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.     

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.     

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.     

Using FAME profiles for the characterization of animal wastes and vermicomposts

This study investigated the possibility of fingerprinting different organic wastes (cow, pig and horse manure) and the vermicomposts produced by different earthworm species (Eisenia andrei, Eudrilus eugeniae and Lumbricus rubellus) analyzing the profiles of fatty acid methyl esters (FAMEs). We found clear differences between their microbial communities, demonstrating the power and sensitivity of the total FAME analysis. In addition, qualitative and quantitative analyses of specific biomarkers permitted to determine differences between samples and to evaluate the effect of earthworms in the decomposition of organic matter. Fatty acid profiles were largely determined by the different vermicomposting earthworm species. Fatty acid 18:2ω6 increased significantly in horse manure vermicomposted by L. rubellus and in cow manure vermicomposted by the three earthworm species, whereas it decreased significantly in pig manure vermicomposted by L. rubellus and E. eugeniae. Fatty acid 20:4ω6 increased significantly in all vermicomposts obtained with the three earthworm species.     

Effect of earthworms on decomposition processes in raw humus forest soil: A microcosm study

Summary The earthworms Lumbricus rubellus (Hoffmeister) and Dendrobaena octaedra (Savigny) were studied in the laboratory to determine their effects on decomposition and nutrient cycling in coniferous forest soil. CO₂ evolution was monitored, and pH, PO ₄ ^3– –P, NH ₄ ⁺ –N, NO ₃ ^– –N, total N, and total C in the leaching waters were measured. After three destructive samplings, numbers of animals, mass loss, pH, and KCl-extractable nutrients were analysed.The earthworms clearly enhanced the mass loss of the substrate, especially that of litter. L. rubellus stimulated microbial respiration by 15–18%, whereas D. octaedra stimulated it only slightly. The worms significantly raised the pH of the leaching waters and the humus; L. rubellus raised the value by 0.2–0.6 pH units and D. octaedra by 0.1–0.4 units. Both worms increased N mineralization. Although the biomass of both worms decreased during the experiment, the N released from decomposing tissues did not explain the increase in N leached in the presence of earthworms. The worms influenced the level of PO ₄ ^3– –P only slightly.     

Earthworm response to 10 weeks of incubation in a pot with acid mine spoil,sewage sludge,and lime

Applications of sewage sludge and lime have been used to restore some of the nearly 1.0 million ha of unreclaimed acid mine spoils in the United States. Earthworms might also aid in the reconstruction of mine spoils, but the earthworm response to mine spoils and sludge has not been widely studied. The objective of the present study was to examine growth of the earthworm Lumbricus terrestris in pots containing acidmine spoils, sewage sludge, and lime, and the growth of two common reclamation grasses, timothy (Phleum pratense L.) and tall fescue (Festuca arundinacea Schreb.), to the addition of earthworms. After 10 weeks, earthworms growing in the mine spoil treated with sewage sludge showed an increase in mean specific mass of 26.9% and in projected specific area of 24.5%. In contrast, earthworms growing on mine spoils without sludge decreased in mass by an average of 39.6% and in area by 21.0%. Soil pH influenced earthworm area, but not mass: earthworms growing on mine spoils (with or without sludge) showed an increase in mean surface area of 2.9% at pH 5.3 and a decrease of 11.2% at pH 6.5. The presence of earthworms significantly increased the belowground production of plant roots, but had no effect on either soil bulk density or above-ground production of plant biomass. The addition of earthworms to acid mine spoils treated with sewage sludge and lime might aid in the redevelopment of soil quality and biological diversity.     

Effects of earthworms on nitrogen mineralization

The influence of earthworms (Lumbricus terrestris and Aporrectodea tuberculata) on the rate of net N mineralization was studied, both in soil columns with intact soil structure (partly influenced by past earthworm activity) and in columns with sieved soil. Soil columns were collected from a well drained silt loam soil, and before the experiment all earthworms present were removed. Next, either new earthworms (at the rate of five earthworms per 1200 cm³, which was only slightly higher than field numbers and biomass) were added or they were left out. At five points in time, the columns were analyzed for NH ₄ ⁺ , NO ₃ ^– , and microbial biomass in separate samples from the upper and lower layers of the columns. N mineralization was estimated from these measurements. The total C and N content and the microbial biomass in the upper 5 cm of the intact soil columns was higher than in the lower layer. In the homogenized columns, the C and N content and the microbial biomass were equally divided over both layers. In all columns, the concentration of NH ₄ ⁺ was small at the start of the experiment and decreased over time. No earthworm effects on extractable NH ₄ ⁺ were observed. However, when earthworms were present, the concentration of NO ₃ ^– increased in both intact and homogenized cores. The microbial biomass content did not change significantly with time in any of the treatments. In both intact and homogenized soil, N mineralization increased when earthworms were present. Without earthworms, both type of cores mineralized comparable amounts of N, which indicates that mainly direct and indirect biological effects are responsible for the increase in mineralization in the presence of earthworms. The results of this study indicate that earthworm activity can result in considerable amounts of N being mineralized, up to 90 kg N ha^–1 year^–1, at the density used in this experiment.     

Effects of biomass and size of Millsonia anomala (Oligochaeta: Acanthodrilidae) on particle aggregation in a tropical soil in the presence of Panicum maximum (Gramineae)

Summary The present study assessed the effect of the tropical geophagous earthworm, Millsonia anomala, on the aggregate-size distribution of a sieved (2 mm), tropical ferruginous soil in the presence and absence of the perennial tropical grass Panicum maximum. The effect of two size groupings and graded biomass densities of M. anomala on soil aggregation was analysed in time and with depth in the containers within which the plants were grown. In the absence of earthworms, aggregation was rapid although limited (13.5% of soil as aggregates >2.0 mm), and probably arose from a combination of microbial activity and physical processes (interparticle bonding due to clays and other colloids). The roots of the test species contributed little to aggregation. In contrast, the effect of earthworm activity on soil aggregation was rapid and important. The effects of both biomass and, to a lesser extent, size were significant. After 79 days, aggregation reached a maximum with 3 g per container of small earthworms (ca. 59% of soil as aggregates >2.0 mm) and a minimum with 1 g per container of large earthworms (ca. 35% of aggregates >2.0 mm). Aggregation was considered to occur through three different mechanisms: (1) A rapid aggregation due to the interactions of colloids; (2) an intermediate aggregation due to a combination of unquantified processes related to earthworm activity (mucus secretion, development of fungus hyphae); (3) egestion of soil as earthworm casts which are stable macroaggregates.     

Effects of seasonal and diurnal temperature fluctuations on population dynamics of two epigeic earthworm species in forest soil

Temperature fluctuations are a fundamental entity of the soil environment in the temperate zone and show fast (diurnal) and slow (seasonal) dynamics. However, responses of soil ecosystem engineers, such as earthworms, to annual temperature dynamics are virtually unknown. We studied growth, mortality and cocoon production of epigeic earthworm species (Lumbricus rubellus and Dendrobaena octaedra) exposed to temperature fluctuations in root-free soil of a mid-European beech-oak forest. Both earthworm species (3 + 3 individuals of each species) were kept in microcosms containing soil stratified into L, F + H and A_h horizons. In the field, earthworm responses to smoothing of diurnal temperature fluctuations were studied, simulating possible global change. In the laboratory, earthworm responses to seasonal (±5 °C of the annual mean) and diurnal temperature fluctuations (±5 °C of the seasonal levels) were analyzed in a two-factorial design. Both experiments lasted 12 months to differentiate between seasonal and diurnal responses. In the third experiment overwintering success of both earthworm species was investigated by comparing effects of constant temperature regime (+2 °C), and daily or weekly temperature fluctuations (2 °C ± 5 °C).Temperature regime strongly affected population performance of the earthworms studied. In the field, smoothed temperature fluctuations beneficially affected population development of both earthworm species (higher biomass, faster maturity and reproduction, lower mortality). Consequently, density of both species increased faster at smoothed than at ambient temperature conditions. In the laboratory, responses of L. rubellus and D. octaedra to temperature treatments differed; however, in general, earthworms benefited from the absence of diurnal fluctuations. Total earthworm numbers were at a maximum at constant temperature and lowest in the treatment with both diurnal and seasonal temperature fluctuations. However, after one year L. rubellus tended to dominate irrespective of the temperature regime. In the overwintering experiment L. rubellus sensitively responded to even short-term winter frost and went extinct after one week of frost whereas D. octaedra much better tolerated frost conditions. Earthworms of both species which survived frosts were characterized by a significant body weight decrease during the period of frosts and fast recovery in spring suggesting a different pattern of individual resource expenditure as compared with constant +2 °C winter regime. Contrasting trends in the population dynamics of L. rubellus and D. octaedra during the frost-free period and during winter suggest that in the long-term temperature fluctuations contribute to the coexistence of decomposer species of similar trophic position in the forest litter. The results are discussed in context of consequences of climate change for the functioning of soil systems.     

Earthworm biomass and population structure are negatively associated with changes in organic residue nitrogen concentration during vermicomposting

Vermicomposting is an efficient and environmentally friendly technology to dispose of agricultural organic residues. The efficiency of organic residue decomposition during vermicomposting is directly affected by the biomass and population structure of earthworms. In this study, we investigated how the earthworm biomass and population structure responded to changes in the physicochemical properties of six types of organic residue (cattle dung, herbal waste, rice straw, soybean straw, garden waste, and tea residues) during vermicomposting. Each type of organic residues was placed in a pot with earthworms Eisenia fetida, and the physicochemical properties of the organic residues and earthworm growth dynamics were recorded at 0, 30, 60, and 90 d of vermicomposting. The biomass and population structure of earthworms were stable or increased in rice straw, garden waste, and cattle dung within 60 d of vermicomposting, whereas in tea residues and herb waste, very little earthworm activity (3 adults and 2 cocoons) was recorded on day 30. Among the physicochemical parameters, the substrate C/N ratio was negatively correlated with earthworm growth dynamics. Decomposing organic residues showed higher NH₄⁺-N and NH₃^--N concentrations but a lower total organic carbon content, which negatively affected earthworm growth and reproduction. We recommend that chemical properties of vermicomposting systems should be monitored regularly. At the threshold levels of decomposing organic residue NH₄⁺-N and NH₃^--N concentrations, earthworms should be removed and the vermicompost can be harvested. Small- and large-scale farmers thus need to monitor the physicochemical properties of vermicompost to sustain active earthworm populations.     

Influence of clay content and acidity of soil on development of the earthworm <Emphasis Type="Italic">Lumbricus rubellus</Emphasis> and its population level consequences

In this paper we report on the influence of clay content and acidity of soil on growth and reproduction of the epigeic earthworm species Lumbricus rubellus (Hoffm.), which is common in most temperate soils and abundant in grasslands. Growth, cocoon production and survival of L. rubellus were tested in 12 Dutch soils which differed in soil properties. A matrix model was used to assess the population-level consequences of changes in growth and reproduction. Soil acidity had a strong negative effect on earthworm survival, and the maturation weight decreased with clay content. Individual weight gain in L. rubellus decreased with both acidity and clay content. The acidity of soils had a larger influence on population growth rate than the clay content. The acidity of the soil also changed the population composition towards younger age classes, whereas in soils rich in clay, the population composition did not change. The average individual weight of L. rubellus in clayey soils, however, was lower compared with that in soils low in clay, a result that agrees with literature data.     

Genetic and ecological impacts of heavy metal and flooding stress on the earthworm Lumbricus rubellus in floodplains of the Rhine river

In the highly polluted river Rhine system, earthworms face environmental stress resulting from flooding and elevated heavy metal concentrations in the floodplain soil. Previous field studies have revealed adaptation to flooding for the earthworm species Lumbricus rubellus as this species matures at a lower weight in floodplain sites with a high frequency of flooding compared to less frequently flooded sites. Also heavy metals have effects on L. rubellus and heavy metals are influencing the genetic composition of this species. In this study, it was tested whether flooding and heavy metals had an impact on the genetic composition of L. rubellus living in floodplains along the river Rhine system. Earthworms were sampled at three sites previously studied along the river to assess earthworm diversity, biomass, density, and individual weight, and developmental status of L. rubellus. The genetic variation by means of isozymes was studied for 175 individuals. The results showed lowest density of L. rubellus adult and sub-adult life-stages and lowest individual weight of these life-stages at the frequent inundated site. The genetic composition, however, showed no effects of flooding on the genetic composition, but effects of heavy metals could not be ruled out.     

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.     

Effect of Hormogaster elisae (Oligochaeta; Hormogastridae) on the stability of soil aggregates

The production and stability of soil aggregates produced by laboratory cultures of the endogeic earthworm Hormogaster elisae was studied using three different techniques: the determination of the soil mean weight diameter (MWD), the aggregate tensile strength, and by the Blanchart method, which involves three different tests. The MWD index of soils was higher in microcosms containing H. elisae. Tensile strength was significantly higher in earthworm casts than in naturally formed aggregates. The Blanchart method also showed aggregates produced by earthworms to be more stable. The results of all three methods concur in that aggregates produced by H. elisae are larger and more stable than those produced in control microcosms without earthworms.     

Influence of cadmium,copper, and pentachlorophenol on growth and sexual development of Eisenia andrei (Oligochaeta; Annelida)

Summary In the existing guidelines for earthworm toxicity testing, mortality is the only test criterion. Mortality is, however, not a very sensitive parameter, and from an ecological point of view growth and reproduction are more important for a proper risk assessment of chemicals in soil. In this study the growth and sexual development of juvenile earthworms were considered as test criteria in a standardized earthworm toxicity test. The effect of Cd, Cu, and pentachlorophenol on the growth and sexual development of juveniles of the species Eisenia andrei was studied in an artificial soil substrate. Two tests with Cd were carried out to study the effects of the mode of application of the food source (cow dung). EC₅₀ (50% effective concentration) values for the effect of Cd, Cu and pentachlorophenol on the growth of E. andrei were 33–96, >100, and >32 mg kg^-1 dry soil, respectively, and there was no observed effect at 18–32, 56, and 32 mg kg^-1 dry soil, respectively. Sexual development of the earthworms was inhibited at 10 mg Cd kg^-1 and 100 mg Cu kg^-1 dry soil, but was not affected at the highest pentachlorophenol concentration tested (32 mg kg^-1 dry soil). The results were the same whether the food was applied in a hole in the middle of the soil or mixed homogeneously through the soil.     

Mycorrhizal colonization and nitrogen uptake by maize: combined effect of tropical earthworms and velvetbean mulch

Earthworms and mulch can have positive or negative effects on mycorrhizae (fungus-roots) and N uptake by plants. In the present experiment, maize plants were grown under greenhouse conditions with or without tropical earthworms (Balanteodrilus pearsei) and mulch of velvetbean (Mucuna pruriens var. utilis). The formation of vesicles and hyphae of arbuscular-mycorrhizal (AM) fungi in roots and N uptake by maize plants was measured at harvest. The addition of earthworms and velvetbean reduced AM root colonization. Earthworms had no effect on plant root or shoot biomass. In the absence of velvetbean, earthworms reduced AM colonization, but when velvetbean was present, this effect disappeared. The addition of velvetbean mulch, on the other hand, had an effect on plant biomass (above- and belowground) and a positive effect on AM fungal colonization of roots in presence of worms, but a negative effect when worms were absent. When both M. pruriens and B. pearsei were added, shoot and root biomass and N concentrations increased. Vesicle formation was related to velvetbean mulch decomposition as well as the higher N concentration in maize roots. Management of mulch–earthworm interactions may be of value, particularly in low-input and organic agricultural systems, and deserves further investigation.     

Survival of bacteria introduced into soil by means of transport by Lumbricus rubellus

Four strains of bacteria, Rhizobium leguminosarum biovar trifolii, Pseudomonas fluorescens, Pseudomonas cepacia, and Flavobacterium sp., were introduced into loamy sand and then transported by earthworms of the species Lumbricus rubellus to uninoculated soil. Cell densities recovered from the earthworm gut and casts (both expressed per gram dry material) were significantly lower (up to 3 log units) than cell densities recovered from the inoculated soil. Total bacterial counts in casts were similar to those in the inoculated soil. In casts excreted into a sterile environment numbers of colony-forming units (CFU) increased, suggesting a favourable environment for growth. In casts excreted in a non-sterile environment, cell densities of introduced strains decreased. Casts therefore did not offer the introduced bacteria a protective micro-environment for survival in the bulk soil. Transport by worms of R. leguminosarum biovar trifolii and of P. fluorescens appeared to occur mostly by means of cast production; with the Flavobacterium sp. and P. cepacia a large proportion of the cells was possibly transported on the skin of earthworms.     

The role of the earthworm Lumbricus terrestris in the transport of bacterial inocula through soil

Two laboratory experiments were used to investigate the effect of the earthworm Lumbricus terrestris on transport of genetically marked Pseudomonas fluorescens inocula through soil microcosms. The microcosms comprised cylindrical cores of repacked soil with or without earthworms. Late log-phase cells of P. fluorescens, chromosomally marked with lux genes encoding bioluminescence, were applied to the surface of soil cores as inoculated filter paper discs. In one experiment, 5 and 10 days after inoculation, cores were destructively harvested to determine concentrations of marked pseudomonads with depth relative to the initial inoculum applied. Transport of the bacteria occurred only in the presence of earthworms. In a second experiment cores were subjected to simulated rainfall events 18 h after inoculation with lux-marked bacteria at 3-day intervals over a 24-day period. Resulting leachates were analysed for the appearance of the marked bacteria, and after 28 days cores were destructively harvested. Although some marked cells (less than 0.1% of the inoculum applied) were leached through soil in percolating water, particularly in the presence of earthworms, the most important effect of earthworms on cell transport was through burial of inoculated litter rather than an increase in bypass flow due to earthworm channels.     

Development of QSAR's in soil ecotoxicology: Earthworm toxicity and soil sorption of chlorophenols,chlorobenzenes and chloroanilines

Soil adsorption and the toxicity of four chloroanilines for earthworms were investigated in two soil types. The toxicity tests were carried out with two earthworm species, Eisenia andrei and Lumbricus rubellus. LC₅₀ values in mg kg^?1 dry soil were recalculated towards molar concentrations in pore water using data from soil adsorption experiments. An attempt has been made to develop Quantitative Structure Activity Relationships (QSAR's) using these results and data on five chlorophenols and dichloroaniline in four soils and five chlorobenzenes in two soils published previously (Van Gestel and Ma, 1988, 1990; Van Gestel et al., 1991). Significant QSAR relationships were obtained between 1) adsorption coefficients (log K _om ) and the octanol/water partition coefficient (log k _ow ), and 2) LC₅₀ values (in itμmol L^?1 soil pore water) and log K _ow . It can be concluded that both earthworm species tested are equally sensitive to chlorobenzenes and chloroanilines, E. andrei is more sensitive than L. rubellus to chlorophenols.     

Population dynamics of the earthworm Amynthas alexandri (Annelida: Megascolecidae) in a Kumaun Himalayan pasture soil

Ecological studies on earthworms were conducted in a Kumaun Himalayan pasture soil. The C:N ratio in the soil declined with increasing depth. A combination of hand-sorting and formalin application was used to sample the earthworms. Three species, Amynthas alexandri, A. diffringens (Megascolecidae), and Eisenia fetida (Lumbricidae) were found. Of the 13310 individuals collected, 99.9% were A. alexandri. The maximum density (138.8 m^-2) and biomass (25.2 g m^-2) were recorded in the wet season. More than 60% of the total earthworm numbers and biomass were recorded at 0–10 cm in depth. The mean yearly ratio of clitellate to aclitellate worms was 1:7.3.