Molecular detection and quantification of slug parasitic nematodes from the soil and their hosts

Terrestrial gastropod molluscs are widely distributed and are well known as pests of many types of plants that are notoriously difficult to control. Many species of nematodes are able to parasitize land snails and slugs, but few of them are lethal to their host. Species and/or populations of mollusc-parasitic nematodes (MPNs) that kill their hosts are promising for biological control purposes. The recent discovery of new nematode species of the genus Phasmarhabditis in Europe and the associations between Alloionema spp. and slugs are expanding the possibilities of using MPNs as control agents. However, very little is known about the distribution and ecology of these species. Using molecular techniques based on qPCR methods for quick identification and quantification of various species of MPN isolated directly from the soil or from infected hosts can assist in providing information on their presence and persistence, as well as the composition of natural assemblages. Here, we developed new primers and probes for five species of the genus Phasmarhabditis and one species of the genus Alloionema. We employed these novel molecular techniques and implemented a published molecular set to detect MPN presence in soil samples coming from natural and agricultural areas in Switzerland. We also developed a method that allows the detection and quantification of Phasmarhabditis hermaphrodita directly from the tissues of their slug host in a laboratory experiment. The new molecular approaches were optimized to a satisfactory limit of detection of the species, with only few cross-amplifications with closely related species in late cycles (>32). Using these tools, we detected MPNs in 7.5% of sampled sites, corresponding to forest areas (P. hermaphrodita and Alloionema appendiculatum) and wheat-oriented agricultural areas (Phasmarhabditis bohemica). Moreover, we confirmed that the method can be used to detect the presence of P. hermaphrodita inside slug hosts, with more detections in the susceptible slug Deroceras larvae compared to the resistant Arion vulgaris. These primers/probe sets provide a novel and quick tool to identify MPNs from soil samples and infected slugs without having to culture and retrieve all nematode life stages, as well as a new tool to unravel the ecology of nematode-slug complexes.This work was funded by the Swiss National Science Foundation: Grants NRP68 and SNSF Div. I-III, reference 166632. The Government of Spain supports RCH with a Ramón y Cajal contract award: RYC-2016-19939.Peer reviewe

The evaluation of entomopathogenic nematode soil food web assemblages across Switzerland reveals major differences among agricultural, grassland and forest ecosystems

Entomopathogenic nematodes (EPNs) occur in natural and agricultural soils and contribute to the control of soil dwelling insect pests. Ecosystems differ in their soil parameters (pH, moisture, texture, etc.) and microhabitat conditions (presence of roots, plant cover, belowground fauna, etc.), which can affect the EPN soil food web assemblage in an unpredictable manner. By comparing soils that represent different ecological scenarios, we can link the natural distribution of the EPN to abiotic and biotic factors that shape the assemblages of soil food web to unravel the factors that determine EPN abundance and activity. We hypothesized that the EPN soil food web assemblages are affected by agricultural management practices and that this should be reflected when compared to natural ecosystems, such as forests and grasslands. By combining traditional and state-of-the-art molecular tools, we targeted 25 soil organisms to explore EPN food web in 40 Swiss georeferenced sites that can be categorized as “agricultural area”, “forest”, and “grassland”. EPNs abundance, richness and diversity did not vary among the different ecosystems. However, EPN activity (capability to kill insects) was higher in grasslands. Similarly, the free-living nematodes (FLNs) that compete with EPN for the cadavers were much more abundant in grassland, while reduced in the forest soils, suggesting contrasting conditions between these two natural areas. Nematophagous fungi (NF) were more diverse and present in agricultural areas, suggesting that the abiotic conditions in the agricultural areas may favor NF presence. Six soil properties and environmental factors shaped the EPN soil food web in Swiss soils (pH, elevation, clay content, soil water content, temperature, and rainfall), which explained 54% of the community variation in multivariate analysis. These observations were consistent with the key abiotic variables described for subtropical and Mediterranean regions. Identifying the links between the abiotic and biotic factors in very distinct areas can be the basis for predicting EPN soil food web assemblages. Such information can be of value for developing strategies to favour EPN resilience in a changing environment and enhance their capacity as biocontrol agents.This work was supported by an economic stimulus grant (51NF40-144621) and by the National Research Program 68 (NRP68) grant (406840_143065) from the Swiss National Science Foundation. GJ was supported by an assistantship from the University of Neuchâtel and XC was supported by a PhD fellowship from the Commission Fédérale des Bourses pour Etudiants Etrangères CFBE (Confédération Suisse). RCH was supported by The Government of Portugal (Investigator Program award, IF/00552/2014).Peer reviewe

Mercury in European agricultural and grazing land soils

Agricultural (Ap, Ap-horizon, 0–20 cm) and grazing land soil samples (Gr, 0–10 cm) were collected from a large part of Europe (33 countries, 5.6 million km2) at an average density of 1 sample site/2500 km2. The resulting more than 2 x 2000 soil samples were air dried, sieved to <2 mm and analysed for their Hg concentrations following an aqua regia extraction. Median concentrations for Hg are 0.030 mg/kg (range: <0.003–1.56 mg/kg) for the Ap samples and 0.035 mg/kg (range: <0.003–3.12 mg/kg) for the Gr samples. Only 5 Ap and 10 Gr samples returned Hg concentrations above 1 mg/kg. In the geochemical maps the continental-scale distribution of the element is clearly dominated by geology. Climate exerts an important influence. Mercury accumulates in those areas of northern Europe where a wet and cold climate favours the build-up of soil organic material. Typical anthropogenic sources like coal-fired power plants, waste incinerators, chlor-alkali plants, metal smelters and urban agglomerations are hardly visible at continental scales but can have a major impact at the local-scale

Geogenic and agricultural controls on the geochemical composition of European agricultural soils

Concern about the environmental impact of agriculture caused by intensification is growing as large amounts of nutrients and contaminants are introduced into the environment. The aim of this paper is to identify the geogenic and agricultural controls on the elemental composition of European, grazing an nd agricultural soils

GEMAS: Source, distribution patterns and geochemical behaviour of Ge in agricultural and grazing land soils at European continental scale

Agricultural soil (Ap-horizon, 0–20 cm) and grazing land soil (Gr-horizon, 0–10 cm) samples were collected from a large part of Europe (33 countries, 5.6 million km2) as part of the GEMAS (GEochemical Mapping of Agricultural and grazing land Soil) soil mapping project. GEMAS soil data have been used to provide a general view of element mobility and source rocks at the continental scale, either by reference to average crustal abundances or to normalized patterns of element mobility during weathering processes. The survey area includes a diverse group of soil parent materials with varying geological history, a wide range of climate zones, and landscapes. The concentrations of Ge in European soil were determined by ICP-MS after an aqua extraction, and their spatial distribution patterns generated by means of a GIS software. The median values of Ge and its spatial distribution in Ap and Gr soils are almost the same (0.037 vs. 0.034 mg/kg, respectively). The majority of Ge anomalies is related to the type of soil parent material, namely lithology of the bedrock and minor influence of soil parameters such as pH, TOC and clay content. Metallogenic belts with sulphide mineralisation provide the primary source of Ge in soil in several regions in Europe, e.g. in Scandinavia, Germany, France, Spain and Balkan countries. Comparison with total Ge concentrations obtained from the Baltic Soil Survey shows that aqua regia is a very selective method with rather low-efficiency and cannot provide a complete explanation for Ge geochemical behaviour in soil. Additionally, large differences in Ge distribution are to be expected when different soil depth horizons are analysed

Arsenic in agricultural and grazing land soils of Europe

Arsenic concentrations are reported for the <2 mm fraction of ca. 2200 soil samples each from agricultural (Ap horizon, 0\u201320 cm) and grazing land (Gr, 0\u201310 cm), covering western Europe at a sample density of 1 site/2500 km2. Median As concentrations in an aqua regia extraction determined by inductively coupled plasma emission mass spectrometer (ICP-MS) were 5.7 mg/kg for the Ap samples and 5.8 mg/kg for the Gr samples. The median for the total As concentration as determined by X-ray fluorescence spectrometry (XRF) was 7 mg/kg in both soil materials. Maps of the As distribution for both land-use types (Ap and Gr) show a very similar geographical distribution. The dominant feature in both maps is the southern margin of the former glacial cover seen in the form of a sharp boundary between northern and southern European As concentrations. In fact, the median As concentration in the agricultural soils of southern Europe was found to be more than 3-fold higher than in those of northern Europe (Ap: aqua regia: 2.5 vs. 8.0 mg/kg; total: 3 vs. 10 mg/kg). Most of the As anomalies on the maps can be directly linked to geology (ore occurrences, As-rich rock types). However, some features have an anthropogenic origin. The new data define the geochemical background of As in agricultural soils at the European scale