Earthworm effects on selected physical and chemical properties of soil aggregates

Summary Some physical and chemical properties of 1-to 2-mm aggregates obtained from casts and the burrow-wall material of the earthworm species Lumbricus terrestris, Aporrectodea longa, and Aporrectodea caliginosa were determined in order to show the effects of earthworms on the stabilization of soil aggregates. The results were compared with those of the natural soil from the Ap horizon of a Parabraunerde (Luvisol, FAO). Both the tensile strength and the water stability of aggregates from casts and burrow-wall material were reduced compared with those of the natural aggregates but were increased compared with those of remoulded aggregates. These results indicate that to a great extent existing bonds are destroyed by earthworm ingestion. Nevertheless, earthworm activities are advantageous for the stabilization of reformed aggregates. The coarse sand fraction is reduced by selective ingestion by earthworms. The organic C content is increased by 4.1–21.0% for burrow-wall material and by 21.2–43.0% for casts. The carbonate content of aggregates from casts and burrow-wall material of L. terrestris was reduced by more than 50%, while that of A. longa showed no noticeable changes and that of A. caliginosa was increased by more than 60%. The total content of polysaccharides was increased by 35–87% for casts and by 33–46% for the burrow-wall material of all earthworm species. The most frequently detected monosaccharides were glucose, galactose, and glucosamine. L. terrestris appeared to have the strongest effect on the interparticle bonding of the reformed aggregates, measured both as tensile strength and water stability, followed by A. longa and A. caliginosa.     

A simple and effective method to keep earthworms confined to open-top mesocosms

Earthworms can have a profound effect on a myriad of soil physical, chemical and microbial parameters. To better understand their role in the soil, they are often studied under controlled conditions. However, a persistent problem in such controlled experiments is the ability of earthworms to escape from experimental units with open tops (e.g. for plant growth). Here, we tested whether adhesive hook tape applied to the inside of mesocosms is effective in confining them to their experimental units. A mesocosm study was set up with hook tape treatments (control, one layer, two layers), mesocosm material (polyvinylchloride – PVC, polypropylene – PP) and earthworm species (Lumbricus rubellus (Hoffmeister), Aporrectodea caliginosa (Savigny), Lumbricus terrestris (L.) + Aporrectodea longa (Ude)) as different factors to study the escape of earthworms during 24 h. In the treatments without hook tape, individuals of L. rubellus and A. caliginosa escaped, with highest escape rates (80%) for L. rubellus from the PP mesocosms, and lowest escape rates (20%) for A. caliginosa from the PVC mesocosms. When hook tape was applied, in either one or two layers, no individuals of those species escaped. The two anecic earthworm species, L. terrestris and A. longa did not escape from any mesocosms, irrespective of the presence of hook tape. As not a single earthworm escaped from the hook tape treatments, we conclude that applying hook tape is a simple, inexpensive and effective method to keep earthworms confined to experimental units.     

Factors affecting surface casting behaviour in several species of earthworm

Summary Surface cast production was investigated for several species of earthworms, including some not normally considered to produce surface casts. In single-species culture, the amount of cast material deposited on the surface by different species varied, with Allolobophora chlorotica < Lumbricus rubellus < Aporrectodea caliginosa < Aporrectodea longa. In field communities, results indicated that a single species dominated surface casting activity. The order of species dominance was consistent with the above findings from single-species cultures, if Lumbricus terrestris was considered to be equivalent to Ap. longa.Surface casting is an essential function within earthworm communities which maintains their living space. However, it involves an energy cost and carries a risk of predation. Therefore, there are disadvantages associated with this activity. All of the species studied produced surface casts unless other, usually larger, species were present.     

The development of sustainable earthworm populations at Calvert landfill site,UK

Earthworms Allolobophora chlorotica and Aporrectodea longa were inoculated into Calvert landfill site in spring 1992, in conjunction with the planting of two tree species Alnus glutinosa and Acer pseudoplatanus. Monitoring has taken place over a period of 11 years. Sampling in 2003 revealed that earthworm distribution no longer equated to the inoculation treatments; the worms had spread extensively. The presence of A. glutinosa had a significant effect (p<0ċ01) on earthworm number (mean density 198 m⁻²) and biomass (34 g m⁻²) compared to plots where A. pseudoplatanus had been planted and subsequently died (mean density 118 m⁻²; biomass 21 g m⁻²). Results suggest that tree presence may be critical to earthworm community development. In 2002, the spread of A. chlorotica from the original points of inoculation had reached 60 m with the highest recorded population density at 108 m⁻² with a mass of 18ċ6 g m⁻². A. longa was recorded at a distance of 132 m from the nearest point of inoculation with the highest recorded population density at 70 m⁻² with a mass of 49ċ3 g m⁻², 10 m from the original inoculation grid. Other species recorded (and % of total) were Aporrectodea rosea (0ċ9) Lumbricus castaneus (7ċ4), Eiseniella tetraedra (21ċ5) and Lumbricus rubellus (4ċ5). The two inoculated species, A. chlorotica (40ċ4) and A. longa (25ċ3), accounted for two thirds of the earthworms found on site. The highest earthworm community density was 213 m⁻² with a mass of 73ċ9 g m⁻² at 10 m from original point of inoculation. In 1999, treatments of surface organic matter (OM), in the form of composted green waste, and rotavation were applied to non‐replicated plots of 50 m² with the effects on earthworm distribution and abundance recorded in 2002. Addition of OM alone led to an increase in number and mass (331 m⁻²; 95 g m⁻²) compared to the control (233 m⁻²; 51 g m⁻²), while rotavation alone (111 m⁻²; 36 g m⁻²) had a detrimental effect over the given time period. This long‐term monitoring programme has demonstrated the development of sustainable earthworm communities on a landfill site. Natural nutrient accumulation and addition of OM on or into the soil‐forming material appeared to assist this process. This work may help to inform post‐capping treatment at similar landfill sites Copyright © 2004 John Wiley & Sons, Ltd.     

Earthworm channels in cultivated clayey and loamy Norwegian soils

Studies of earthworm species and their activity, expressed as channels, on cultivated loamy (Humic Cryaquept) and clayey soils (Typic Endoaqualf and Typic Cryaquept) were conducted in southern and central Norway before conversion from conventional to organic cropping systems. At all the three study areas: Landvik (Grimstad), Voll (Ås) and Kvithamar (Stjørdal), the earthworm species Aporrectodea caliginosa, Aporrectodea rosea, Allolobophora chlorotica and Lumbricus rubellus were found. At Landvik, where the deep-burrowing species Aporrectodea longa, A. caliginosa and Lumbricus terrestris dominated, medium (4–6 mm) and coarse (>6 mm) earthworm channels were most numerous below the plough layer. Almost no coarse pores were found at Voll and Kvithamar. The volume of earthworm channels below the plough layer was 0.6–0.8% of total soil volume at Landvik and Voll and 0.3–0.4% at Kvithamar. Earthworm channels >6 mm below the plough layer were useful to identify present and previous activity of deep-burrowing earthworms such as L. terrestris. Below the plough layer, roots were almost entirely restricted to earthworm channels and interaggregate spaces.     

Colonization of PAH-contaminated dredged sediment by earthworms

In freshly deposited dredged sediment contaminated with PAHs, we followed the colonization of earthworm species by monthly monitoring over two years. Already five months after deposition the first species, Lumbricus castaneus, appeared, although only temporarily. The first permanent colonizing species was L. rubellus, soon followed by Aporrectodea caliginosa and L. castaneus, and a few months later Eiseniella tetraeda. At the end of the two-year observation period some first few specimen of Allolobophora rosea were present. These earthworm species colonized the deposited sediment apparently in succession. The colonization of each individual species did not show a gradual influx from the bordering dikes at both sides of the deposit, but a fast colonization over the whole width, presumably by surface dispersal, although at low and variable numbers, followed by a gradual increase of population numbers. Modeling the dispersal showed that diffusion was the primary driving factor. Also juvenile earthworms were observed locally in high numbers, so reproduction did occur. Total earthworm numbers in the deposit reached a maximum of 80% of the numbers in the bordering dikes consisting of loamy and clayey soils. Numbers were highest in periods with warm and rainy weather. The appearance of earthworms improved the soil development, stimulated a faster desiccation and aeration of the sediment and may have contributed to the increased degradation of PAHs, especially three- and four-ring PAHs.     

Impact of earthworms on decomposition of garden refuse

Summary Decomposition of garden refuse was studied in containers with and without the earthworm species Eisenia andrei and Lumbricus rubellus. The reduction of cellulose and hemicellulose was greater where earthworms were present. Respiration was similar regardless of the presence of earthworms, whereas dry matter reduction, on average, was greatest without earthworms. The earthworm biomass decreased during the 58 days of the experiment; E. andrei increased in biomass, whereas L. rubellus died out.     

Axial and radial pressure exerted by earthworms of different ecological groups

 The aim of this study was to measure the pressures exerted by earthworms during burrowing. For this purpose we developed two methods with which to quantify the axial and radial pressure. The data were recorded with an electronic balance that was connected to a PC. Artificial earthworm burrows were used to standardize the measurements. Plexiglas tubes with diameters ranging from 2 to 6.3 mm which corresponded to the diameter of the earthworms were used. A pin was placed inside the tubes, on which the earthworms exerted a pressure by peristaltic locomotion. Only the maximum values of the pressure measurement were taken into account for evaluation, and the arithmetic mean was calculated. The measurements were conducted with Aporrectodea longa, Lumbricus terrestris, Aporrectodea caliginosa, Octolasion cyaneum, Allolobophora chlorotica, Aporrectodea rosea, Lumbricus rubellus and Dendrobaena octaedra. The species examined were classified into ecological groups. The mean axial pressures exerted by each group were in the order: epigeic (14–25 kPa), endogeic (27–39 kPa) and anecic (46–65 kPa). For the mean radial pressure the order was: epigeic (39–63 kPa), anecic (72–93 kPa) and endogeic (59–195 kPa). It was apparent from the results that radial pressure is the most important pressure with respect to the burrowing activity of earthworms. Received: 28 April 1998     

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 Bouché 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.     

Impact of five different tillage systems on soil organic carbon content and the density,biomass, and community composition of earthworms after a ten year period

To assess the impact of different types of soil tillage on the density, biomass, and community composition of earthworms, a long-term field study was performed in which soils were tilled in different ways for ten years. This study included five different types of tillage: (i) plough, (ii) grubber, (iii) disc harrow, (iv) mulch sowing, and (v) direct sowing. At the end of the experiment the earthworm density, biomass, and community composition, and the SOC (soil organic carbon) content were determined. The results show that density, biomass, and community composition of earthworm populations varied in relation to the type of soil tillage used. The density of anecic earthworm species decreased when soils were managed by conventional ploughing, relative to reduced tillage practices, whereas conversely the density of endogeic species increased. Additionally, the varying types of soil tillage influenced the abundance and biomass of different earthworm species in different ways. The density of Aporrectodea caliginosa was positively influenced by ploughing, whereas Aporrectodea longa, Lumbricus castaneus, and Satchellius mammalis showed a positive relationship to the grubber and Allolobophora chlorotica to direct sowing. We attribute these changes to modifications in the vertical distribution of SOC and varying potentials for mechanical damage of earthworms by tillage. A decrease in tillage intensity modified the vertical SOC distribution in the topsoil and consequently revealed positive effects on earthworm biodiversity, thus sustaining soil functioning.     

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 O₂ 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.     

The effect of earthworms (Lumbricidae) on nitrogenase activity in soil

Summary Nitrogenase activity associated with earthworms, their faeces and activity in soil was measured by the acetylene reduction technique. A clear increase in nitrogenase activity was found in field-deposited casts of Aporrectodea caliginosa in comparison with surrounding soil, although potential nitrogenase activity was significantly higher in soil than in casts. Nitrogenase activity associated directly with earthworms (Lumbricus rubellus ) was detected, indicating the presence of active N₂-fixing bacteria on the body surface and/or in the gut. Laboratory experiments showed that nitrogenase activity in the casts of L. rubellus was higher than in unmodified soil, and that nitrogenase activity in soil was significantly increased by the burrowing and feeding activity of these worms. This paper discusses the possible causes of these earthworm effects on soil nitrogenase activity and some methodological problems of determining the nitrogenase activity.     

Earthworms of different functional groups affect the fate of the Bt-toxin Cry1Ab from transgenic maize in soil

The fate of the insecticidal Cry1Ab protein from crop residues (leaves and roots) of the transgenic maize variety MON810 was studied in the presence and absence of two earthworm species (Lumbricus terrestris, Aporrectodea caliginosa; separate incubations) in soil microcosms. The recombinant Cry1Ab protein was quantified using a highly sensitive ELISA. Control microcosms received corresponding non-transgenic plant material. All earthworms survived in the microcosms over a period of 5 weeks, irrespective of whether they received MON810 or non-transgenic plant material. Weight loss was observed for both earthworm species, independent of the plant material or transgenic modification. A strong decline of immunoreactive Cry1Ab in plant residues (mean initial concentration approx. 5000 ng g⁻¹) of MON810 was observed in all treatments, but in microcosms with earthworms this decline was significantly higher with less than 10% of the initial Cry1Ab concentration remaining after 5 weeks. Cry1Ab concentrations in casts were only 0.1% of those found in remaining plant material of the respective microcosms. No immunoreactive Cry1Ab proteins were found in earthworm tissues (threshold of detection: 0.58 ng g⁻¹ fresh weight). No further decline was found for Cry1Ab concentrations in casts of A. caliginosa during a subsequent period of 3 months of incubation in bulk soil (<0.1 ng g⁻¹) after removal of the earthworms from the microcosms, while in casts of L. terrestris the concentration decreased from 0.4 to below 0.1 ng g⁻¹. In conclusion, this study demonstrates that earthworms enhance the decline of immunoreactive Cry1Ab proteins from maize residues.     

Earthworms in a 15 years agricultural trial

Alternative cropping systems have been proposed to enhance sustainability of agriculture, but their mid and long-term effects on soil biodiversity should be studied more carefully. Earthworms, having important agro-ecological functions, are regarded as indicators of soil biological health. Species composition, abundance, and biomasses of earthworms were measured in autumn 2005–2007 (period 1) and 2011–2013 (period 2) in a trial initiated in 1997 near Paris, France. A conventional, an organic and a direct seeded living mulch-based cropping systems were compared. Earthworms were sampled in a wheat crop by combining the application of a chemical expellant and hand-sorting.In period 1, earthworm abundance did not usually differ in the three cropping systems, but sometimes it was higher in the conventional system. Mean total abundance was 122, 121 and 149 individuals m⁻² in period 1 and 408, 386 and 216 in period 2 in the organic, living mulch and conventional systems respectively. While earthworm abundance and biomass increased slightly in the conventional system between the two periods, they at least tripled in the other two systems. This was mainly due to the species Aporrectodea caliginosa and Aporrectodea longa in the living mulch cropping system, and to A. caliginosa, Lumbricus castaneus, Lumbricus terrestris and A. longa in the organic system.After at least 14 years, organic and living mulch cropping systems contained between 1.5 and 2.3 times more earthworms than the conventional system. Considering the inter-annual variations in earthworm communities due to climatic conditions and cultural practices, earthworm communities should be assessed over several years before conclusions can be drawn. Moreover, since changes in cultural practices may take a long time to affect earthworm communities, mid and long-term trials are needed to assess the effects of cropping systems on soil biodiversity.     

Changes in potassium availability and other soil properties due to soil ingestion by earthworms

An incubation experiment was conducted to study the changes that occur in potassium availability and other soil properties with ingestion of soil by earthworms. Two soils were used. Raumai soil with high non-exchangeable K and Milson soil with low non-exchangeable K were incubated with two species of earthworm, Aporrectodea caliginosa and Lumbricus rubellus, for 8 weeks. The casts and soil samples were analysed for exchangeable K, Ca, Mg, Na, and H, pH, organic C, and texture. The results indicated that in Raumai soil, the exchangeable K levels of the casts of both earthworm species were significantly higher than for the control soil, the effect being more marked for L. rubellus than for A. caliginosa. In Milson soil, the exchangeable K levels were significantly lower in the casts of both types of earthworm than in the control soil. The nitric acid-extractable K of the soil and casts was not markedly different for either soil type, but available non-exchangeable K values were significantly higher for the casts of L. rubellus from Milson soil than for the noningested Milson soil. In Raumai soil, the exchangeable Ca was higher in the casts of L. rubellus, exchangeable Mg and H were reduced, and exchangeable Na did not change markedly in the cast compared to the control soil. For Milson soil, the casts contained lower exchangeable Ca and H but higher Na and Mg than the control. The casts of both species of earthworm had significantly higher pH values for both soil types. There was no marked difference in the organic C content of the control soil and cast samples for Milson but a reduction in the casts of A. caliginosa for the Raumai soil. Finer fractions increased in the casts of both earthworm species in both soil types.     

Influence of organic matter on earthworm production and behaviour: a laboratory-based approach with applications for soil restoration

Restored soils are often low in organic matter (OM). As a result, OM is applied to increase soil fertility. Earthworms can assist soil incorporation of OM, but feeding behaviours, and as a result their roles in this process, differ between species. Laboratory experiments examined the effects of OM availability on the growth and behaviour of Aporrectodea longa and Lumbricus terrestris. Hatchling growth was recorded from 1 l vessels containing soil and OM (separated cattle solids), either surface applied (SUR) or mixed into the soil (MIX). Growth of L. terrestris was also recorded where separated cattle solids (SCS) were concentrated in bands at the surface (SUR) or at depths of 0.03 (UPP) or 0.08 m (LOW). In a further experiment, L. terrestris and L. rubellus were kept in mono-species cultures and paired combination, in treatments with selected SCS placements, which allowed assessment of OM position on species interactions. After 28 weeks, both L. terrestris and A. longa exhibited significantly greater growth rates (P < 0.05) in SUR treatments. The behaviour of both species changed with time. L. terrestris were located in areas where OM was concentrated. After 24 weeks, mean masses of 3.1, 2.2 and 1.6 g were recorded for SUR, UPP and LOW treatments, respectively. Where L. rubellus and L. terrestris were co-cultured, the former had significant (P < 0.05) negative effects on the growth of the latter, but only when surface OM was limited. At restored sites, application of OM may be important in the development of sustainable earthworm populations and hence their role in soil amelioration.     

Effects of heavy metals on the litter consumption by the earthworm Lumbricus rubellus in field soils

Aim of this study was to determine effects of heavy metals on litter consumption by the earthworm Lumbricus rubellus in National Park the “Brabantsche Biesbosch”, the Netherlands. Adult L. rubellus were collected from 12 polluted and from one unpolluted field site. Earthworms collected at the unpolluted site were kept in their native soil and in soil from each of the 12 Biesbosch sites. Earthworms collected in the Biesbosch were kept in their native soils. Non-polluted poplar (Populus sp.) litter was offered as a food source and litter consumption and earthworm biomass were determined after 54 days. Cd, Cu and Zn concentrations were determined in soil, pore water and 0.01 M CaCl₂ extracts of the soil and in earthworms. In spite of low available metal concentrations in the polluted soils, Cd, Cu and Zn concentrations in L. rubellus were increased. The litter consumption rate per biomass was positively related to internal Cd and Zn concentrations of earthworms collected from the Biesbosch and kept in native soil. A possible explanation is an increased demand for energy, needed for the regulation and detoxification of heavy metals. Litter consumption per biomass of earthworms from the reference site and kept in the polluted Biesbosch soils, was not related to any of the determined soil characteristics and metal concentrations.     

Population dynamics of earthworm communities in corn agroecosystems receiving organic or inorganic fertilizer amendments

 The dynamics of earthworm populations were investigated in continuously-cropped, conventional disk-tilled corn agroecosystems which had received annual long-term (6 years) amendments of either manure or inorganic fertilizer. Earthworm populations were sampled at approximately monthly intervals during the autumn of 1994 and spring and autumn of 1995 and 1996. The dominant earthworm species were Lumbricus terrestris L. and Aporrectodea tuberculata (Eisen), which comprised 50–60% and 8–13%, respectively, of the total annual earthworm biomass. Lumbricus rubellus (Hoffmeister) and Aporrectodea trapezoides (Dugés) were much less abundant and contributed a small fraction of total earthworm biomass. Earthworm numbers and biomass were significantly greater in manure-amended plots compared to inorganic fertilizer-treated plots during the majority of the study period. Seasonal fluctuations in earthworm numbers and biomass were attributed to changes in soil temperature and moisture, and cultivation. Unfavorable climatic conditions in the summer and autumn of 1995 caused earthworm abundance and biomass to decline significantly. Mature L. terrestris, L. rubellus and A. tuberculata were most abundant in May and June of 1995 and 1996, and cocoon production was greatest in June and July 1995 and June 1996. Recruitment of juveniles of Lumbricus spp. and Aporrectodea spp. into earthworm communities occurred primarily in the autumn. Long-term amendments of manure or inorganic fertilizer did not change the species composition of earthworm communities in these agroecosystems. The earthworm populations in both manure and inorganic fertilizer plots have declined significantly after 5 years of continuously-cropped corn. Received: 24 August 1997     

Quantitative image analysis of earthworm-mediated soil displacement

The way soil is disrupted and deformed by earthworm movement is hard to quantify non-destructively. Two anecic earthworm species, Aporrectodea longa (Ude) and Lumbricus terrestris L., were compared in their effect on the soil around them as they burrow. Image analysis (particle image velocimetry, PIV) was used successfully to quantify the distance and direction of soil particle displacement by earthworm locomotion giving a unique insight into their effect on the soil structure development. The data collected from both species using PIV show a decline in soil displacement at increasing distance from the earthworm’s body. The quantity of soil being displaced was more to the sides of the earthworms (radially) than in front of the prostomium (axially). Also, L. terrestris displaced more soil than A. longa both axially and radially. The findings from this study suggest that PIV image analysis is a viable tool for examining soil displacement by earthworms and the method used has the potential to be applied to other soil organisms.     

Earthworm species composition affects the soil bacterial community and net nitrogen mineralization

Knowledge of the effects of species diversity within taxonomic groups on nutrient cycling is important for understanding the role of soil biota in sustainable agriculture. We hypothesized that earthworm species specifically affect nitrogen mineralization, characteristically for their ecological group classifications, and that earthworm species interactions would affect mineralization through competition and facilitation effects. A mesocosm experiment was conducted to investigate the effect of three earthworm species, representative of different ecological groups (epigeic: Lumbricus rubellus; endogeic: Aporrectodea caliginosa tuberculata; and anecic: Lumbricus terrestris), and their interactions on the bacterial community, and on nitrogen mineralization from ¹⁵N-labelled crop residue and from soil organic matter.Our results indicate that L. rubellus and L. terrestris enhanced mineralization of the applied crop residue whereas A. caliginosa had no effect. On the other hand, L. rubellus and A. caliginosa enhanced mineralization of the soil organic matter, whereas L. terrestris had no effect. The interactions between different earthworm species affected the bacterial community and the net mineralization of soil organic matter. The two-species interactions between L. rubellus and A. caliginosa, and L. rubellus and L. terrestris, resulted in reduced mineral N concentrations derived from soil organic matter, probably through increased immobilization in the bacterial biomass. In contrast, the interaction between A. caliginosa and L. terrestris resulted in increased bacterial growth rate and reduced total soil C. When all three species were combined, the interaction between A. caliginosa and L. terrestris was dominant. We conclude that the effects of earthworms on nitrogen mineralization depend on the ecological traits of the earthworm species present, and can be modified by species interactions. Knowledge of these effects can be made useful in the prevention of nutrient losses and increased soil fertility in agricultural systems, that typically have a low earthworm diversity.