Endogeic Species Research Articles

Accumulation of heavy metals from single and combined olive mill wastewater and pomace in soil and bioaccumulation in tissues of two earthworm species: Endogeic (Aporrectodea trapezoides) and Epigeic (Eisenia fetida).

Soil and earthworms are threatened by anthropogenic contamination resulting from olive mill waste dumping on the soil due to their pollutant properties. While several studies have explored the effects of olive mill waste on soil properties and the accumulation of heavy metals in soil, there is currently a gap in the literature regarding the potential bioaccumulation of heavy metals from olive mill waste in earthworms. In this study, soil with earthworms from two ecological categories (endogeic: Aporrectodea trapezoides and epigeic: Eisenia fetida) was treated with increasing doses of olive mill wastewater (OMWW) and olive mill pomace (OMP), applied individually or combined, in an indoor experiment in plastic containers, under laboratory conditions. The results revealed the presence of significant concentrations of heavy metals in the two types of wastes ranging as follows: Fe˃ Zn˃ Cu˃ Cd˃ Cr for OMWW, and Fe˃ Zn˃ Cu˃ Cr for OMP (with Cd below the detection limit). The study demonstrated distinct effects of OMWW and OMP, both individually and in combination, on soil heavy metal content, ranging as follows: soil OMWW > soil Combination > soil OMP for Cd; soil Combination > soil OMWW > soil OMP for Cr and Fe; and soil Combination > soil OMP > soil OMWW for Cu and Zn. Additionally, our investigation showed that both earthworm species exhibited significant uptake of these metals into their tissues, particularly the endogeic species. Interestingly, the most significant difference between species was in the accumulation of Cu, with the epigeic species accumulating significantly lower amounts.

Earthworms enhance the performance of organic amendments in improving rice growth and nutrition in poor ferralsols

In the Highlands of Madagascar, providing organic amendments (OAs) is the main farmer fertilization practice in upland rainfed agrosystems dominated by nutrient-depleted Ferralsols. Therefore, enhancing the performance of OAs on plant functions is particularly important for improving both plant productivity and agrosystem sustainability. Earthworms are well-known ecosystem engineers involved in the decomposition of organic matter and play a critical role in nutrient turnover. Inoculating earthworms could be a promising approach to improve the fertilizer performance of OAs. However, there is limited knowledge regarding the interaction between earthworms and OAs of varying biochemical qualities on plant growth and nutrition. In this microcosm experiment, we assessed the effect of different types of OAs (i.e., unamended control, conventional farmyard manure, kraal manure, improved farmyard manure, compost, vermicompost, urban waste, taroka, poultry droppings, pig manure) and earthworm inoculation (with and without earthworms) on the growth and nutrition of rice. The endogeic species Pontoscolex corethrurus (Rhinodrilidae) was used in the experiment. After eight weeks of growth, the poultry droppings had the best fertilizer performance, followed by improved farmyard manure and pig manure in treatments without earthworms. The main driver of fertilizer performance appeared to be the quality of OAs. However, other mechanisms, such as an increase in soil pH, may also play a significant role. The inoculation of earthworms significantly enhanced the fertilizer performance of OAs but the magnitude of this enhancement depends on the OAs. Overall, OAs with low fertilizer performance showed a more pronounced response to earthworms. Additionally, earthworms improved the performance of high-quality OAs likely by enhancing the availability of P and Mg. Our findings emphasize the synergistic effects of earthworms and OAs of various qualities on plant growth and nutrition, offering valuable insights for improving fertilization practices in nutrient-poor Ferralsols of Madagascar.

Local variations in soil compaction in the drilosphere of a wide range of earthworms and links with ecological categories and functional traits

Earthworms can compact the soil through the production of casts and by pushing the soil when burrowing. However, how different ecological categories differently affect these processes is poorly known. This study aimed to expand our knowledge on the compaction within the drilosphere and to examine similarities and differences between ecological categories. We sampled 21 earthworm species in Vietnam whose bioturbating behaviours and morpho-anatomical traits had been previously studied. One individual was incubated in soil core for four weeks under laboratory conditions. After incubation, the following drilosphere properties were assessed using X-ray computed tomography: the volume and compaction of casts, the volume of empty burrows, the compaction of burrow walls and the radius of lateral compaction around burrows. The drilosphere volume decreased in the following order: anecic (8.5%), endogeic (2.5%), intermediate (1.5%) and epigeic species (0.5%). Together, casts and lateral compaction occupied more than 70% of the whole drilosphere regardless of the ecological category. Both anecic and endogeic species had relatively similar effects on soil compaction. They compacted surface casts (up to 1.45-fold), belowground casts (up to 1.20-fold), and burrow walls (up to 1.25-fold) and induced the widest lateral compaction around burrows (up to 11 mm). Conversely, epigeic species had markedly fewer effects, increasing compaction from 1.10- to 1.20-fold and producing the narrowest lateral compaction (1 mm). Intermediate species showed large variability, which included species with little and large effects on compaction. Finally, we showed that food ingestion, muscle thickness and body size were the most related to the compaction of the drilosphere. It is concluded that the soil volume compacted by the earthworms is larger than the volume of empty burrows. Additionally, our study encourages further investigations using functional traits to overcome some limitations associated with the traditional ecological category approach.

Earthworms and plants can decrease soil greenhouse gas emissions by modulating soil moisture fluctuations and soil macroporosity in a mesocosm experiment.

Earthworms can stimulate microbial activity and hence greenhouse gas (GHG) emissions from soils. However, the extent of this effect in the presence of plants and soil moisture fluctuations, which are influenced by earthworm burrowing activity, remains uncertain. Here, we report the effects of earthworms (without, anecic, endogeic, both) and plants (with, without) on GHG (CO2, N2O) emissions in a 3-month greenhouse mesocosm experiment simulating a simplified agricultural context. The mesocosms allowed for water drainage at the bottom to account for the earthworm engineering effect on water flow during two drying-wetting cycles. N2O cumulative emissions were 34.6% and 44.8% lower when both earthworm species and only endogeic species were present, respectively, and 19.8% lower in the presence of plants. The presence of the endogeic species alone or in combination with the anecic species slightly reduced CO2 emissions by 5.9% and 11.4%, respectively, and the presence of plants increased emissions by 6%. Earthworms, plants and soil water content interactively affected weekly N2O emissions, an effect controlled by increased soil dryness due to drainage via earthworm burrows and mesocosm evapotranspiration. Soil macroporosity (measured by X-ray tomography) was affected by earthworm species-specific burrowing activity. Both GHG emissions decreased with topsoil macropore volume, presumably due to reduced moisture and microbial activity. N2O emissions decreased with macropore volume in the deepest layer, likely due to the presence of fewer anaerobic microsites. Our results indicate that, under experimental conditions allowing for plant and earthworm engineering effects on soil moisture, earthworms do not increase GHG emissions, and endogeic earthworms may even reduce N2O emissions.

Earthworms increase soil greenhouse gas emissions reduction potential in a long-term no-till Mollisol

Earthworm activity and plant residues in the soil can strongly influence soil organic carbon (SOC) dynamics. However, studies on how earthworms, especially epigeic and endogeic species alone or together, affect the main soil greenhouse gas (GHG) emissions (CO2 and N2O) and SOC under the long-term no-till (NT) and conventional tillage (CT) in Mollisols in Northeast China are unclear. The effects of two different species of earthworms (epigeic, Eisenia nordenskioldi; endogeic, Metaphire tschiliensis) on the soil GHG emissions and the SOC content were studied in NT and CT soils in a 337-day mesocosm experiment. The presence of earthworms enhanced the soil cumulative CO2 and N2O emissions in both NT and CT soils, and the soil GHG emissions (expressed in terms of the global warming potential, GWP) were increased by 20.43 %–42.99 % in NT soil and by 0–55.62 % in CT soil, respectively. Compared to E. nordenskioldi, the presence of M. tschiliensis (endogeic species) significantly increased soil GHG emissions. Earthworms in NT soil induced less soil GHG emissions than those in CT soil. The presence of earthworms did not increase the SOC content in CT soil but significantly increased the SOC content in NT soil. Our study suggests that earthworms in the long-term no-till soil can contribute to the reduction of soil GHG emissions. This research helps to understand the effects of different ecological categories of earthworms on soil GHG emissions and SOC dynamics under different tillage systems and to mitigate soil GHG emissions.

Spatial patterns and species associations of earthworms in relation to micro-topography and insolation

Despite significant advancements in our understanding of the relationship between soil animal life and environmental gradients, as well as their impact on ecosystem functioning, there is a growing need for quantitative research that considers the spatial and temporal heterogeneity of soil biodiversity. Such research can help to address current knowledge gaps and support the development of legislation and conservation measures aimed at preserving soil biodiversity in the future. Earthworms, one of the most important group of soil animals, show patchy horizontal distribution in response to spatial heterogeneity in soil physico-chemical parameters, food availability and biological interactions at various scales.The aim of this study was to explore whether the spatial and temporal variability and co-occurrence probability of earthworm species and ecological categories (epigeic, endogeic and anecic) can be characterized by exploiting habitat micro-topography and insolation.Field research was carried out in spring and summer at seven locations using a regular grid of 49 sampling points with 5 m inter-sample distance over an altitudinal gradient. The results of Geary's C and Moran's I indices, as well as the semivariograms calculated for each species, season and location confirmed a patchy spatial distribution. The range of semivariograms varied from 3.2 m to 32.8 m in spring, and from 0.3 m to 32.8 m in summer. Overall (all locations and both seasons), the mean range was similar for adult (8.4 m) and juvenile (9.2 m) earthworms. In spring, epigeic species had a larger range than endogeic species. Abundances of juvenile earthworms were negatively correlated with microtopographic elevation in spring (at most locations) and in summer (at all locations). The relationship between adult earthworms and microtopographic elevation could not be interpreted generally within season. Additionally, correlations between earthworm abundance and average monthly insolation were weak. Pairwise analysis of species co-occurrence revealed a random pattern for most species. In the analysis of co-occurrence of ecological categories, endogeics and epigeics had more positive probabilities than other pairs. The obtained results could be useable in soil biodiversity assessments, or creation of monitoring protocols.

IMPACT OF HABITAT DEGRADATION ON BIODIVERSITY OF EARTHWORM IN RAEBARELI DISTRICT

The land-use pattern in the Raebareli district exhibits a gradient of increasing human-caused land-use intensification. Deforestation for agriculture causes agroecosystems to be left fallow in order to recover vegetation and enhance soil fertility. Due to extensive grazing pressure, a lack of plant cover, and soil erosion that is accelerated by a higher pH value brought on by sodicity, fallows have significantly degraded ecosystems. Using biological restoration techniques, agroecosystems have transitioned from being externally regulated to becoming an internally managed, sustainable ecosystem. Eutyphoeus nicholsoni, Eutyphoeus orientalis, and Metaphire anomala in the forest, successfully surviving there. Three species were still present in the mechanized agroecosystem; Eutyphoeus waltoni invaded and replaced Eutyphoeus orientalis due to the alteration in land use pattern from forest to agroecosystem. The fallow contained Eutyphoeus incommodus and Eutyphoeus nicholsoni. Earthworms could not thrive in the soil there because of the high pH and low nutrient value of the sodic land earthworm. As a result of the conversion of land from a forest to an agroecosystem, endemic species predominated over foreign species, and this pattern continued in fallows and reclaimed agroecosystems. Endogeic species dominated in the forest, but a change in land use caused a reduction in their population in agriculture, which allowed anacic species to take their position in the fallow. Simpson's diversity index was higher in the less disturbed reclaimed agroecosystem, whereas the earthworm diversity index declined as farming intensified.

Insights into the molecular mechanisms of pesticide tolerance in the Aporrectodea caliginosa earthworm

Diffuse pollution of the environment by pesticides has become a major soil threat to non-target organisms, such as earthworms for which declines have been reported. However some endogeic species are still abundant and persist in intensively cultivated fields, suggesting they become tolerant to long-term anthropogenic pressure. We thus considered the working hypothesis that populations of Aporrectodea caliginosa earthworms from conventionally managed fields developed a tolerance to pesticides compared with those from organically managed fields. To investigate this hypothesis, we studied earthworm populations of the same genetic lineage from soils that were either lowly or highly contaminated by pesticides to detect any constitutive expression of differentially expressed molecular pathways between these populations. Earthworm populations were then experimentally exposed to a fungicide—epoxiconazole—in the laboratory to identify different molecular responses when newly exposed to a pesticide. State-of-the-art omics technology (RNA sequencing) and bioinformatics were used to characterize molecular mechanisms of tolerance in a non-targeted way. Additional physiological traits (respirometry, growth, bioaccumulation) were monitored to assess tolerance at higher levels of biological organization. In the present study, we generated the de novo assembly transcriptome of A. caliginosa consisting of 64,556 contigs with N50 = 2862 pb. In total, 43,569 Gene Ontology terms were identified for 21,593 annotated sequences under the three main ontologies (biological processes, cellular components and molecular functions). Overall, we revealed that two same lineage populations of A. caliginosa earthworms, inhabiting similar pedo-climatic environment, have distinct gene expression pathways after they long-lived in differently managed agricultural soils with a contrasted pesticide exposure history for more than 22 years. The main difference was observed regarding metabolism, with upregulated pathways linked to proteolytic activities and the mitochondrial respiratory chain in the highly exposed population. This study improves our understanding of the long-term impact of chronic exposure of soil engineers to pesticide residues.

Earthworm biodiversity in Morocco: First survey of earthworm richness, diversity and distribution in the Souss-Massa region

Although earthworms are the key drivers of most valuable ecosystem services and the main indicators of soil health, the existing ecotypes in Moroccan soils are largely unknown. The lack of records for many regions and limited data for others is a major obstacle to making the most of earthworms in sustaining the key ecosystem services they provide. This study investigates, for the first time, the earthworm biodiversity in cultivated soils in 4 irrigated perimeters of the arid region of Souss-Massa. Soil pits (25 x 25 x 30cm, n = 5) at 40 sampling sites were examined by digging, hand-sorting, and using a chemical expellant solution. From the 200 pits dug, 418 adult earthworms and 1182 juveniles were collected. Five new regional records of earthworms, namely Aporrectodea caliginosa, Aporrectodea longa, Aporrectodea rosea, Eiseniella tetraedra, and Microscolex dubius, were identified. A. longa was identified as a new species record for the earthworm fauna of Morocco raising the numbers from 13 declared species to 14. Most earthworms (60 %) were endogeic species in the majority of sampled sites. The occurrence of A. rosea (50% of sampled sites) and A. caliginosa (48% of sampled sites) reflects their frequent detection in the study area. Our results indicate that earthworms do exist in arid and semi-arid climates at significant densities, particularly along the crop rows where the drip irrigation laterals lie.

Gut content metabarcoding and citizen science reveal the earthworm prey of the exotic terrestrial flatworm, Obama nungara

The metabarcoding of digestive contents is a powerful approach to study the diet of newly introduced predatory species, and therefore to forecast their potential impact on native species. Obama nungara (Platyhelminthes: Geoplanidae) is an exotic terrestrial flatworm, which recently invaded several Western European countries and predates on earthworms. Because O. nungara is known to live above ground, we hypothesize that it consumes earthworms living on or coming frequently to the soil surface i.e. epigeic or anecic species, respectively. In this study, we undertook the metabarcoding of O. nungara gut contents to characterize more precisely the earthworm prey it consumes in its invaded range. This species is only known to date in anthropized, mostly privately-owned, environments and the contribution of citizen science volunteers to the reporting of species and their collection is of critical value. We first validated the development of the method, by extracting the digestive contents of O. nungara obtained through citizen science contributions throughout France, amplifying a 70bp earthworm-specific fragment of the 16S RNA gene and sequencing amplicons with a high-throughput approach. Secondly, the taxonomic affiliation of the sequences allowed identifying one to five species of earthworms in the digestive content of each flatworm. Contrary to our hypothesis, O. nungara seems also to consume endogeic species living within the soil and rarely coming out to the surface, as well as intermediate ecological categories. These results, by expanding the range of potential prey of O. nungara, confirm its status as a threat to native soil fauna.

Two decades of monitoring earthworms in translocated grasslands at Manchester Airport

Construction of a second runway at Manchester Airport included a mitigation package of habitat restoration with relocation of earthworms as prey items for protected vertebrates. Translocation of turf in blocks was the standard method used for four of five monitored sites with loose soil moved at the other. To assess earthworm communities at these translocated grassland sites, monitoring was undertaken each October (1998–2019) by digging and hand sorting of soil, followed by vermifuge application. Fourteen earthworm species were recorded, representing all ecological groups, but the majority were endogeic species, dominated by Aporrectodea caliginosa. Total earthworm numbers fluctuated during the monitoring period, with lowest density at 4 m−2 and highest more than a hundred times larger. The overall mean from all sites across the monitoring period was 151 ind. m−2. The differences between sites such as total earthworm numbers and species richness were clearly influenced by the translocation method and specific site topography. Created Hummocks to 3 m for hibernating amphibians proved successful with grassland soil establishing well. Lumbricus terrestris failed to establish due to translocation technique. Using non-metric multidimensional scaling, integration of environmental data with earthworm records showed effects of soil moisture content, pH and rainfall on abundance of ecological groupings and particular species. In general, earthworm community composition was dynamic over the monitoring period suggesting that this and population size needs to be appraised over realistic timescales, which may be best monitored in decades.

Gunnera tinctoria invasions increase, not decrease, earthworm abundance and diversity

Invasive plants often modify soil biotic communities through changes in soil physicochemical characteristics or the amount and/or quality of litter inputs. We assessed the impacts of Gunnera tinctoria invasions on soil and the earthworm community, on Achill Island, Co. Mayo, Ireland. We compared replicated (n = 5) areas invaded by G. tinctoria with uninvaded semi-natural grasslands, as well as with areas subjected to mechanical removal or herbicide treatment. Modifications in physiochemical properties included lower soil temperatures and higher soil pH during the summer in invaded areas, yet little effect on C and N stocks, or soil moisture. Marked differences in litter were observed, however, with invaded areas having c. 20-fold higher (above-ground) litter input than uninvaded ones, as well as lower C:N ratio (17 vs. 29). This was associated with a significantly higher overall abundance and biomass of earthworms in invaded plots (375 individuals m–2, 115 g biomass m–2), compared to the uninvaded control (130 individuals m–2, 45 g biomass m–2), with removal treatments having intermediate values. Earthworm communities comprised 10 species, typical for Irish grasslands, dominated by the common endogeic species Allolobophora chlorotica, Aporrectodea caliginosa and Aporrectodea rosea. Both earthworm species richness and Shannon diversity were significantly higher in invaded areas, but only in spring samples. Based on this new information, plant invaders may increase the abundance and diversity of earthworms, mainly due to much larger litter inputs, increased soil pH and possibly lower soil temperatures in the summer.

Effects of Forest Harvesting Operations on the Recovery of Earthworms and Nematodes in the Hyrcanain Old-Growth Forest: Assessment, Mitigation, and Best Management Practice

The quality and performance of forest soil is closely related to the characteristics of the faunal community in the soil. Focusing on soil organisms can provide good indicators to choose the best soil restoration methods to improve the properties of degraded forest soils. Therefore, the present study aimed to evaluate the effects of the tree litter of different species on the recovery of soil organisms (earthworms and nematodes) from skid trails over a 20-year period after harvest operations. For this purpose, three skid trails with different ages after harvest operations (6, 10, and 20 years), considering three tree litter treatments (beech, beech–hornbeam, and mixed beech) and three traffic intensity classes (low, medium, and high), were identified. The combination of treatments was carried out in the forest with three replications, and a total of 18 sample plots of 0.5 m2 were harvested to measure earthworms and nematodes. The results showed that 20 years after harvest operations, the highest values of earthworm density (5.72 n m−2), earthworm biomass (97.18 mg m−2), and total nematodes (313.65 in 100 g of soil) were obtained in the mixed beech litter treatment compared to other litter treatments. With decreasing traffic intensity from high to low, the activity of soil organisms increased, and the highest values of earthworm density (5.46 n m−2), earthworm biomass (87.21 mg m−2), and soil nematodes (216.33 in 100 g soil) were associated with low traffic intensity. Additionally, in all three litter treatments and traffic intensities, the epigeic ecological species were more abundant than the anecic and endogeic species. Key soil variables including water content, porosity, available nutrients, pH, total organic C, and total N were significantly correlated with earthworm density and biomass and soil nematode population. Litter management and addition to compacted soil can support the functional dynamics and processes of the soil and maintenance of the abundances and activities of the soil fauna.

Earthworms (Annelida: Oligochaeta, Lumbricidae) of the Kopaonik National Park (Serbia)

This paper presents the first list of earthworm fauna of the Kopaonik National Park, a total of 16 taxa, belonging to eight genera of the family Lumbricidae. The genera with the largest number of the registered taxa are Dendrobaena and Lumbricus, while the genera Aporrectodea, Bimastos, Eisenia, Eiseniella, Octodrilus and Octolasion are represented by one species each. Also, the review of zoogeographical types and ecological categories of registered species are presented. Half of the species are peregrine, while the rest are autochthonous. Regarding ecological categories, anecic (2) and endogeic (4) species are more sensitive to high mountain environmental conditions than epigeic (12) species, which are more adapted to such conditions. Overall, our results highlight how little was previously known about the earthworm fauna in this area and emphasize the need for further collecting to better understand the hidden earthworm diversity in Kopaonik NP.

Integrating earthworm movement and life history through dynamic energy budgets.

Earthworms are considered ecosystem engineers and, as such, they are an integral part of the soil ecosystem. The movement of earthworms is significantly influenced by environmental factors such as temperature and soil properties. As movement may directly be linked to food ingestion, especially of endogeic species like Aporrectodea caliginosa, changes in those environmental factors also affect life history traits such as growth and reproduction. In our laboratory studies, earthworms showed a decrease in burrowing activity with decreasing moisture levels and, to some extent, the organic matter content. The burrowing activity of earthworms was also affected by temperature, for which the casts produced per earthworm was used as a proxy in laboratory experiments. We integrated changes in earthworm movement and life histories in response to temperature, soil organic matter content and the moisture level, as observed in our experiment and reported in the literature, through dynamic energy budget (DEB) modelling. The joint parametrization of a DEB model for A. caliginosa based on movement and life history data revealed that food ingestion via movement is an integral part of the earthworms' energy budgets. Our findings highlight the importance of soil properties to be considered in the model development for earthworms. Furthermore, by understanding and incorporating the effect of environmental factors on the physiology, this mechanistic approach can help assess the impact of environmental changes such as temperature rise or drought.

Earthworm communities are supported by perennial bioenergy cropping systems

During the last decade a variety of perennial bioenergy crops (PECs) have been introduced into European agriculture. This study was designed to investigate the impact of various PECs on earthworm community patterns (species composition, numbers, biomass, α-diversity, life-form categories) at a landscape scale in Western Germany. The PECs investigated were cup plant (CP), tall wheatgrass (TW) and giant knotweed (GK). In total, 4 field replicates of each perennial crop were investigated at 9 study sites with the exception of CP, for which only 3 replicate sites were available. PECs were compared with silage maize as an annual bioenergy crop (AEC) and permanent grasslands (PGL). The earthworm community of the study area consisted of 13 species in total. Mean species number ranged from 2.7 (AEC) < 2.8 (GK) < 3.8 (TW) < 3.9 (PGL) < 4.2 (CP). Overall, PECs took an intermediate position between AEC and PGL concerning earthworm population data including α-diversity and community structure as indicated by Shannon-Weaver index (H’), species number and Evenness (E). There was a clear and close to significant (p < 0.1) increase in the mean total earthworm number in the range AEC (43.3 ind. m−2) – PECs (86.7 ind. m−2) – PGL (114.4 ind. m−2). Fresh earthworm biomass varied from 21.1 g m−2 (AEC) to 35.7 g m−2 (PGL) to 40.1 g m−2 (PECs), however, this difference was only significant for mean biomass of juveniles. Endogeic species were highly dominant in soils cultivated with PECs. Generalized linear mixed models revealed that soil pH, amounts of soil organic carbon and plant available soil water content were partly significant environmental driving variables for the improvement of the earthworm community in soils cultivated with PECs.

Distribution of epi-endogeic and endogeic earthworm species (Oligochaeta: Lumbricidae) in the forest belt of the Northwest Caucasus.

The distribution of the often dominant in density and biomass epi-endogeic and endogeic earthworm species in forests of the Northwest Caucasus was estimated based on a large array of field data and GIS modeling of modern potential areas. Quantitative accountings of earthworms were conducted annually from 2014 to 2019 in different types of forests: sticky alder forest, small-leaved forests, broadleaf forests (hornbeam and beech forests), coniferous-deciduous forests, dark coniferous forests, and pine forests (792 geographic locations). It is shown that the native species of the Caucasian fauna dominate in the number and biomass from piedmont to high mountain forests. The most widespread species that is found in all types of forests from low to high mountains and makes the main contribution to the biomass of earthworms is the Crimean-Caucasian subendemic Dendrobaena schmidti. Peregrine species of epi-endogeic and endogeic earthworms inhabit sticky alder forest, small-leaved, broadleaf and pine forests in which they inhabit together with native species, while not dominating either in numbers or in biomass among other species. Dark coniferous forests are inhabited mainly by the native endogeic species D. schmidti and A. jassyensis. Maxent modeling shows that the species of the endogeic earthworm group have wider potential areas than epi-endogeic species. The most significant bioclimatic factors that make the greatest contribution to the distribution: amount of precipitation in the driest month, altitude above the sea level, isothermality.

Distribution of earthworm communities in agroecosystems with forested riparian buffer strips: A multiscale study

Knowledge is lacking on the factors controlling the structure and spatial distribution of earthworm communities within agroecosystems. We first hypothesized that forested riparian buffer strips (FRBS) within agricultural landscapes would be a refuge for earthworms, as we predicted higher soil moisture and organic matter inputs in FRBS than in adjacent agricultural fields (treatments = FRBS vs. Field). We further hypothesized that earthworms would be most abundant where the chemical quality of above- and belowground plant litter is high, or where soil disturbance is low. We conducted a field survey to quantify earthworm species abundances in FRBS and adjacent agricultural fields in two bioregions, namely Eastern Canada and Central Europe. At each of 77 sites, we collected and identified earthworms from three plots within FRBS and within adjacent agricultural fields. In each plot, we identified the tree species, understory vegetation, soil drainage class, agricultural crop as well as five soil physicochemical properties. In each bioregion and treatment, we found proportionately more endogeic than anecic or epigeic earthworm species. In Eastern Canada, there were proportionately fewer anecic and more epigeic individuals in FRBS than in fields; in Central Europe there were fewer endogeic and more anecic earthworms in FRBS than in fields. We found significant bioregion × treatment interactions on earthworm abundance and soil moisture. More specifically, in Eastern Canada we found higher earthworm abundance and soil moisture in FRBS, whereas in Central Europe we found higher earthworm abundance in fields and no treatment effect on soil moisture. In both bioregions, we found higher organic matter in FRBS than in fields. In Eastern Canada, earthworm abundance in deciduous and mixedwood stands were higher than in coniferous stands; in Central Europe, earthworm abundance was highest in deciduous stands only. Within FRBS in Eastern Canada, the abundance of the prominent endogeic species, Apporectodea rosea, was correlated with herbaceous plants, notably ferns and graminoids. Conditional regression tree analysis revealed positive relationships between earthworms and soil clay content, pH, moisture and organic matter. Our results suggest that local and landscape patterns in earthworm diversity can be predicted by soil and vegetation attributes, however the relative importance of these factors changes across continental scales due to differences in precipitation patterns and soil moisture availability. Comparing the distributions of earthworms across different scales provides insights into the potential of different species to spread into new habitats with climate change.

Assessment of heavy metal contamination and its effect on earthworms in different types of soils

Earthworms encourage the mineralization of soil organic matter, the production of nutrients and the growth of plants through their feeding habits in the soil. But unsustainable development along with rapid urbanization and industrialization degrades the soils at an alarming rate which increases the level of different contaminants, i.e., heavy metals in the soil. The present study was conducted to assess the heavy metals, pH and organic carbon in agricultural, non-agricultural and industrial soils and their effects on the earthworm community structures. A total of seven earthworm species belonging to two families (Megascolecidae and Octochaetidae) were reported in this study. The earthworm species Metaphire posthuma was the most abundant in all collected soils, i.e., agricultural, non-agricultural and industrial soil with a relative abundance of 76.56%, 77.19% and 78.85%, respectively. The abundance and biomass of M. posthuma were in the order of agricultural soil > non-agricultural soil > industrial soil. It was also reported that the abundance of both anecic and endogeic species was higher in agricultural soils followed by non-agricultural and industrial soil. The findings of heavy metals indicated that industrial soil has the highest concentration of heavy metals followed by non-agricultural and agricultural soils. The contamination factor, enrichment factor, geoaccumulation index, pollution index and modified pollution index showed high, moderate and less pollution levels at industrial, non-agricultural and agricultural soil, respectively. The present study also indicated that Cd and As showed severe contamination in all studied soil types.

Decreased burrowing activity of endogeic earthworms and effects on water infiltration in response to an increase in soil bulk density

Endogeic earthworms live and burrow in the soil to find their food. They burrow by pushing the soil aside or ingesting it and are thus sensitive to soil compaction. However there is a scarcity of data regarding the effects of soil bulk density on the burrowing behavior and activity of endogeic earthworms. We carried out laboratory experiments using repacked soil cores with various levels of bulk density (from 1.18 to 1.38 g cm−3) in which individuals of Aporrectodea caliginosa or Allolobophora chlorotica were incubated for six weeks. The burrow systems inside the soil cores and the compaction around the burrows were then analyzed using X-ray tomography. Soil water infiltration measurements were also carried out. The increase in bulk density had a negative impact on all burrow system characteristics (length, volume, diameter, continuity, number of burrows). When bulk density increased from 1.18 to 1.38 g cm−3, volume, diameter, continuity and the number of burrows decreased on average by 77 %, 21 %, 81 % and 58 %, respectively. The increase in density due to compaction around the burrows was similar whatever the species and the bulk density. Increasing soil bulk density from 1.18 to 1.38 g cm-3 also greatly decreased water infiltration (−89 % for both species) and increased breakthrough time (10 and 25-fold for A. chlorotica and A. caliginosa respectively). However, compared to a control without earthworms, water infiltration in cores incubated with endogeic species was only increased significantly at 1.18 and 1.23 g cm−3. This illustrates that burrows made by endogeic earthworms moderately increase water infiltration and only when the soil bulk density is low. Data provided in this study could be used to refine simulation models of earthworm burrowing behavior where burrowing is assumed to be mainly governed by soil water content, temperature and soil bulk density.