Aporrectodea Giardi Research Articles

Evaluation the Toxicity of Heavy Metal Mixtures in Anecic Earthworms (Aporrectodea giardi).

Using earthworms as bioindicators of heavy metal contamination in soils is a relevant tool for environmental risk monitoring. This study examines the combined effects of four distinct concentrations mixtures (M1, M2, M3 and M4) containing Cd, Cr, Cu, Ni, Fe and Mn on Aporrectodea giardi earthworms after 12 and 24days (12D/24D) of exposure via the monitoring of certain biomarkers of stress including total protein content, glutathione (GSH), metallothionein (MT), catalase and lipoxygenase (LOX) activities. The results show a decrease in the total protein level for the M3 mixture after 24D, whereas it increases for all other treatments regardless of exposure time. Glutathione and metallothionine levels increased for M2 and M3 and decreased for M1 and M4 after 12D; they increased after 24D for all the mixtures. Regarding enzyme activities, catalase activity was decreased for all the treatments unless for M3 (P > 0.05). However, LOX increased for M1, M2 and M4 except for M3 after 12D, when inhibition of this biomarker was observed. LOX activity was inhibited for all the mixtures at the end of the treatment. All the mixtures generated oxidative stress in Aporrectodea giardi, which is minimized by increasing MT levels to remove the metal ions and triggering the antioxidant system, composed primarily of GSH and LOX to restore cellular homeostasis. These findings suggest that the species Aporrectodea giardi could be an excellent candidate for ecotoxicological risk assessment of soils contaminated by metal mixtures and it can be used in bioremediation for its fitness which allows it to tolerate high concentrations of metal mixtures.

Two distinct ecological behaviours within anecic earthworm species in temperate climates

Earthworm species in temperate climates have usually been classified into three main ecological categories according to their morpho-anatomical, physiological and ecological traits: epigeic, endogeic and anecic. However, since these ecological categories were first defined, many studies on the ecological traits of widespread anecic species: Lumbricus centralis (Bouché, 1972), Lumbricus terrestris (Linnaeus, 1758), Aporrectodea longa longa (Ude, 1885) and Aporrectodea giardi (Ribaucourt, 1901) have revealed two distinct feeding behaviours, as well as differences in their growth rates and burrowing behaviour. In this review we highlight that within anecic earthworms, Lumbricus anecic species (here after “LAS”) mainly consume fresh plant-derived materials on the soil surface modifying the quantity and spatial organisation of said materials. In contrast, Aporrectodea anecic species (here after “AAS”) consume mainly aged plant-derived materials already incorporated into the soil and only a small proportion of surface-available plant-derived materials. Furthermore, the AAS have a denser and more complex burrow network than LAS. This suggests that AAS burrow into the soil to search for soil organic matter incorporated in the soil whereas the LAS essentially focus on burying the surface litter into their burrow. Consequently, LAS seem to benefit from easily assimilated substrates, grow faster and reach maturity in a shorter time span than AAS species. This distinction between anecic Lumbricus and Aporrectodea earthworms is expected to have different consequences for soil trophic network and soil functioning such as carbon and nutrient cyclings, water regulation and soil structure maintenance.

Toxicological and Histopathological Impact of Insecticide Acetamiprid and Agricultural Fertilizer Activeg on Earthworm (Aporrectodea giardi)

Earthworms provide important information about the environmental risks so serve as useful biological indicators of soil contamination. The present study was aimed to assess the impact of insecticide ‘Acetamiprid’ and fertilizer ‘Activeg’ (widely used fertilizer in Algeria), on earthworm Aporrectodea giardi. The earthworms were subjected to four different doses of Acetamiprid viz., 25, 50, 100 and 200 mg 500 mg-1 soil for four periods viz., 24, 48, 72 and 96 h. The toxicological and histopathological evaluations were also conducted. Based on physiochemical analysis, soil proved to be a convenient environment for earthworms. The soil was sandy loam in texture, neutral in pH and rich in organic matter (8.93%) with a field capacity of 19.37. Earthworm mortality showed increase with increase in Acetamiprid dose with LD50 value varying from 89.03 to 240.23 mg kg-1. Histological studies revealed marked alterations in epidermal and intestinal cells. Earthworm exposed to fertilizer Activeg showed neither earthworm mortality nor any toxicological effects on their tissue structure. The study confirmed the deleterious effect of Actamiprid on A. giardi, so it should be used with prudence in order to save the soil animal fauna.

A two years field experiment to assess the impact of two fungicides on earthworm communities and their recovery

Recent EFSA (European Food Safety Authority) reports highlighted that the ecological risk assessment of pesticides needed to go further by taking more into account the impacts of chemicals on biodiversity under field conditions. We assessed the effects of two commercial formulations of fungicides separately and in mixture, i.e., Cuprafor Micro® (containing 500 g kg−1 copper oxychloride) at 4 (C1, corresponding to 3.1 mg kg−1 dry soil of copper) and 40 kg ha−1 (C10), and Swing® Gold (50 g L−1 epoxiconazole EPX and 133 g L−1 dimoxystrobin DMX) at one (D1, 5.81 10−2 and 1.55 10−1 mg kg−1 dry soil of EPX and DMX, respectively) and ten times (D10) the recommended field rate, on earthworms at 1, 6, 12, 18 and 24 months after the application following the international ISO standard no. 11268-3 to determine the effects on earthworms in field situations. The D10 treatment significantly reduced the species diversity (Shannon diversity index, 54% of the control), anecic abundance (29% of the control), and total biomass (49% of the control) over the first 18 months of experiment. The Shannon diversity index also decreased in the mixture treatment (both fungicides at the recommended dose) at 1 and 6 months after the first application (68% of the control at both sampling dates), and in C10 (78% of the control) at 18 months compared with the control. Lumbricus terrestris, Aporrectodea caliginosa, Aporrectodea giardi, Aporrectodea longa, and Allolobophora chlorotica were (in decreasing order) the most sensitive species to the tested fungicides. This study not only addressed field ecotoxicological effects of fungicides at the community level and ecological recovery, but it also pinpointed some methodological weaknesses (e.g., regarding fungicide concentrations in soil and statistics) of the guideline to determine the effects on earthworms in field situations.

Response of temperate anecic earthworm individual biomass to species interactions

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.

The dispersal of the earthworm Aporrectodea giardi responds faster to habitat quality than to cumulative use of habitat in experimental conditions

The study of the spatial distribution of soil organisms is one of the key research areas for understanding soil functioning. However, we still know little about the role of dispersal in the distribution of soil organisms such as earthworms. Critically, the relative strength of the external factors that trigger dispersal movements has not been documented. In this work, we test the relative importance of habitat quality and the cumulative use of habitat as drivers of dispersal of an anecic earthworm (Aporrectodea giardi) by observing their dispersal rates over 1, 2, 4, 8, 16 and 32 days. The results suggest that cumulative dispersal rates were higher and reached a maximum value more rapidly when individuals were introduced into unsuitable rather than suitable soil. This suggests that earthworm dispersal responded more rapidly and this response was more pronounced with respect to the cumulative use of the habitat. It seemed that there were two types of dispersal: one triggered quickly to escape unsuitable conditions and another in response to a cumulative use of the habitat.

Application of X-ray tomography to evaluate liming impact on earthworm burrowing activity in an acidic forest soil under laboratory conditions

This study investigated the burrowing activity responses of two earthworm species (Aporrectodea caliginosa and Aporrectodea giardi) with contrasting ecological strategies to lime application under laboratory conditions. The impact of liming on earthworm burrowing activity was measured in 25-cm, repacked soil cores sampled from an acidic forest of the Vosges Mountains (North-eastern, France). Soil treatments included: (i) a non-limed field soil (OH horizon, 0–5cm, pH=3.8; A horizon, 5–25cm, pH=4.5) that had received decades of atmospheric acidic deposition, (ii) an in situ limed soil (OH, 0–5cm, pH=4.1; A horizon, 5–25cm, pH=4.7) that had been limed at 2.5tha−1 six years prior to sampling for this experiment and (iii) an in vitro non-limed field OH horizon limed in the laboratory to 2.5tha−1 equivalence over a non-limed A horizon (OH, 0–5cm of core, pH=5.4; A horizon, 5–25cm, pH=4.5). After 9weeks of incubation, X-ray computed tomography was used to characterize the burrow system of the two earthworm species for each of the three soil treatments. Soil pH, amount of surface casts, and earthworm biomass were also measured. All earthworms were alive at the end of the experiment. A. giardi lost significantly less weight and produced more surface casts than A. caliginosa. The in vitro liming increased total burrow volume and length of A. giardi. Liming had no effect on A. caliginosa biomass, surface cast production or total burrow system volume and length. However, in vitro liming significantly enhanced A. caliginosa burrowing activity in the OH horizon. Finally, for both species, the burrowing activity was not improved into the in situ limed treatment.

Earthworm activity alters geogenic arsenic and soil nutrient dynamics

Abstract Environmental pollution due to arsenic (As) has been well studied and most investigations have focused on inorganic As coming from industrial areas. However, the natural rock-borne contamination of this metalloid has been underestimated and few studies focusing on annelids have addressed the question of geogenic As distribution in earthworm biogenic structures. Our study concentrated on the earthworm drilosphere and investigated the distribution of As in surface-casts and burrow-linings. In this context, we assumed that the concentration of geogenic As should differ in biogenic structures (faeces, burrow-linings) compared to non-ingested soil. To test our hypothesis, microcosms in controlled conditions were filled with soil containing 157 mg As kg −1 from a geogenic origin. The soil was collected from a meadow in the Jura Mountains. The earthworm Aporrectodea giardi was selected because of its natural presence in the meadow and its anecic behaviour. We found that while earthworm surface-casts were enriched in carbon, nitrogen and available phosphorus compared to non-ingested soil, no enrichment was found for geogenic arsenic. The coarse sand fraction contained 3.5 times more As than silt and clay fractions but no significant difference existed between surface-casts and non-ingested soil. Iron was shown to be the main mineral bearing phase for As and predominated in the coarse sand fraction. No retention effect of organic matter on geogenic arsenic was observed. In conclusion, it appeared that geogenic As did not affect biological components and environmental aspects. These findings are particularly encouraging considering that most of the environments at an altitude of 1330 m in the Jura Mountains have exposed rocks, especially on meadows that are regularly grazed by cattle.

Movement response of Collembola to the excreta of two earthworm species: Importance of ammonium content and nitrogen forms

Several studies reported variable effects of earthworms on microarthropod density and variety. The present study tests the attraction of seven collembolan species belonging to four families, to the excreta of two earthworm species belonging to two families and two ecological categories, Aporrectodea giardi and Hormogaster elisae. Our objectives were (1) to better understand the impact of earthworms on the composition and density of Collembola communities, and (2) to dissect mechanisms involved in the attraction. Experiments were performed in Petri dishes containing two half-disks of filter paper, one with earthworm excreta, i.e. casts or a mix of mucus and urine, and the other with natural soil aggregates or water, respectively. Collembola were introduced half-way between the two half-disks and their number was counted on each half-disk and compared over 140 min. The content of ammonium in casts and mucus-urine of both earthworm species was analyzed to determine whether it altered the responses of Collembola faced with different types of earthworm excreta. The behaviour of Collembola varied strongly among the seven collembolan species, and with type of excreta and earthworm species. Six collembolan species were attracted to the mucus and urine of at least one earthworm species. The mucus-urine mixture of A. giardi, with low ammonium content, was generally more attractive than that of H. elisae, which was even repulsive in some cases, probably because of high levels of ammonium. The attraction to casts of the two earthworm species was less frequent and more variable. Folsomia candida was neither attracted to the casts nor to the mucus and urine of any earthworm species. Therefore, (1) earthworm species with different ecology, and different nitrogen excretion pathway impact differently the behaviour of collembolan species belonging to the same family or arising from the same habitat, and (2) variations in the sensitivity to ammonium among collembolan species partially explain the variable response of Collembola to earthworm excreta.

The effect of tillage type and cropping system on earthworm communities, macroporosity and water infiltration

To test the assumption that changes to earthworm communities subsequently affect macroporosity and then soil water infiltration, we carried out a 3 year study of the earthworm communities in a experimental site having six experimental treatments: 2 tillage management systems and 3 cropping systems. The tillage management was either conventional (CT; annual mouldboard ploughing up to −30 cm depth) or reduced (RT; rotary harrow up to −7 cm depth). The 3 cropping systems were established to obtain a wide range of soil compaction intensities depending on the crop rotations and the rules of decision making. In the spring of 2005, the impact of these different treatments on earthworm induced macroporosity and water infiltration was studied. During the 3 years of observation, tillage management had a significant effect on bulk density (1.27 in CT and 1.49 mg m −3 in RT) whereas cropping system had a significant effect on bulk density in RT plots only. Tillage management did not significantly affect earthworm abundance but significantly influenced the ecological type of earthworms found in each plot (anecic were more abundant in RT). On the contrary cropping system did have a significant negative effect on earthworm abundance (104 and 129 ind. m −2 in the less and most compacted plots, respectively). Significantly higher numbers of Aporrectodea giardi and lower numbers of Aporrectodea caliginosa were found in the most compacted plots. CT affected all classes of porosity leading to a significant decrease in the number of pores and their continuity. Only larger pores, with a diameter superior to 6 mm, however, were adversely affected by soil compaction. Tillage management did not change water infiltration, probably because the increase in macroporosity in RT plots was offset by a significant increase in soil bulk density. However, cropping system had a significant effect on water infiltration (119 vs 79 mm h −1 in the less and most compacted plots, respectively). In RT plots, a significant correlation was observed between larger macropores (diameter > 6 mm) and water infiltration illustrating the potential positive effect of earthworms in these plots.

Experimental evidence for the role of earthworms in compacted soil regeneration based on field observations and results from a semi-field experiment

In laboratory experiments, earthworms are often observed to burrow through compacted soil layers, leading to the general assumption that these animals play a significant role in regenerating compacted soils in agricultural plots. To demonstrate this role under field conditions, the abundance of earthworm macropores inside compacted zones was estimated on plots under reduced (RT) or conventional tillage (CT). Then, different types of compacted zones typically found in CT (plough pan and compacted clods) and RT plots (compacted volume under wheel tracks) were experimentally simulated in wooden boxes, buried in the field and inoculated with different earthworm species. After 6 weeks of incubation, the number of macropores inside the compacted zones was examined. Field observations showed that approximately 10% and 30% of the compacted zones were colonised by at least one macropore in CT and RT plots, respectively. A significantly greater number of anecics was found in RT plots, but we could not conclude that this ecological type of earthworm plays a more major role in the regeneration process in these plots since there were fewer compacted zones and these covered a smaller area in CT. The semi-field experiment provided evidence that earthworm-mediated regeneration of compacted zones is possible and its nature varies between ecological types of earthworm. Lumbricus terrestris, which makes individual burrows that are vertical and deep, was the main species to cross through the plough pan. The other three earthworm species ( Aporrectodea giardi, A. caliginosa and A. rosea) did burrow inside the other types of compacted zones (“wheel tracks” and “compacted clods”). In every case, however, macropore density was far greater in non-compacted zones, illustrating that avoidance of compacted soil by earthworms is important and should be taken into account when extrapolating results from laboratory studies.

Effect of earthworm activity (Aporrectodea giardi) on atrazine adsorption and biodegradation

SummaryWe investigated the influence of earthworm (Aporrectodea giardi) activity on soil properties and on atrazine (AT) adsorption and biodegradation by comparing a coarse‐textured smectite‐free wetland soil (Brittany, France) with the earthworm casts derived from the top horizon of this soil. Casts are characterized by lower pH, are enriched in organic carbon (OC) and clay content, have a larger cation exchange capacity, and a greater exchangeable Ca content. The clay mineralogy of the soil studied and casts is characterized by a muscovite–kaolinite–chlorite association. In addition, the clay fraction of the soil contains lepidocrocite (γ‐FeOOH), which was not found in the casts. Atrazine adsorption isotherms were reasonably well described by the Freundlich equation and were all non‐linear. The mean amounts of adsorbed AT for starting concentrations of 3–30 mg litre−1 ranged from 8 to 34%, being largest in earthworm casts. Soil AT adsorption capacity was well correlated with OC content. Non‐decomposed organic matter present in the coarse size fractions and specific compounds present in earthworm casts (proteins, mono‐ and polysaccharides, polyphenols, sugars, lignin) and microbial and fungal biomass contribute to AT adsorption. Weak electrostatic (physical) sorption of AT on organic compounds and on mineral surfaces prevails. For casts, the formation of additional hydrophobic interactions between AT and SOM is proposed. We also studied AT biodegradation by the model bacterium Pseudomonas sp. strain ADP in the presence of soils or earthworm casts. An enhancement of the AT disappearance rate was observed in the presence of all the solid matrices tested compared with that obtained in an aqueous medium. The biodegradation rate was shown to be dependent not only on the OC content of the solid matrix, but mainly on its composition and structure.

Earthworms and collembola relationships: effects of predatory centipedes and humus forms

Relationships between anecic earthworms ( Lumbricus terrestris and Aporrectodea giardi) and the collembolan species Heteromurus nitidus (Templeton, 1835), which is known to be attracted to earthworms, were investigated in an 8-week laboratory experiment. Our aims were (1) to assess whether earthworms influence the population dynamics of H. nitidus, and (2) to study pathways of influence and how earthworm effects are modified by humus forms and predators. Using microcosms with three defaunated humus forms, then provided with earthworms and predators, we intended to demonstrate that, amongst possible favourable effects of earthworms on springtail populations, earthworm activity may provide greater access and more pathways for springtails to explore soil and avoid predation. We expected that the effects of predators (centipedes) on the abundance of H. nitidus would increase from less (calcic mull) to more (moder) compact soil, and we hypothesized that earthworms would reduce predation pressure on H. nitidus by providing escape routes through increased macroporosity. Humus forms and earthworms only affected the population size of H. nitidus under high predation pressure, when collembolan numbers were higher in calcic mull than in moder, and were increased by the presence of earthworms. These results corroborate the hypothesis that earthworms, by increasing soil macroporosity, improve the escape routes for Collembola and thus evade predation. In moder humus earthworms increased the density of H. nitidus whether predators were present or not, so we cannot exclude that earthworms were also directly beneficial to H. nitidus. However, the hypothesis of a functional relationship mediated by soil macroporosity seems relevant since it was supported by differences observed when considering body size. When two size classes were distinguished within populations of H. nitidus (1) the positive effect of earthworms in moder was observed only on larger Collembola (>1 mm), (2) the density of the larger Collembola was decreased by predation only in moder and not in mull, (3) the effects of predators on the smaller individuals were not influenced by the presence of earthworms whatever the humus form, and was not decreased by the presence of earthworms. Nevertheless, factors other than macroporosity may operate as the presence of earthworms in acidic mull led to an unexplained decrease in the abundance of small-sized H. nitidus.

Impact of soil compaction on earthworm burrow systems using X-ray computed tomography: preliminary study

This study is a first approach of the impact of soil compaction due to trafficking by machinery on earthworm burrow systems. To this end, two experiments were established. In the first one, microcosms were incubated in the laboratory for 70 d with Lumbricus terrestris or Aporrectodea giardi. In the second experiment, soil cores were excavated from a sugar beet field mainly colonised by L. terrestris and Aporrectodea caliginosa. The cores were then artificially compacted at 0.12 MPa or 0.25 MPa (which corresponds to the compaction due to trafficking by machinery in the field) or remained non-compacted. The whole cores were submitted to an X-ray computed tomography scan. This method allowed to compare the characteristics of the entire burrow system (total and mean burrowed length, mean length and number of burrows) and of the burrows themselves (number, area and roundness of pores constituting the burrows) in the compacted and non-compacted cores. The results showed that soil compaction contributes to close numerous pores, reduce mean length of burrows and increase the number of fragmented burrows. We concluded that soil compaction affects to a large extent the functionality of burrow systems by fragmenting them and affecting their continuity. This impact increases with the intensity of compaction. The applied soil compaction mainly affected the burrows located in the upper part of the soil. From a general point of view and especially for the upper part of the cores, horizontal burrows seemed to be more affected by compaction than vertical or oblique ones. Globally, the effects of soil compaction were especially observed at the greatest applied pressure (0.25 MPa). At 0.12 MPa, the damage to the burrows was less obvious.

Earthworm excreta attract soil springtails: laboratory experiments on Heteromurus Nitidus (Collembola: Entomobryidae)

Microarthropods are often found more abundantly in soils with earthworms than in soils without. Earthworms probably create a favourable environment for microarthropods but few studies have aimed to explain this earthworm effect. The soil collembolan (Hexapoda) Heteromurus nitidus, living in soils at pH>5 only and thus rich in earthworms, is particularly attracted by earthworms in humus cores. The effect of earthworms on the distribution of H. nitidus can be mediated either by direct contact or by odour perception. Two experimental designs were used to determine the pathway of attraction. The first set of experiments studied the effect of direct contact with earthworm excreta on the distribution of H. nitidus. The mixture of urine and mucus of the lumbricid earthworms Aporrectodea giardi and Alollobophora chlorotica significantly attracted H. nitidus as compared to deionized water while fresh earthworm casts were not preferred to calcic mull made of older casts. The same experiment involving direct contact with mucus and methyl blue showed that Collembola sucked on mucus/urine, indicating that the interaction of Collembola and earthworms was at least partly trophic. The second experiment demonstrated that H. nitidus was attracted by the odour of Aporrectodea giardi at short distance. The odour of excreta (mucus, urine and casts) of Aporrectodea giardi also attracted H. nitidus but this attraction was weaker and did not occur constantly, possibly due to interactions with light and aggregation pheromones. We conclude that the prominent pathway by which earthworms could attract H. nitidus in the field is through direct contact with earthworm mucus and urine. The acid-intolerant distribution of this species in the field could be partly explained by a trophic interaction with some earthworm species.

Morphological, physical and biochemical characteristics of burrow walls formed by earthworms

The influence of two anecic earthworm species, Lumbricus terrestris and Aporrectodea giardi, on the soil adjacent to their burrows was studied in the laboratory. The morphological, physical and biochemical characteristics of the burrow walls were compared with those of casts and surrounding soil by scanning electron microscopy and measurement of water stable aggregation (WSA), enzymatic activities and elemental content (C and N). For both species, we observed a reduction in porosity in the inner layer and to a lesser extent in the outer layer of burrow walls as compared to the surrounding soil. This is apparently due to the fine texture of subsurface casts constituting the inner walls, and to the compaction occurring during burrow formation and use. In contrast, the WSA of the burrow walls was not increased compared to the surrounding soil. Enzymatic activities and C and N content of burrow walls and casts were enhanced compared to the parent material. The behaviour of earthworms in, e.g. incorporation of litter into burrows, selection of the finest soil particles providing adsorption sites for enzymes, re-using burrows resulting in a frequent input of mucus to the burrow walls, may explain the observed differences. These differences were more or less pronounced depending on the morphoecological characteristics of the earthworms. The results indicate that earthworm burrow walls may influence the movement of water and solutes from channels to soil matrix and vice versa and may also have a great impact on microbial activities.

Interactions between earthworm species in artificial soil cores assessed through the 3D reconstruction of the burrow systems

The aim of this study was to determine the impact of the interactions between different earthworm species on the individual burrowing activity and especially on the characteristics of burrow systems. Towards this end, individuals of different earthworm species ( Lumbricus terrestris, Aporrectodea giardi, A. caliginosa) were inoculated as single or paired species treatments into artificially packed soil columns. After 8 months, the soil columns were scanned by X-ray computed tomography. Three-dimensional skeletons of the burrow systems were then computed to characterise the burrow systems (burrow number, total and mean burrowed length, segment distribution in relation to depth, and rate of branching). Pronounced differences between species were found. L. terrestris built a permanent burrow system characterised by low burrowed length, few connections and low rate of branching. On the contrary, A. giardi and A. caliginosa dug temporary burrow systems. The burrow system of A. giardi was the most interconnected and showed the highest total and mean burrowed lengths. Differences observed between single and paired species treatments mainly concerned the distribution of the burrow system in relation to soil depth in the core and total burrowed length. The burrow system of L. terrestris was much less deep and showed a higher length when the species was incubated together with A. caliginosa. The burrow system of A. caliginosa was much deeper when the worm was cultivated with A. giardi. Differences in the rate of branching were also shown in paired species treatments compared to single species treatments.

Burrowing activity of the earthworms Lumbricus terrestris and Aporrectodea giardi and consequences on C transfers in soil

Two earthworms species, Lumbricus terrestris (epianecic) and Aporrectodea giardi (anecic) were incubated in microcosms with an epigeic 13C-labelled litter for 246 d. At the end of the experiment, different soil compartments (surface casts, walls and peripheries of burrows, and surrounding soil) were sampled for 13C analysis. Two-dimensional images acquired using X-ray computed tomography allowed to estimate the weight of the ‘burrow wall’ and ‘burrow periphery’ compartments which are required to establish C balance. In the case of L. terrestris, the formed structures were more C litter enriched compared to the other species. The permanent character of the burrow system could lead to a high and constant enrichment of the entire burrow system. As consequence, the percentage of C litter in the ‘burrow wall’ and ‘burrow periphery’ compartments was important in spite of their low volume. The denser system developed by A. giardi resulted in C litter dilution in the whole formed structures. The C litter enrichment decreased with the soil depth, but owing to the intensity of the burrowing activity, the C litter transfers into the ‘burrow walls’ and ‘burrow periphery’ were important and the C litter was homogeneously distributed throughout the whole column.

Characterization of the burrow system of the earthworms Lumbricus terrestris and Aporrectodea giardi using X-ray computed tomography and image analysis

The burrow systems of two earthworm species (Lumbricus terrestris and Aporrectodea giardi) were studied in artificially packed soil columns placed in controlled conditions in the laboratory. At the end of the incubation, which lasted 246 days, the burrow systems were characterized on the undisturbed columns using X-ray computed tomography. This method provided a set of digitized images corresponding to horizontal 3-mm-thick sections. The following parameters were measured using image analysis on each section: number of biopores, their volume, and their individual orientation calculated using an elliptical model of the earthworm channel. The profiles of these parameters through the columns showed that the burrow systems of L. terrestris and A. giardi, which are both anecic species, were very different in terms of total volume, number of burrows, burrow orientation and extension with soil depth. These results led us to conclude that the burrow system of L. terrestris can be considered as a permanent structure whereas that of A. giardi is closer to the burrow system of endogeic species.

Effects of four ecological categories of earthworms on carbon transfer in soil

A laboratory experiment was performed to determine the effects of 4 ecological categories of earthworms on the transfer of organic carbon derived from surface litter in different soil compartments (surface casts, below-ground casts, burrow walls and surrounding soil). The earthworm species chosen were Eisenia andrei (epigeic), Lumbricus terrestris (epianecic), Aporrectodea giardi (anecic) and Aporrectodea caliginosa (endogeic). The earthworms were incubated with 13 C -labelled litter in rebuilt soil columns for 246 days. At the end of the experiment, surface casts, below-ground casts and burrow walls were significantly enriched with litter C compared to the control soil and surrounding soil. Surface and below-ground casts were most enriched. About 50% of the total organic C in the surface casts of the epigeic and epianecic species was derived from the litter compared with 40% in the casts of the anecic and endogeic species. Below-ground casts, mainly produced in this study by L. terrestris and A. giardi, were on average enriched with 47.5% of litter C. The litter C enrichment of the burrow wall was high and constant whatever the depth (43.3% organic C derived from the litter on an average) with L. terrestris, whereas it was lower and tended to decrease with soil depth with A. caliginosa and A. giardi. On the other hand, the intensive burrowing activity of the anecic and endogeic species led to an even distribution of the litter C in the soil column whereas with the epianecic species the distribution was more localized.