Inefficiency of mustard extraction technique for assessing size and structure of earthworm communities in UK pasture

An assessment of the efficiency of the mustard extraction method to quantify the total earthworm community structure on UK earthworms was carried out on a permanent pasture in Bedfordshire, UK. Earthworms were collected using mustard extraction and control treatments. Numbers and community structure of worms expelled from soils after surface applications of expellants were determined, and underlying soil from each replicate was hand-sorted to recover residual earthworms. The mustard-based treatment was the only method to expel earthworms to the surface, and 35.7% of the extant population emerged. The apparent earthworm community structures expelled indicated that mustard extraction was biased towards large, sexually mature anecic earthworms. This is likely due to the connectivity of burrows of these earthworms to the surface and hence a biased incursion of mustard solution down such channels. The mustard extraction technique is therefore inappropriate where accurate assessment of earthworm communities is required.     

An overview of some tillage impacts on earthworm population abundance and diversity — implications for functioning in soils

Conflicting reports in the literature on the effects of tillage on earthworms are reviewed in the light of their roles in agro-ecosystem functioning. Tillage can change the abundance (by 2–9 times) as well as the composition (diversity) of earthworm populations. The actual impact is dependent on soil factors, climatic conditions and the tillage operations but hitherto this information was seldom provided in research reports. The declines in earthworm population often reported in conventionally tilled soils are associated with undesirable changes in the soil environmental conditions resulting from excessive tillage. Different species of earthworm respond differently to tillage. While the abundance of the deep burrowing species (anecic) tends to decline under tillage, particularly under deep ploughing, endogeic species can actually increase in number especially when there is increased food supply. Under conservation tillage systems, earthworms can potentially play a more important role than under conventional tillage in the functioning of the farming systems because of their abilities to modify the soil physical environment and nutrient cycling. However, adoption of conservation tillage does not automatically result in an optimal earthworm population in terms of abundance and diversity. There are opportunities to introduce more beneficial species to improve the ecological performance of agro-ecosystems. More research is needed to fully understand the ecology of different earthworm species, their interactions and their potential roles in promoting more sustainable farming systems.     

Volume density of earthworm burrows in compacted cores of soil as estimated by direct and indirect methods

After earthworms of the species Aporrectodea caliginosa and A. rosea had burrowed in compacted cores of soil for 68 days the cores were sectioned horizontally. The upper surface of each sectioned layer of soil was photographed before it was dissected and the dimensions of all burrows within the layer measured. Volume densities calculated from the direct measurement of burrows were compared with the values calculated by stereology from data obtained from two image analysis methods, computerised image analysis and point counting with a systematic lattice. The assumption implicit in all stereology calculations was satisfied for this experiment in that the burrows of both species showed no preferred orientation in the compacted soil. Computerised image analysis could not measure the density of all burrows in the photographs because of the lack of contrast between cast-filled burrows and the soil and the complex shapes of the burrows. Although the volume densities of A. caliginosa burrows calculated from point counts were correlated with the values calculated from direct measurement, point counting over-estimated volume densities by two to three times. In the experiment, A. rosea produced too few airfilled burrows for the lattice to detect. The relative ratios of air-filled to cast-filled burrows calculated from the point counts suggested that approximately two-thirds and eight-ninths of the burrows of A. caliginosa and A. rosea, respectively, were filled with casts.     

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

Abstract

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.     

Fate of prions in soil: Degradation of recombinant prion in aqueous extracts from soil and casts of two earthworm species

Prions represent the active agent in transmissible spongiform encephalopathy (TSE) diseases and can remain infective to mammals even after prolonged periods in soil. The influence of mesofauna on prion dispersal and degradation in soil, however, remains unknown. In this study the effect of earthworms on the retention/dissemination of TSEs in soil was evaluated using a model recombinant prion protein (recPrP) and aqueous extracts from soil and fresh casts of two earthworm species, Lumbricus terrestris and Aporrectodea caliginosa. Our results showed that earthworm gut-derived enzymes did not enhance the degradation of recPrP in comparison to soil, even though non-prion related proteolytic activity was higher in fresh worm excrements than in soil samples. Complete degradation of recPrP occurred in the aqueous extracts from all samples within up to 6 days at +15 °C. The proteolytic enzymes responsible for degrading recPrP were inhibited by aprotinin and leupeptin and studies in pure cultures suggested these were most probably of soil microbial origin.     

A vagrant clone in a peregrine species: Phylogeography, high clonal diversity and geographical distribution in the earthworm Aporrectodea trapezoides (Dugès, 1828)

The peregrine lumbricid Aporrectodea trapezoides is originally from the Palaearctic region but is distributed worldwide. Little is known about its clonal diversity or the existence of a pattern of biogeographical diversification of clones. This study aimed to explore the evolutionary history of A. trapezoides by analysing the mitochondrial (COI and COII) and nuclear (28S rRNA and histone H3) DNA sequences of individuals collected in 11 different countries. High clonal diversity was found for this species, with thirty-seven clones clearly divided into two distinct lineages (I and II). The marked biogeographical boundary between these lineages corresponds to the line separating the Eurosiberian and Mediterranean climates in North Spain. Clone 1 was shared by one-third of the earthworms. While this clone was found in most of the sampled localities, the rest of the clones showed geographically-restricted distributions. This clone may have originated in the Mediterranean area of Central Spain. As it was obviously introduced in Australia and it was found in locations occupied by members of both lineages, we hypothesise that it may have also been introduced in other countries and that it could be a general-purpose genotype able to adapt to a wide range of niches.     

A comparison of three earthworm bioassay procedures for the assessment of environmental samples containing hazardous wastes

Summary Three different laboratory earthworm protocols for assessing the potential toxicity of environmental samples were evaluated using Eisenia fetida. The 48-h Contact Test (CT) is a short test and may indicate the presence of water-soluble chemicals. The 14-day Soil Test (ST) is best suited to assess chemical impacts of either known or unknown chemicals in soils. The Giant Axon Conduction Velocity protocol (GACVT) used with either the CT or the ST can detect sublethal neurotoxic effects in shorter periods of time and at lower chemical concentrations than mortality tests. The use of these tests is suggested as an estimate of potential toxicity of environmental soil samples.     

Spatial variability of earthworm populations in a permanent polder grassland

Summary We studied the earthworm distribution in a permanent polder grassland by making two detailed surveys in 1983 and in 1990. Geostatistical procedures were used to investigate the changes in species composition and to determine the dispersal rate. Attention was focused on two soil survey variables closely related to earth-worm distribution, the thickness of the A_h horizon and the number of burrows. The dispersal rate between the two survey dates was 13 m year^–1 compared with 10 m year^–1 before 1983. The difference was attributed either to the development of new population centres due to dispersal by cow's feet or tractor wheels, this altering the spatial dynamics, or to a lag phase in population development in the years following inoculation.     

Allometric estimation of earthworm ash-free dry mass from diameters and lengths of select megascolecid and lumbricid species

We present novel length to ash-free dry mass and preclitellar diameter to ash-free dry mass allometric equations for seven earthworm species from the families Megascolecidae and Lumbricidae, all of which are exotic and most of which are of ecological concern in North America: Eisenia hortensis, Eisenia fetida, Dendrodrilus rubidus, Lumbricus rubellus, Octolasion sp., Amynthas hilgendorfi, and Perionyx excavatus. We also present a length-biomass allometric equation for one enchytraeid, Mesenchytraeus sp. All relationships between length and biomass, and diameter and biomass were statistically significant at the species and family level (P<0.001). The predictive powers of these allometric regressions (as coefficients of determination, r²) were species-specific, and ranged widely from 0.27 to 0.93. Length-biomass regressions provided more predictive power and precision overall than preclitellar diameter-biomass calculations at both the species and the family levels. An ANCOVA followed by orthogonal contrasts determined that, while the slopes of these regressions did not differ significantly between the two earthworm families, significant differences in slopes of length-biomass regressions existed among species within families, indicating the utility of having species-level equations for accurate biomass predictions. With these allometric relationships, we aim to improve the estimation of earthworm biomass in order to facilitate investigations of how exotic-invasive earthworm species impact soil ecosystems.     

Fungal abundance and diversity in earthworm casts and in uningested soil

Earthworm casts and adjacent uningested soil from 30 different locations were compared to determine the abundance and diversity of fungal species. The casts contained larger fungal populations (g^-1 dry soil weight) and numbers of fungal species than the soil. Variations in these parameters between casts and soil were statistically significant (P=0.05). Fungal populations and the number of fungal species in casts and soil also varied significantly (P=0.05) between samples from different locations. A total of 27 fungal species were recorded from the casts and soil. Indices of dominance (0.084 casts; 0.14 soil) and general diversity (2.53 casts; 2.02 soil) demonstrated that the casts displayed more diverse fungal flora than the soil. The diversity of fungal species increased in earthworm casts after passing through the earthworm gut.     

Soil partitioning effect of an earthworm burrow system

Summary Through the simulation of an earthworm burrow system and the calculation of the shortest pathway from the bottom of the system to the surface, using a succession of burrows, it is shown that the borrow system leads to a partition of soil space. The characteristics of the resulting heterogeneity, the size of this partitioning and the length of the shortest pathways are discussed with regard to the functional relationship between the burrow system and the soil.Dedicated to the late Prof. Dr. M. S. Ghilarov     

Influence of earthworm middens on the distribution of soil microarthropods

Summary Earthworm middens and non-midden soil were sampled for microarthropods in a mowed recreational field and and adjacent woodlot site. Samples were taken in fall 1983 and spring 1984. The earthworm middens of the mowed field supported a higher density of micrarthropods (especially Collembola and prostigmatid mites) than adjacent non-midden soil. This positive midden effect in the mowed field was more pronounced in the fall than in the spring. Woodlot earthworm middens examined in the fall had lower densities of microarthropods (especially oribatid mites) than adjacent non-midden soi, but in the spring woodlot middens supported greater densities of microarthropods (especially Collembola) than adjacent, non-midden soil.     

The hormone-like effect of earthworm casts on plant growth

Summary The fertilizing effect of earthworm casts depends on microbial metabolites, mainly growth regulators. The hormone-like effect of earthworm casts is discussed with reference to the literature and ad hoc experiments. When used in plant propagation, earthworm casts promote root initiation and root biomass and increase root percentage. When applied as a casing layer, earthworm casts stimulate carpophore formation in Agaricus bisporus, and N assimilation. When used in horticulture, earthworm casts have a hormone-like effect, influencing the development and precociousness of plants or inhibiting them. These effects are dependent on dose, application time and plant species. In addition, results recorded on dwarfing, stem elongation and precociousness of flowering suggest that the biological effect of earthworm casts is linked to microbial metabolites that influence plant metabolism, growth and development.     

Rapid isocratic HPLC quantification of metallothionein-like proteins as biomarkers for cadmium exposure in the earthworm Eisenia andrei

Metallothioneins (MTs) are regarded as sensitive biomarkers of cadmium (Cd) exposure in a number of organisms. An isocratic high-performance liquid chromatography (HPLC) method using the fluorophore ammonium-7-fluorobenz-2-oxa-1,3-diazole-4-sulfonate (SBD-F) and UV detection was developed for the quantification of MT-like proteins (MTLPs) in earthworm. This method was developed using a rabbit MT (MT-1) standard, and optimized concentrations of reagents including EDTA, SBD-F, and tris(2-carboxyethyl)phosphine (TCEP). The fluoro-tagged MT-1 (SBD-MT) and MTLP (SBD-MTLP) co-eluted at 7.2-7.3 min retention time on HPLC chromatograms. The optimized method was applied to quantify MTLPs in earthworms exposed to increasing concentrations of Cd (0, 2.7, 26.7, and 267.5 μg g⁻¹ of wet artificial soil) for 1-4 weeks. The amounts of MTLPs increased significantly in a dose- and time-dependent manner except in controls and in earthworms exposed to the lowest concentration of Cd. Since earthworm MTLPs are temporal- and dose-responsive to Cd exposure, they can be used as biomarkers to assess the impact of Cd contamination in soils. The method appeared to be rapid, sensitive, and suitable for direct quantification of total earthworm MTs.     

The effects of earthworm functional group diversity on nitrogen dynamics in soils

A novel experimental design, based on the simplex model, was used to study the effects of earthworm functional group diversity on nitrogen dynamics in soils. This mesocosm experiment was carried out at two densities of earthworm and at two levels of food supply. Leachate was collected and analysed over a 20-week period. Soil nitrogen content was measured when the soil columns were destructively sampled on week 30.Results showed the presence of variation among the functional groups in their effects on N dynamics and that both population densities and levels of resource availability were significant. Ammonium concentrations in leachate were generally higher with anéciques and endogées; the opposite was true for nitrate-N, which under certain circumstances was higher with epigées. A significant synergy between the endogées and anéciques was shown in terms of nitrate in soil. Earthworm biomass was important in some instances. For example, larger amounts of soil nitrate were present at higher densities of endogées. A varying effect of food supply was seen for the three functional groups. For example, there were reduced concentrations of nitrate-N in the leachate from the anecic monocultures at low levels of food supply, while increased amounts were leached from the epigées at low food supply. Greater concentrations of ammonium-N were leached from anéciques monocultures at low levels of food supply. Increased food supply resulted in increased amounts of soil nitrate-N in monocultures of both epigées and endogées. It was apparent that nitrogen transformations and amounts available in soil water are dependant on the composition of the earthworm community.