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Attempts to restore native biodiversity into agricultural landscapes in New Zealand appear to be compromised both by soil nitrogen enrichment from farming and N-leakage to the wider environment. We investigated whether interactions between native earthworms and a native rhizobium-inoculated leguminous shrub (Sophora microphylla) have a measurable effect on the mobility of nitrogen in an agricultural soil that has been nitrogen-enriched and colonised by exotic earthworms. Plants grew better in the presence of both native and exotic soil-burrowing earthworms. Rates of root nodulation were considerably enhanced in the presence of the native megascolecid anecic earthworm Maoridrilus transalpinus. This species consumed more organic matter in the presence of inoculated plants whilst marginally lowering soil pH and enhancing critical concentrations of nitrate, but also reducing nitrous oxide emissions. Earthworms raised dehydrogenase enzyme activity and microbial activity in soil, but this was not commensurate with rates of nodulation. Our results show that some combination of earthworm-mediated soil aeration, modification of moisture conditions in the rhizosphere and drilosphere, and comminution of organic matter, modify microbial communities and significantly impact the N cycle.

International audience; The positive effect of earthworms on soil processes and plant growth has been extensively documented. The capacity of earthworms to decompose organic matter has been attributed to the microbial communities that inhabit their digestive track or the structures they build, which in turn contribute to make up the drilosphere, a hotspot for microbial activity. However, how earthworms modify the structure of soil microbial communities and how these changes affect soil microbial processes is still unclear. Do earthworms reduce microbial abundance and activity because they feed on microorganisms or do they select and stimulate specific microbial groups? We hypothesise that “the effect of earthworms on nutrient cycling and plant growth is not only a direct effect but is mainly mediated indirectly, via modifications of the microbial community.” The objective of this review is to synthesize the existing literature concerning the influence of earthworms on the structure and function of soil microbial communities, as well as to understand how earthworm-induced changes in the soil microbiota would in turn impact soil processes, particularly those occurring in the rhizosphere and involved in plant growth and health. Recent reports have shown that specific bacterial groups consistently increase in soils where earthworms are present, regardless of the earthworm functional group. The extent of this increase seems to be dependent upon the type of substrate under study. Our synthesis also reveals that endogeic and anecic earthworms regularly induce an increase in soil nutrients, whilst this positive effect is not as evident in the presence of epigeic earthworms. The effect of earthworms on nutrient cycling has been further investigated with microbial functional genes, although existing reports largely focus on nitrogen cycling. Earthworms seem to enhance denitrification, most likely through the increase in organic compounds due to organic matter decomposition. By enhancing soil nutrient availability, earthworms indirectly promote plant growth, which has also been attributed to the induction of signal molecules. However, no experiment to date has been able to prove a direct causal relationship between specific signal molecules, earthworms and plant growth promotion. Finally, we propose a framework for earthworm-microbiota interactions and recommend further research.

Earthworms play important roles in no-till cropping systems by redistributing crop residue to lower soil horizons, providing macropores for root growth, increasing water infiltration, enhancing soil quality and organic matter, and stimulating nitrogen cycling. The soil impacted by earthworm activity, including burrows, casts, and middens, is termed the drilosphere. The objective of this study was to determine the effect of earthworms on soil microbial community composition in the drilosphere at different landscape slope positions. Soil cores (50 cm depth) were extracted from three landscape locations (top, middle and bottom slope positions) on a sloping aspect of a no-till wheat farm. Soil was sampled at the bottom of the soil core from inside multiple earthworm (Lumbricus terrestris) channels (drilosphere) and from adjacent bulk soil. Bacterial communities were characterized for 16S rRNA gene diversity using high-throughput sequencing and functional denitrifier gene abundance (nirK, nirS and nosZ) by quantitative PCR. Bacterial communities were structured primarily by the landscape slope position of the soil core followed by source (bulk versus drilosphere soil), with a significant interaction between core position and source. The families AKIW874, Chitinophagaceae, and Comamonadaceae and the genera Amycolatopsis, Caulobacter, Nocardioides, and Variovorax were more abundant in the drilosphere compared to the bulk soil. Most of the individual bacterial taxa enriched in the drilosphere versus bulk soil were members of Actinobacteria, including Micrococcales, Gaiellaceae, Solirubrobacterales, and Mycobacterium. In general, the greatest differences in communities were observed in comparisons of the top and bottom slope positions in which the bottom slope communities had statistically significantly greater richness, diversity, and denitrifier abundance than the top slope position. Populations of denitrifiers(i.e. ratio of nirK+nirS to 16S rRNA) were more abundant in earthworm-impacted soils and there was a significant impact of L. terrestris on soil community composition was observed only in the top landscape position. There were significant correlations between the abundance of nirK and nirS and taxa within Proteobacteria, Acidobacteria, Actinobacteria, Verrucomicrobia, and Chloroflexi, suggesting a broad diversity of denitrifying bacteria. Earthworms influence the soil microbial communities, but the impact depends on the slope location in a variable landscape, which likely reflects different soil characteristics.

Earthworms have long been recognized as ecosystem engineers, and their activity has been linked to increases in plant growth and yield in agroecosystems. Past research has demonstrated many positive impacts of earthworm activity on soil physical properties such as infiltration, aggregate stability, and water-holding capacity. In most cases, these studies have been conducted at the mesocosm, pedon, or plot scale and do not address the fine-scale reorganization of soil structure and molecular alteration of drilosphere soil ultimately responsible for increased plant growth. Past studies have also largely focused on determining the impact of earthworms on a single soil property or process. By using a combination of relatively new methodologies such as tomography and advanced microspectroscopic tools, the consequences of spatial reorganization by earthworms on biogeochemical properties may be determined. Likewise, microscale information on the biochemical environment will help elucidate processes through which earthworms alter soil physical properties. These types of microscale spatially explicit studies will be especially important in understanding how soil ecosystem engineers influence water and nutrient uptake by plants. This article focuses on reviewing our current state of knowledge regarding earthworm influences on physical properties and drilosphere-level studies of biogeochemical properties and processes. Examples of emerging techniques that are capable of studying drilosphere properties are given.

Earthworms are implicated in denitrification, the microbially mediated reaction that results in gaseous nitrogen (N 2 O and N 2 ) loss from terrestrial ecosystems. At the physiological scale, the anaerobic earthworm gut is a favorable microsite for endemic and transient denitrifiers that produce up to 11 nmol N 2 O g −1 earthworm h −1 . Besides this direct earthworm–denitrifier interaction, the earthworm's ability to consume, fragment and mix organic residues with soil will accelerate N mineralization and create suitable conditions for opportunistic soil denitrifiers. At the drilosphere scale, earthworm biostructures (burrows, casts) and earthworm-worked soil create gradients of redox conditions and are enriched in inorganic N and soluble C substrates used by denitrifiers. Therefore, earthworms indirectly stimulate soil N 2 O emissions by soil denitrifiers. Although these small-scale effects may imply that ecosystems with large earthworm populations are more likely to lose N through denitrification, there is scant experimental data to confirm this supposition. Evidence from simulated streams and agroecosystems suggests that earthworms can stimulate N 2 O emissions at the ecosystem-scale, but environmental factors (temperature and moisture) may overwhelm earthworm-induced denitrification. A critical review of earthworm–denitrifier interactions in riparian buffers, a hotspot for both groups of organisms, indicated that hydrodynamics controls denitrification during flooding periods by profoundly changing soil moisture and substrate concentrations that favor denitrifier activity. Earthworm effects on denitrifiers may be detected during drier periods. Thus, earthworm–denitrifier interactions cannot be extrapolated from the physiological- and drilosphere-level to explain denitrification in riparian ecotones due to seasonal variation in hydrological processes occurring at this scale.

Observations of earthworm colonization on sites where they were absent previously, such as on post-mining heaps, indicate that they may substantially alter soil conditions as well as soil microbial communities. However, long-term effects of earthworms on microbial activity of soil ecosystems remains poorly understood. To improve this situation, we set up microcosm experiments with clay only, with clay and litter, and with clay, litter and earthworms. Microcosms were sampled after 3, 60, 180 and 395 days of cultivation and divided into three subsamples: clay, litter, and drilosphere (earthworm tunnels and associates casts), when present. Microbial respiration, microbial biomass carbon, species composition, metabolic activity using BIOLOG, PLFA concentration, isoprenoid quinones content and DGGE fingerprints were analysed in all microcosms and at all subsamples. Microbial biomass carbon and basal soil respiration were significantly affected by type of microcosms and time of sampling. Microbial biomass in drilosphere was significantly higher than in clay and litter. The CFU (colony forming units) were significantly affected by presence of earthworms having significantly higher CFU in drilosphere than in all other subsamples. Analysis of PLFA indicated highest relative biomass of fungi and bacteria in clay from microcosms with earthworms. The DGGE analysis showed various compositions of microbial communities among subsamples from various treatments taken at different time. Finally, our results revealed significant effect of earthworms on activity and biomass of soil microbial community under long-term laboratory incubation.

Biotic interactions in the soil food web have been increasingly recognized as crucial for ecosystem functioning, however there are still knowledge gaps in terms of the associations between macrofauna and microorganisms, particularly in soil hotspot microsites. A manipulative study was performed to investigate the protist community in the drilosphere and casts of three earthworm species (epigeic Amynthas cortices, anecic Amynthas hupeiensis and endogeic Drawida gisti) and a control soil without earthworms. Results showed that earthworm presence significantly increased the relative abundance of parasitic protists (p

Vermiremediation is an expanding technology that uses earthworms to remediate organically contaminated soils and has been attracting attention from researchers gradually. This review outlines general aspects of vermiremediation, including its concepts, processing of organics-polluted soils, its advantages and limitations, the methods for enhancing vermiremediation, and other peripheral issues. Processes involved in vermiremediation of soils contaminated by organic chemicals mainly include vermiaccumulation and vermiextraction, vermitransformation, and drilodegradation. Vermiaccumulation plays an important role in vermiremediation and should be highlighted. Vermiremediation technology can be characterised as environmentally friendly, effective, sustainable. Strategies for enhancing vermiremediation might include the use of surfactants, nutrient amendments, management strategies, or combinations with other remediation technologies. Unlike previous reviews, peripheral issues such as the inoculation and colonising of earthworms in contaminated field and methods for harvest and disposal of earthworms used in vermiremediation are also discussed. However, there are many issues need to be clarified, including i) the capacity, contribution, and mechanisms of different vermiremediation processes; ii) the behaviour of organic pollutants in the drilosphere, iii) enhancement measures for vermiremediation and their side effects, and iv) earthworm collection methods in polluted soil and their post-harvest disposal. This review gives a general outline of vermiremediation, which is expected to promote further studies and practical application of vermiremediation in organically contaminated soils.

Soils are the most heterogeneous parts of the biosphere, with an extremely high differentiation of properties and processes within nano- to macroscales. The spatial and temporal heterogeneity of input of labile organics by plants creates microbial hotspots over short periods of time – the hot moments. We define microbial hotspots as small soil volumes with much faster process rates and much more intensive interactions compared to the average soil conditions. Such hotspots are found in the rhizosphere, detritusphere, biopores (including drilosphere) and on aggregate surfaces, but hotspots are frequently of mixed origin. Hot moments are short-term events or sequences of events inducing accelerated process rates as compared to the average rates. Thus, hotspots and hot moments are defined by dynamic characteristics, i.e. by process rates. For this hotspot concept we extensively reviewed and examined the localization and size of hotspots, spatial distribution and visualization approaches, transport of labile C to and from hotspots, lifetime and process intensities, with a special focus on process rates and microbial activities. The fraction of active microorganisms in hotspots is 2–20 times higher than in the bulk soil, and their specific activities (i.e. respiration, microbial growth, mineralization potential, enzyme activities, RNA/DNA ratio) may also be much higher. The duration of hot moments in the rhizosphere is limited and is controlled by the length of the input of labile organics. It can last a few hours up to a few days. In the detritusphere, however, the duration of hot moments is regulated by the output – by decomposition rates of litter – and lasts for weeks and months. Hot moments induce succession in microbial communities and intense intra- and interspecific competition affecting C use efficiency, microbial growth and turnover. The faster turnover and lower C use efficiency in hotspots counterbalances the high C inputs, leading to the absence of strong increases in C stocks. Consequently, the intensification of fluxes is much stronger than the increase of pools. Maintenance of stoichiometric ratios by accelerated microbial growth in hotspots requires additional nutrients (e.g. N and P), causing their microbial mining from soil organic matter, i.e. priming effects. Consequently, priming effects are localized in microbial hotspots and are consequences of hot moments. We estimated the contribution of the hotspots to the whole soil profile and suggested that, irrespective of their volume, the hotspots are mainly responsible for the ecologically relevant processes in soil. By this review, we raised the importance of concepts and ecological theory of distribution and functioning of microorganisms in soil.

Our current knowledge about the effects of earthworms on microbial communities derives from studies on a few peregrine species, and there is a lack of data for most of the uncommon worms. Therefore, we studied the effects of Allolobophora hrabei ( Cernosvitov, 1935 ), a key earthworm species in fragile fragments of steppe ecosystems in central Europe. We found that the burrowing activity of A. hrabei as well as deposition of casts caused significant differences in the community composition of three domains of soil microorganisms including bacteria, archaea, and fungi. The richness of bacteria and fungi was significantly lower in casts than in the surrounding soil, however, that of archaea showed the opposite trend. Archaea and fungi were less susceptible to the burrowing activity than bacteria; earthworms significantly shifted the composition of bacterial communities between the soil and drilosphere. Deposition of casts was the main factor in affecting soil microorganisms. Cast profiles of all three microbial domains created separate clusters, indicating significantly different communities at all monitoring sites in both years of the study. In general, the activity of A. hrabei can be considered as an important factor that affects the soil microbial communities, and its casts represent a substantial habitat for selected soil microorganisms in steppe grasslands.

Spatial and temporal dynamics of microbial community structure and function in subsoils have been rarely studied in the past. In this paper we present data on how bacterial communities as well as selected functional groups of microbes change in the rhizosphere, the drilosphere, and in bulk soil over time in topsoil as well as in subsoil. We show that the overall richness of bacteria and abundance of nitrifiers and denitrifiers decreases in bulk soil with soil depth. However, these effects were not or to a much lower degree observed in the rhizosphere and the drilosphere. Temporal fluctuations contributed by far less than spatial factors to the dynamics of bacterial communities and abundance of nitrifiers and denitrifiers in all compartments independent from the soil depth.

Strains of Trichophaea abundans (Ascomycota, Pezizales, Pyrenomycetaceae) were isolated from Haplic Cambisol, Haplic Cambisol (Eutric), Litic Leptosol (Sceletic), Haplic Umbrisol, and Fulvic Andosol soils in Slovakia and from Rendzic Leptosol, Chernozem, Cambisol, drilosphere, and feacal pelets of the earthworm Allolobophora hrabei collected in southern Moravia. The Slovak soils markedly differ in pH, from extremely acidic (pHH2O 3.9) to weakly alkaline (pHH2O 7.4). T. abundans appeared as a post-burn species on Haplic Cambisol, which experienced a wildfire after a windthrow event (November 2004). In Moravia T. abundans was also isolated from sites situated in southern slopes, from time and time they affected by fires. We also note the growth of T. abundans on the surface of Fulvic Andosol after gradual heating in the lab to temperatures reaching 105°C. These findings confirmed by a review of the literature, indicate that T. abundans belongs to the group of heat-resistant fungi appearing in soils regularly influenced by the fire or grass calcining.

Microbial degradation of 2-methyl-4-chlorophenoxyacetic acid (MCPA) in soil is enhanced by earthworms and initiated by tfdA -like, cadA and r/sdpA gene encoding oxygenases. Copy numbers of such genes increased during MCPA degradation in soil, and MCPA stimulated transcription of tfdA -like and r/sdpA genes up to 4×. Transcription of cadA was detected in the presence of MCPA only. DNA stable isotope probing after consumption of 0.6–0.8 mg 13 C-MCPA g dw − 1 in oxic microcosms indicated diverse labeled oxygenase genes in bulk soil, burrow walls, and cast. 9, 6, and 3 operational taxonomic units of tfdA -like, cadA , and r/sdpA genes, respectively, were labeled and affiliated with group 2 Alphaproteobacteria including Bradyrhizobia and group 1 class III Betaproteobacteria . New genes encoding putative MCPA degrading oxygenases were identified. Diversity of labeled OTUs tended to be lower for cast than for bulk soil. The collective data indicate (1) hitherto unknown active MCPA degraders and/or oxygenase genes in soil; (2) that multiple oxygenases are associated with MCPA degradation in soil at the same time; (3) that earthworms impact the capability of MCPA degraders in soil to respond to MCPA; and (4) the collective data enable a more in-depth analysis of MCPA degrader communities in soil by future structural gene-based experimental strategies.

Soil microbial communities provide a wide range of soil functions including nutrient cycling, soil formation, and plant growth promotion. On the small scale, nutrient rich soil hotspots developed from soil animal or plant activity are important drivers for microbial communities and their activity pattern. Nevertheless, in subsoil, the spatial heterogeneity of microbes with diverging lifestyles has been barely considered so far. In this study, the phylogenetic composition of the bacterial and archaeal microbiome based on 16S rRNA gene pyrosequencing was investigated in the soil compartments bulk soil, drilosphere, and rhizosphere in topsoil and in the subsoil of an agricultural field. With co-occurrence network analysis, the spatial separation of typically oligotrophs and heterotrophs in subsoil and hotspots was assessed. Four co-occurring bacterial communities were identified and attributed to bulk topsoil, bulk subsoil, drilosphere, and rhizosphere. The bacterial phyla Proteobacteria and Bacteroidetes, which represent many copiotrophic bacteria, are affiliated to the hotspot communities – the rhizosphere and drilosphere – both in topsoil and subsoil. Acidobacteria, Actinobacteria, Gemmatimonadetes, Planctomycetes, and Verrucomicrobia with many oligotrophic bacteria, are the abundant groups of the bulk subsoil community. The bacterial core microbiome in this soil was estimated and only covers 7.6% of the bacterial sequencing reads but includes both oligotrophic and copiotrophic bacteria. Instead, the archaeal core microbiome includes 56% of the overall archaeal diversity and comprises only the ammonium oxidizing Nitrososphaera. Thus, the spatial variability of nutrient quality and quantity strongly shapes the bacterial community composition and their interaction in subsoil, whereas archaea are a stable backbone of the soil prokaryotes.

Earthworms play an important role in the functioning of many terrestrial ecosystems, and while their importance is frequently acknowledged significant challenges still remain in determining their operant roles within the soil. This lack of knowledge becomes increasingly important as the spatial scale of analysis increases from individuals to populations within the landscape. To effectively develop understanding, research techniques must be able to determine the effects that earthworms have on the soil system, as well as to establish how many and which species are present. A range of techniques are required to facilitate meaningful analysis from the micro-scale within a soil profile (e.g. drilosphere effects) to a field scale or landscape scale. Furthermore, an additional framework of understanding is required to investigate the role of earthworms in the biogeochemical cycles. By critically evaluating recent advances in methods and data analysis techniques in three areas of earthworm research we highlight that combinations of common approaches often offer the most significant insights into the functional roles of earthworms within a soil system. Through particular reference to earthworm sampling and identification, biochemical functions and persistent pollutant ecotoxicology of temperate ecosystems we emphasise how a range of investigation methods can be a hindrance to developing a whole-system level understanding. The complex and diverse nature of soil systems means that a traditional compartmentalised approach studying single species using a single research technique is no longer sufficient to gain further insights into the earthworm contribution to ecosystem goods and services delivered at the whole landscape scale. The integration of technologically advanced methods in combination with systems based modelling will be critical to develop landscape scale understanding of the functions of earthworms as individuals and as populations within in their ecosystems.

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.

Summary Current knowledge of earthworm feeding ecology is reviewed, with particular reference to food selection, ingestion, digestion and assimilation, and the use of novel techniques to advance understanding of the functional significance of these processes. Traditional research methods including direct observation of feeding behaviour, gut content analysis, choice tests, and litter bags have provided a wealth of information on earthworm feeding. However, there is a lack of the mechanistic, quantitative information required to characterise adequately their functional role in soil ecosystem processes such as soil C sequestration and loss, decomposition of organic residues, the maintenance of soil structure and trophic interactions with plants and microorganisms. Stable isotope ratio analysis of light elements (C, N, and S) offers a powerful research tool to reveal and quantify trophic relationships of earthworms in soil food webs, while molecular techniques can further enhance understanding of the interactions between earthworms and microorganisms and their functional significance.

We evaluated the role of soil water content in controlling C and N dynamics within the drilosphere created by the anecic earthworm Lumbricus terrestris (L.). Mesocosms (volume = 3.1 l) were each amended with corn litter and three earthworms. Control treatments received no earthworms and no other earthworm species were present in the soil. WET and DRY treatments received a total of 9.25 cm and 3.25 cm of water, respectively. Water was added on weeks 1, 3, 7, and 10 at a rate of 2.0 cm per mesocosm for WET treatments and 0.5 cm per mesocosm for DRY treatments. Mesocosms were sampled destructively after incubation at 18–20 8C for 0, 3, 7, and 13 weeks. The water content of WET burrow soil ranged from 0.12 g g � 1 to 0.18 g g � 1 and was significantly higher than in the DRY treatment throughout the incubation period. The live weight of earthworms was significantly higher in the WET treatment only on week 13, whereas litter consumption was significantly lower in the DRY treatment for week 13. Carbon mineralization, measured as CO2 evolved after a 24-h incubation, was consistently higher in WET than in DRY burrow soil. Effects of differences in soil water content were also apparent for biomass C and metabolic quotient. Soil water content did no affect the total C concentration of burrow soil. DRY burrow soil had consistently lower levels of nitrate than WET soil throughout the experiment. Lower levels of ammonium and inorganic N were observed for WET burrow soil on weeks 3 and 7. Water content did not have a significant effect on burrow soil total N. We concluded that the water content of the drilosphere affects both C and N dynamics and can affect the speciation of inorganic N; yet, the effects of soil water content do not appear to result from differences in the feeding activities of anecic earthworms. # 2004 Elsevier B.V. All rights reserved.

Anecic (deep-burrowing) earthworms are important for soil biogeochemical functioning, but the fine-scale spatial range at which they incorporate C and N around their burrows (the drilosphere sensu stricto) needs to be investigated under realistic conditions. We conducted a field experiment to delimit spatially the extent to which soil around natural Lumbricus terrestris burrows is influenced biochemically. We placed plant litter dual-labelled with C-13 and N-15 stable isotope tracers on L terrestris burrow openings and we measured residue-derived C-13 and N-15 in thin concentric layers (0-2, 2-4, 4-8 mm) around burrows with or without a resident earthworm. After 45 days, earthworms were significantly enriched in C-13 and N-15 as a result of feeding on the plant litter. At 0-5 cm soil depth, soil N-15 concentrations were significantly higher around occupied than unoccupied burrows, and they were significantly higher in all burrow layers (including 4-8 mm) than in bulk soil (50-75 mm from burrow). This suggests that biochemical drilosphere effects of anecic earthworms, at least in the uppermost portion of the burrow, extend farther than the 2 mm layer assumed traditionally. (C) 2013 Elsevier Ltd. All rights reserved.

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.

The moment the soil enters into contact with an earthworm, both superficially and internally, physicochemical and biological changes take place. The drilosphere represents the whole soil volume under earthworm influence. Thus it includes the body surfaces, the gut and all the internal features of the worm that are in contact with the ingested soil, as well as the external structures (casts, burrows, middens) created by earthworm activities. The extent of the drilosphere and its particular characteristics depend on the species and ecological categories of the earthworm community present as well as the spatial and temporal scale of interest. Spatially, the drilosphere can interact with other soil functional domains and lead to significant changes in the litter system or detritusphere (generally decreasing litter stocks) and the rhizosphere (affecting both root biomass and density), the two main sources of organic matter (OM) additions to the soil, as well as in the aggregatusphere and the porosphere. Drilosphere effects on microbial activity and OM decomposition can be completely different (and opposite) depending on the spatio-temporal scale of observation. At the level of the gut, microbial activity is dramatically stimulated in a matter of a few hours via a mutualistic digestion system. In this process, water and soluble-C in the form of intestinal mucus (the Kiss) produced by the earthworm (Prince Charming) awakens the dormant microflora (Sleeping Beauties), thereby increasing decomposition of the stable forms of soil OM ingested. During gut passage populations of other organisms (e.g. protozoa, nematodes, fungi) may decline with digestion, although these organisms probably form a minor component of the earthworm’s energy needs. In the casts and on the burrow walls, the abundant nutrient resources for soil microflora continue the priming effect of the gut, increasing over a short time period mineralization rates and plant nutrient bio-availability. However as castings, particularly of the ‘compacting group’, and burrow walls begin to dry and stabilize with age (days to weeks), OM decomposition, nutrient mineralization and microbial activity decrease, often reaching levels lower than uningested soil due to ‘protection’. Finally at the scale of years to decades and soil profile, it appears that the drilosphere can exert an important regulation on OM incorporation and turnover rates, and soil C stocks.

Earthworms play an active role in soil nitrogen cycling. Past research has shown that earthworm castings are enriched in NO3− and NH4+ and show a high potential for microbial nitrification and denitrification. Little information is available on microbial populations and N transformations in the 1–2 mm thick soil lining of earthworm burrows (the drilosphere). We measured nitrifying bacterial populations, denitrifying bacterial populations, nitrification rates and denitrification rates of drilosphere and nondrilosphere soils. These measurements, in addition to measurements of NO3− concentration, NH4+ concentration, soluble organic-C, pH and water content, were performed on drilosphere material from laboratory microcosms inoculated with Lumbricus terrestris L. and on drilosphere material collected from earthworm burrows in long term no-till plots. The drilosphere soil was enriched in NO3−, NH4+ and soluble organic C and these soils had elevated populations of nitrifying and denitrifying bacteria relative to nondrilosphere soil. Drilosphere soil also had higher nitrification and denitrification rates. We postulate that earthworm-derived C and N deposited in the drilosphere facilitates the enrichment of N-transforming bacterial populations and that the elevated N-transformation rates results in an enrichment of NO3− in the earthworm burrow. This phenomenon has the potential for increased downward NO3− transport; however, the extent to which this potential is realized is not known.

It is a critical issue for the application of animal slurry in water protection areas whether macropores such as earthworm burrows can contribute to the contamination of groundwater with faecal organisms. The aim of the current field experiment was to investigate the effects of the factors: slurry addition, land use (grassland/arable land), sampling date, depth (15, 45 and 75 cm), and drilosphere (soil surrounding an earthworm burrow) on the movement of faecal indicator organisms (total coliforms, faecal coliforms and faecal streptococci) into the subsoil. The experiment was carried out under worst case conditions, i.e., a soil at field capacity, irrigated directly after application of fresh cattle slurry with high rates of water. Under these conditions, we showed that significant numbers of faecal coliforms were transferred after slurry addition down earthworm burrows to the subsoil. We also showed that the numbers transferred in the grassland soil exceeded those of the arable soil. However, only about 0.16% (=1.3×103 m−2) of the applied faecal coliforms were found under grassland around the earthworm burrows at a depth of between 40 and 80 cm. Total coliforms or faecal streptoccoci were not affected by slurry addition at any depth. In the drilosphere, the numbers of all faecal indicator organisms were always significantly increased in comparison to the bulk soil and also the contents of microbial biomass which were similar to those of the surface horizons. This means that the competition with the autochthonous soil microflora and thus, the decay rate of the introduced faecal bacteria, were also similar to the surface soil. Total and faecal coliforms were significantly related to each other and to the total microbial biomass, indicating that a certain percentage of these two groups belongs to the autochthonous soil bacterial microflora. The number of faecal streptococci varied enormously between replicate plots and the variation appeared to be independent of the factors studied.

Several studies have emphasised the ability of Near Infrared Reflectance Spectroscopy (NIRS) to identify surface earthworm casts in the field. However, less is known about casts deposited within the soil, which usually represent the majority found in the field. This study tested the ability of NIRS to identify belowground casts in agricultural systems. Casts and surrounding soils were sampled at depths of 20–30 cm in a loamy soil under no tillage for 12 years. To distinguish different types of cast, sizes and orientations relative to the horizontal plane were measured. NIRS analyses and analyses of carbon and nitrogen content were also performed to compare casts to surrounding soils. Casts were classified into 4 size classes, with no preferential orientation. Cast carbon and nitrogen content were not influenced by their size and did not differ from surrounding soils. PCAs performed on the NIRS data did not allow casts to be differentiated from surrounding soils, regardless of size class. However, soil aggregates were clearly differentiated probably due to their spatial distribution in the soil. Although this study did not identify specific NIRS signatures for casts, it shows the utility of this method to investigate the origin of the soil consumed by earthworms. In our case, NIRS analyses suggest that the high bulk density of the soil (1.42 g cm−3) forced ingestion by endogeic earthworms, simply to move around, without preferential selection for organic matter. Consequently, their casts were deposited a few mm from where they had ingested soil with similar organic matter quality.

Long-term watershed studies at the North Appalachian Experimental Watershed, Coshocton, Ohio have shown that when corn ( Zea mays L.) is planted in soil covered by the residue of the previous crop (i.e. no-tillage management), surface runoff from summer storms is greatly reduced. In addition, the residue cover provides a favorable environment for various soil invertebrates, especially earthworms. During high-intensity rainstorms, some of the water that infiltrates in no-till corn fields moves rapidly downward in burrows made by the earthworms Lumbricus terrestris L. Samplers were developed for collecting infiltrating rain water flowing in L. terrestris burrows at a depth of 45cm below the soil surface. With annual surface applications of 175 kg N ha −1 as NH 4 NO 3 , concentrations of NO 3 -N in water flowing in individual burrows during growing season storms ranged up to 152 mg l −1 . Concentrations of NO 3 -N tended to be lowest after prolonged wet soil conditions and highest after intermittent warm, dry periods. Distilled water poured directly into the surface openings of L. terrestris burrows and immediately collected as it drained into samplers, contained up to 40 mg of NO 3 -N I −1 , a value greater than that measured in many of the samples resulting from natural rain storms. Water and herbicide mixtures poured through L. terrestris burrows showed that the linings of the burrow, or drilosphere, may contribute nitrogen to the infiltrating water while greatly reducing the concentrations of atrazine and alachlor.

This chapter describes the drilosphere, which is defined as an earthworm population, all the biogenic structures that they build in the soil, and the communities of smaller organisms that inhabit these structures. The chapter shows that drilospheres have all the characteristics of self-organizing systems. It also discusses the theoretical and practical meaning of this organization. The chapter presents the interactions with micro-organisms and other inhabitants of the drilosphere that allow earthworms to derive energy from decomposing organic matter. The chapter describes the physical domains created in soils by the accumulation and spatial array of biogenic structures (earthworm casts, galleries, voids, and middens), addressing the effects of this system on the soil environment and the possible positive feedbacks provided in return to earthworms and inhabitants of the drilosphere. It also discusses how effective management of the drilospheres relates to sustained provision of soil ecosystem services, such as water infiltration and storage, C-sequestration, and nutrient cycling.

To link earthworm burrow distribution with the spatial variability of soil functions, accurate mapping of their spatial burrowing patterns is required. Eight natural soil cores (25 cm in diameter; up to 60 cm long) were collected from a pasture in spring 2001–2003. Earthworm populations were sampled on the first date and the anecic species Nicodrilus giardi was found to be dominant (55% of the average density of 101 worms m−2). Soil cores were imaged using medical X-ray tomography equipment. These tomography images served as a basis for 3D reconstructions generated using specifically written software. Finally, the reconstructed burrow systems were measured and analysed using mathematical morphological approaches. The 3D reconstructions thus derived showed dense systems of interconnected burrows. A number of burrows extending vertically from the top to the bottom of the cores, but most were short, disconnected burrows. These two classes of burrows could not be linked with the activity of a particular species. In addition to the visual appraisal of the burrow system shape, structural parameters such as burrow volume, burrow wall surface area, burrow length density, topology and burrow angles were computed from the 3D reconstructions. Total burrow length density ranged from 687 to 1212 m m−3. Burrow volume density represented less than 2.5% of total soil volume and ranged from 13.3 × 103 to 24.2 × 103 cm3 m−3. Inspite of the apparently high continuity of burrows, only 9–43% of the volume was connected to the soil surface. Total burrow wall area ranged from 7721 to 12764 cm2 m−3 while surface-connected burrow wall surface area ranged from 1069 to 7237 cm2 m−3. The drilosphere volumes (i.e. a 2 mm thick sheath around burrows) were estimated to range from 44.9 × 103 to 52.9 × 103 cm3 m−3. Earthworm activity was found to vary throughout the year as revealed by changes in burrowing patterns. The burrow systems in spring 2001 were denser than that in others years, and the burrow systems in spring 2003 appeared to be partially re-filled close to the surface. This temporal variability demonstrates that it is virtually impossible to obtain true replicates of burrow systems of a given earthworm community without knowing (1) which burrows were created by which species and (2) the burrows age. However, the accurate description and quantification of earthworm burrow systems using powerful image processing tools allows a detailed discussion of the potential impact of earthworms on soil functions under natural conditions.

Much of the work regarding earthworm effects on other organisms has focused on the functional significance of microbial-earthworm interactions, and little is known on the effects of earthworms on microfloral and faunal diversity. Earthworms can affect soil microflora and fauna populations directly and indirectly by three main mechanisms: (1) comminution, burrowing and casting; (2) grazing; (3) dispersal. These activities change the soil's physico-chemical and biological status and may cause drastic shifts in the density, diversity, structure and activity of microbial and faunal communities within the drilosphere. Certain organisms and species may be enhanced, reduced or not be affected at all depending on their ability to adapt to the particular conditions of different earthworm drilospheres. A large host of factors (including CaCO3, enzymes, mucus and antimicrobial substances) influence the ability of preferentially or randomly ingested organisms to survive (or not) passage through the earthworm gut, and their resultant capacity to recover and proliferate (or not) in earthworm casts. Small organisms, particularly microflora and microfauna, with limited ability to move within the soil, may benefit from the (comparatively) long ranging movements of earthworms. Microflora and smaller fauna appear to be particularly sensitive to earthworm activities, and priming effects enhancing nutrient release, particularly in casts, are common. Larger fauna such as microarthropods, enchytraeids and Isopods may be enhanced under some conditions (e.g., in earthworm middens), but in other cases earthworm activity may lead to a decrease in their populations due to competition for food (microbes and organic materials), and spatial and temporal changes in food abundance. Nevertheless, considering the presently available data, the beneficial interactions of earthworms and microflora and fauna appear to far outweigh the potential negative effects. However, much is still unknown regarding the interactions of earthworms of different ecological categories on the diversity and function of microfloral and faunal communities, and much more interdisciplinary research is needed to assess the potential role of earthworms in regulating the diversity of microflora and fauna in soil systems and the potentially beneficial or harmful effects this regulation may have on ecosystem function and plant growth in different ecosystems.