LC₅₀ values decreased for cadmium but not or only slightly for mercury and lead. The 28 days EC₅₀ was 60.0 for cadmium, 0.23 for mercury and 428 mg/kg for lead. Significant changes in r_i of P. kimi were closely followed by the changes in the sublethal endpoint measured (reproduction) and populations were heading toward extinction (r_i = 0) at concentration of 129, 2.0 and 1312 mg/kg dry soil for cadmium, mercury and lead, respectively. P. kimi was found to be more sensitive to all heavy metals tested than F. candida, confirming its suitability as a bioindicator species for soil toxicological testing in Korea.     

Sensitivity to cadmium of the standard test species Folsomia candida compared to two other species, Onychiurus yodai and Sinella umesaoi (Collembola)

Knowing whether test species used for single-species toxicity tests are representative of other species provides valuable information because contaminant effects are often extrapolated to the community level based on these tests. To evaluate how representative the sensitivity of the standard test collembolan species Folsomia candida is for Collembola, we devised toxicity tests using the collembolan species Onychiurus yodai and Sinella umesaoi, which exhibit life-forms different from F. candida. Sensitivity to cadmium (Cd) was compared between F. candida and the novel test species. The 50% effective concentrations for reproduction were 154.7, 72.2 and 40.9 mg Cd/kg dry soil for O. yodai, F. candida and S. umesaoi, respectively. Thus, the reproductive sensitivity of F. candida to Cd was between that of the other two species. Increasing reproductive sensitivity to Cd corresponded to increasing activity levels and a more surface-dwelling life-form. Our data may facilitate the generalisation of effect data for F. candida to other species.     

DIBOA: Fate in soil and effects on root-knot nematode egg numbers

The benzoxazinoid 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) is produced by rye (Secale cereale) and may contribute to plant-parasitic nematode suppression when rye plants are incorporated as a green manure. We investigated the fate of DIBOA in soil and DIBOA's effects on nematode reproduction. Soil in plastic bags was treated with DIBOA at concentrations ranging from 1.1 to 18 μg g⁻¹ dry soil, and with the root-knot nematode Meloidogyne incognita. Control soils were treated with water or with 0.31% methanol, with or without nematodes. DIBOA concentrations extracted from the soil were measured at selected times for 5 consecutive days. The soil from each bag was then placed into a pot in the greenhouse, and a cucumber seedling was transplanted into each pot. Five weeks later, only the highest DIBOA concentration, 18 μg g⁻¹ soil, reduced nematode egg numbers. At 0 h, DIBOA measured in soil ranged from 19.68 to 35.51% of the initial DIBOA concentration, and was dependent on the concentration added to the soil. DIBOA half-life was from 18 to 22 h, and very little DIBOA was present in soil after 120 h. Identified breakdown products accounted for only 4% at maximum of the initially added DIBOA. The results of our study demonstrate that high soil concentrations of DIBOA are necessary to suppress M. incognita; DIBOA may not be a major factor in nematode suppression by a rye cover crop.     

Temperature dependence of soil CO2 efflux is strongly modulated by seasonal patterns of moisture availability in a Mediterranean ecosystem

Extensive research has focused on the temperature sensitivity of soil respiration. However, in Mediterranean ecosystems, soil respiration may have a pulsed response to precipitation events, especially during prolonged dry periods. Here, we investigate temporal variations in soil respiration (R_s), soil temperature (T) and soil water content (SWC) under three different land uses (a forest area, an abandoned agricultural field and a rainfed olive grove) in a dry Mediterranean area of southeast Spain, and evaluate the relative importance of soil temperature and water content as predictors of R_s. We hypothesize that soil moisture content, rather than soil temperature, becomes the major factor controlling CO₂ efflux rates in this Mediterranean ecosystem during the summer dry season. Soil CO₂ efflux was measured monthly between January 2006 and December 2007 using a portable soil respiration instrument fitted with a soil respiration chamber (LI-6400-09). Mean annual soil respiration rates were 2.06 ± 0.07, 1.71 ± 0.09, and 1.12 ± 0.12 μmol m⁻² s⁻¹ in the forest, abandoned field and olive grove, respectively. R_s was largely controlled by soil temperature above a soil water content threshold value of 10% at 0-15 cm depth for forest and olive grove, and 15% for abandoned field. However, below those thresholds R_s was controlled by soil moisture. Exponential and linear models adequately described R_s responses to environmental variables during the growing and dry seasons. Models combining abiotic (soil temperature and soil rewetting index) and biotic factors (above-ground biomass index and/or distance from the nearest tree) explained between 39 and 73% of the temporal variability of R_s in the forest and olive grove. However, in the abandoned field, a single variable - either soil temperature (growing season) or rewetting index (dry season) - was sufficient to explain between 51 and 63% of the soil CO₂ efflux. The fact that the rewetting index, rather than soil water content, became the major factor controlling soil CO₂ efflux rates during the prolonged summer drought emphasizes the need to quantify the effects of rain pulses in estimates of net annual carbon fluxes from soil in Mediterranean ecosystems.     

Avoidance response of different collembolan species to Betanal

Laboratory avoidance tests were conducted to assess the behavioural reactions of five common collembolan species (Isotoma anglicana, Heteromurus nitidus, Lepidocyrtus violaceus, Folsomia candida, Onychiurus armatus) towards the herbicide Betanal (active ingredient: phenmedipham) in soil. Betanal exerted a dose-dependent repellent action on all tested species. In the case of O. armatus, the sensitivity of the avoidance test exceeded that of mortality and reproduction tests. It is concluded that, in addition to ecotoxicological tests on mortality and reproduction, a test system for assessing behavioural responses could provide more detailed information on the impact of pesticides and other harmful substances on Collembola.     

Food choice and reproductive success of Folsomia candida feeding on copper-contaminated mycelium of the soil fungus Alternaria alternata

We examined collembolan food preference for fungal mycelium grown on copper-contaminated medium, and the relationship between copper content, food selectivity and collembolan fitness when fed contaminated mycelium.To clarify whether collembolan food selectivity is related to fitness parameters, Folsomia candida were fed mycelium of the dark-pigmented fungus Alternaria alternata grown on medium with different copper concentrations. Copper-contaminated food (fungus grown on 50, 125, 250 and 500 μg Cu g^?1 medium, fresh wt.) was offered together with untreated food for 4 weeks. F. candida fed selectively on the provided mycelium and discriminated clearly between mycelium grown on high and low levels of contamination, distinctly preferring fungus grown on medium with a total copper concentration of 50 and 125 μg g^?1. In contrast, fungus grown on highly contaminated medium (250 and 500 μg g^?1) was avoided. Collembolan food preference generally matched fitness parameters. Reproduction was significantly affected by the total copper concentration of the fungal growth medium. When fed their preferred mycelium, collembolan reproduction was enhanced, whereas a diet of highly contaminated mycelium (250 or 500 μg g^?1) resulted in a strong decrease in reproduction. Adult survival was affected only marginally. Even though heavy metal contamination is a potential stress factor for many soil microarthropods, F. candida is able to discriminate between high and low quality food sources, and even benefits from moderately elevated copper concentrations.     

Double mulching improves soil properties and productivity of maize-based cropping system in eastern Indian Himalayas

A field experiment was conducted for two consecutive years at North Eastern Indian Himalayan region to assess the effect of soil moisture conservation measures on soil and water productivity of different rainfed maize (Zea mays L.) - based cropping sequences. Results revealed that double mulching with in-situ maize stover mulch (MSM) + fresh biomass of white hoary pea (WHP-Tephrosia candida) and MSM + fresh biomass of ragweed (RW- Ambrosia artemisiifolia) improved soil moisture content (SMC) and leaf relative water content of crops during dry season. The soil organic carbon (SOC) content and stocks under MSM + WHP and MSM + RW mulches were significantly higher than that under no mulch at 0–15 cm depth. The soil microbial biomass carbon and dehydrogenase activity were maximum under MSM + WHP/RW. The highest system productivity was obtained from maize-French bean (Pole type-PT) sequence under MSM + RW followed by MSM + WHP. The water productivity was the highest under MSM + WHP. While SOC content was the highest under maize-French bean (PT), the maximum plant available nitrogen and phosphorus were obtained under maize-black gram sequence.Thus, double mulching technology involving MSM and RW (available in plenty) is a viable option for improving soil, crop and water productivity under rainfed hill ecosystems of eastern Indian Himalayas.     

Effects of azoxystrobin,chlorothalonil, and ethoprophos on the reproduction of three terrestrial invertebrates using a natural Mediterranean soil

The potential terrestrial toxicity of three pesticides, azoxystrobin, chlorothalonil, and ethoprophos was evaluated using reproduction ecotoxicological tests with different non-target species: the collembolan Folsomia candida, the earthworm Eisenia andrei, and the enchytraeid Enchytraeus crypticus. All reproduction tests were performed with natural soil from a Mediterranean agricultural area (with no pesticide residues) in order to improve the relevance of laboratory data to field conditions. Controls were performed with natural and standard artificial soil (OECD 10% OM). The fungicide azoxystrobin showed the highest toxicity to earthworms (EC₅₀ = 42.0 mg a.i. kg⁻¹ dw soil). Collembolans were the most sensitive taxa in terms of sublethal effects of chlorothalonil with an EC₅₀ of 31.1 mg a.i. kg⁻¹ dw soil followed by the earthworms with an EC₅₀ of 40.9 mg a.i. kg⁻¹ dw soil. The insecticide ethoprophos was the most toxic to collembolans affecting their reproduction with an EC₅₀ of 0.027 mg a.i. kg⁻¹ dw soil. Enchytraeids were generally the least sensitive of the three species tested for long-term effects. Earthworms were not always the most sensitive species, emphasizing the need to increase the number of mandatory assays with key non-target organisms in the environmental risk assessment of pesticides.     

Microbial growth efficiencies across a soil moisture gradient assessed using C-acetic acid vapor and N-ammonia gas

One integrative measurement of microbial activity in soils is the efficiency by which microbes convert assimilated carbon (C) into biomass C. This efficiency, called the microbial growth efficiency (Y), is a key physiological characteristic that regulates soil carbon sequestration, nutrient immobilization, and greenhouse gas emissions. Changes in rainfall patterns and soil water content as the result of global climate change have the potential to influence microbial activity and lead to changes in Y and thus, nutrient cycling at the ecosystem level. Unfortunately, little information is available on how environmental variables such as soil moisture influence Y. We have developed a new method for injecting ¹³C-labeled carbon as acetic acid vapor into soil that will allow measurement of microbial growth efficiency (as Y_C) without increasing soil moisture content. We compare Y determined with this new approach with an alternate method where injected ¹⁵N-labeled ammonia gas is used to quantify microbial N immobilization, and microbial growth efficiency is calculated based on microbial C:N and respiration rate (as Y_N). We also include injections of a solution containing labeled ammonium and acetate in our experiment to compare the results of our vapor methods with more commonly employed liquid-based methods. The ¹³C-acetic acid vapor, which was supplied to soils with soil moisture content ranging from 0.05 to 0.21 g H₂O g⁻¹ soil, was readily assimilated and respired by microbes. Between 0.10 and 0.21 g H₂O g⁻¹ soil (−0.60 to −0.04 MPa), values of Y_C averaged 0.46, and were significantly lower than values of Y_N, with average values of 0.58. Over this range, soil moisture content had no significant effect on either Y_C or Y_N. However, at the lowest soil moisture content (0.05 g H₂O g⁻¹ soil; <−6.0 MPa), Y_C and Y_N diverged substantially, suggesting that in very dry soils, constraints on microbial growth cause differential uptake of C and N resources.     

Drought-sensitivity ranking of deciduous tree species based on thermal imaging of forest canopies

Most climate change projections for Central Europe predict higher mean summer temperatures and prolonged summer drought periods. However, in diverse mixed forest stands we expect tree species specific responses to water shortage, as tree species are highly variable in rooting depth and physiological traits related to the water balance. Here, we assessed the drought sensitivity of the water relations of six deciduous forest tree species at four sites with contrasting water availability by airborne thermal imagery of canopy foliage temperature, sap flow and soil water potential. Canopy architecture had a consistent influence on canopy foliage temperature with ‘dense canopy’ species (Acer pseudoplatanus, Fagus sylvatica and Tilia platyphyllos) being warmer (0.5-1.5 K) than ‘open canopy’ species (Fraxinus excelsior, Prunus avium and Quercus petraea). While the canopy foliage was close to air temperature at the beginning of the drought period (ΔT_C−A = −0.1 to 0.7 K) it strongly warmed up with ongoing drought, especially at the two ‘dry’ sites with a ΔT_C−A of 3.5-5 K. The pronounced canopy foliage warming at the ‘dry’ sites after 22 days of drought was associated with reduced transpiration rates as sap flow was curtailed by 20-35% in all species except F. excelsior and Q. petraea. Based on canopy foliage temperature and sap flow data, we considered A. pseudoplatanus the most drought sensitive species followed by F. sylvatica, T. platyphyllos and P. avium and the two ring-porous species F. excelsior and Q. petraea being clearly the least sensitive ones. At drier sites, increasing summer temperatures and drought might change the competitive abilities of tree species in favour of those that are able to maintain transpirational fluxes and cooler canopies such as F. excelsior and Q. petraea.     

Effects of decreasing water potential on gross ammonification and nitrification in an acid coniferous forest soil

Changes in the soil water regime, predicted as a consequence of global climate change, might influence the N cycle in temperate forest soils. We investigated the effect of decreasing soil water potentials on gross ammonification and nitrification in different soil horizons of a Norway spruce forest and tested the hypotheses that i) gross rates are more sensitive to desiccation in the Oa and EA horizon as compared to the uppermost Oi/Oe horizon and ii) that gross nitrification is more sensitive than gross ammonification. Soil samples were adjusted by air drying to water potentials from about field capacity to around −1.0 MPa, a range that is often observed under field conditions at our site. Gross rates were measured using the ¹⁵N pool dilution technique. To ensure that the addition of solute label to dry soils and the local rewetting does not affect the results by re-mineralization or preferential consumption of ¹⁵N, we compared different extraction and incubation times.T₀ times ranging from 10 to 300 min and incubation times of 48 h and 72 h did not influence the rates of gross ammonification and nitrification. Even small changes of water potential decreased gross ammonification and nitrification in the O horizon. In the EA horizon, gross nitrification was below detection limit and the response of the generally low rates of gross ammonification to decreasing water potentials was minor. In the Oi/Oe horizon gross ammonification and nitrification decreased from 37.5 to 18.3 mg N kg⁻¹ soil d⁻¹ and from 15.4 to 5.6 mg N kg⁻¹ soil d⁻¹ when the water potential decreased from field capacity to −0.8 MPa. In the Oa horizon gross ammonification decreased from 7.4 to 4.0 mg N kg⁻¹ soil d⁻¹ when the water potential reached −0.6 MPa. At such water potential nitrification almost ceased, while in the Oi/Oe horizon nitrification continued at a rather high level. Hence, only in the Oa horizon nitrification was more sensitive to desiccation than ammonification. Extended drought periods that might result from climate change will cause a reduction in gross N turnover rates in forest soils even at moderate levels of soil desiccation.     

Winter soil CO2 efflux and its contribution to annual soil respiration in different ecosystems of a forest-steppe ecotone, north China

Most soil respiration measurements are conducted during the growing season. In tundra and boreal forest ecosystems, cumulative winter soil CO₂ fluxes are reported to be a significant component of their annual carbon budgets. However, little information on winter soil CO₂ efflux is known from mid-latitude ecosystems. Therefore, comparing measurements of soil respiration taken annually versus during the growing season will improve the accuracy of ecosystem carbon budgets and the response of soil CO₂ efflux to climate changes. In this study we measured winter soil CO₂ efflux and its contribution to annual soil respiration for seven ecosystems (three forests: Pinus sylvestris var. mongolica plantation, Larix principis-rupprechtii plantation and Betula platyphylla forest; two shrubs: Rosa bella and Malus baccata; and two meadow grasslands) in a forest-steppe ecotone, north China. Overall mean winter and growing season soil CO₂ effluxes were 0.15-0.26 μmol m⁻² s⁻¹ and 2.65-4.61 μmol m⁻² s⁻¹, respectively, with significant differences in the growing season among the different ecosystems. Annual Q₁₀ (increased soil respiration rate per 10 °C increase in temperature) was generally higher than the growing season Q₁₀. Soil water content accounted for 84% of the variations in growing season Q₁₀ and soil temperature range explained 88% of the variation in annual Q₁₀. Soil organic carbon density to 30 cm depth was a good surrogate for SR₁₀ (basal soil respiration at a reference temperature of 10 °C). Annual soil CO₂ efflux ranged from 394.76 g C m⁻² to 973.18 g C m⁻² using observed ecosystem-specific response equations between soil respiration and soil temperature. Estimates ranged from 424.90 g C m⁻² to 784.73 g C m⁻² by interpolating measured soil respiration between sampling dates for every day of the year and then computing the sum to obtain the annual value. The contributions of winter soil CO₂ efflux to annual soil respiration were 3.48-7.30% and 4.92-7.83% using interpolated and modeled methods, respectively. Our results indicate that in mid-latitude ecosystems, soil CO₂ efflux continues throughout the winter and winter soil respiration is an important component of annual CO₂ efflux.     

Tolerance of genetically characterized <Emphasis Type="Italic">Folsomia candida</Emphasis> strains to phenmedipham exposure

Background, Aims, and Scope  The springtail Folsomia candida is a commonly used model species in ecotoxicological soil testing. The species reproduces parthenogenetically and, thus, laboratories use different clonal lineages. In this study, we investigated if genetic divergence between F. candida strains impacts the reaction to chemical stress and may thus affect the outcome of toxicity tests. Methods  In two exposure assays (life-cycle reproduction test and avoidance behaviour test), three laboratory strains of F. candida from Portugal (PTG), Spain (SPN) and Denmark (DNK) were exposed to different concentrations of the reference chemical phenmedipham. Genetic divergence among strains was estimated based on mitochondrial COI sequence data. Results  No significant differences between tolerance towards phenmedipham exposure were observed in a reproduction test. In contrast, one strain (SPN) showed a decreased susceptibility to phenmedipham compared to the other strains (PTG and DNK) in the avoidance assay. Discussion  A phylogenetic tree based on mitochondrial COI sequences revealed clear genetic differentiation between both ‘reaction types’. Thus, we found a potential lineage dependent stress reaction in avoidance behaviour towards the pesticide. Conclusions  Our findings have implications for the comparability of test results among laboratories. Reproduction tests seem to be more robust towards interclonal genetic differentiation than avoidance tests. Recommendations and Perspectives  We recommend the use of molecular tools for simple and cost effective genetic characterization of F. candida strains used in chemical avoidance tests. Closer investigations concerning the relation between genetic relatedness and chemical response will provide a more detailed and comprehensive picture on the role of intraspecific genetic differentiation in stress tolerance. ESS-Submission Editor: Prof. Dr. Henner Hollert (henner.hollert@bio5.rwth-aachen.de)     

Soil particle surface electrochemical property effects on abundance of ammonia-oxidizing bacteria and ammonia-oxidizing archaea, NH4 activity, and net nitrification in an acid soil

Soil surface electrochemical properties may have a strong influence on nitrifying microorganisms, H⁺ and NH₄⁺ activities, and therefore on the nitrification process. A gradient of surface electrochemical parameters was obtained by amendment of a subtropical acid pine soil (Oxisol) with 0% (control), 3%, 5%, 8%, 10% and 12% pure Ca-Montmorillonite by weight. The H⁺ and NH₄⁺ activities, the abundance of the ammonia-oxidizing bacterial (AOB) and archaeal (AOA) amoA gene copies, and time-dependent kinetics of net nitrification were investigated. Soil particle surface specific area ranged from 53 to 103 m² g⁻¹ and increased with increasing montmorillonite application rate. Similar to specific area, surface charge quantity, surface charge density, electric field strength and surface potential increased after montmorillonite amendment. The H⁺ and NH₄⁺ activities decreased linearly after montmorillonite addition. AOB amoA gene copy number was 1.82 × 10⁵ copies g⁻¹ for unamended soil, and the highest AOB amoA gene copy numbers were found for the 10% montmorillonite amendment (3.11 × 10⁷ g⁻¹ soil), which was more than 150 times higher than unamended soil. AOA amoA gene copy numbers were 9.19 × 10³ copies g⁻¹ dry unamended soil, and the highest AOA amoA gene copy numbers were found in the 8% montmorillonite amendment (1.22 × 10⁵ g⁻¹ soil). Although pH significantly decreased during the first three weeks of incubation, no significant difference was observed between the unamended control and different rates of montmorillonite addition treatments during the whole incubation. The largest net nitrification (103 mg N kg⁻¹) was observed in the 10% montmorillonite amendment and the lowest in unamended soil (62 mg N kg⁻¹). While montmorillonite did not change the kinetic patterns of net nitrification, the highest nitrification potential (275 mg N kg⁻¹) for the 10% montmorillonite treatment was more than 3 times higher than unamended soil from simulation of time-dependent kinetics. Nitrification was significantly stimulated after montmorillonite amendment in acid soil mainly due to an increase in the quantity and activity of AOB and AOA. We concluded that soil particle surface parameters can significantly influence nitrification, especially in acid soils.     

Recovery of enchytraeid populations after severe drought events

The potential impact of changes in precipitation patterns associated with climate changes was investigated in Enchytraeidae (Oligochaeta) in a Danish heathland. The amount of precipitation was manipulated during spring and summer in an experimental field site in order to reveal effects of three different drought regimes: weak drought (WD), medium drought (MD) and high drought (HD). Enchytraeids were sampled every six to eight weeks (0–9 cm depth) for more than the eight months and soil water potential (SWP) and soil water content (SWC) was measured on a regular basis for five months.The enchytraeid communities were generally reduced due to a natural drought spell. The HD treatment significantly reduced the moisture level of the soil further with SWP below −15 bar (5 and 10 cm depth) and SWC around 5% (v/v) for more than two months. As a result almost no enchytraeids were found in HD plots after two months with high drought stress. Nevertheless, the HD-treated enchytraeid communities recovered within two months, as there was no significant difference in biomass and density of the different treatments at that time. During periods with extreme low SWP enchytraeids were practically absent in the top soil (0–3 cm), but a few animals were found in 3–6 cm. During this period SWP was around −15 bar even in 20 cm depth, indicating that active stages could not have survived. Thus, we suggest that the species present must be dependent on a drought tolerant stage, as vertical migration could not have supported the observed recovery.SWP and SWC were both significantly correlated with the total density and biomass of enchytraeids. However, density was better correlated with the SWP and SWC compared to biomass, which can be due to hatching of cocoons and increased fragmentation rate.