Assessment of the burrow system of Lumbricus terrestris, Aporrectodea giardi, and Aporrectodea caliginosa using X-ray computed tomography

Artificially packed soil columns were inoculated with individuals of different earthworm species (Lumbricus terrestris, Aporrectodea giardi or Aporrectodea caliginosa) and placed under controlled conditions in the laboratory. At the end of the incubation period, which lasted 8 months, three-dimensional reconstructions of the burrow system of each species were obtained using X-ray computed tomography. The particular features of the three burrow systems and the differences between them are discussed in terms of density, orientation and distribution of the burrows and the complexity of the network in relation to variations in soil depth and soil density. Received: 5 February 1997     

Competitive interactions affect the growth of Aporrectodea caliginosa and Lumbricus terrestris (Oligochaeta: Lumbricidae) in single- and mixed-species laboratory cultures

Negative interactions between earthworms may arise from high earthworm population densities. Under high populations in the field, niche separation or migration away from competitive pressure may help to regulate a multi-species population to a given level. This may not be possible in laboratory experiments, leading to an increase in competitive interactions which may alter earthworm growth rates and affect decomposition and nutrient mineralization processes. The objective of this experiment was to determine how growth rates of the endogeic earthworm Aporrectodea caliginosa Sav. and the anecic earthworm Lumbricus terrestris L. are affected by increasing population density and container size in both single- and multi-species cultures. Earthworm growth responses were compared in 1-L cylindrical pots containing disturbed soil and in 2.3-L PVC cores containing undisturbed soil. The relationship describing intra- and inter-specific competition was not affected by container type for both species. Nonetheless, decreasing the container size restricted the growth of L. terrestris in both single- and multi-species cultures, but only restricted the growth of A. caliginosa in multi-species cultures. For both species, a population density greater than one individual per litre reduced earthworm growth rates significantly, while weight loss in monocultures occurred when there were more than 10 A. caliginosa, and more than three L. terrestris per litre. Growth rates of both species were restricted in all population density treatments including the lowest of 0.9 individuals per litre. Further work is needed to find the population density at which growth rates are not affected and which may be used as an appropriate population in laboratory pot experiments to measure the effects of earthworms on soil processes and plant growth.     

C and N turnover of fermented residues from biogas plants in soil in the presence of three different earthworm species (Lumbricus terrestris,Aporrectodea longa,Aporrectodea caliginosa)

A soil microcosm experiment was performed to assess (1) the C- and N- turnover of residues from biogas plants in soils in the presence of three earthworm species (Lumbricus terrestris, Aporrectodea longa and Aporrectodea caliginosa) and (2) the resulting changes in soil chemical and microbiological properties when using these residues as fertilizer in comparison to conventional slurry. Earthworms were exposed in soils, fertilized with an equivalent amount of 120 kg of NH₄-N ha^?1 from: (1) conventional cattle slurry and (2) a fermented residue derived from cattle slurry, grass (silage) and maize. Additional treatments without slurry and earthworms were used as controls.There was considerable evidence that soils fertilized by fermented slurry comprised fewer amounts of readily available nutrients for microbial C and N turnover. We observed significant stimulation of microbial biomass, basal respiration and nitrification in treatments with conventional slurry, especially in the presence of earthworms. However, the stimulation of microbial activity by manure and earthworms were significantly lower in treatments with fermented slurry. Moreover, the results showed clear interactions between different earthworm species and manures. While the biomass of the anecic species (L. terrestris and A. longa) increased in both slurry treatments, the biomass of A. caliginosa (endogeic) decreased, with a significantly stronger biomass decline in treatments with fermented slurry. The metabolic quotients revealed microbial stress metabolism in fermented slurry treatments, predominantly in treatments with A. caliginosa. We conclude that particularly A. caliginosa and soil microorganisms competed for labile C sources in treatments with fermented slurry. An application of these residues as fertilizer might result in a reduction of microbial activity in agricultural soils and in a decline of endogeic earthworms.     

Flooding responses of three earthworm species,Allolobophora chlorotica,Aporrectodea caliginosa and Lumbricus rubellus,in a laboratory-controlled environment

To get a better understanding of earthworm’ responses towards flooding, three laboratory experiments were performed with the species Allolobophora chlorotica, Aporrectodea caliginosa and Lumbricus rubellus.Flooding response was determined in a pot experiment, in which the earthworms were incubated for 42 days in flooded or non-flooded soil, with or without heavy metal pollution. To determine moisture preference, earthworms were incubated for 9 days in aquaria with five compartments, containing soil with a moisture gradient (%, w/w), ranging from 35%, 45% (field capacity), 55%, 65% (saturated) to 65%+ (saturated and an extra water layer). Effects on earthworm health were studied by incubating earthworms of each species for 42 days in soil with the same range of moisture contents and determining the dry/wet weight ratio and dry weight gain as an indication of earthworm health.A. chlorotica was tolerant to water, although the worms tended to escape from flooded soil. Their health was significantly lower in the flooded soils (P<0.05). A. caliginosa showed little response to flooding. This species, however, was affected by the heavy metal pollution in the pot experiment. L. rubellus was sensitive towards flooding, with escape and avoidance behaviour being the main mechanism of survival. This species was able to survive when forced to stay in flooded soil for at least 42 days, but this significantly reduced its health (P<0.05).These results suggest that earthworms are able to survive in inundated soils, but there are large differences between species in response to flooding conditions.     

Comparisons of metal accumulation and excretion kinetics in earthworms (Eisenia fetida) exposed to contaminated field and laboratory soils

The uptake and excretion kinetics of cadmium, copper, lead and zinc were studied for Eisenia fetida exposed to mixtures of these metals in field and OECD artificial soil. Body burdens in worms exposed to all contaminated soils increased over the duration of the experiment. Highest accumulation rates were for worms exposed to the most polluted soils. Pronounced differences were found in the uptake and excretion patterns for essential and non-essential elements (particularly in field soils). For cadmium and lead (non-essential), an equilibrium plateau was not reached during the uptake study and slow excretion was found on transfer of worms to clean soil. For copper and zinc (essential), fast initial uptake was followed by equilibrium after only a few days exposure. Rapid excretion was found after transfer to clean soil, with half-lives of less than 1 day for both metals. A previous study of the effects of metals on worms exposed in OECD and field soils had indicated a higher toxicity in the artificial medium. Thus, in the present study, it was anticipated that greater toxicity would be reflected by increased body burdens for worms in OECD soil. This was, however, not the case. Explanations are given that might account for the fact that the greater toxicity in OECD soil is not invariably accompanied by higher metal burdens. These include the presence of high concentrations of very toxic and highly available ions in laboratory tests and potential differences in the importance of soluble and total metal concentration for determining toxicity and body burdens.     

Mercury methylation,uptake and bioaccumulation by the earthworm Lumbricus terrestris (Oligochaeta)

To date, most studies about mercury (Hg) methylation and bioaccumulation have focused on aquatic ecosystems. In contrast, information regarding the biogeochemical cycle of Hg in terrestrial ecosystems is scarce. Considering the relevance of earthworms in soils, it is very important to study their role in the bioaccumulation and transformation of Hg species (inorganic Hg, IHg, and monomethylmercury, MeHg). The aim of this experimental study was to compare the uptake and bioaccumulation of MeHg and IHg in the earthworm Lumbricus terrestris exposed to soils freshly spiked with inorganic Hg as well as historically contaminated soils. The study consisted of a 28-day uptake phase in Hg (spiked and natural) contaminated and non-contaminated soils followed by a 14-day depuration phase in non-contaminated soils. Soils were characterized by determining not only Hg concentrations (total Hg, MeHg and acid-labile Hg) but also analysed for other physicochemical parameters that can influence the fate of Hg within the earthworm–soil system. Mercury species were determined in earthworms (whole organism) exposed to Hg contaminated and non-contaminated soils. Mercury availability in soils seems to be the main factor controlling the uptake and bioaccumulation of Hg species because, according to kinetic data, the spiked IHg was more readily assimilated and methylated by earthworms. Bioaccumulation factors (BAFs) for MeHg and total Hg were also higher in spiked than in naturally Hg-contaminated soils. In addition, BAFs for MeHg (ranging from 0.8 to 17.3) were higher than those for total Hg (between 0.02 and 0.62) which suggests that MeHg was more easily bioaccumulated by this earthworm species and also that earthworms may actively contribute to MeHg production in soils.     

The earthworm (Aporrectodea caliginosa) primes the release of mobile and available micronutrients in soil

The objectives of our study were to quantify the impact of endogeic earthworms Aporrectodea caliginosa (Savigny) on iron (Fe), manganese (Mn) and zinc (Zn) mobility and availability in soil. Dried rye straw (Cecale cereale L.), clover aboveground parts (Trifolium pratense L.) or calcium carbonate were added to determine the effects on soil micronutrient mobility. To test the importance of soil–water saturation mediated by earthworms, soil samples were modified to 60% (control) and 100% (as in casts) water holding capacity (WHC). To assess availability of micronutrients, a cucumber plant (Cucumis sativus L.) bioassay were used. Earthworm casts had generally higher amounts of water-soluble micronutrients compared with bulk soils regardless of their moisture contents. The increased micronutrient mobility was more pronounced in casts from soil samples amended with plant residues (especially with straw) and was significantly higher than mobility in control soil for at least 1 week after the casts were deposited. Pre-incubation of soils amended with clover or straw with living earthworms for 4 weeks produced an increase in both shoot biomass and translocation rate of micronutrients (Mn, Zn) into xylem sap of cucumber compared to soils not worked by earthworms. The earthworm-mediated plant performances were determined 4 weeks after the earthworms were removed. The results demonstrated that earthworms can significantly impact the formation of mobile and available micronutrients in a soil. The relationship between micronutrient availability to cucumber plants and earthworm contribution to nitrogen (N) mineralization and micronutrient mobility are discussed.     

Moisture preferences,growth and reproduction of the compost worm Eisenia fetida (Oligochaeta)

Summary Although moisture requirements of Eisenia fetida are considered to be generally known, very few in-depth studies have been performed. The moisture preferences of juveniles as well as adults of this species were determined in moisture towers containing cow manure with a particle size bigger than 500 and smaller than 1000 m and an organic matter content of 54%. The clitellate worms showed a wider preference range than the juveniles but deposited most of their cocoons within the narrow range of 65%–70% moisture — a moisture range preferred by 80% of the juveniles. Growth studies of newly hatched worms at various moisture levels over a period of 90 days showed that growth rate and final biomass were influenced by moisture availability with a very low rate of growth at low as well as at high moisture levels. The change in biomass of clitellate specimens as well as their consecutively produced cocoons were monitored at different moisture levels. A clear relationship between mass of cocoons and biomass of the producing worms was established at presumably favourable moisture conditions. Furthermore, the relation between cocoon mass and the production rate of cocoons was also determined, which showed that cocoon mass increased concomitantly with increase in cocoon production. The study also showed that clitellum development was increased at moisture levels above 64%. The onset of cocoon production was, however, earliest at slightly lower moisture levels, from which it is concluded that the optimal moisture level for growth and development of clitella are not necessarily optimal for the production of cocoons.Dedicated to the late Prof. Dr. M.S. Ghilarov     

Chronic and reproductive toxicity of cadmium,zinc, and lead in binary and tertiary mixtures to the earthworm (Eisenia fetida)

Journal of Soils and Sediments - The presence of one metal can alter the toxicity of another metal by having an additive, synergistic, or antagonistic impact. Mixed metal pollution has clear...     

The response of Aporrectodea rosea and Aporrectodea trapezoides (Oligochaeta: Lubricidae) to moisture gradients in three soil types in the laboratory

The question of whether the response of earthworms to soil moisture is governed by their reaction to soil wetness (moisture content) or to soil water energy (matric suction) was examined in two species of earthworm using moisture gradients in three contrasting soil types with clay contents varying from 4 to 39%. Gravimetric moisture gradients ranging over 5–30% were established in horizontal cores comprising 12 or 14 sections containing loosely packed soil. Earthworms were introduced to each section at the beginning of each experiment. The earthworms moved from sections containing dry soil into adjacent sections containing moister soil. Clear effects were evident after 6 h but these became more obvious after 96 h. For the earthworm Aporrectodea rosea, the threshold soil mositure level at which earthworms were induced to move away from dry soil was a matric suction of about 300 kPa (pF 3.4) and was independent of soil type. In contrast, for A. trapezoides, the threshold soil moisture varied with soil type (sandy loam 15 kPa, loam 25 kPa, clay 300 kPa). We conclude that, for the earthworm A. rosea, matric suction and not water content of soil provided the cue by which the earthworm recognized dry soil. For A. trapezoides, there was an interaction between matric suction and soil type in which the response of A. trapezoides to soil moisture varied with soil texture and the threshold for avoidance of dry soil ranged from a matric suction of 300 kPa (20% w/w) in clay to 15 kPa (10% w/w) in sandy loam.     

Microfungal communities in soil,litter and casts of Lumbricus terrestris L. (Lumbricidae): a laboratory experiment

The anecic earthworm Lumbricus terrestris L. was kept in laboratory microcosms containing beech forest soil without litter, with beech leaf litter or with lime leaf litter. The structure of microfungal communities in soil, litter and fresh and aged (100 days) earthworm faeces was analysed using the washing and plating technique. The passage of mineral soil through the gut of L. terrestris affected the structure of the fungal community only little. In contrast, in the litter treatments the structure of the fungal community in fresh earthworm casts significantly differed from that in soil and litter. The majority of soil and litter inhabiting fungi survived passage through the gut of L. terrestris and the fungal community in casts consisted of a mixture of soil and litter inhabiting fungi. However, the frequency of Cladosporium spp., Alternaria spp., Absidia spp., and other taxa was strongly reduced in fresh casts. The degree of colonization of litter particles (number of isolates per number of plated particles) also decreased, but some fungi (mainly Trichoderma spp.) benefited from gut passage and flourished in fresh casts. During ageing of cast material the dominance structure of the fungal community changed. Both the degree of colonization of organic particles and the species diversity increased and approached that in soil. However, the structure of the fungal community in casts remained cast specific even after 100 days of incubation. It is concluded that the feeding and burrowing activity of L. terrestris accelerates the colonization of litter by the edaphic mycoflora but also extends the range of occurrence of litter-associated fungi into mineral soil layers.     

Growth and survival of Eisenia fetida (Sav.) (Oligochaeta: Lumbricidae) in relation to temperature,moisture and presence of Enchytraeus albidus (Henle) (Enchytraeidae)

Summary The aim of this study was to investigate the environmental requirements of Eisenia fetida (Lumbricidae) and its relation to Enchytraeus albidus (Enchytraeidae). Specimens of Eisenia fetida were cultured at two different temperatures (15°C and 25°C) and moisture conditions (50% and 80%) in presence or absence of Enchytraeus albidus. Eisenia fetida grew best at the higher temperature and amount of moisture. Enchytraeus albidus impaired the growth of Eisenia fetida at the higher temperature. When Enchytraeus albidus was present, the mortality of Eisenia fetida increased.Interaction between Eisenia fetida and Enchytraeus albidus was shown, although the mechanisms remain unclear. These species, coexisting in the same habitat (compost), appear to have slightly different niches: Eisenia fetida favours warmer, moister conditions than Enchytraeus albidus.Dedicated to the late Prof.Dr. M.S. Ghilarov     

Leaf-litter consumption and assimilation by juveniles of Lumbricus terrestris L. (Oligochaeta,Lumbricidae) under different environmental conditions

Summary The rate of consumption of dandelion leaves per g earthworm dry weight per week was described by non-linear functions of soil temperature, soil water potential, and food availability. The optimum temperature and soil water potential for food consumption are about 22°C and-7 kPa, respectively. Zero consumption occurred at about-40 kPa. Food consumption increased with greater food availability, but only up to 1.05 (dandelion) and 1.23 (grass) g dry weight per g earthworm dry weight per week at 15°C. A general consumption function to account for all three environmental factors is given. The assimilation rate per g earthworm dry weight per week was defined as the sum of the growth rate and the maintenance rate. Maintenance was calculated according to respiratory measurements reported previously, whereas growth was measured. High temperatures and limiting environmental conditions, such as a low food availability and a low soil water potential, led to an increase in the assimilation efficiency of Lumbricus terrestris. At-7 kPa and 15°C, L. terrestris assimilated 55 and 43% of the ingested dandelion if 0.25 and 1.0 g dry weight of food was available per g earthworm dry weight per week, respectively. it is concluded that L. terrestris has a strong, direct effect on the decomposition of highly palatable plant materials.     

Interaction between tolerance and 70 kDa stress protein (hsp70) induction in collembolan populations exposed to long-term metal pollution

Induction of the 70 kDa stress proteins (hsp70) as a marker for cellular stress response was investigated in two species of Collembola from a metal concentration gradient near a brass mill in the vicinity of Gusum, Sweden. In the field, populations of Orchesella bifasciata (Nicolet 1841) in the middle of the gradient, which ranged from about 60 to 3800 mg of Zn+Cu per kg dry wt. litter, had 40% higher hsp70 levels than populations from the least and most contaminated sites, but differences were not significant. All but one of the populations, inhabiting a severely polluted area, approached lower hsp70 values when they were fed algae containing very high metal concentrations; the hsp70 level in specimens from the control site exposed to polluted algae was below the detection limit, most probably due to pathological cell damage. The hsp70 levels in specimens from contaminated sites with the highest in situ hsp70 levels could not be distinguished from those of control site individuals after they were reared on litter from the control site, and the hsp70 level of control site individuals increased by nearly 100% when they were reared on litter from one of the contaminated sites. Tomocerus flavescens (Tullberg 1871) had higher hsp70 levels than O. bifasciata at the contaminated sites but responded similarly to the experimental treatments. A model is presented to interpret the observations as the result of the dual role of hsp70 to maintain cellular protein homeostasis and to stabilise protein folding in metal tolerant specimens. Differences in tolerance between individuals and heterogeneous distribution of metals in the litter may account for the large intraspecific variability found in hsp70 levels.     

Effects-based Assays in the Earthworm Aporrectodea caliginosa: Their Utilisation for Evaluation of Contaminated Sites before and after Remediation (8 pp)

Goal, Scope and Background   In a preliminary ecological risk assessment, potential adverse effects of contaminants are often evaluated by measuring chemical residues and comparing these with regulatory guidelines. However limitations with this approach with regards to establishing actual effects have resulted in the increasing usage of sublethal effects-based assays, including biomarkers, to evaluate the hazard posed by contaminants in the environment. In this study a number of effects-based endpoints in the earthworm Aporrectodea caliginosa were evaluated to determine their comparative sensitivity for assessment of adverse effects of soil contaminated with petroleum hydrocarbons. Methods   Adult and juvenile earthworms were exposed for 4 weeks to sublethal concentrations of soil collected before and after remediation of a petroleum-contaminated site. A suite of endpoints were measured in these earthworms, including mortality, fecundity, growth, and juvenile maturation, and two less traditional endpoints, the biomarker, the neutral red retention assay (NRRA) and an avoidance behaviour test. Results and Discussion   Cocoon viability in this species is not a reliable parameter to measure, due to low viability in controls and a high coefficient of variation. Growth in adult earthworms was a more sensitive parameter than cocoon production. Maturation and growth of juveniles have been proposed as more sensitive endpoints than adult cocoon production and growth respectively. This was not apparent in the growth parameters, but maturation of juveniles did appear to be more sensitive than cocoon production by adults. The NRRA was a more sensitive parameter than cocoon production, and the NRRA and growth were both affected at the lowest concentration tested. The NRRA response appeared to be more sensitive than growth, but NRRT was only evaluated in one soil only, while the other parameters were assessed in two soils. However, the NRRA has previously been found to be more sensitive than growth after exposure to a number of contaminants. The avoidance behaviour assay exhibited similar sensitivity to growth and fecundity and could therefore be useful as a simple pre-screening test. Conclusion   The chronic endpoints, growth, cocoon production, and juvenile maturation parameters, were all sensitive endpoints for detecting exposure to the petroleum-hydrocarbon-contaminated soil. The NRRA was the most sensitive of the endpoints assessed and could be used as an early-warning indicator to predict adverse impacts. Avoidance behaviour could be used as a simple pre-screening test to evaluate contaminated soils prior to more extensive and invasive testing. Recommendations and Perspective   Measuring chemical concentrations in environmental samples is not always useful, as the toxicological impacts of exposure to these concentrations are not always discernible. However, the use of effects-based endpoints, either in situ or in the laboratory using laboratory-reared earthworms, can account for the bioavailability of chemicals in the soil, and can therefore provide information on the toxicological impacts of exposure. The assays tested in this research were sensitive indicators of exposure, and therefore can be used to determine potential ecological risks at contaminated sites and to monitor the progress of remediation at these sites.     

Modifications to a defined medium for the study of the biology and toxicology of the earthworm Eisenia fetida (Oligochaeta)

Defined and standardised media for the investigation of growth and reproduction of earthworms from a juvenile stage have been developed, but still retain a measure of components that are difficult to characterise completely. A defined medium, based on vermiculate, cellulose, humic acid and other components that are commercially available, and that supports growth and reproduction of E. fetida, added as juveniles, has previously been developed. However, one of the nutrients is not available anymore, and modifications were required. A series of various combinations were evaluated using commercially available nutrients such as fatty acids, organic phosphates and oxy-humic acids. All of the media supported growth (excepting one containing creatinine), but cocoons were only produced in some. It was shown that the growth and reproduction of E. fetida could be studied in a defined medium for up to 70 days (starting with 20-day old juveniles) without additional feeding. The various defined media reported here can be adopted to study specific aspects of earthworm biology and ecotoxicology in the laboratory, but would not replace the existing OECD methods.     

外源有机酸对蚯蚓Zn积累的影响及毒性研究

为研究外源有机酸是否会增加土壤动物蚯蚓对重金属的吸收,从而加剧重金属对土壤生态系统的危害,采用溶液法,以锌为目标污染物,研究添加有机酸(乙酸、草酸、柠檬酸和EDTA)后,重金属对蚯蚓的毒害效应。结果表明,有机酸能有效缓解Zn对蚯蚓的毒性,缓解强弱顺序为EDTA柠檬酸草酸乙酸,主要表现为蚯蚓死亡率降低。暴露在Zn浓度为5,10,15 mg/L的溶液中时,死亡率分别为20%,55%,83.75%,随着有机酸浓度增加,蚯蚓死亡率下降越显著;抗氧化酶(SOD、CAT)和丙二醛(MDA)含量下降,不同的有机酸对蚯蚓SOD、CAT活性的影响不一,MDA含量则有明显的下降趋势,甚至接近于对照水平。这主要是由于有机酸抑制了蚯蚓对Zn的富集,有机酸的络合作用改变了Zn的亚细胞分布,E(胞残渣)组分的比例下降,而H(热稳定组分)组分上升,从而降低了重金属所引起的毒害。因此,有机酸在控制重金属的生物可利用性方面具有重要作用。     

Microbial communities of Lumbricus terrestris L. middens: structure, activity, and changes through time in relation to earthworm presence

Background, aim, and scope  Earthworms make a major contribution to decomposition in ecosystems where they are present, mainly acting in the drilosphere, that is, galleries, burrows, casts, and middens. Earthworm middens are hot-spots of microbial activity and nutrient dynamics and represent a suitable model for studying earthworm-mediated influences on soil microbial communities by alteration of the patch structure of the microbial environment. We studied the structure and activity of the microbial communities in the soil system formed by middens of Lumbricus terrestris and the soil below and surrounding them and the role of earthworms in maintaining these structures through time. Material and methods  We set up an experiment in which middens were either left (control) or removed from their original place (translocated) and left in a nearby area free of earthworm activity for 2 months. After 1 and 2 months we sampled middens, soil below them, and surrounding soil. We analyzed the phospholipid fatty acid (PLFA) profiles and measured respiratory fluxes of CO₂ and CH₄. Results  Microbial communities of middens clearly differed from those of soil below and surrounding soil samples, showing higher bacterial and fungal PLFAs (p < 0.0001 and p < 0.01, respectively); furthermore, changes in microbial communities were stronger in control middens than in translocated middens. Moreover, gram positive and negative bacterial PLFAs were greater in translocated than control middens (p < 0.0001 and p < 0.001, respectively), as well as total organic carbon (p < 0.001). Microbial activity was higher in middens than in soil below and surrounding soil samples both for CO₂ (p < 0.0001) and CH₄ (p < 0.0001). Discussion  Soil bioturbation by the earthworm L. terrestris was strong in their middens, but there was not any effect on soil below and surrounding soil. Microbial communities of middens maintain their biomass and activity when earthworms were not present, whereas they decreased their biomass and increased their activity when earthworms were present. Conclusions  Earthworms strongly enhanced microbial activity measured as CO₂ production in middens, which indicates that there are hot spots for soil microbial dynamics and increasing habitat heterogeneity for soil microorganisms. Moreover, our data strongly support the fact that the impact of this earthworm species in this soil is restricted to their middens and increasing soil heterogeneity. Recommendations and perspectives  Our data indicate that it is not clear if earthworms enhance or depress microbial communities of middens since the microbial activity increased, but did not modify their biomass and this was not dependent on soil organic C content. These results indicate no competence for C pools between this anecic earthworm and microorganisms, which has been found for other earthworm species, mainly endogeics. Conversely, they suggest some type of facilitation due to the release of additional nutrient pools in middens when earthworms are present, through the digestion of middens' material or the addition of casts produced from other food sources.