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For the first time, a comparative study of the influence of two species of earthworms (Aporrectodea caliginosa and Lumbricus terrestris) on the composition of the prokaryotic complex of Umbric Albeluvisols was carried out using the methods of metagenomics. Prokaryotes in the soil and casts were represented mostly by Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Gemmatimonadetes, Planctomycetes, Proteobacteria, and Verrucomicrobia phyla. The passage of soil through the earthworm intestines changed significantly the abundance of some taxa in the soil prokaryotic block, but not general indicators of biodiversity. In the casts of earthworms of both species, a decrease in the abundance of Acidobacteria and Gemmatimonadetes phyla, including predominantly oligotrophic bacteria, was observed. Casts of L. terrestris were characterized by an increase in the proportion of Actinobacteria and Firmicutes phyla, which were mainly represented by copiotrophs and hydrolytic bacteria. In addition, the abundance of Clostridiaceae anaerobic bacteria and Flavobacterium capable of nitrate respiration increased in the casts of L. terrestris, which could be due to the appearance of anaerobic conditions in the biogenically transformed soil. Generally, the changes in the taxonomic structure of prokaryotes in the soil treated by L. terrestris were greater than those in the soil treated by A. caliginosa. These differences among casts of different earthworm species could be due to the specificity of functioning of their digestive systems adapted to transformation of different food sources.

Background and aim Plant pathogenic and mycotoxin-producing Fusarium species are globally widespread and lead to large annual yield losses in maize production (ecosystem disservice). Systems with reduced tillage and mulching are particularly under threat. In the present study, the bioregulatory performance (ecosystem service) of the common earthworm species Lumbricus terrestris was analysed regarding the suppression of three economically relevant Fusarium species, and the reduction of their mycotoxins in the maize mulch layer, taking into account the size of maize residues. Methods A mesocosm field experiment was conducted in a reduced tillage long-term field trial on loam soil. Artificially Fusarium-infected maize residues of two size classes were used as a mulch layer. Impacts of the earthworm species on DNA amounts of Fusarium graminearum, F. culmorum, and F. verticillioides and concentrations of the mycotoxins deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-AcDON), and zearalenone (ZEN) were analysed. Results The results reflect that Fusarium regulation by L. terrestris was species-specific and covered the whole spectrum from suppression (F. graminearum) to slight promotion (F. verticillioides). Regarding the mycotoxins, a significant acceleration of the degradation of all three toxins was detected. Fine chopping of the chaff (< 2 cm) did not significantly alter the earthworms’ regulatory capacity. Conclusion While L. terrestris can shift the ecosystem service/disservice balance in both directions with respect to Fusarium regulation, it shifts it towards ecosystem services with respect to mycotoxin degradation. In synergy with adapted agricultural management, this natural bottom-up effect can help to keep soils healthy for sustainable production in the long run.

The role of below-ground interactions between microbial biocontrol agents and soil fauna for combatting soil-borne plant diseases have not been studied sufficiently. This study tested the hypothesi...

Soil structure is closely linked to biological activities. However, identifying, describing and quantifying soil aggregates remain challenging. X‐ray micro computed tomography (X‐ray μCT) provides a detailed view of the physical structure at a spatial resolution of a few microns. It could be a useful tool to discriminate soil aggregates, their origin and their formation processes for a better comprehension of soil structure properties and genesis. Our study aims to (a) determine different X‐ray μCT‐based aggregate parameters for differentiating earthworm casts belowground (earthworm aggregates) from aggregates that are not formed by earthworms (non‐earthworm aggregates), and (b) to evaluate if these parameters can also serve as specific “tomographic signatures” for the studied earthworm species. For this purpose, we set up a microcosm experiment under controlled conditions during 8 weeks, including three species of earthworms tested separately: the epigeic Lumbricus rubellus, the anecic Lumbricus terrestris and the endogeic Allolobophora chlorotica. Our results show that X‐ray μCT analysis helps distinguish earthworm aggregates from non‐earthworm ones using (a) the relative volume of the components within aggregates and (b) the volumetric mass of aggregates and their global volume. In particular, the volume ratio of mineral grains within the aggregates is significantly different according to earthworm species. So, X‐ray μCT is a powerful and promising tool for studying the composition of earthworm casts and their formation. However, future research is needed to take into account the shapes and spatial distribution of the aggregates' components, in particular the different states of organic matter decomposition. HIGHLIGHTS: Can earthworm belowground casts be differentiated from other soil aggregates using X‐ray μCT? The use of X‐ray μCT for characterizing soil aggregates at a spatial resolution of a few microns. A combination of X‐ray μCT variables discriminates earthworm casts from non‐earthworm aggregates. X‐ray μCT, used alone, is relevant for defining species‐specific signatures of earthworm casts.

We carried out mesocosm experiments using either the anecic earthworm Lumbricus terrestris or the endogeic earthworm Allolobophora chlorotica and loam, silt loam and sandy loam soils to investigate the differing impact of these earthworm of different ecotypes on aggregate formation (percentage water stable aggregates, %WSA) and soil water holding capacity (WHC), two soil properties that underpin many of the ecosystem services provided by soils. Earthworms significantly increased %WSA (by 16–56% and 19–63% relative to earthworm-free controls for L. terrestris and A. chlorotica, respectively). For L. terrestris, this increase was significantly greater in the upper 6.5 cm of the soil where their casts were more obviously present. Allobophora chlorotica treatments significantly increased WHC by 7–16%. L. terrestris only caused a significant increase in WHC (of 11%) in the upper 6.5 cm of the sandy loam soil. Linear regression indicated a consistent relationship between increases in %WSA and WHC for both earthworm species. However, for a given %WSA, WHC was higher for A. chlorotica than L. terrestris likely due to the known differences in their burrow structure. Overall, earthworms increased soil %WSA and WHC but the significant species/ecotype differences need to be considered in discussions of the beneficial impacts of earthworms to soil properties.

Earthworms are an integral part of soil ecosystems, especially for their role in soil functions such as organic matter (OM) decomposition and nutrient cycling. Earthworms and microorganisms are interdependent, and a considerable portion of the contribution earthworms make to influencing OM fate is through interactions with microorganisms. However, the importance of the earthworm-associated microbiome is not fully understood, because it is difficult to separate the direct influence of the earthworms from the indirect influence of their microbiome. Here, we evaluated an antibiotic-based procedure to suppress the microbiome of individuals of ecologically-contrasting earthworm species (Eisenia fetida, Lumbricus terrestris, Allolobophora chlorotica) as the first step towards soil studies aimed at understanding the importance of the earthworm microbiome for host health and function. Individual earthworms were exposed to antibiotics: cycloheximide (150 μg ml−1), ampicillin (100 μg ml−1), ciprofloxacin (50 μg ml−1), nalidixic acid (50 μg ml−1), and gentamicin (50 μg ml−1) either singly or in a cocktail via culture (96 h) in a semi-solid agar carrier. Compared to the non-antibiotic treated control, the cocktail (for all three species) and ciprofloxacin (for E. fetida and A. chlorotica) treatments significantly reduced (P < 0.05) culturable microbial abundance on nutrient agar and potato dextrose agar. The microbial counts were reduced to below detection (

A column experiment with five different pore densities (0, 1, 2, 3, and 4 pores column−1) and two varying moisture regimes (comparatively dry and comparatively moist regime) in the subsoil part of the columns was established. In each pore, Lumbricus terrestris was introduced for 28 days before sowing wheat plants. After 40 days of plant growth, watering was stopped to induce progressive topsoil drying. Parameters describing the shoot hydration, mineral uptake, and aboveground biomass were quantified. Root biomass and root length densities (RLD) were measured separately for six soil layers. Under dry subsoil conditions, plants grown under increasing biopore density showed an increase of the RLD and an improved shoot hydration but the aboveground biomass was unaffected. Since RLD but not root biomass was enhanced, it is assumed that roots were able to explore a larger volume of soil with the same amount of root biomass. Thereby, subsoil water likely was used more efficiently leading to an improved hydration. Under moist subsoil conditions, plants grown with increasing biopore density revealed enhanced shoot biomasses and nutrient uptake while the belowground biomass was unaffected. The improved nutrient uptake can be ascribed to, first, the higher subsoil water availability favoring mass flow driven nutrient uptake, and second, to direct and indirect effects of earthworms on the availability of soil nutrients. It is concluded that high biopore abundancies have the potential to improve not only the belowground but also the aboveground biomass. This, however, largely depends on subsoil moisture. Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie http://dx.doi.org/10.13039/501100010571 Humboldt-Universität zu Berlin (1034)

The purpose of our study was to determine whether earthworms facilitate the burial of surface-applied wood ash. We mixed a fluorescent tracer powder with fly ash from a commercial biomass boiler to track and quantify ash burial in microcosms containing different densities of the deep-burrowing anecic earthworm Lumbricus terrestris L. While passive incorporation of the wood ash-tracer mix from the surface in the absence of earthworms was limited (rarely penetrating more than 2 cm below the surface), earthworms increased the amount of ash-tracer found belowground and the maximum depths at which ash-tracer was observed (up to 16 cm deep). We suspect that earthworms facilitated wood ash burial primarily by creating burrows down which wood ash could be carried by water and by burying wood ash-covered leaf litter. Earthworms may help increase the efficacy of wood ash amendment in ecosystems where it is impractical to manually mix amendments into the soil (e.g. forests).

Earthworms provide important ecosystem services in agricultural systems. However, little is known with regards to which extent earthworms feed on soil-borne plant fungal pathogens, thereby potentially reducing pathogen infection of crops. Using a food choice arena in the laboratory, we examined (i) whether the hardened resting structures (i.e., sclerotia) of white mould (Sclerotinia sclerotiorum (Lib.) de Bary) are consumed by the earthworm Lumbricus terrestris L. (Lumbricidae) and (ii) to what extent this consumption is affected by a possible hydration of sclerotia. We found that earthworms fed on sclerotia, preferably when sclerotia were hydrated. After 13 weeks of sclerotia hydration, on average, 61.1 ± 26.0% were consumed. In field plots, we further tested the interaction between earthworms, cover crops (mustard (Sinapis alba L.), oilseed radish (Raphanus sativus subsp. oleiferus M.), oat (Avena sativa L.), grass pea (Lathyrus sativus L.)) and sclerotia. After eight months, the number of remained sclerotia was lower when earthworms had access (51 ± 19%) than when earthworm had restricted access (79 ± 11%; Sidak; P = 0.01). Oilseed radish increased earthworm abundance, however cover crops did not directly reduce sclerotia. Our findings indicate that sclerotia can be reduced by supporting cover crops that favour earthworms rather than having bare fallow.

Anthelmintic drugs are used to control intestinal parasitic worms in animals worldwide. Although generally effective in managing animal health, such treatment can introduce anthelminthic compounds to the wider environment as active ingredients and metabolites are often excreted. This can have detrimental effects on non-target species, especially when drugs are used excessively. Here, we examine the effects that two environmentally-realistic concentrations of four anthelminthics have on the common earthworm Lumbricus terrestris (Linnaeus, 1758), a species with a cosmopolitan distribution and that is often vital in maintaining functional edaphic ecosystems. The drugs were ivermectin (0.502 and 2.511 mg kG−1 active ingredient), fenbendazole (0.309 and 1.547 mg kG−1), pyrantel (79.480 and 397.400 mg kG−1), and praziquantel (2.299 and 11.499 mg kG−1): these concentrations were typical of soils where pasture grazed by animals treated with anthelminthics. Both lethal effects (mortality) and sub-lethal effects (motility) were considered. Earthworms exposed to fenbendazole and praziquantel over a 12-week period experienced high mortality (55.0% and 32.5%, respectively). Mortality rates among earthworms exposed to pyrantel and ivermectin were much lower (2.5% and 7.5%, respectively). However, earthworms exposed to pyrantel and ivermectin suffered decreased motility (time to burrow into substrate when exposed to heat and light) relative to a control group. Burrowing times were up to 40% longer for pyrantyl-exposed earthworms and 28% longer for ivermectin-exposed earthworms. For both drugs, the magnitude of the effect increased as concentration increased; all differences were statistically significant. There was little effect of fenbendazole and praziquantel on motility. Based on this study, which is seemingly the first to examine effects of ivermectin/fenbendazole on earthworm motility and the first to consider any effects of praziquantel/pyrantel, we conclude that environmentally-realistic concentrations of all four anthelmintics have sub-lethal (pyrantel and ivermectin) or lethal (fenbendazole and praziquantel) effects on a vital keystone species. Methods to reduce carry-over effects in ecologically-important, non-target, organisms should be urgently sought and care should be taken not to use anthelminthics routinely without first testing helminth burden to determine whether there is clinical need.

Protein hotspots in soil, such as those associated with decaying soil fauna or plant litter, may produce ephemeral patches of disproportionately high soil nutrients. These hotspots may occur at the macro- and microscale in close proximity to plant roots, however, the likely concentration of soluble products produced in these hotspots remains poorly understood. To address this, we buried two contrasting biomass residues in soil, namely earthworm (Lumbricus terrestris) and clover (Trifolium repens). Their transformation to amino acids, NH4+ and NO3− were monitored continually over 6 days using microdialysis. All treatments showed greater soluble nitrogen (N) concentrations compared to the unamended controls. The highest concentrations of both amino acids (12.9 mM after 12 h) and NH4+ (45.3 mM after 6 h) were generated in the vicinity of decomposing earthworm. In comparison, dried clover residues yielded 2.7 mM of amino acids at 6 h. After 12 h, amino acid and NH4+ concentrations in both earthworm and dried clover treatments showed a steep decline, returning close to background levels (

Mercury (Hg) is a contaminant of global importance but its fate and impact in soils is overlooked. Earthworms are responsible for soil bioturbation but their interaction with Hg is poorly described. This study was conducted on a Hg contaminated site in Switzerland. The objectives were to determine the Hg tolerance of Lumbricus terrestris and Aporrectodea nocturna, and their capability to redistribute Hg from deep contaminated soil layers to remediated topsoil layers. Earthworms were incubated for 30 days in 35 cm height soil columns with soil Hg contents ranging from 0.19 to 83 mg Hg kg−1. 100% survival was observed except for the highest soil concentration (67% survival). Corresponding bioaccumulation factors ranged from 1 to 17. In parallel, Hg upward transfer by earthworms from a deep contaminated soil layer to a non-contaminated 40 cm thick surface layer was studied in 80 cm repacked soil columns. After 70 days, total Hg content of surface casts was 10 times higher than the non-contaminated soil. Furthermore, the 25–30 and 35–40 cm layers had a Hg content of 0.537 and 8.54 mg Hg kg−1 respectively, both exceeding the local threshold intervention value of 0.5 mg Hg kg−1. We concluded that (i) earthworms not acclimated to polluted soils can survive Hg levels as high as 85 mg Hg kg−1 in mesocosms, and (ii) a 40 cm thick remediated layer would be recontaminated after 6 months of earthworm activity if the underneath layer remained contaminated.

Earthworms have a profound effect on the soil they inhabit, but our current understanding of the chemical factors and molecular mechanisms that attract or repel earthworms from a specific area of soil is limited. In this study, we developed a soil T-maze assay allowing for the examination of earthworm behavioral responses to repellent chemicals. This tests earthworms individually, and thus the potential confounds of worms being influenced by conspecifics signals are avoided. Canadian nightcrawlers (Lumbricus terrestris) can detect the canonical Transient Receptor Potential Ankyrin 1 (TRPA1) agonist, allyl isothiocyanate (AITC), but not the canonical Transient Receptor Potential Vanilloid 1 (TRPV1) agonist capsaicin. In the T-maze assay L. terrestris avoided TRPA1 activators AITC, cinnamaldehyde and menthol in a dosage dependent manner. The single subject T-maze assay is a useful tool to study the avoidance of earthworms to chemical compounds and provides behavioral evidence for a TRPA1 ortholog in L. terrestris.

International audience; Earthworms feed on organic matter present at the soil surface or within the soil. Thus, its distribution in the soil profile is likely to greatly influence earthworm behavior and, in turn, their burrow system. To test this idea, two anecic and two endogeic earthworm species were introduced into repacked soil cores (depth = 30 cm) upper half filled with a top soil containing 4% organic matter (0–15 cm) and lower half filled with a deep soil at 2% organic matter (15–30 cm). Earthworm behavior was studied using X-ray tomography combined with luminophores (colored particulate tracers of 63–125 μm size) placed at 0, 3, and 12 cm depth, a method widely used in sediment ecology. We observed that anecic and endogeic earthworms had contrasting reactions to the conditions with only endogeic species burrowing more intensively in the upper part. From a quantitative point of view, only a few percent of luminophores were displaced. However, luminophore displacements also provided qualitative information to complement the tomography: (i) endogeic species and especially Aporrectodea caliginosa bioturbated the most soil close to the surface (3 cm depth) and (ii) the two anecic species influenced the luminophore distribution differentially with Lumbricus terrestris displacing significantly more luminophores, whatever their initial depth, than Aporrectodea nocturna due to intense surface cast activity. Beyond methodological developments, our study found that endogeic earthworms burrow more in zones with higher organic matter contents and this explains why they are mainly found close to the soil surface in non-tilled soils.

In the context of sustainable agriculture, a deeper knowledge of the effects of soil management on soil annelids is needed, as they play an important role in many soil processes. In a laboratory mesocosm experiment, we compared the simulated effect of ploughing by inverting the top soil (crop residues at 15 cm depth) to a non-inversion treatment (crop residues on the soil surface) using the soil type Haplic Luvisol. We investigated the response of earthworms and enchytraeids and the consequences for microbial and chemical soil parameters. Four treatments with soil fauna were established by adding: (i) endogeic earthworms (Octolasion cyaneum), (ii) anecic earthworms (Lumbricus terrestris), (iii) a combination of two enchytraeid species (Enchytraeus crypticus and Enchytraeus christenseni) and (iv) having control columns (without annelids). Feeding behaviour of annelids was investigated using isotopic analysis (δ13C, δ15N), and chemical and microbial soil properties were measured. Carbon and nitrogen losses in the form of gas emissions (CO2, N2O) and leachate were recorded during the time of incubation. We found no interactions of soil inversion and annelid addition on chemical and microbial soil properties; these properties were closely related to crop residue placement, indicated by the effect of soil inversion between 0 and 20 cm. Below 20 cm, this effect disappeared. Here, the presence of enchytraeids enhanced soil microbial properties, regardless of soil inversion. Stimulating microbial activity and increasing soil aeration seem to be the most important factors that increase CO2-C emissions in the presence of anecic earthworms. N2O-N emissions were consistently higher (+188%) in the inverted columns. Our results show that regardless of the placement of crop residues, anecic earthworms and enchytraeids fed more on crop residue derived carbon than endogeic earthworms, while endogeic earthworms appeared to avoid feeding at the soil surface. Moreover, it was found that the inversion and the annelid effects did not interact in an experimental setting where soil inversion is carried out in a form without detracting or impairing the annelids directly.

Interactions of earthworm species with their environment and in particular the soil they inhabit is poorly understood. In this study, we aimed to use mid infrared absorption (MIR) spectroscopy of earthworm bodies in combination with discriminant analysis of principal components (DAPC), in order to investigate if their biogeochemical composition is determined by their species belonging or the soil they inhabit. Our conceptual approach included the comparison of MIR spectra of four earthworm species (Lumbricus terrestris, Allolobophora chlorotica, Aporrectodea caliginosa and Aporrectodea icterica) sampled from four different agricultural fields in France. Moreover, we tested the influence of the habitat on the earthworm MIR spectra by exchanging individuals and soils in an incubation experiment. MIR spectra varied according to species and sampling site. The MIR spectra of earthworm bodies also changed during the incubation experiment, and for L. terrestris, A. chlorotica and A. icterica depended on the properties of the soil ingested. This suggested that the food source in different habitats impacted the biogeochemical composition of earthworm bodies. DAPC allowed for the identification of earthworm species ranging from 64 to 100% of accuracy (mean 78%). We thus conclude that MIR spectroscopy may be a suitable approach to identify earthworm species, but that their signature may also allow to investigate their ecology as determined by the soil they inhabit.

Earthworms are considered as “ecosystem engineers” impacting soil properties as well as nutrient and element cycles. As they move through soil, earthworms secrete cutaneous mucus which is metabolized by soil microorganisms and a source of plant-available nutrients. Earthworm-processed soil contains carbon enriched, earthworm-specific soil aggregates (e.g. casts and middens) in comparison to earthworm unaffected soil. The reason could be that organic polymeric substances in earthworm mucus bind to soil minerals. The objective of this study was to investigate the small-scale interactions between earthworm mucus and secondary soil minerals, e.g. goethite and illite, leading to the formation of organo-mineral associations. We characterized the chemical composition of earthworm mucus by FTIR and 13C-NMR spectroscopy and compared spectra of mucus to microbial extracellular polymeric substances (EPS), an abundant and well-known type of organic matter that binds with soil minerals. Mucus from anecic (Lumbricus terrestris L.) and endogeic (Aporrectodea caliginosa Sav.) earthworm species was dominated by proteins and carbohydrates. Between 21 and 36% of the total organic carbon in the mucus containing treatments adsorbed to illite and goethite, and most of the binding with goethite was associated with phosphorus containing mucus compounds. The surface charge of newly-formed organo-mineral associations was determined by measuring the isoelectric point (IEP). The IEP of mucus-goethite associations was 6.8, which was lower than the bare goethite IEP of 8.4. The zeta potential of mucus-illite associations was greater than bare illite. We conclude that the specific adsorption of earthworm mucus constituents to soil minerals leads to the formation of mucus-mineral associations. These associations contribute to retention of organic substances from earthworm mucus in soil (micro-)aggregates and explain the altered physicochemical properties of earthworm-formed aggregates in comparison to the earthworm unaffected “bulk” soil material.

There has been minimal study of how ecosystem engineering anecic earthworms such as Lumbricus terrestris L. may influence the distribution of mulch amendments across the soil surface by collecting residues into middens. The two primary research objectives of this study were: (1) to determine how rapidly earthworms change the surface distribution of mulch following amendment, and (2) to produce a more spatially explicit map of earthworm aggregation of mulch. This study used a microcosm experiment to assess the immediate, short-term impacts of earthworms on recently added mulch at a small scale, and an opportunistic field study of the longer-term impacts of earthworms on the distribution of corn ‘stubble’ mulch in a former agricultural field. In the microcosm experiment, earthworms rapidly redistributed mulch within the first week post amendment, decreasing initial ground cover (15-29% decrease). Over the subsequent five weeks, initial cover continued to decrease (20-45% decrease) as mulch was spread thinly onto adjacent, initially bare soil (49-69% increase). Higher mulch amendment mitigated losses in initial cover. In the field study, earthworms aggregated mulch across the soil surface, collecting 40% of the woody corn residues into 17% of the total area in regularly distributed middens. These results demonstrate the potential for L. terrestris to alter the distribution of mulch rapidly in the first several days and weeks following application and in the longer term over several years, increasing the spatial heterogeneity of soil resources. This physical redistribution has only been minimally investigated and may help inform models of earthworm impacts on various ecological processes and improve soil amendment and residue management in earthworm-occupied soils.

We investigated the dynamics of different earthworm species through the soil profile, which had received short-term amendments of either organic or inorganic fertilizer in an orchard during the spring of 2016. Earthworm populations were sampled at two consecutive depths of soil on 20 and 60 days after addition of fertilizers. The dominant earthworm species were Eisenia fetida (Savigny, 1826), Dendrobaena veneta (Rosa, 1886), Dendrobaena hortensis (Michaelsen, 1890), Lumbricus terrestris (Linnaeus, 1758) and Aporrectodea longa (Ude, 1885). Seven different types of fertilizers including Urea, Ammonium sulfate (AS), Diammonium phosphate (DAP), Solupotas, NPK (15-5-25), (NPK+OM) and organic manure (OM) as experimental treatments were studied. Fluctuations in earthworm numbers and biomass were attributed to changes in time and depth of sampling, in addition to the types of fertilizers. The results of the means comparison showed that on the 20th day, at 0-20 cm soil depth, E. fetida species abundance was decreased significantly in AS and Urea treatments compared to the control plot (p˂0.05). We highlighted that from epigeic group, D. hortensis species had a better chance to survive and its population in AS treatment was more than that of Urea treatment. Results also showed that the anecic L. terrestris , had a greater tolerance to chemical fertilizers compared to the A. Longa species. The results of this study outline more clear horizons in managing the use of chemical fertilizers while simultaneously maintaining the biodiversity of soil organisms.

International audience; Earthworms contribute to a wide range of ecosystem services provided by the soil. Nevertheless, synecology of these organisms is still not properly elucidated especially in terms of species interactions. The aim of the present study was to determine the effects of anecic earthworm species interactions on their individual biomass. These effects were measured using three epi-anecic species, Lumbricus rubellus rubellus (Hoffmeister, 1843), Lumbricus centralis (Bouché, 1972), Lumbricus terrestris (Linné 1758), and three strict-anecic species, Aporrectodea caliginosa meridionalis (Bouché, 1972), Aporrectodea nocturna (Evans, 1946), Aporrectodea giardi (Savigny, 1826). Twenty-one pairs of individuals were established following five assemblages: monospecific pairwise assemblages of epi- and strict-anecic earthworms (2 × 3 treatments), bispecific pairwise assemblages within epi- and within strict-anecic earthworms (2 × 3 treatments) and bispecific pairwise assemblages with one epi- and one strict-anecic earthworm (3 × 3 treatments). Treatments were maintained in mesocosms for 30 days under controlled conditions (food provided at the soil surface at the beginning of the experiment) and changes in the earthworm individual biomass were measured. Strict-anecic earthworms in monospecific or bispecific assemblages maintained their initial biomass. In contrast, epi-anecic earthworms exhibited an increase of 12.4% and 23.7% of their biomass in monospecific and bispecific assemblages, respectively. In bispecific assemblages combining one epi- and one strict-anecic earthworm, epi-anecic earthworms solely gained biomass leading to a total increase of a 6.9%. Surprisingly, the biomass' changes were not homogenous within the two sub-categories as the six earthworm species exhibited species-specific responses. The greatest increases in individual biomass were recorded for epi-anecic earthworms in the bispecific assemblages. This study provides further evidence for the distinction between the two anecic sub-categories, as it indicates that species interactions is positive only for epi-anecic earthworm biomass.

Lead (Pb) is recorded as the second most hazardous pollutant of the environment. Previous cases of Pb bioremediation has been reported using single biosystem, but very few reports are available in biological approaches using multi-biosystems to achieve an enhanced bioremoval of Pb. The present study evaluated the capacity of a unique association of Pennisetum purpureum, a hyperaccumulator plant, and Lumbricus terrestris (earthworm) bioaugmented with a Pb-resistant bacterium, obtained from an industrially contaminated site and identified as isolate VITMVCJ1 Klebsiella variicola, to bioremediate Pb. The Pb-resistant gene was amplified in the bacterial isolate VITMVCJ1. The study was conducted for 60 d. Results verified that the bioaugmentation process enhanced 1) root and shoot length of the plants, 2) chlorophyll content of the plants, and 3) biofilm-producing ability of the microbes from the rhizosphere region of the plants. The total phenolic and flavonoid contents were found to be lower in the plants in the bioaugmented setup. The study also observed a reduction in the toxic effects of Pb on earthworm and plant. The earthworm was used to assess the Pb-induced stress syndrome after exposure to sublethal concentrations of Pb in the soil. A reduction in the content of malondialdehyde, a potential biomarker, on exposure to Pb demonstrated the role of the inoculum to alleviate heavy metal-induced stress in earthworms. All three symbionts accumulated Pb; Pb was accumulated mainly in the root of the plant, and poorly in the shoot of the plant and body mass of the earthworm. The bioaugmentation system exhibited stable and excellent uptake of Pb from the contaminated soils. The results of the present study suggest the positive effect of the synergistic association of the plant and earthworm with appropriate microbes for the bioremoval of Pb.

The study aims to analyse the effects of the herbicide glyphosate (Roundup 360 ® ) on three key earthworm species. The taxa collected from treated and untreated sites were subsequently bred in uncontaminated soil terraria with serial concentrations of the herbicide. The chosen taxa included two anecic ( Lumbricus terrestris and Octodrilus complanatus ) and one endogeic ( Aporrectodea caliginosa ) earthworms. Lumbricus terrestris collected from uncontaminated soil (Lt1) and in a conventionally managed vineyard (Lt2). Aporrectodea caliginosa and Octodrilus complanatus collected from the same uncontaminated site where L. terrestris (Lt1) were collected. Uncontaminated natural grassland soil filling the terraria was characterized for physical-chemical properties. The reproduction rate expressed in earthworms cocoon production was the measure for the effects on worms survival after 21 and 42 days of exposure to 0.59, 2.9, 5.79 g/m 2 of glyphosate, where the dose applied in vineyards in the North-East of Italy goes from 0.72 g/m 2 to 4.32 g/m 2 . Earthworms in untreated terraria were found all alive, while specimens exposed to glyphosate (Roundup 360 ® ) showed a decreasing survival rate and a sharp decline in the number of cocoons. L. terrestris (Lt2) showed a survival rate between 64% and 92% after 21 days, and between 44% and 76% after 42 days. L. terrestris (Lt1) showed a lower resistance to herbicide (survival rate: 36%–84% after 21 days and 12%–76% after 42 days). A. caliginosa was also affected (survival rate: 32%–76% after 21 days and 12%–68% after 42 days). Glyphosate demonstrated severe effects on Oc. complanatus, collected on non-contaminated soils, with the lowest values of survival rate (33% after 21 days and 7% after 42 days of exposure). A significant reduction in the cocoons number (about 70%) was observed for L. terrestris (Lt1) and A. caliginosa after 21 days of exposure, whereas L. terrestris (Lt2) showed about 50% of cocoon production. Results indicate the occurrence of some resistance mechanisms on anecic earthworms in vineyards that have been exposed to glyphosate for at least three decades. However in spite of the long period of application of glyphosate the impact of this largely applied herbicide is still serious (up to 26% of mortality) especially on the deep-burrowing earthworms species ( Oc. complanatus and L. terrestris ).

With a growing body of research dedicated to understanding earthworm seed preferences, we conducted a preliminary investigation of two previously unconsidered factors: seed density and previous earthworm egestion. We used no-choice feeding experiments with the common European earthworm Lumbricus terrestris L. and seed of the biennial forb Alliaria petiolata (M. Bieb) Cavara & Grande. Earthworm seed ingestion increased exponentially when available seed density was doubled (+305%) and was reduced when encountering seed that had previously been egested by another earthworm (−30%). Impacts of seed density and previous earthworm egestion have broader ecological implications for earthworm granivory behaviour and earthworm-plant interactions in natural and managed ecosystems. We recommend both factors as promising candidates for future experimentation.

Compaction is an important and increasing threat for forest soils. In addition to preventive approaches, remediation solutions are needed. Among them, the release of anecic earthworms is thought to be a promising approach. However, most previous attempts in compacted forest soils failed to retrieve the introduced earthworms. To gain more insight on the feasibility of releasing Lumbricus terrestris adults, we performed both a laboratory and a field study. Under laboratory conditions, the L. terrestris behavior was assessed in repacked soil cores with increasing soil bulk density (1.3, 1.4, 1.5 and 1.6 g cm−3 for a silt-loam soil). We found that burrowing (burrow volume, diameter and maximal burrow depth) as well as casting and feeding behavior were significantly reduced (−95%, −50% and −65%, respectively) at the highest bulk density compared to the lowest. For the field study, we released L. terrestris in a 10-year old experimental forest site in which two factors were studied: soil compaction and liming. To prevent them from escaping, the earthworms were caged in PVC cylinders in compacted (or not) and limed (or not) plots. After six months, we assessed the burrowing behavior and litter consumption of the earthworms. L. terrestris showed a good survival rate (>52%), as assessed by surface activity, in all situations. Liming had no detectable effect whereas the increase in bulk density in compacted plots (from 1.29 to 1.36 g cm−3) led to a significant decrease in the burrow volume. This suggests that, when forced to do so, L. terrestris is able settle in compacted and acidic soils and then perform its functional role (burrow creation and litter burial).

Earthworms have proved to contribute to plant health indirectly, by improvement of soil physical and chemical properties, as well as directly, through suppression of plant pathogens. Fusarium Head Blight, caused primarily by Fusarium graminearum, is one of the most important cereal diseases, with severe detrimental effects on yield and grain quality worldwide, and significant effect on grain safety due to the accumulation of mycotoxins produced by the fungus. Earthworms could reduce the residue-borne inoculum density of F. graminearum through different mechanisms, including direct competition by residue consumption, growth inhibition caused by the earthworm coelomic fluid, mechanical disruption of fungal hyphae, and burying crop residue which reduce the chances for the fungus to release spores for head infection. Thus, the aim of this study was to assess the effects of anecic and epigeic earthworms on wheat straw and on F. graminearum inoculum. For this, PVC cylinders (microcosms 14.5 cm diameter, 30 cm height) were filled with moist soil mix, wheat straw was evenly distributed on the soil surface (inoculated with Fusarium, soil microorganisms or sterile) and three earthworm species (Aporrectodea longa, Lumbricus rubellus or Lumbricus terrestris) were tested. Since the response of earthworms may change according to conditions of soil moisture and food availability, two different experiments were arranged. The first Experiment represented a sub-optimal situation for earthworms regarding soil moisture and feeding conditions, which was obtained by scarce watering of the microcosms with a consequent decrease in soil water content during incubation, and by not adding cow manure as supplementary food source. In the second experiment, soil was enriched with cow manure as feed for the earthworms and soil moisture was maintained above 25%. Results from qPCR analysis revealed that F. graminearum inoculum on straw was reduced to undetectable amounts by L. rubellus and A. longa when the feeding conditions were limited, while no significant differences compared with the control without earthworms were found when earthworms had high food availability (α = 0.05). Straw coverage on soil surface was reduced by L. rubellus (epigeic) in both experiments (p

Transport by earthworms contributes to the secondary dispersal of seeds and influences patterns of plant community structure and function. To date, however, research on earthworm seed dispersal has focused primarily on vertical transport and the collection of seeds into middens at the soil surface, with no efforts to map horizontal distribution after burial. This study used an emergence depth assay and depth-stratified seedling emergence from soil microcosm cross-sections to map earthworm seed transport in three dimensions using commercial grass seed and the anecic earthworm Lumbricus terrestris L. While specific seed burial profiles should not be considered representative of burial under field conditions (due primarily to high earthworm densities under artificially limiting microcosm conditions), we created what we believe to be the first three-dimensional and most detailed map of earthworm seed burial, visualizing and quantifying the ability of L. terrestris to redistribute seed both vertically and horizontally throughout the soil profile. L. terrestris buried 6.5 to 17.4% of the total seeds and reduced aboveground grass biomass by 59–65 %. Vertically, L. terrestris buried seeds evenly across the 13 cm deep microcosms. Horizontally, L. terrestris aggregated seeds into small clusters aligned obliquely across soil depths, which suggest seeds being deposited in burrow walls (variance to mean ratio: 3.39 ± 2.49). Seeds were aggregated regardless of L. terrestris density but covered a greater cross-sectional area of the soil profile when more earthworms were present. Spatial patterning of shallow buried seed still capable of emergence is a newly described mechanism by which L. terrestris might influence the spatial structure of plant communities.

When temperate forests of North America are exposed to long-term experimental levels of atmospheric nitrogen (N) deposition that mimic predicted future rates, elevated concentrations of inorganic N suppress microbial decay processes and increase the mass of the forest floor, storing more carbon (C) as soil organic matter. However, when non-native earthworms were serendipitously introduced to forests subjected to long-term experimental atmospheric N deposition, the greater forest floor mass with a higher N concentration had a positive effect on earthworm activity by increasing earthworm abundance and consumption of the forest floor. Here, we present evidence from a long-term experimental N deposition study showing how the abundance of the introduced earthworm, Lumbricus terrestris, increased significantly under elevated rates of atmospheric N deposition (+363%) in one of four study sites and contributed to a decline in the forest floor (−50%). In addition, mineral soil C (+97%) and N (+117%) concentrations increased as earthworms redistributed a greater proportion of organic matter belowground under experimental N deposition. We conclude that earthworm-induced changes to the forest floor can supersede a decline in microbial decay under experimental N deposition that has previously increased both forest floor mass and turnover time, thereby potentially negating increases in soil C storage.

Earthworms benefit agriculture by providing several ecosystem services. Therefore, strategies to increase earthworm abundance and activity in agricultural soils should be identified, and encouraged. Lumbricus terrestris earthworms primarily feed on organic inputs to soils but it is not known which organic amendments are the most effective for increasing earthworm populations. We conducted earthworm surveys in the field and carried out experiments in single-earthworm microcosms to determine the optimum food source for increasing earthworm biomass using a selection of crop residues and organic wastes available to agriculture. We found that although farmyard manure increased earthworm populations more than cereal straw in the field, straw increased earthworm biomass more than manures when milled and applied to microcosms. Earthworm growth rates were positively correlated with the calorific value of the amendment and straw had a much higher calorific value than farmyard manure, greenwaste compost, or anaerobic digestate. Reducing the particle size of straw by milling to < 3 mm made the energy in the straw more accessible to earthworms. The benefits and barriers to applying milled straw to arable soils in the field are discussed.

Biopores are hotspots of nutrient mobilisation and shortcuts for carbon (C) into subsoils. C processing relies on microbial community composition, which remains unexplored in subsoil biopores. Phospholipid fatty acids (PLFAs; markers for living microbial groups) and amino sugars (microbial necromass markers) were extracted from two subsoil depths (45–75 cm ; 75–105 cm) and three biopore types: (I) drilosphere of Lumbricus terrestris L., (II) 2-year-old root biopores and (III) 1.5-year-old root biopores plus six 6 months of L. terrestris activities. Biopore C contents were at least 2.5 times higher than in bulk soil, causing 26–35 times higher Σ PLFAs g-1 soil. The highest Σ PLFAs were found in both earthworm biopore types; thus, the highest soil organic matter and nutrient turnover were assumed. Σ PLFAs was 33% lower in root pores than in earthworm pores. The treatment affected the microbial community composition more strongly than soil depth, hinting to similar C quality in biopores: Gram-positives including actinobacteria were more abundant in root pores than in earthworm pores, probably due to lower C bioavailability in the former. Both earthworm pore types featured fresh litter input, promoting growth of Gram-negatives and fungi. Earthworms in root pores shifted the composition of the microbial community heavily and turned root pores into earthworm pores within 6 months. Only recent communities were affected and they reflect a strong heterogeneity of microbial activity and functions in subsoil hotspots, whereas biopore-specific necromass accumulation from different microbial groups was absent.

It is generally accepted that populations of most species experience some level of density dependence; however, this has rarely been shown for soil-dwelling invertebrate species, in particular for earthworms. Experimental data, mostly obtained at high laboratory densities, suggest intense intraspecific competition for resources and/or living space and density-dependent dynamics in earthworm populations, irrespective of their ecological group affiliation. In the present study performed in large field microcosms, I investigated whether density-dependent responses occur within the earthworm density gradients more realistic for the natural sites. Five lumbricid species from epigeic ( Dendrobaena octaedra , Lumbricus rubellus ), endogeic ( Allolobophora chlorotica , Aporrectodea caliginosa ) and anecic ( Lumbricus terrestris ) ecological groups were tested. Soil systems populated with earthworm monocultures in large (20-L) microcosms were exposed in a beech-oak forest for 4.5 months; each species was represented by two ( L. terrestris ) or three treatments forming gradients of increasing density. In two endogeic species, manifold and generally similar density-dependent responses (a retardation of growth, maturation and reproduction rates, but higher mortality rates with density increase) were revealed, likely explained by spatial competition rather than by direct food competition. In each of epigeic species density-dependent responses were less variable and more species-specific. In contrast to endogeics, direct food competition was presumably a more important cause of density-dependence. In L. terrestris no significant density-dependent responses in adult earthworms were revealed; however, they need to be further investigated in relation to the age and territorial behaviour of individual earthworms. Importantly, in any earthworm species the density variations in the reproducing generation had significant consequences for the advancing generation, affecting either the numbers or/and the size (individual weight) of the cocoons produced. It is suggested that an underestimation of density-dependent processes may cause inaccurate estimates of the activities of local lumbricid populations.

Deep burrowing earthworms are important ecosystem service providers but their populations are reduced by arable cultivations. We need to both better understand the impact of changes in crop management on earthworms and implement practices to enhance their in-field populations. Two current trends in arable cropping are the increased use of non-inversion tillage and over winter cover crops. Lumbricus terrestris abundances were estimated using midden counting on two field trials comparing tillage and cover cropping management practices. The long running (8-year) field trial showed that shallow non-inversion tillage had significantly (p < 0.01) greater L. terrestris abundances at 4.3 middens per m2, in comparison to deep (ca. 20 cm) non-inversion tillage (3 middens per m2) and conventional ploughing (ca. 25 cm) (1.9 middens per m2), indicating that it is inversion rather than the depth of soil disturbance that is detrimental to their abundance. All trials showed that cover cropping with oilseed radish had no significant (p > 0.05) effect on L. terrestris midden counts, either during winter cover cropping or within the arable rotation. Field observations identified that 93% of middens were associated with crop leaves (still attached to the stem) incorporated into the burrow which may be a novel route of agrochemical exposure and needs further investigation.

It is difficult to obtain non-destructive information on the seasonal dynamics of earthworms in northern forest soils. To overcome this, we used a Rhizotron facility to compile 7 years of data on the activity of anecic (Lumbricus terrestris) and endogeic (Aporrectodea caliginosa complex) earthworms in two contrasting soil/plant community types. We hypothesized that L. terrestris burrows would be used for longer than a typical L. terrestris lifetime, and that the distribution and activity pattern of the two earthworm species would respond differently to changes in soil moisture and temperature. For 7 years we recorded earthworm distribution and activity state bi-weekly to a depth of 1.5 m, tracked L. terrestris burrows using images captured annually, and measured soil temperature and moisture. Activity and vertical distribution of earthworms was closely linked to earthworm species and soil temperature in the fall, winter and spring. Lumbricus terrestris typically remained active through the winter, whereas the A. caliginosa complex was more likely to enter an aestivation period. Activity of all earthworms decreased substantially in July and August when soil temperature was at its highest and soil moisture at its lowest for the year. Most L. terrestris burrows were used continuously and moved very little during the 7-year study, likely creating spatiotemporally stable hotspots of soil resources. The different patterns of response of these species to soil temperature and moisture suggests that endogeic earthworms are more likely than anecic earthworms to adjust activity states in response to climate change mediated shifts in soil moisture and temperature.

This work assessed populations of the anecic, deep burrowing earthworm Lumbricus terrestris on two recently established (3 years) and two long running (20–170 years) organic matter amended, conventionally managed arable field trials in SE England. Validated midden counts and DNA analyses were used to estimate L. terrestris populations and check species identity (>98% match, n = 10). Population estimates ranged between 0 and 1.3 L. terrestris middens per m 2 on conventionally (inorganic fertiliser only) managed plots. Surface wheat straw applications ( p ≤ 0.05) or wastes mixed with barley straw ( p ≤ 0.05) enhanced L. terrestris midden abundances. However, these were very low at L. terrestris middens per m 2 and a population collapse was recorded under oat cropping. We found a residual population ranging between 0.1–3.6 L. terrestris middens per m 2 on the long running field trials. Further investigations are needed to identify if L. terrestris is functionally extinct at these densities.

Earthworms are important for soil functioning in arable cropping systems and earthworm species differ in their response to soil tillage and crop residue management. Lumbricus terrestris (Linnaeus, 1758) are rare in intensively tilled arable fields. In two parallel field trials with either non-inversion (NIT) or conventional tillage (CT), we investigated the feasibility of inoculating L. terrestris under different crop residue management (amounts and placement). Simultaneously, we monitored the response of the existing earthworm communities to L. terrestris inoculation and to crop residue treatments in terms of earthworm density, species diversity and composition, ecological groups and functional diversity. L. terrestris densities were not affected by residue management. We were not able to infer effects of the inoculation on the existing earthworm communities since L. terrestris also colonized non-inoculated plots. In NIT and two years after trial establishment, the overall native earthworm density was 1.4 and 1.6 times higher, and the epigeic density 2.5 times higher, in treatments with highest residue application (S 100 ) compared to 25% (S 25 ) or no (S 0 ) crop residues, respectively. Residue management did not affect earthworm species composition, nor the functional trait diversity and composition, except for an increase of the community weighted means of bifide typhlosolis in S 0 compared to S 100 . In CT, however, crop residues did have a strong effect on species composition, ecological groups and functional traits. Without crop residues (S 0 ), epigeic density was respectively 20 and 30% lower than with crop residues placed on the soil surface (S 100 ) or incorporated (I 100 ). Community composition was clearly affected by crop residues. Trait diversity was 2.6 to 3 times larger when crop residues were provided, irrespective of placement. Crop residues in CT also resulted in heavier earthworms and in a shift in the community towards species with a thicker epidermis and cuticle, a feather typhlosolis shape, and a higher average cocoon production rate. We conclude that earthworm communities under conventional tillage respond more strongly to the amount of crop residue than to its placement. Under non-inversion tillage, crop residue amounts affected earthworm communities, but to a smaller degree than under conventional tillage.

Phosphorus (P) is an important nutrient for plant growth. However, P is often poorly available for uptake by roots because it strongly adsorbs to the soil mineral phase. Recent research shows that earthworms can temporally and locally increase P availability to plants. However, the pathways through which they do so are not fully understood, and it remains unclear to what extent this capacity varies among earthworm species. Here we study the variation among earthworm species with respect to readily-available P in casts as well as other physico-chemical cast properties, in a greenhouse pot experiment using a soil with a low P status. The earthworms belong to eight commonly occurring earthworm species in the Netherlands: two epigeic species (a mixture of the compost earthworms Dendrobaena veneta/Eisenia fetida; Lumbricus rubellus); four endogeic species (Allolobophora chlorotica, Aporrectodea caliginosa, Aporrectodea rosea, Octolasion lacteum); and two anecic species (Aporrectodea longa; Lumbricus terrestris). For all species, the pH in water extracts of earthworm cast (pH = 7.4–8.2) was significantly higher (p < 0.001) than for the control bulk soil (pH = 6.6) and differed significantly (p = 0.003) among earthworm species. Similarly, the dissolved organic carbon (DOC) concentration in the same water extracts was an order of magnitude higher in earthworm cast compared to the control bulk soil and varied among species (p < 0.001). The size of the total pool of reversibly adsorbed P in earthworm cast was greater than in the control bulk soil, but no significant differences were found among earthworm species. Differences among species were present for the readily-available P pools extracted from casts, including P-Olsen and water-extractable ortho-P. Water-extractable ortho-P concentrations were much higher in the casts of all species as compared to the control bulk soil (0.9–6.8 vs 0.06 mg l−1 or to 9.0–68 vs 0.6 mg kg−1). Highest ortho-P levels were measured in L. rubellus casts and the lowest in casts of A. chlorotica. A positive correlation between the concentrations of DOC and ortho-P was observed (R2 = 0.72, p < 0.001). The observed variation in all measured physico-chemical cast properties could not be explained by conventional ecological earthworm classifications. Our results show that the nature and magnitude of earthworm-induced increased P availability differs dramatically among earthworm species. This strongly suggests that, apart from its size, species composition of the earthworm community is key to optimizing P availability to plants.

While many studies have examined the effects of flooding on earthworm population distributions, few studies have investigated physiological and behavioural responses of earthworms to the low oxygen conditions caused by flooding. An earthworm's skin is its oxygen exchange organ, allowing earthworms to survive in flooded environments provided that the water contains sufficient dissolved oxygen. Individuals of three species of earthworm, the anecic Lumbricus terrestris (Linneaus, 1758), the green morph of the endogeic Allolobophora chlorotica (Savigny, 1826) and the epigeic Lumbricus castaneus (Savigny, 1826) were placed in reconstituted groundwater that was either kept aerated or kept in a sealed container so that dissolved oxygen was gradually consumed as the earthworm respired. Oxygen saturation of the water was measured over time in sacrificial triplicate replicates from each treatment at discrete time points; earthworm mortality and mass were recorded. Before treatments, oxygen levels in all treatment tubes were 9.53 (±0.64) mg O2 L−1. L. terrestris, a large species which emerges at night to forage at the soil surface died when oxygen levels reached 0.82 (±0.46) mg O2 L−1 after approximately 36 h. L. castaneus, a smaller species which lives on the soil surface, died when oxygen levels reached 3.60 (±2.01) mg O2 L−1 after approximately 168 h. A. chlorotica, which is similar in size to L. castaneus, lives in the upper 20 cm of soil and is known to aestivate during the summer, did not die, even when oxygen levels reached 1.49 (±0.40) mg O2 L−1 after 280 h. The results suggest that earthworm respiration is closely linked to both body size and to behavioural ecotype. These findings suggest that if flooding increases in frequency resulting in episodic reductions in soil oxygen levels, the species composition of earthworm communities may change, with an increased presence of endogeic earthworms which show a responsive plasticity to flooding events.

Biopores are pores or voids in soil produced by roots, by earthworms, or by the occupation of earthworms in root pores, which are considered important microbial hotspots, especially in subsoil. We hypothesized that earthworms (Lumbricus terrestris L.) exert stronger effects on microbial activities than decaying plant roots (of Cichorium intybus L.) in the subsoil because of the addition of pre-digested organic material. We tested this hypothesis by analyzing microbial biomass (Cmic), total organic C (Corg), and activities of eight enzymes (cellobiohydrolase, β-glucosidase, xylanase, acid phosphomonoesterase, leucine aminopeptidase, tyrosine aminopeptidase, chitotriosidase, and n-acetylglucosaminidase) down to 105-cm depth. The Cmic increase was associated with a two- to threefold increase of Corg content in biopores as compared to bulk soil. The highest percentage of Cmic-to-Corg (3.7 to 7.3 %) in the drilosphere demonstrated the enhancement of microbial efficiency for organic matter decomposition by earthworms. The availability of organic matter in biopores increased the activities of C- and N-targeting enzymes by 1.2–11.3 times, but reduced acid phosphomonoesterase activity by 10–40 % in biopores versus bulk soil. Introducing earthworms in root biopores caused 1.5–1.8 times higher microbial biomass and 1.2–1.9 times increased enzyme activities compared to the sole effect of earthworms. Soil depth showed a strong effect on the drilosphere, but only slight effects on the biochemical properties of root biopores and bulk soil. In conclusion, biopores are important microbial hotspots of C, N, and P transformations in subsoil. Earthworms exerted stronger effects on biochemical properties of biopores than decaying roots.

We performed a greenhouse experiment to test how the functional diversity of earthworms, the dominant group of soil macro-invertebrates in many terrestrial ecosystems, affects nitrogen cycling and plant growth. Three species were chosen to represent a range of functional traits: Lumbricus terrestris (large, mainly detritivorous, makes vertical permanent burrows open at the surface), Aporrectodea longa (medium-large, feeds on both detritus and soil, makes burrows more branched than L. terrestris), and Allolobophora chlorotica (small, geophagous, makes ephemeral burrows below the soil surface). Mesocosms with ryegrass (Lolium perenne) were inoculated with none to all three species (similar total biomass), using an experimental design (Simplex) suited to partition single species and diversity effects. Two contrasting N sources, urea or mammalian dung, were labelled with 15N so that the acquisition by plants and earthworms and recovery of applied 15N could be estimated. Over 3 months, plant production was higher with urea applications, but there were also species-specific earthworm effects: A. chlorotica and, to a lesser extent, A. longa increased shoot biomass, whereas L. terrestris increased root biomass. Earthworms did not affect soil N concentrations or leaching losses, whereas more N was leached under urea. A. chlorotica tended to increase dung-15N recovery in grass shoots, but in interaction with A. longa had the opposite effect, possibly through increased N immobilization in the microbial biomass. Earthworms assimilated negligible amounts of urea-15N but a substantial proportion (17% on average) of the dung-15N, with no clear-cut differences between species. Our findings show that earthworm species may have similar trophic response to N sources and yet different effects on plant N uptake and primary production, and that inter-specific earthworm interactions can result in non-additive diversity effects.

Earthworms boost microbial activities and consequently create hotspots in soil. Although the presence of earthworms is thought to change the soil enzyme system, the distribution of enzyme activities inside worm burrows is still unknown. For the first time, we analyzed enzyme kinetics and visualized enzyme distribution inside and outside worm burrows (biopores) by in situ soil zymography. Kinetic parameters ( V max and K m ) of 6 enzymes – β-glucosidase (GLU), cellobiohydrolase (CBH), xylanase (XYL), chitinase (NAG), leucine aminopeptidase (LAP) and acid phosphatase (APT) – were determined in pores formed by Lumbricus terrestris L. In earthworm burrows, the spatial distributions of GLU, NAG and APT become observable in zymogram images. Zymography showed a heterogeneous distribution of hotspots in the rhizosphere and worm burrows. The hotspot areas were 2.4–14 times larger in the burrows versus reference soil (soil without earthworms). The significantly higher V max values for GLU, CBH, XYL, NAG and APT in burrows confirmed that earthworms stimulated enzyme activities. For CBH, XYL and NAG, the 2- to 3-fold higher K m values in burrows indicated different enzyme systems with lower substrate affinity compared to reference soil. The positive effects of earthworms on V max were cancelled by the K m increase for CBH, XYL and NAG at a substrate concentration below 20 μmol g −1 soil. The change of enzyme systems reflected a shift in dominant microbial populations toward species with lower affinity to holo-celluloses and to N-acetylglucosamine, and with higher affinity to proteins as compared to the reference soil. We conclude that earthworm burrows are microbial hotspots with much higher and denser distribution of enzyme activities than reference soil.

Earthworms are one of the dominant groups of soil macro-invertebrates in many terrestrial ecosystems affecting nutrient cycling and plant growth. However, it is not well known how earthworms can influence availability of silicon (Si) as an element whose beneficial role in agricultural systems has been widely recognized. The objectives of this study were: (1) to determine the effect of earthworms on the mobility of Si in soil, and (2) to determine whether earthworm induced effects on Si mobility are of importance for the availability of Si to plants (Cucumis sativus L. and Zea mays L.). Two soils (a sandy loam soil and a sandy soil) with two levels of two independent treatments (±CaCO3 and ± earthworms) were used. Concentrations of water-extractable Si and monosilicic acid (Si(OH)4) in casts/soils and Si movement via xylem of plants were measured. Casts of earthworms – endogeic Aporrectodea caliginosa (Savigny) and anecic Lumbricus terrestris L., had generally higher amounts of water-extractable Si (by 2.0–12.0 times) and Si(OH)4 (by 1.3–3.5 times) compared with bulk soils, irrespective of soil type and application of CaCO3. Bioturbation of the sandy loam soil by living earthworms were generally of major importance in improving xylem translocation of Si from roots to shoots in cucumber and maize. The results highlight for the first time the importance of earthworms in plant acquisition of Si and biogeochemistry of Si.

Reduced tillage has several advantages over conventional tillage (CT), including the promotion of earthworm communities and the reduction of input of energy and labour. However, its application in organic farming is mainly hindered through increasing weed pressure. One way to counteract this drawback might be to introduce occasional reduced tillage (ORT), which means applying methods of reduced tillage only in combination with selected crops. Against this background we hypothesized that (i) ORT rapidly promotes biomass, abundance and species richness of earthworm communities and that (ii) ORT generates a financial surplus for farmers. Therefore, a field experiment was established for triticale (x Triticosecale) cultivation on loamy soils in Northern Germany. The influence of tillage regimes on earthworms was investigated in a non-randomized design with n = 3 fields for the ORT and CT treatment. Earthworm biomass, abundance and species richness were investigated in October 2012 and in April and October 2013. Yields were determined for the three fields under each tillage system, each field with four non-randomized replicates, before harvest in 2013. The ORT treatment consisted of two to three tillage operations prior to seeding with a maximal cultivation depth of 15 cm and without ploughing, whereas the CT treatment consisted of a ploughing depth of 25–30 cm and one to four other steps for seedbed preparation prior to seeding. In total, seven earthworm species were identified. Our data revealed that earthworm biomass was significantly reduced under CT, both four weeks and about seven months after tillage. This effect holds true for the number of earthworm individuals in autumn (four weeks after ploughing), but not for the number of earthworm individuals in spring (seven months after ploughing). Results of contribution margin analysis showed no consistent trend referring to tillage measures. Two fields, which performed well under CT, showed a financial surplus (+24% and +13%) when managed with ORT. At the same time one field, performing poorly under CT, generated financial deficits (-10%) under ORT. Overall ORT had immediate positive effects on earthworm populations. Furthermore, this management scheme might have positive effects on the economic outcomes of organic crop rotations if overall growing conditions are sufficient. Along with methods usually applied to investigate earthworm performance, we checked whether the number of surface casts could help estimate earthworm performance. It became apparent that the number of surface casts cannot be used as a general predictor of earthworm performance. The number of individuals of Lumbricus terrestris, the number of anecic individuals and the total earthworm biomass can be estimated the most reliable by counting surface casts.

Invasive earthworm communities are expanding into previously earthworm-free forests of North America, producing profound ecosystem changes. Lumbricus terrestris is an invasive anecic earthworm that consumes a large portion of the detritus on the soil surface, eliminating forest floor organic horizons and reducing soil organic matter. Two mesocosm experiments were used to examine the individual and combined effects of litter and soil type on the growth of L. terrestris. The litter type experiment tested nine different food source treatments (7 tree leaf litters, deer fecal pellets, and a control), while the soil × litter type experiment used five different soil treatments (4 soil types and one soil type with A horizon material removed) in combination with four different food source treatments. We found that leaf litter type (p = 0.001) and soil type (p = 0.018) significantly affected earthworm growth rates, with growth rates on deer pellets similar to many high quality deciduous leaf litters. Of soil variables, exchangeable Ca (r 2 = 0.99), sum base cations (r 2 = 0.98), % organic matter (r 2 = 0.93), %N (r 2 = 0.89), %C (r 2 = 0.87), and exchangeable Mg (r 2 = 0.85) were all significant predictors of earthworm growth. Litter disappearance of all litter types was linearly related to growth, suggesting similar growth efficiency on different litter types. However, chemical properties, specifically foliar C:N and a linear combination of a suite of other chemical properties predicted growth, suggesting that consumption or gut passage rates were regulated by litter quality. This information about soil and litter characteristics that regulate L. terrestris growth should improve models of their distribution, spread and abundance.

Earthworms are recognized to affect soil nutrient cycling with important consequences for plant growth. Nutrient bioavailability is often limited in calcareous soils. Exactly how earthworms can impact availability of nutrients in higher plants grown on calcareous soils still remains an open question. The objectives of this study were to investigate in pot experiments complex nutrient dynamics of interactions between non-calcareous soil and earthworms with special emphasis on the availability of iron (Fe), zinc (Zn), manganese (Mn) and nitrogen (N) to plants (Cucumis sativus L. and Zea mays L.) subjected to calcium carbonate (CaCO3) excess. A combination approach was performed including analysis of nutrient mobility in casts/soil, micronutrient movement via xylem of plants and plant elemental analysis. Addition of CaCO3 (5% DW) significantly lowered the concentrations of Zn and Mn in xylem sap and/or shoot (by 1.8–5.7 times) of both cucumber and maize in comparison with plants that had not received CaCO3. Bioavailability of Fe, however, was not affected by CaCO3 treatment. Beneficial effects of earthworms— endogeic Aporrectodea caliginosa (Savigny) and anecic Lumbricus terrrestris L., for plant nutrient acquisition include an increased mobility of all micronutrients (by 1.3–4.0 times) and N (by 1.5–27 times) in casts or soil either with or without CaCO3 treatment. However, these earthworm species were generally not of major importance in improving Zn and Mn translocation from roots to shoot in cucumber and maize, which was strongly impaired in CaCO3 applied soil. The results clearly demonstrated that earthworm capabilities to alleviate plant Zn and Mn deficiencies induced by CaCO3 applications are limited.

In 2011 and 2013, mesocosm-studies were conducted in the field to assess the degradation performance of soil fauna (earthworms: Lumbricus terrestris, collembolans: Folsomia candida and nematodes: Aphelenchoides saprophilus) on mycotoxin-contaminated crop residues. The aim of the study was to investigate the potential of anecic earthworms in the regulation of the mycotoxin deoxynivalenol (DON) and whether the degradation capacity is influenced by the presence of collembolans and nematodes. After 4 and 8 weeks, DON concentrations in residual straw and in soil samples of all faunal treatments (containing earthworms, collembolans and nematodes in different combination) and the non-faunal control treatments were determined using an ELISA-method. After 4 weeks, the DON concentration in straw decreased in all treatments: faunal treatments 2011: 97–99 %; 2013: 78–94 %; non faunal treatments 2011: 88 %; 2013: 68 %. After 8 weeks a further decline of DON concentrations was measured in all faunal treatments (2011: 58–91 %; 2013: 50–86 %). DON concentration of the non-faunal treatments increased during the final four weeks. In soil the DON concentration was below quantification limits (

Loss of plant diversity resulting from forecasted drought events is likely to alter soil functioning and affect earthworm communities. Plant-soil interactions are expected to play an important role in mediating climate change effects on soil decomposers. In this study, we test above-belowground linkages after drought by focusing on the effects of subordinate plant species on earthworm communities. Using a combination of subordinate species removal and experimental drought, we show that subordinate species, when present, increased in biomass after drought and induced an increase in total earthworm biomass. These effects were thought to be associated with the maintenance of food quantity and quality (e.g. nitrogen-rich litter) in relation to subordinate species. In support to this hypothesis, we found a positive correlation between the abundance of juvenile earthworms and plant community biomass hence litter quantity, and between the total biomass of earthworms and the abundance of subordinate species. Anecic earthworms were the most benefited by the presence of subordinate species under drought, especially Lumbricus terrestris, which was significantly correlated to the biomass of the nitrogen-rich subordinate species Veronica chamaedrys. Results of a multiple factor analysis (MFA) also highlighted positive associations between earthworm and subordinate species, independently of the drought treatment. Our study highlights how climate change, in this case reduced summer rainfall, can influence plant functional groups, with cascading effects on earthworms. It is therefore crucial, considering forecasted climate change, to understand these processes in order to better predict ecosystem responses and to adapt grassland management.

Anecic earthworms such as Lumbricus terrestris create effective channels for the translocation of organic substances, nutrients (N, P) and water between top- and subsoil. However, studies on localized and linked microbial activities with the biochemical mechanisms within drilosphere are missing. To clarify the enzymatic mechanisms, zymography was combined with 14C imaging by placing 14C-labeled wheat litter on the surface of mesocosms with top- and subsoil to feed earthworms. Cellobiohydrolase and acid phosphatase activities were compared in drilosphere and bulk soil to test two hypotheses: i) a positive spatial correlation between 14C images and enzyme activities at burrow edges reflects the interactions between substrate distribution and microbial activities; ii) the drilosphere has higher enzyme activities and faster substrate turnover compared to bulk soil independent on depth. In line with the first hypotheses, the localization of substrates (14C) overlapped with enzyme activities for 68%. Spatial distribution of enzyme activities had stronger gradients within 2 mm of burrow edges in topsoil and 4 mm in subsoil. The mineralization of the wheat litter was faster in drilosphere than in the bulk soil. In contrast to our second hypothesis, the substrate turnover was depth dependent: 14CO2 efflux was fourfold faster in topsoil than subsoil drilosphere. The decline of enzyme activities with depth, accompanied by decreasing catalytic efficiency, implies microbial production of more efficient enzymes in top-than in the subsoil. We conclude that interactions between enzymes and substrates are more tight in the drilosphere, making it microbial hotspots. Thus, earthworm activities lead to microbial localization and acceleration of litter decomposition and C turnover in drilosphere. Therefore, both direct hotspot and indirect (soil heterogeneous content) effects need to be explicitly considered when attempting to model and predict how bioturbation evens will alter ecosystem dynamics and ecological development of (micro)habitats.

Summary Earthworm-seed interactions are increasingly recognized as ecologically important. Efforts to study these interactions make use of either no-choice or choice feeding trials due to logistical constraints or differing objectives, however, evidence is lacking regarding the consistency of feeding preferences by earthworms between these scenarios. We conducted a small-scale study in which we compared ingestion and egestion of eleven seed species by the anecic earthworm Lumbricus terrestris L. between no-choice and choice feeding dish trials. We found that seed ingestion and egestion differed between species and the seed ingestion preferences were relatively consistent (Pearson Correlation, r = 0.695) between the feeding trials. These results indicate that seeds preferred in isolation are similarly detectable and preferred alongside other options, aiding in the interpretation of results of other anecic earthworm-seed feeding experiments and suggesting that L. terrestris has a surprisingly strong ability to discriminate between and selectively consume specific seeds from a larger and diverse pool of species options.

Anecic earthworms such as Lumbricus terrestris are ecosystem engineers whose impacts on soil fertility and remediation have been extensively researched. The majority of L. terrestris used for such research and practical remediation applications are procured through the largely unknown bait worm market that serves freshwater recreational fishermen across North America and Europe. Some earthworm researchers have questioned the use of these bait worms for research and soil inoculations because of their untraceable origins, unknown environmental exposures and growing conditions, as well as the sustainability of harvesting practices. However, there has been no recent study of this unique industry and how it hand-picks hundreds of millions of L. terrestris worms annually from a single region in southwestern Ontario. This paper provides a detailed description of how land and labour are currently organized to supply the world market for the valuable L. terrestris, commonly known as the “Canadian Nightcrawler” bait worm. Based on 59 semi-structured depth interviews, the findings show there are an estimated 500 to 700 million worms picked annually from farmer fields that stretch between Toronto and Windsor, Ontario. Dairy farms in particular have emerged as de facto L. terrestris production sites because of their perennial alfalfa crops, heavy manure application, and reduced tillage practices. This has made L. terrestris the most lucrative crop in the region with many farmers leasing land to worm-picking operations for over $1000 CND per year ($750 USD/ €685) — approximately four times the regional rental rates. Worm-pickers have historically been recent immigrants to Ontario with the majority of current pickers coming from Vietnam. Worm pickers make $20CND ($15 USD, €13.50) per thousand worms, and can pick over 20,000 worms per night in optimal field conditions (moisture, temperature, wind, moonlight). The piece-rate wages tend to reward speed and efficacy with some pickers capable of making over $600 in a single night. This peculiar arrangement between dairy farmers, soils, and worm pickers opens avenues for socio-economical, agronomical and ecological studies of commercial L. terrestris harvesting.