Endogeic Species Research Articles

Does the influence of earthworms on water infiltration, nitrogen leaching and soil respiration depend on the initial soil bulk density? A mesocosm experiment with the endogeic species Metaphire posthuma

Soil compaction has a negative impact on both earthworm abundance and diversity. Recent studies, however, suggest that earthworm cast properties are not influenced by the initial soil bulk density. With time, earthworms could therefore transform soils with different bulk densities into a soil with the same physical state and thus with a similar ecological functioning. This study aimed to test this hypothesis in two laboratory incubation experiments. First, we measured the influence of soil bulk density (1.1 or 1.4 g cm−3) on the production of cast by the endogeic earthworm species Metaphire posthuma. In a second experiment, we investigated the effect of M. posthuma on water infiltration, NH4+, and NO3− leaching and soil respiration at the same two soil bulk densities. Although initially higher, earthworm casting activity in soil at 1.4 g cm−3 decreased until it reached the same level of activity as earthworms in soil at 1.1 g cm−3. This behavioral plasticity led to a transformation of compacted and loose soils, with their own functioning, to a third and similar state with similar hydraulic conductivity, nitrogen leaching, and soil respiration. The consequences for soil organization and soil functioning are discussed.

Pyrosequencing of prey DNA in reptile faeces: analysis of earthworm consumption by slow worms

Little quantitative ecological information exists on the diets of most invertebrate feeding reptiles, particularly nocturnal or elusive species that are difficult to observe. In the UK and elsewhere, reptiles are legally required to be relocated before land development can proceed, but without knowledge of their dietary requirements, the suitability of receptor sites cannot be known. Here, we tested the ability of non-invasive DNA-based molecular diagnostics (454 pyrosequencing) to analyse reptile diets, with the specific aims of determining which earthworm species are exploited by slow worms (the legless lizard Anguis fragilis) and whether they feed on the deeper-living earthworm species that only come to the surface at night. Slow worm faecal samples from four different habitats were analysed using earthworm-specific PCR primers. We found that 86% of slow worms (N=80) had eaten earthworms. In lowland heath and marshy/acid grassland, Lumbricus rubellus, a surface-dwelling epigeic species, dominated slow worm diet. In two other habitats, riverside pasture and calciferous coarse grassland, diet was dominated by deeper-living anecic and endogeic species. We conclude that all species of earthworm are exploited by these reptiles and lack of specialization allows slow worms to thrive in a wide variety of habitats. Pyrosequencing of prey DNA in faeces showed promise as a practical, rapid and relatively inexpensive means of obtaining detailed and valuable ecological information on the diets of reptiles.

Local land use effects and regional environmental limits on earthworm communities in Finnish arable landscapes

In many arable soils, earthworms form the key component of the soil animal community and greatly contribute to soil quality. Our goal was to identify variables that can explain the variation of earthworm communities across Finnish arable fields by focusing on both regional aspects, such as climate and inherent soil properties, and local aspects, such as field management practices and field margins. We sampled the earthworms during the autumn of 2004 and 2005 at 53 sites of cultivated fields and margins, distributed to 11 localities ranging from the southern parts of Finland to the Arctic Circle. Simultaneously, information was collected on topsoil properties, cultivation history, and climatic factors. We found that soil type was by far the best regional variable to explain the variation in total earthworm density, the density being highest in medium coarse soils, i.e., silts and very fine sands. However, soil type had a significant interaction with soil C:N ratio. After accounting for the effect of soil type, no clear geographical trends remained in the regional variation, except that coastal areas with thin snow cover and deep frost had lower earthworm density than inland areas with deep snow cover and shallow frost. Of the local variables, tillage frequency, grazing, and field margins were the most influential. Frequent tillage led to earthworm communities heavily dominated by endogeic species, while grazed pastures had more than three times the earthworm biomass in comparison to non-grazed fields. Field margins harbored over twice the density and almost double the number of species in comparison to the adjacent cultivated fields, and eight of the nine species had wider regional distribution in the margins than in the fields. Inside the fields, species richness tended to decrease gradually with increasing distance to the margin. Our results suggest that, while soil texture and climatic factors set the general limits to earthworm communities in Finnish arable soils, field management practices can override these limits at the local scale. Cultivation in general simplifies the earthworm community, and this is particularly clear in the fields that are frequently tilled, whereas pastures and field margins seem to effectively preserve the biomass and diversity of earthworms.

Ecological transfer of radionuclides and metals to free-living earthworm species in natural habitats rich in NORM

Transfer of radionuclides (232Th and 238U) and associated metals (As, Cd, Pb and Cr) from soil to free-living earthworm species was investigated in a thorium (232Th) rich area in Norway. Sampling took place within former mining sites representing the technologically enhanced naturally occurring radioactive materials (TENORM), at undisturbed site with unique bedrock geology representing the naturally occurring radioactive materials (NORM) and at site outside the 232Th rich area taken as reference Background site. Soil analysis revealed the elevated levels of investigated elements at NORM and TENORM sites. Based on sequential extraction, uranium (238U) and cadmium (Cd) were quite mobile, while the other elements were strongly associated with mineral components of soil. Four investigated earthworm species (Aporrectodea caliginosa, Aporrectodea rosea, Dendrodrilus rubidus and Lumbricus rubellus) showed large individual variability in the accumulation of radionuclides and metals. Differences in uptake by epigeic and endogeic species, as well as differences within same species from the NORM, TENORM and Background sites were also seen. Based on total concentrations in soil, the transfer factors (TF) were in ranges 0.03–0.08 and 0.09–0.25, for 232Th and 238U, respectively. TFs for lead (Pb), chromium (Cr) and arsenic (As) were low (less than 0.5), while TFs for Cd were higher (about 10).Using the ERICA tool, the estimated radiation exposure dose rate of the earthworms ranged from 2.2 to 3.9μGy/h. The radiological risk for investigated earthworms was low (0.28).The obtained results demonstrated that free-living earthworm species can survive in soil containing elevated 232Th and 238U, as well As, Cd, Pb and Cr levels, although certain amount of radionuclides was accumulated within their bodies.The present investigation contributes to general better understanding of complex soil-to-biota transfer processes of radionuclides and metals and to assessment of risk for non-human species in the ecosystem with multiple contaminants.

Earthworm indicators as tools for soil monitoring, characterization and risk assessment. An example from the national Bioindicator programme (France)

Considering the limited number of bioindicators available to assess soil quality, a national research programme was set up in France to develop such indicators (2006-2012), the Bioindicator programme. This programme tested 47 biological parameters (i.e. microorganisms, fauna, flora) including earthworms, in several sites differing in terms of land use, contamination type - PAHs or metals - and pollution levels. The present study proposes some study objectives for bioindicator approaches, based on the earthworm results from the programme. Therefore, different earthworm descriptors were tested at the community level (e.g. abundance, biomass, species and functional structures, and ecological traits) as well as the organism level (i.e. measuring the metallothionein coding gene expression level in earthworms). The present results, obtained from the programme's spring 2009 sampling campaign, discriminated among the different descriptors and showed that earthworm and endogeic abundance as well as the individual weight of endogeics seem to be good indicators in non-contaminated (cultivated) sites, while the ecological structure, namely the proportion of anecic vs. endogeic species, and the proportion of non-vulnerable species should be used as indicators of contaminated soils. Furthermore, the first results obtained for Lumbricus terrestris and L. rubellus rubellus are encouraging as they show that metallothionein expression increases in metal-contaminated soils. The relevance of these descriptors, which have to be considered in study objectives, requires the analysis of 2010 results.

Diversity and abundance of earthworms in land use systems in central-western Colombia

The neotropical landscapes of Colombia's Andean region are characterized by a mosaic of agroecosystems presenting a range of vegetational cover for which soil fauna adaptation is still unknown. To analyze the diversity and abundance of earthworm species in relation to changes in selected soil physical and chemical parameters (bulk density, C stock, N stock, %C, %N, 13C, 15N, C:N ratio), these systems were classified into five categories according to land use intensity: non-intensive (NI), low intensity (LI), medium intensity (MI), high intensity (HI), and maximum intensity (IN). The influence of livestock production was confirmed in the significant differences observed in bulk density and 15N between NI, HI, and IN (P < 0.05). The C and N contents of IN systems (pastures) differed significantly (P < 0.05) in comparison with the other categories. Average δ 13C at the three soil depths evaluated (0–10, 10–20, and 20–30 cm) ranged between −24.9 for LI and −22.87 for IN, indicating that soil organic carbon was related to C3-type vegetation for all land uses and vegetation covers. Overall, 26 earthworm species were recorded, of which 16 showed a high capacity to adapt to natural, NI, LI, and MI systems. Depending on land use intensity, significant differences were also observed (P < 0.05) in the origin and ecological category of earthworms, mainly in terms of the following variables: diversity of native species, diversity of endogeic species, abundance of native species, biomass of native species, and abundance of exotic species. Based on the results obtained, the most favorable mosaic systems for agrobiodiversity conservation were identified as well as those subsystems that require special management to solve problems of habitat degradation.

Associations between soil texture, soil water characteristics and earthworm populations in grassland

The aim of the present study was to investigate the relationships between soil physical characteristics and earthworms in a regional-scale field study in Denmark. The earthworm populations along within-field gradients in soil texture were quantified at five field sites, representing dominant soil types of Denmark. Eleven earthworm species were found, but populations were mainly dominated by Aporrectodea tuberculata and A. longa. Despite considerable variation in soil parameters across the five study sites the results suggest that the biomass of anecic worms (or A. longa as a species) was not causally associated with the soil parameters studied. This indicates that there must be other causal factors associated with the abundance (and composition) of anecic worms that are not among the soil texture and structure parameters studied. On the other hand, soil texture (Coarse sand) was associated with the abundance of the dominant endogeic species, A. tuberculata, but not endogeic worms in general. It was hypothesized that anecic and endogeic earthworms might respond to local soil water characteristics rather than soil texture, but this hypothesis could not be confirmed with the present data.

Earthworm-induced N2O emissions in a sandy soil with surface-applied crop residues

Abstract Earlier research with endogeic and epigeic earthworm species in loamy arable soil has shown that both earthworm groups can increase nitrous oxide (N 2 O) emissions, provided that crop residue placement matches the feeding strategy of the earthworm ecological group(s). However, it is not yet clear whether these effects also occur in sandy soils which typically contain less soil organic matter and have low soil aggregation levels. Here, we aimed to quantify N 2 O emissions as affected by endogeic and/or epigeic earthworm species, and to relate changes in N 2 O emissions to earthworm-induced changes in soil properties in a sandy soil. A 90 day mesocosm study was conducted with sandy soil and 15 N-labeled radish ( Raphanus sativus cv. Adagio L.) residue applied on top. Treatments included: (i) no earthworm addition, (ii) addition of the endogeic species Aporrectodea caliginosa (Savigny), (iii) addition of the epigeic species Lumbricus rubellus (Hoffmeister), and (iv) both species combined. An additional treatment was included without earthworms and with residue manually incorporated into the soil. L. rubellus significantly increased cumulative N 2 O emissions from 228 to 859 μg N 2 O–N kg −1 ( F 1,12 = 83.12, P A. caliginosa did not affect N 2 O emissions. In contrast to earlier studies in loamy soil, no positive interaction between both species with regard to N 2 O emissions was found. This was probably related to high competition for organic resources in the relatively poor soil and a low potential for stable soil aggregate formation (and associated anaerobic microsites) by endogeic worms in sandy soil. 15 N isotope analysis revealed that the activity of L. rubellus significantly increased ( F 1,12 = 6.20, P = 0.028) the recovery of 15 N in the 250–8000 μm size fraction, indicating incorporation of crop residues into the mineral soil. When residues were manually incorporated, N 2 O emissions were significantly ( P 2 O–N kg −1 ) than when incorporated by L. rubellus . The high N 2 O emissions in the presence of L. rubellus , when compared to manual mixing, suggest a stimulation of microbial activity and/or changes in the microbial community composition. Insights on the earthworm effects on N 2 O emission from such soils are discussed.

Earthworm abundance and species composition in organic forage production systems of northern Colorado receiving different soil amendments

We evaluated the effects of soil amendments on earthworm communities in organic annual forage and perennial pasture systems in northern Colorado. In the annual forage study (1) an annual warm season grass teff (Eragrostis tef) and (2) bare fallow were main plot treatments and received one of three soil amendments: (1) composted dairy manure (CDM), (2) raw dairy manure (RDM), and (3) no amendment as control. For the perennial pasture study, CDM was topdressed onto a grass mixture consisting of orchardgrass, smooth and meadow bromegrass at rates ranging from 0 to 44.8Mgha−1. At both sites, earthworm and soil samples were collected in July 2009. The earthworms identified from both systems were composed of endogeic species Aporrectodea rosea (Savigny), A. tuberculata (Eisen), and A. turgida (Eisen), the first being found only in the perennial pasture. In the annual forage study, earthworm total abundance did not differ between teff and bare fallow treatments. However, within bare fallow treatment, earthworm total abundance was significantly affected by soil amendment, with CDM averaging approximately 1.4 and 5.4 times greater earthworm total abundance than RDM and the control, respectively. Earthworm total abundance was found to be positively correlated with soil Cu (R=0.51, P=0.03) and K (R=0.58, P=0.01). In the perennial pasture, earthworm total abundance tended to increase with an increase in the CDM rate to 33.6Mgha−1. However, no further increase was observed when the CDM rate was increased to 44.8Mgha−1. At this site, earthworm total abundance was negatively correlated with EC (R=−0.37, P=0.02). Our results suggest that high quality (low C/N ratio) dairy manure is important for maintaining a high earthworm population. Larger CDM application rates appear to discourage earthworm populations probably due to salinity stress. Further study is necessary to elucidate the exact effects of manure quality and quantity on earthworm populations in annual forages and perennial pastures.

Soil fertility management: Impacts on soil macrofauna, soil aggregation and soil organic matter allocation

Maintenance of soil organic matter through integrated soil fertility management is important for soil quality and agricultural productivity, and for the persistence of soil faunal diversity and biomass. Little is known about the interactive effects of soil fertility management and soil macrofauna diversity on soil aggregation and SOM dynamics in tropical arable cropping systems. A study was conducted in a long-term trial at Kabete, Central Kenya, to investigate the effects of organic inputs (maize stover or manure) and inorganic fertilizers on soil macrofauna abundance, biomass and taxonomic diversity, water stable aggregation, whole soil and aggregate-associated organic C and N, as well as the relations between these variables. Differently managed arable systems were compared to a long-term green fallow system representing a relatively undisturbed reference. Fallowing, and application of farm yard manure (FYM) in combination with fertilizer, significantly enhanced earthworm diversity and biomass as well as aggregate stability and C and N pools in the top 15 cm of the soil. Earthworm abundance significantly negatively correlated with the percentage of total macroaggregates and microaggregates within macroaggregates, but all earthworm parameters positively correlated with whole soil and aggregate associated C and N, unlike termite parameters. Factor analysis showed that 35.3% of the total sample variation in aggregation and C and N in total soil and aggregate fractions was explained by earthworm parameters, and 25.5% by termite parameters. Multiple regression analysis confirmed this outcome. The negative correlation between earthworm abundance and total macroaggregates and microaggregates within macroaggregate could be linked to the presence of high numbers of Nematogenia lacuum in the arable treatments without organic amendments, an endogeic species that feeds on excrements of other larger epigeic worms and produces small excrements. Under the conditions studied, differences in earthworm abundance, biomass and diversity were more important drivers of management-induced changes in aggregate stability and soil C and N pools than differences in termite populations.

Invasion by Exotic Earthworms Alters Biodiversity and Communities of Litter- and Soil-dwelling Oribatid Mites

Exotic earthworms are drivers of biotic communities in invaded North American forest stands. Here we used ecologically important oribatid mite (Arachnida: Acari) communities, as model organisms to study the responses of litter- and soil-dwelling microarthropod communities to exotic earthworm invasion in a northern temperate forest. Litter- and soil-dwelling mites were sampled in 2008–2009 from forest areas: (1) with no earthworms; (2) those with epigeic and endogeic species, including Lumbricus rubellus Hoffmeister; and (3) those with epigeic, endogeic, and anecic earthworms including L. terrestris L. Species richness and diversity of litter- and soil-dwelling (0–2 cm soil depth) oribatid mites was 1–2 times higher in sites without earthworms than in sites with worms. Similarly, litter-dwelling oribatid mites were between 72 and 1,210 times more abundant in earthworm-free sites than in sites with worms. Among earthworm invaded sites, abundance of litter-dwelling oribatid mites in sites without the anecic L. terrestris was twice as high in May and 28 times higher in October, compared to sites with L. terrestris. Species richness, diversity, and abundance of oribatid mites were greater in litter-layers than in the soil-layers that showed a varied response to earthworm invasion. Species compositions of both litter- and soil-dwelling oribatid mite communities of forests with no earthworms were markedly different from those with earthworms. We conclude that exotic earthworm invasions are associated with significant declines of species diversity, numbers, and compositional shifts in litter- and soil-inhabiting communities. These faunal shifts may contribute to earthworm effects on soil processes and food web dynamics in historically earthworm-free, northern temperate forests.

Using X-ray tomography to quantify earthworm bioturbation non-destructively in repacked soil cores

X-ray tomography is used increasingly to study the macroporosity resulting from earthworm activity. However, macropores are not the only features visible on the images; other zones resulting from bioturbation by earthworms can be detected due to differences in greylevels. Four different soil cores were incubated with two earthworm species at two different densities (4 or 8 adults of the endogeic species Allolobophora chlorotica or 2 or 4 adults of the anecic species Aporrectodea nocturna). A fifth core without earthworms was used as a control. After six weeks, the cores were analysed by X-ray tomography using a medical scanner. The 3D earthworm burrow systems were reconstructed and a new and specific algorithm was used to determine other bioturbated zones (BZ) that were physically influenced by the earthworms. Expected differences in the structure of the burrow systems between the endogeic and anecic species were observed: the A. chlorotica burrows were narrower and more numerous, more branched and less vertical. When the earthworm density doubled, the volume and length of the A. chlorotica burrow system increased whereas no increase was observed for A. nocturna. The BZ, which were located in the upper section of the cores, represented almost the same volume as the macropores. These zones tended to be located further from the burrows in the A. chlorotica cores: 50% of the voxels corresponding to BZ were at a distance greater than 4 and 5.5 mm from the closest macropore for A. nocturna and A. chlorotica, respectively. Three processes may have contributed to form these zones, which are characterised by increased soil density: (i) soil compaction around the burrows during burrow creation, (ii) cast deposition in the burrows (burrow backfilling) and (iii) crushing of casts on the burrow walls (so called cutanes). The longer distance between BZ and macropores in A. chlorotica cores suggests that the proportion of burrow backfilling is higher for the endogeic species compared to the anecic species. If we assume that BZ located further than 10 mm from any burrow are actually burrows backfilled with casts, the volume of burrow backfilled in our study ranged from 14 to 18% for A. chlorotica and from to 8 to 10% for A. nocturna.

Invasion of Pontoscolex corethrurus (Glossoscolecidae, Oligochaeta) in landscapes of the Amazonian deforestation arc

Pontoscolex corethrurus (Glossoscolecidae, Oligochaeta) is an invasive endogeic earthworm that has colonized most land transformed by human activities in the humid tropics. When installed, populations can change soil physical properties, biogeochemical processes and microbial communities. The aim of this study was to determine whether P. corethrurus establishment is a result of (1) a competitive exclusion of native earthworm species or (2) the exploitation of a new niche created by anthropogenic disturbance that native earthworm species cannot use. We tested these hypotheses by doing a survey of earthworm communities in 270 sites that represented the diversity of land use systems encountered in two contrasted regions of the Amazonian arc of deforestation located in Brazil and Colombia respectively. When present in forests, P. corethrurus had no negative effect on the native species communities that had similar (epigeic species) or even higher densities (endogeic species) in the presence of the invasive species. These results suggest the absence of competitive exclusion. The first two axes of a PCA multivariate analysis of communities represented the densities of native species (axis 1) and P. corethrurus (axis 2) respectively. This suggests that respective densities of the two groups respond to different conditions and that their variations are independent. The density of P. corethrurus co-varied with soil N content and pH in Colombian sites while the densities of other species did not. Our results thus suggest that this invasive species, unlike native species, is able to feed and develop in environments where litter resources are decreased while soils have been enriched in C and nutrients by deforestation and burning. We discuss the reasons why some primary forests in Central America have large populations of P. corethrurus.

Different earthworm ecological groups interactively impact seedling establishment

There is increasing evidence that direct interactions between earthworms and seeds impact the assembly of plant communities. However, effects of earthworms of different ecological groups and their interactions on plant germination and establishment are little known. We set up a full-factorial greenhouse experiment in order to explore impacts of different ecological groups of earthworms (epigeic, endogeic and anecic) on the establishment of seedlings. The three ecological groups of earthworms affected seedling establishment in an interactive way with the effects varying in time. While anecic earthworms detrimentally affected the number of established seedlings, impacts of epigeic and endogeic species depended on the presence of earthworms belonging to other ecological groups. Impacts of anecic earthworms were more significant and consistent than those of epigeic and endogeic ones pointing to the dominance of the effect of anecic earthworms for seedling establishment. The initial positive effect of the combined presence of epigeic and endogeic earthworms compared to treatments with only endogeic and only anecic earthworms was likely due to the acceleration of seed germination and elevated nutrient availability for seedlings in earthworm casts. By contrast, reduced numbers of seedlings in presence of both epigeic and endogeic earthworms compared to the control treatment might have been due to seedling predation after the litter layer had disappeared. The results extend current knowledge on interactions between earthworms and seeds by showing that, in addition to anecic species, also epigeic and endogeic species influence seedling establishment with their effect depending on the presence of anecic species. Moreover, the results indicate that impacts of earthworms vary with the developmental stage of seedlings highlighting the importance of interactions between earthworms and seeds.

Prey choice by carabid beetles feeding on an earthworm community analysed using species- and lineage-specific PCR primers

The carabid beetle Pterostichus melanarius is a major natural enemy of pests, such as aphids and slugs in agricultural systems. Earthworms are a dominant non-pest component of the diet of P. melanarius which help sustain the beetles during periods when the pest population is low or absent. In this study we wanted to test whether this predator exercises prey choice among different earthworm species or ecological groups. High levels of genetic diversity within morphological species of earthworm necessitated the development of primers that were specific not just to species but lineages and sub-lineages within species as well. Gut samples from beetles were analysed using multiplex-PCR and fluorescent-labelled primers. Calibratory feeding trials were undertaken to calculate median detection times for prey DNA following ingestion. Extensive testing demonstrated that the primers were species-specific, that detection periods were negatively related to amplicon size and that meal size had a highly significant effect on detection periods. Monte Carlo simulations showed that, in general, worms were being predated in proportion to their densities in the field with little evidence of prey choice, other than probable avoidance of the larger, deep-living species. There was no evidence that epigeic species were being taken preferentially in comparison with endogeic species. There was also no evidence that defensive secretions by Allolobophora chlorotica reduced predation pressure on this species by P. melanarius. We concluded that any management system that increases earthworm densities generally, regardless of component species, is likely to be optimal for increasing numbers of this beneficial beetle predator.

Distribution of Octolasion cyaneum (Savigny, 1826) in Estonia 1993–2008

The aim of the paper is to give an overview about distribution of the endogeic species Octalasion cyaneum (Savigny, 1826) in Estonia. First time, this endogeic species was found in 1980s in the Tallinn Botanical Garden (Northern-Estonia). The new results show that O. cyaneum is slowly expanding into Estonian territory and becoming more abundant.

Influence of texture and amendments on soil properties and earthworm communities

In Canada, the influence of earthworms on soil is considered particularly important in the Southern regions where agriculture has developed. A field experiment was duplicated on a clay loam and a sandy loam soil in the Saint-Lawrence Valley. Both sites were enriched with urban compost or mineral amendment. The effects of amendments on soil properties and the earthworm community were evaluated by uni- and multivariate analyses at two soil depths (0–10 and 10–20 cm) and after two growth seasons. Compost-amended plots had higher pH, wet aggregates stability, total N and C, OM, K and Ca in the 0–10 cm soil layer than plots receiving mineral fertilizer. Two endogeic species, Aporrectodea caliginosa and Allolobophora chlorotica were dominant in both sites. Other species were all epigeic and were rare. Abundance and biomass of earthworms (0–10 cm) were significantly higher in clay loam, with a similar proportion in A. caliginosa (263 ind m −2) and A. chlorotica (228 ind m −2). In sandy loam, A. caliginosa was the most abundant (18 ind m −2), A. chlorotica was scarce (1.3 ind m −2) and epigeic species were absent. The density and biomass of earthworms were significantly higher with compost amendment, up to 12 times in clay loam: A. chlorotica reached a mean density of 420 ind m −2 vs. 36 ind m −2 with mineral amendments, A. caliginosa 344 ind m −2 vs. 183 ind m −2 and epigeic earthworms 19 ind m −2 vs. 12 ind m −2. In co-inertia analysis, the main factors explaining data heterogeneity were soil texture (axis 1) and organic matter content (axis 2). A. chlorotica was associated with OM, while A. caliginosa was associated with silt and clay contents. Additionally, soil wet aggregate stability was the variable that best correlated with endogeic species. The overall earthworm population was low, which is common for tilled agricultural soils, but clearly benefited from the OM input from the urban compost, providing further evidence that fertilization based on organic residues, as implemented in organic agriculture, is highly beneficial for earthworms and soil quality.

Plant community impacts on the structure of earthworm communities depend on season and change with time

Declining plant diversity potentially threatens essential ecosystem functions driven by the decomposer community, such as litter decomposition and nutrient cycling. Currently, there is no consensus on the interrelationships between plant diversity and decomposer performance and previous studies highlighted the urgent need for long-term experiments. In the Jena Experiment we investigated the long-term impacts of plant community characteristics on the structure of earthworm communities representing key decomposers in temperate grassland. We repeatedly sampled plots varying in plant species richness (1–16 species), plant functional group richness (1–4 groups), and presence of certain plant functional groups (grasses and legumes) three, four, and six years after establishment of the experiment in spring and autumn. The results show that earthworm performance is essentially driven by the presence of certain plant functional groups via a variety of mechanisms. Plant productivity (root biomass) explained most of the detrimental grass impacts (decrease in earthworm performance), while beneficial legume effects likely were linked to high quality inputs of plant residues (increase in earthworm performance). These impacts depended on the functional group of earthworms with the strongest effects on surface feeding anecic earthworms and minor effects on soil feeding endogeic species. Remarkably, effects of plant community characteristics on the composition and age structure of earthworm communities varied between seasons. Moreover, plant diversity effects reported by a former study decreased and detrimental effects of grasses increased with time. The results indicate that plant community characteristics, such as declining diversity, indeed affect the structure of earthworm communities; however, loss of key plant functional groups is likely to be more important than plant species number per se. However, in frequently disturbed ecosystems plant species richness might be important for the recovery and resilience of belowground functions. Moreover, the results accentuate the importance of long-term repeated measurements to fully appreciate the impacts of plant community composition and diversity on ecosystem properties. Single point observations may be misleading and potentially mask the complexity of above-belowground interrelationships.

Oxygen consumption of the earthworm species Dendrobaena mrazeki

Dendrobaena mrazeki is an endemic earthworm species inhabiting dry habitats such as pine and thermophilous oak forests in Central Europe. Metabolically, D. mrazeki showed some features typical for endogeic species and some of epigeic ones. In comparison with the related Dendrobaena octaedra, D. mrazeki was a larger earthworm with fresh body mass of adult and subadult individuals of W = 0.59 ± 0.05 g. Its body mass-specific oxygen consumption ( M/ W = 48 ± 5 μl O 2 g −1 h −1, at 15 °C) was the lowest of all earthworms studied ( Aporrectodea caliginosa, Aporrectodea rosea, D. octaedra, Lumbricus castaneus, Lumbricus rubellus and Octolasion lacteum), being strongly dependent on W ( b from the equation M/ W = aW b about −0.8). D. mrazeki had low relative water content (77.4% of fresh body mass) and small relative amount of dry weight of the intestinal content (20.1% of dry body mass), which is similar to the epigeic D. octaedra. The respiration rate of D. mrazeki remained the lowest even after recalculating M/ W to respiration rate per dry mass or per dry mass without the intestine content to correct for the differences among species in body water content and gut content.

Earthworm burrowing behaviour in 2D terraria with single- and multi-species assemblages

Experiments were performed in 2D terraria to investigate the burrowing behaviour of different earthworm species from various ecological categories in single- and multi-species assemblages. The burrowing behaviour was quantified using image analysis software during a 2-week period. Terraria were found to reveal realistic impressions of the burrowing behaviour of various species according to the ecological classification of Bouche into epigeic, endogeic and anecic species. Results of the study also permit the recommending of classifying various earthworms as intermediate species, e.g. Aporrectodea longa as endo-anecic and Lumbricus rubellus as epi-endogeic. Burrowing activity of endogeic species was significantly reduced in multi-species compositions compared to single-species treatments. Moreover, burrowing activity of Octolasion tyrtaeum was significantly reduced in the presence of Lumbricus terrestris compared to the specific single treatment. This endogeic species profited from the burrowing behaviour, e.g. bioturbation, of L. terrestris, and as such this is circumstantial evidence for commensalism (species interaction, in which one partner benefits while the other is unaffected) between anecic and endogeic earthworm species. Simultaneous burrowing activity of a combined assemblage of both endogeic species, Aporrectodea caliginosa and O. tyrtaeum, was also significantly reduced compared with the particular single treatments. Thus, this seems likely to be a response of interspecific competition and trophic niche separation between endogeic species.