Endogeic Earthworms Research Articles

Interspecies variation in survival of soil fauna in flooded soil

While many studies have examined the effects of flooding on earthworm population distributions, few studies have investigated physiological and behavioural responses of earthworms to the low oxygen conditions caused by flooding. An earthworm's skin is its oxygen exchange organ, allowing earthworms to survive in flooded environments provided that the water contains sufficient dissolved oxygen. Individuals of three species of earthworm, the anecic Lumbricus terrestris (Linneaus, 1758), the green morph of the endogeic Allolobophora chlorotica (Savigny, 1826) and the epigeic Lumbricus castaneus (Savigny, 1826) were placed in reconstituted groundwater that was either kept aerated or kept in a sealed container so that dissolved oxygen was gradually consumed as the earthworm respired. Oxygen saturation of the water was measured over time in sacrificial triplicate replicates from each treatment at discrete time points; earthworm mortality and mass were recorded. Before treatments, oxygen levels in all treatment tubes were 9.53 (±0.64) mg O2 L−1. L. terrestris, a large species which emerges at night to forage at the soil surface died when oxygen levels reached 0.82 (±0.46) mg O2 L−1 after approximately 36 h. L. castaneus, a smaller species which lives on the soil surface, died when oxygen levels reached 3.60 (±2.01) mg O2 L−1 after approximately 168 h. A. chlorotica, which is similar in size to L. castaneus, lives in the upper 20 cm of soil and is known to aestivate during the summer, did not die, even when oxygen levels reached 1.49 (±0.40) mg O2 L−1 after 280 h. The results suggest that earthworm respiration is closely linked to both body size and to behavioural ecotype. These findings suggest that if flooding increases in frequency resulting in episodic reductions in soil oxygen levels, the species composition of earthworm communities may change, with an increased presence of endogeic earthworms which show a responsive plasticity to flooding events.

Assimilation of Aboveground Litter Carbon Versus Soil Carbon by Collembola and Lumbricidae in Spruce Forest: A Litter Replacement Experiment

In a small-scale field experiment, we estimated the contribution of aboveground litter to the energy budget of different collembolan and earthworm species. In a 50-year-old spruce plantation, the natural spruce litter was replaced by an equivalent amount of maize litter. The natural difference in the isotopic composition of carbon (C) between the spruce and maize allowed us to estimate the proportions of different carbon sources in the tissues of soil animals. The dependence on litter-derived C was least pronounced in Collembola having low δ15N values, indicating the feeding on non-vascular plants. In contrast, collembolans having high δ15N values belonged to the food chains based on fresh plant residuals. These results suggest that different species of litter-dwelling collembolans may regulate substantially different energy channels. Some species of endogeic earthworms (Aporrectodea rosea and A. caliginosa) utilize aboveground plant residues, though soil organic matter and other belowground sources of carbon prevail in the energy budget of their populations.

Soil dissipation and bioavailability to earthworms of two fungicides under laboratory and field conditions.

The representativeness of laboratory studies of the fate of pesticides in soil in field conditions is questionable. This study aimed at comparing the dissipation and bioavailability to earthworms of two fungicides, dimoxystrobin (DMX) and epoxiconazole (EPX), over 12months under laboratory and field conditions. In both approaches, the fungicides were applied to the same loamy soil as a formulated mixture at several concentrations. We determined total DMX and EPX concentrations in the soil using exhaustive extraction, their environmental availability using mild extraction and their bioavailability through internal concentrations in exposed earthworms. The initial fungicide application appeared as much better controlled in terms of dose and homogeneity in the laboratory than in the field. One year after application, a similar dissipation rate was observed between the laboratory and field experiments (ca 80% and 60% for DMX and EPX, respectively). Similarly, the ratio of available/total concentrations in soil displayed the same trend whatever the duration and the conditions (field or lab), EPX being more available than DMX. Finally, the environmental bioavailability of the two fungicides to earthworms was heterogeneous in the field, but, in the laboratory, the bioaccumulation was evidenced to be dose-dependent only for DMX. Our findings suggest that the actual fate of the two considered fungicides in the environment is consistent with the one determined in the laboratory, although the conditions differed (e.g., presence of vegetation, endogeic earthworm species). This study allowed better understanding of the fate of the two considered active substances in the soil and underlined the need for more research dedicated to the link between environmental and toxicological bioavailability.

Elucidating pesticide sensitivity of two endogeic earthworm species through the interplay between esterases and glutathione S-transferases

Earthworms are common organisms in soil toxicity-testing framework, and endogeic species are currently recommended due to their ecological role in agroecosystem. However, little is known on their pesticide metabolic capacities. We firstly compared the baseline activity of B-esterases and glutathione-S-transferase in Allolobophora chlorotica and Aporrectodea caliginosa. Secondly, vulnerability of these species to pesticide exposure was assessed by in vitro trials using the organophosphate (OP) chlorpyrifos-ethyl-oxon (CPOx) and ethyl-paraoxon (POx), and by short-term (7 days) in vivo metabolic responses in soil contaminated with pesticides. Among B-esterases, acetylcholinesterase (AChE) activity was abundant in the microsomal fraction (80% and 70% of total activity for A. caliginosa and A. chlorotica, respectively). Carboxylesterase (CbE) activities were measured using three substrates to examine species differences in isoenzyme and sensitivity to both in vitro and in vivo exposure. CbEs were mainly found in the cytosolic fraction (80% and 60% for A. caliginosa and A. chlorotica respectively). GST was exclusively found in the soluble fraction for both species. Both OPs inhibited B-esterases in a concentration-dependent manner. In vitro trials revealed a pesticide-specific response, being A. chlorotica AChE more sensitive to CPOx compared to POx. CbE activity was inhibited at the same extent in both species. The 7-d exposure showed A. chlorotica less sensitive to both OPs, which contrasted with outcomes from in vitro experiments. This non-related functional between both approaches for assessing pesticide toxicity suggests that other mechanisms linked with in vivo OP bioactivation and excretion could have a significant role in the OP toxicity in endogeic earthworms.

Evidence for substantial acetate presence in cutaneous earthworm mucus

Earthworm mucus is a ubiquitous source of C and N for soil biochemical processes and likely fuels direct interactions with other soil organisms; however, its chemical composition is little known and was the research question addressed by this research. A method was developed for the collection of sufficient amounts of cutaneous mucus from highly isotopically labelled earthworms with the objective to analyse mucus chemically by state-of-the-art nuclear magnetic resonance (NMR) techniques. A clean sand method was developed to collect cutaneous mucus from highly 13C, 15N-labelled endogeic earthworms (Allolobophora chlorotica). Mucus was analysed by 1D and 2D NMR. NMR spectra showed a complex mixture dominated by carbohydrates with a high aliphatic/lipid content and relatively few resonances for protein/peptide material. A very large contribution from acetate was detected, likely in the form of acetylated carbohydrates. The ample presence of acetate is noteworthy because acetate is an important component in soil carbon cycling and methanogenic pathways. Earthworm mucus may be involved in novel direct biochemical interactions with soil (and possibly also sediment) microorganisms and plant roots that have not been recognised before.

Shift in phagocytosis, lysosomal stability, lysozyme activity, apoptosis and cell cycle profile in the coelomocytes of earthworm of polluted soil near a tannery field of India.

Calcutta Leather Complex of the state of West Bengal, India has been designated as an industrially active zone with around 400 active tannery units. This area spanning 4.5 km2 is surrounded by human habitation. The soil of this region is contaminated with metal pollutants and exhibited an alteration in selected physicochemical parameters, namely cation exchange capacity, moisture content, pH, total nitrogen, total organic carbon and water holding capacity. Metaphire posthuma, a common variety of endogeic earthworm inhabiting this region is thus continuously exposed to these toxic metals. Coelomocytes, the chief immune effector cells of earthworm presented a shift in phagocytosis, lysosomal membrane stability, lysozyme and phosphatase activity, physiological apoptosis and cell cycle profile of M. posthuma sampled from the soil of tannery industry. Presence of high concentration of toxic metals and change in the physicochemical characteristics of soil led to a state of cellular stress and immunocompromisation in M. posthuma, a common inhabitant of soil of this region. Experimental endpoints bear ecotoxicological significance as biomarkers of physiological stress in earthworm for monitoring the health of soil around this tannery industrial zone.

Impact assessment of legacy wastes from ancient mining activities on current earthworm community

Mineral resource exploitation by human societies throughout history led to the deposit of mining and smelting wastes and the subsequent contamination of surrounding soils by trace metals. After several centuries, the impact of these legacy hazardous wastes may remain a cause of environmental concern, especially for indigenous soil invertebrate populations such as earthworms. Therefore, we conducted a passive biomonitoring campaign in a former metallurgical district (Vosges Mountains, eastern France). According to community descriptors, we evidenced a significant decrease of anecic and endogeic earthworm density in the former mining stations. To link these results to soil contamination and bioaccumulation levels in earthworm tissues, we propose an original modelling approach using nonlinear mixed-effects regression models. Beyond a dose-response relationship between metal internal concentrations and their levels in soils, we highlighted contrasted behaviors according to ecological groups (epianecics and endogeics most impacted). We interpreted these results in relation to some eco-physiological features without completely exclude the influence of textural characteristics of soil, especially for deep-burrowing species such as anecic strict. Nonetheless, the presence of earthworm populations currently living in highly contaminated sites and handling elevated internal concentrations raises the question of the acquisition of genetic adaptive traits and the trophic transfers of metals.

Impact of different earthworm ecotypes on water stable aggregates and soil water holding capacity

We carried out mesocosm experiments using either the anecic earthworm Lumbricus terrestris or the endogeic earthworm Allolobophora chlorotica and loam, silt loam and sandy loam soils to investigate the differing impact of these earthworm of different ecotypes on aggregate formation (percentage water stable aggregates, %WSA) and soil water holding capacity (WHC), two soil properties that underpin many of the ecosystem services provided by soils. Earthworms significantly increased %WSA (by 16–56% and 19–63% relative to earthworm-free controls for L. terrestris and A. chlorotica, respectively). For L. terrestris, this increase was significantly greater in the upper 6.5 cm of the soil where their casts were more obviously present. Allobophora chlorotica treatments significantly increased WHC by 7–16%. L. terrestris only caused a significant increase in WHC (of 11%) in the upper 6.5 cm of the sandy loam soil. Linear regression indicated a consistent relationship between increases in %WSA and WHC for both earthworm species. However, for a given %WSA, WHC was higher for A. chlorotica than L. terrestris likely due to the known differences in their burrow structure. Overall, earthworms increased soil %WSA and WHC but the significant species/ecotype differences need to be considered in discussions of the beneficial impacts of earthworms to soil properties.

Earthworms offset straw-induced increase of greenhouse gas emission in upland rice production

Increasing water scarcity and rapid socio-economic development are driving farmers in Asia to transform traditionally flooded rice cropping systems into non-flooded crop production. The management of earthworms in non-flooded rice fields appears to be a promising strategy to support residue recycling and mitigate greenhouse gas (GHG) emissions triggered by residue amendment. We conducted a field experiment on non-flooded rainfed rice fields, with and without residue amendment. In-situ mesocosms were inoculated with endogeic earthworms (Metaphire sp.), with either low (ET1: 150 individuals m−2), or high density (ET2: 450 individuals m−2), and a control (ET0: no earthworms). We measured GHG emissions (methane (CH4); nitrous oxide (N2O); carbon dioxide (CO2)) twice a week during the cropping season with static chambers. Effects of earthworms on yield and root growth were additionally assessed. Earthworms offset the enormous increase of CH4 emissions induced by straw amendment (from 4.6 ± 5 to 75.3 ± 46 kg CH4-C ha−1 in ET0). Earthworm activity significantly reduced CH4 release, particularly at ET2, by more than one-third (to 22 ± 15 kg CH4-C ha−1). In contrast, earthworm inoculation did not affect N2O emission. Straw amendment more than doubled the global warming potential (GWP). Earthworms reduced GWP by 39% at low (ET1) and 55% at high densities (ET2). Earthworm activity reduced root mass density under conditions of straw amendment but did not affect yield. Earthworms can significantly reduce detrimental effects of rice crop residue amendment on GHG release under upland rice production. Organic carbon (C) might be preserved in earthworm casts and thereby limit C availability for CH4 production. At the same time, earthworm activity might increase methanotrophic CH4 consumption, due to improved soil aeration or less root exudates. Consequently, earthworms have a strong potential for regulating ecosystem functions related to rice straw decomposition, nutrient allocation and thus GHG reduction.

Preliminary study on the effect of endogeic earthworm on metabolic changes of blood-disease-infected banana

Metabolic changes in plants may serve as an early signal for infection in response to pathogen intrusions. In this study, metabolomic fingerprinting analysis was conducted on banana plantlets inoculated with endogeic earthworms and blood disease bacterium (BDB). It was found that infected stems and roots exhibited the lower metabolic intensities than uninfected ones. Principle component analysis (PCA) showed a clear discrimination between the 1H NMR spectra of banana roots infected with BDB and with the presence of earthworms. Earthworms were found to induce the host plants to produce compounds that were associated to disease resistance. This indicated that earthworms led to the alteration of metabolic reactions in the host plants in response to BDB infection. Future attempts that determine the relationship between the presence of earthworms and the production of key compounds that are responsible for plant defence mechanisms are important to explore the potential role of earthworms in disease remediation.

Do cryptic species of earthworms affect soil arthropods differently? The case of the Carpetania elisae complex in the center of the Iberian Peninsula

In recent years, it has been discovered that the endemic earthworm Carpetania elisae (formerly Hormogaster elisae) consists of a complex of at least six cryptic species. Studying the relationships between these new cryptic species and other soil animal communities may be important to understand their functional role in the soil, and eventually to detect possible differences that may help in the delimitation of these species. We have studied the effects of two of these cryptic species (species I from El Molar [Ce1] and species II from El Tomillar [Ce2]) on soil microarthropod communities. Several laboratory experiments were performed with both cryptic species, in the soils of both localities inhabited by these earthworm species, to determine their effects on soil microarthropod communities. Both earthworm species grew quite well throughout the experiment in their original soil, but while Ce1 grew up well when cultivated in the opposite soil from El Tomillar, Ce2 cultivated in the soil from El Molar survived but did not grow. Ce1 from El Molar showed a clear negative effect on microarthropods from El Molar and El Tomillar, whereas Ce2 from El Tomillar had a clear negative effect on soil microarthropods from its original soil but not on the ones from the opposite soil of El Molar. This paper demonstrates differences of both cryptic species on their effects on soil community, which suggest that they may play different roles in the soil system. Several mechanisms likely involved on the effect of earthworms on soil arthropods are discussed, being the competition for organic matter the most probable one in the case of these endogeic earthworms.

Evolutionary Origin and Host Range of Plagiotoma lumbrici (Ciliophora, Hypotrichia), an Obligate Gut Symbiont of Lumbricid Earthworms.

Four common earthworm species, the anecic Lumbricus terrestris, the endogeic Octolasion tyrteum as well as the epigeic Eisenia fetida and Dendrobaena veneta, were examined for the presence of the microbial gut symbiont Plagiotoma lumbrici. The evolutionary origin of this endobiotic microbe was reconstructed, using the 18S rRNA gene, the ITS1-5.8S-ITS2 region, and the first two domains of the 28S rRNA gene. Plagiotoma lumbrici was exclusively detected in the anecic Lumbricus terrestris. Multigene analyses and the ITS2 secondary structure robustly determined the phylogenetic home of Plagiotoma lumbrici populations within the oxytrichid Dorsomarginalia (Spirotrichea: Hypotrichia) as a sister taxon of the free-living Hemiurosomoida longa. This indicates that earthworms obtained their gut endosymbiont by ingesting soil/leaf litter containing oxytrichine ciliates that became adapted to the intestinal tract of earthworms. Interestingly, according to the literature data, Plagiotoma lumbrici was detected in multiple anecic and some epigeic but never in endogeic earthworms. These observations suggest that Plagiotoma lumbrici might be adapted to certain gut conditions and the lifestyle of anecic Lumbricidae, such as Lumbricus, Aporrectodea, and Scherotheca, as well as of some co-occurring epigeic Lumbricus species.

Dominant tree species and earthworms affect soil aggregation and carbon content along a soil degradation gradient in an agricultural landscape

Soil organic matter (SOM) is considered an important determinant of soil fertility in tropical agroecosystems. While numerous studies have shown the value of agroforestry in increasing soil nutrients and improving crop yield, few have addressed the systematic impacts of duration of cultivation on soil aggregation and C storage in such systems. A study was conducted in South Nandi (Kenya) to assess spatial influence of three dominant trees (Croton megalocarpus, Eucalyptus grandis and Zanthoxylum gilletii) on soil aggregation and C content in agroforestry systems. The study was conducted in a chronosequence experimental set-up where farms were continuously cultivated for 10, 16 and 62 years since conversion from primary forest. It was hypothesized that soil aggregates and whole soil and aggregate-associated C would decrease with duration of cultivation, with the magnitude of influence being reduced by the presence of trees and abundance of earthworms and termites. Greater abundance of small macroaggregates and microaggregates were recorded in soils under the canopy of Z. gilletii with an average weight of 62.8 g and 9.4 g 100 g−1 of soil compared to 53.9 g and 3.1 g 100 g−1 in soils under C. megalocarpus and 48.7 g and 3.9 g 100 g−1 in soils under E. grandis, respectively. These differences could be attributed to the high number of endogeic earthworm species, Nematogenia lacuum (Ocnerodrilidae) in soils under the canopy of Z. gilletii trees. Since N. lacuum is a small-sized species (40–55 mm long), it produces small faecal pellets and thus, we could infer that this species may have contributed to the fragmentation of large macroaggregates into small macroaggregates and microaggregates. The C content decreased by almost 40% in soils under longer duration of cultivation, with higher magnitude of differences associated with Z. gilletii trees. Increased microbial population in earthworms’ casts can increase mineralization rates, which may explain the low aggregate-associated C content under Z. gilletii trees where high number of N. lacuum were recorded. This study shows the significance of specific trees in shaping soil aggregation process and soil C content which could have far-reaching implications for the long-term C storage in the soil and hence net contributions to climate change mitigation.

Integrative taxonomy of five astome ciliates (Ciliophora, Astomatia) isolated from earthworms in Central Europe

Four earthworm species, the endogeic Octolasion tyrtaeum (Savigny, 1826), the anecic Lumbricus terrestris Linnaeus, 1758 as well as the epigeic Eisenia fetida (Savigny, 1826) and Dendrobaena veneta (Rosa, 1886), were examined for the presence of astome ciliates. Based on the integrative taxonomic approach, five ciliate species were recognized in their gastrointestinal tracts: Metaradiophrya lumbrici (Dujardin, 1841), M. varians (de Puytorac, 1954), Anoplophrya lumbrici (Schrank, 1803), A. vulgaris de Puytorac, 1954 and A. nodulata (Dujardin, 1841). Their distinctness was assessed using the multivariate morphometric approach and molecular phylogenetic analyses. Although the two species of Metaradiophrya Jankowski, 2007 on the one hand and the two former species of Anoplophrya Stein, 1860 on the other, were not distinctly separated by the multivariate morphometric analyses, they were clearly delimited by the 18S rRNA gene sequences. Species within each genus also differed by their hosts, M. lumbrici and A. lumbrici occurred only in anecic earthworms while M. varians and A. vulgaris occured exclusively in epigeic earthworms. Only a single species, A. nodulata, was detected in endogeic earthworms. It was morphologically distinct from and did not cluster with the two other species of Anoplophrya but was nested within the paraphyletic assemblage containing other astomes from endogeic earthworms. This indicates that the evolution of endosymbiotic ciliates from earthworms has very likely proceeded through a specialization to various ecological groups of their host organisms.

Coprolites Production of Native Earthworms in Braquiaria Fields Under Biofertilization

Aims: The objective of this study was to evaluate the coprolite production of native earthworms in a pasture with Brachiaria, with and without liquid-enriched biofertilization.
 Place and Duration of Study: The experiment was carried out between April of 2014 and August of 2015 at the Centro de Ciências Agrárias da Universidade Federal da Paraíba – UFPB.
 Methodology: A randomized complete block experimental design was used, with subdivided plots and four replicates, with a total of 40 plots in a 5x3x2 factorial arrangement, five grass species (Brachiaria brizantha, B. decumbens, B. humidicola, B. ruziziensise e B. brizantha MG5) and three sampling times, with and without liquid-enriched biofertilization. The plot area was composed of 50.0 m2 (10 m x 5 m) with subplots of 0.25 m2 (0.5 m x 0.5 m). Six foliar fertilization were performed in intervals of fifteen days, with three applications in the drought period and three applications in the rainy season. Each application consisted of 5% of biofertilizer (100 mL of biofertilizer diluted in 2 L of water), each plot received 2 L of biofertilizer.
 Results: In the dry season there was a significant difference in the means between the fertilization treatments, leading to the absence of fertilization, obtaining a better result, varying of 48, 24% in relation to the treatments that received fertilization, and there was no significant difference between the brachiaria. In the rainy season, it was verified that there was no significant difference in the means between the fertilization treatments, but there was a significant difference between the brachiaria.
 Conclusion: The study concludes that earthworm coprolites production is higher under pasture with B. MG5 during the dry season. In the rainy season, production increased under pasture with B. humidicula. Brachiaria fertilized with liquid-enriched biofertilizer provided lower results in the production of biogenic aggregates (earthworm coprolites). Under conditions of the present study, the hypothesis that the effect of the liquid -enriched biofertilizer increases the production of endogeic earthworm coprolites has not been proven.

Nitrogen supply reduces the earthworm-silicon control on rice blast disease in a Ferralsol

Revealing belowground-aboveground relationships (BAR) is essential to drive ecological processes to address agriculture dysfunctions, especially in the management of aboveground plant diseases. Earthworms are one of the most important soil organisms involved in BAR, and silicon (Si) has been identified as a crucial element regulating aboveground plant health. How earthworm-Si interactions induce BAR in poor- and rich-nutrient soil contexts is still poorly understood, despite a growing interest in agricultural sustainability. We investigated the potential of BAR induced by the earthworm-silicon interaction to control the severity of rice blast disease in a Ferralsol in Madagascar, with or without NPK fertilization. We conducted a greenhouse microcosm experiment in which we manipulated the presence of the endogeic earthworm Pontoscolex corethrurus and the fungus Pyricularia oryzae in a Ferralsol supplied or not with Si and fertilized with macronutrients (nitrogen, phosphorus and potassium, i.e., NPK). After eight weeks of growth, plant biomass, nutrition and disease severity were measured. Our results validated the hypothesis that a dual treatment of earthworm inoculation and Si fertilization in a nutrient-poor tropical soil confers a higher tolerance of rainfed rice to P. oryzae, in comparison with treatments with only earthworms or Si, providing the optimal agronomic balance between a gain in biomass (and nutrition) and a reduction in disease severity. The supply of macronutrients altered this positive BAR by favouring the phenomenon of N-induced susceptibility. The aboveground plant C:N ratio of 15 is a threshold below which any increase in N per C unit likely enhances blast disease. The role of belowground interactions to counteract agricultural dysfunctions is supported by our study. To accomplish ecological intensification and provision of ecosystem services such as disease regulation, our findings recommend replacing excessive use of macronutrient fertilizer with sustained agricultural practices promoting the development of earthworm populations, such as organic matter inputs, superficial or no tillage, and the use of cover crops or conservation agriculture.

Land management modulates the environmental controls on global earthworm communities

AbstractAimSoils and their biological communities face increasing pressure from multiple global drivers, including land management and climate change. In soils, earthworms play key roles in ecosystem functioning, but the environmental controls on their global communities are not fully understood. Here, an earthworm dataset was compiled to investigate the effects of environmental variables and land management on global earthworm communities.Location40° S–65° N.Time period1962 to 2016.Major taxa studiedEarthworms.MethodsA dataset of 899 earthworm community observations, together with environmental variables, was compiled across 169 globally distributed sites. Sites included natural forest and grassland or managed arable, pasture and plantation ecosystems. Total, anecic, endogeic and epigeic abundances and total species richness were compared in natural and managed ecosystems to quantify the effects of land management across climates. A hierarchical model was used to test the importance of environmental controls in predicting the relationship between total earthworm species richness and abundance at a global scale.ResultsLand management prompted little change in total earthworm abundance at the global scale, but reduced species richness and shifted community composition. Endogeic earthworms were more abundant in managed ecosystems, while anecic and epigeic earthworms showed variable responses across ecosystem types. Global relationships between total earthworm species richness and abundance were explained by climate, soil pH and land management.Main conclusionsLand management modulates the effects of environmental controls on global earthworm communities, through direct disturbance and indirect changes in edaphic conditions.

Analysis of oxidative stress and cellular aggregation in the coelomocytes of earthworms collected from metal contaminated sites of industrial and agricultural soils of West Bengal, India.

Endogeic earthworm Metaphire posthuma (Valliant, 1868) is a common biological component of the tropical soil of India and other countries. The species is reported to influence fertility and porosity of soil and bear a high composting potential. Intensive agricultural, industrial, and mining activities increase the amount of toxic metals in soil causing physiological adversity in earthworm and other biotic components in soil. Coelomocytes, the chief immunoeffector cells of earthworm, perform diverse physiological functions under the challenge of toxins and pathogens. The experimental earthworms collected separately from soils with agricultural and tannery activities were subjected to quantitation of prooxidation and antioxidation parameters for estimation of oxidative stress. Total count, cellular aggregation, generation of reactive oxygen species (ROS), superoxide anion, nitric oxide, activities of phenoloxidase, superoxide dismutase, catalase and glutathione-s-transferase, and amount of total protein were estimated in the coelomocytes of M. posthuma as experimental end points of toxicity screening. Concentrations of cadmium, chromium, lead, and mercury were determined in the soil samples to assess the degree of toxic contamination. The increase in the amount of prooxidants and decrease in the activities of antioxidant enzymes indicated the signs of oxidative stress in the coelomocytes of the organism. Aggregation of circulating coelomocytes is considered as an immune response involved in pathogen encapsulation response as reported in many invertebrates. Decrease in coelomocyte aggregation in earthworm collected from contaminated sites suggested a state of inappropriate shift of the innate immune status. Toxin-induced oxidative stress and reductions in cell aggregation response are the signs of immunocompromisation of M. posthuma. Present findings bear a prospect of this experimental species as an indicator of soil pollution.

Tree species identity governs the soil macrofauna community composition and soil development at reclaimed post-mining sites on calcium-rich clays

We tested the effect of main soil characteristics and tree species on earthworm community composition and abundance in reclaimed spoil heaps planted with five different tree species. Earthworm and soil macroarthropod abundance and biomass were highest in alder plantations, followed by oak plantations. The numbers of soil macrofauna were positively correlated with the total soil N content, which was highest in alder plantation. The correlation was strongest for endogeic earthworms (genus Aporrectodea and Octolasion). Soil moisture, measured in top 10 cm, affected only endogeic species. Other soil variables (pH, Ca) did not have a strong effect on earthworms. The earthworm community composition was similar in alder and oak, with most species occurring at both types of forest; however, in alder forest the epigeic species Dendrobaena octaedra was more common, whilst in oak forest the epigeic earthworms form genus Lumbricus were more abundant (L. rubellus and L. castaneus). The anecic species Aporrectodea longa was more abundant at alder sites, but L. terrestris was more abundant under oak. The alder forest was characteristic by a thick humus layer (10–15 cm), which at oak and larch sites was thinner (4–7 cm) and at pine and spruce stands was absent. Soil compaction was lower under the deciduous trees (alder, oak, larch), than under spruce and pine. We conclude that the alder plantations have most palatable litter and lowest C/N ratio and therefore support the highest numbers of soil macrofauna, which affects the humus layer thickness and soil compaction in the surface layers.

Do earthworms affect the fractionation of silicon in soil?

It is known that earthworms can increase the content of water-extractable silicon (Si) in soil, thus contributing to the availability of Si for plants. However, effects of earthworms on other Si fractions in soil, such as adsorbed Si, Si bound to SOM, Si occluded in pedogenic oxides and amorphous silica have not yet been studied. Therefore, we investigated the effects of the endogeic earthworm Octolasion cyaneum Savigny on the fractionation of Si in soils and that of the epigeic earthworm Eisenia andrei Bouché on the release of Si from model substances (quartz, wheat straw, bioopal). We quantified the amounts of Si in different soil fractions and those released from model substances before and after passage through the earthworm gut by sequential Si extraction. The amounts of Si extracted from the earthworms’ casts were generally larger than in the undigested samples. This was especially pronounced for Si bound to soil organic matter (SOM; up to 41%), and for Si in wheat straw (up to 71%) and quartz (up to 1730%). With the soils, the increase in extracted Si was pronounced for the more mobile fractions (Si bound to SOM and occluded in pedogenic oxides) at the expense of amorphous silica. The amounts of mobile and adsorbed Si (plant-available Si) in soil tended to decrease after the passage through the earthworm gut, possibly by occlusion of adsorbents in aggregates formed in the gut. Our results indicate that both mechanical weathering of ingested Si-containing particles and microbial processes, promoting aggregate formation, SOM transformation and mineral solubilization, contribute to the increased release of Si, which induced the redistribution of Si among fractions.