Surface cast production by the earthworm Aporrectodea nocturna in a pre-alpine meadow in Switzerland

Field and laboratory experiments were carried out to describe the effects of Aporrectodea nocturna on soil characteristics in a pre-alpine meadow and to support the development of a model of cast production. In the prealpine meadow, increased cast production, first observed about 20 years ago around a newly planted hedge, was recorded to a distance of maximal 170 m from the hedge. Numbers of A. nocturna between 130 and 165 m from the hedge decreased from 164 to 16 individuals m^-2. In the same area cast production steadily decreased from about 1.5 kg m^-2 week^-1 to nil, the plant community structure changed and the microbial biomass decreased, but the root biomass and the moisture content did not change. Laboratory experiments demonstrated that high cast production was not a specific feature of the A. nocturna population nor of the soil in the meadow. Diapause of A. nocturna was terminated in the laboratory during September. A model of cast production potential by the earthworm A. nocturna was established using laboratory determinations of the relationships with body weight, temperature, and water potential. The model was shown to predict cast production in the field given the assumption that the water potential was 0 MPa. According to the model, 81% of surface cast production was by juveniles, and 19% by adults of A. nocturna.     

Differences in burrowing behaviour and spatial interaction between the two earthworm species Aporrectodea nocturna and Allolobophora chlorotica

 To study intraspecific and interspecific interactions between different ecological types of earthworm, the burrowing behaviour of two earthworm species (the anecic earthworm Aporrectodea nocturna and the endogeic earthworm Allolobophora chlorotica) was observed in a microcosm. Earthworms were either alone in the microcosm, together with a conspecific earthworm, or with an earthworm of the other species. Observations under red light, including those of the position of the animals and the burrow dug, were recorded 4 times a day for 8 days and provided the data needed to reconstruct the probable trajectories of each earthworm. Differences in movement and burrowing behaviour were observed. Comparisons between the two species confirmed the expected behaviour of each ecological type: A. nocturna reused its burrow system regularly, whereas A. chlorotica rarely did. Moreover, it was shown that A. chlorotica burrowed less and explored a smaller surface when in the presence of A. nocturna. Besides, A. nocturna burrowed less and explored a smaller surface when in the presence of another A. nocturna. If these interactions occur under natural conditions, they could affect the structure of the burrow systems of the earthworm species examined. Received: 15 January 1999     

Lethal and sublethal effects of imidacloprid on two earthworm species (Aporrectodea nocturna and Allolobophora icterica)

The chemical imidacloprid is the major component of many widely used insecticides and is relatively persistent in soils. A set of experiments was carried out to estimate the lethal (mortality) and sublethal (weight loss) effects of one of these insecticides, Confidor, on two earthworm species commonly found in agricultural soils. A preliminary experiment in the absence of earthworms showed that imidacloprid was not rapidly degraded, with a decrease of less than 10% after 2 weeks, and that it was distributed in a reasonably homogeneous manner throughout the soil (less than 10% of variation between samples). The LC₅₀ of imidacloprid for the anecic species Aporrectodea nocturna and the endogeic species Allolobophora icterica was between 2 and 4 mg kg^–1 dry soil. This result is consistent with previous findings obtained with other earthworm species and natural soils. When sublethal effects were examined, significant decreases in weight were observed at concentrations of 0.5 and 1 mg kg^–1 dry soil for the two earthworm species whereas no effect was observed at a concentration of 0.1 mg kg^–1 dry soil (NOEC value). These concentrations are close to 0.33 mg kg^–1 which is the Predictive Environmental Concentration. Weight loss appears to be a valuable endpoint that can be used with worms freshly collected in the field as long as variability in the response of a control is taken into account.     

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

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

Weight response to the soil water potential of the earthworm Aporrectodea longa

Summary To assess the ability of endogeic earthworms to tolerate variations in soil water potential, groups of these worms were subjected to different, constant levels of soil water suction () over a period of 17 days. At water suctions varying from 0.3 kPa (pF 0.5) to 1990 kPa (pF 4.3), the earthworms showed no physiological ability to a maintain constant internal water content as assessed by the fresh weight. The relationship between weight loss and the increase in water, suction was modelled and the following critical thresholds were identified: <60 kPa did not affect earthworm weight; >620 kPa led to diapause; between these two values, earthworm weight was closely governed by the variation in . At the intermediate suction of 167 kPa, the exchange of water between the earthworms and the soil was at a maximum, and this value is therefore proposed as the level at which the diapause is induced. These modelled values were the diapause is induced. These modelled values were compared with those obtained under field conditions.     

Dynamic study of the burrowing behaviour of Aporrectodea nocturna and Allolobophora chlorotica: interactions between earthworms and spatial avoidance of burrows

The behaviour of earthworms belonging to two different species and ecological types (Aporrectodea nocturna and Allolobophora chlorotica) was studied using two-dimensional (2D) terraria. Two experiments were set up to gain insight into the nature of interactions between these earthworms. Firstly, the evolution of the burrow systems was analysed with the density of the earthworms varying from one to five individuals. Secondly, a burrow system was first established by using one earthworm which was then removed before the introduction of a second earthworm. This second earthworm therefore encountered a burrow system created either by a conspecific earthworm or by an earthworm of the other species. These experiments showed that: (1) intra- and interspecific interactions occur between earthworms, (2) these interactions are dependent on the physical presence of the earthworms, and (3) spatial avoidance can occur (A. chlorotica avoiding burrows created by A. nocturna). The results suggest that earthworm burrow systems are "individual structures", rarely used by other earthworms when inhabited. When abandoned, the burrows may be recolonised depending on the ecological type of the earthworm under consideration.     

Burrowing ability of the earthworm Aporrectodea longa limited by soil compaction and water potential

Summary Adult earthworms (Aporrectodea longa) were maintained for 199 days in soil columns (h=30 cm; ø=10 cm) where the water potential ranged from -7 to-65 kPa and compaction from 50 to 350 kPa. The weight of casts on the soil surface was measured at the end of two periods of activity (spring and autumn). Cast production increased with bulk density, but the activity of earthworms was limited both by the mechanical strength of the soil and by decreasing water potential. The results obtained in the laboratory conditions of this study were consistent with field observations on casting and burrowing activities. The effects of water potential and soil compaction on these activities were estimated.     

Assessment of the burrow system of Lumbricus terrestris, Aporrectodea giardi, and Aporrectodea caliginosa using X-ray computed tomography

Artificially packed soil columns were inoculated with individuals of different earthworm species (Lumbricus terrestris, Aporrectodea giardi or Aporrectodea caliginosa) and placed under controlled conditions in the laboratory. At the end of the incubation period, which lasted 8 months, three-dimensional reconstructions of the burrow system of each species were obtained using X-ray computed tomography. The particular features of the three burrow systems and the differences between them are discussed in terms of density, orientation and distribution of the burrows and the complexity of the network in relation to variations in soil depth and soil density. Received: 5 February 1997     

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

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

Maize residue application reduces negative effects of soil salinity on the growth and reproduction of the earthworm Aporrectodea trapezoides,in a soil mesocosm experiment

We studied the effects of maize residue application on some life-cycle parameters of the earthworm Aporrectodea trapezoides in saline agricultural soils with electrical conductivity (EC) ranging from 1.58 to 7.35 dS m⁻¹. This experiment was carried out under controlled laboratory conditions for 150 days. Results showed that soil salinity significantly affected the growth and reproduction of earthworms, decreasing survival, numbers and mean fresh weights of adults, juveniles and cocoons. Maize residue application gave a greater survival of earthworms at all salinity levels, but the differences were only significant at an EC of 7.35 dS m⁻¹, although the mean weight of adult earthworms was significantly increased by maize residue application at all salinity levels. At an EC of 1.58 dS m⁻¹ and 3.35 dS m⁻¹, the application of maize residues gave significantly higher numbers of cocoons and juveniles, but in soils with 5.26 dS m⁻¹ and 7.35 dS m⁻¹ earthworms did not produce any cocoons over the experimental period, irrespective of maize residue application. These results indicated that maize residue application alleviated the negative effects of soil salinity on the growth and reproduction of A. trapezoides up to 3.35 dS m⁻¹, above which maize residues only increased the growth but not on the reproduction of earthworms.     

The earthworm (Aporrectodea caliginosa) primes the release of mobile and available micronutrients in soil

The objectives of our study were to quantify the impact of endogeic earthworms Aporrectodea caliginosa (Savigny) on iron (Fe), manganese (Mn) and zinc (Zn) mobility and availability in soil. Dried rye straw (Cecale cereale L.), clover aboveground parts (Trifolium pratense L.) or calcium carbonate were added to determine the effects on soil micronutrient mobility. To test the importance of soil–water saturation mediated by earthworms, soil samples were modified to 60% (control) and 100% (as in casts) water holding capacity (WHC). To assess availability of micronutrients, a cucumber plant (Cucumis sativus L.) bioassay were used. Earthworm casts had generally higher amounts of water-soluble micronutrients compared with bulk soils regardless of their moisture contents. The increased micronutrient mobility was more pronounced in casts from soil samples amended with plant residues (especially with straw) and was significantly higher than mobility in control soil for at least 1 week after the casts were deposited. Pre-incubation of soils amended with clover or straw with living earthworms for 4 weeks produced an increase in both shoot biomass and translocation rate of micronutrients (Mn, Zn) into xylem sap of cucumber compared to soils not worked by earthworms. The earthworm-mediated plant performances were determined 4 weeks after the earthworms were removed. The results demonstrated that earthworms can significantly impact the formation of mobile and available micronutrients in a soil. The relationship between micronutrient availability to cucumber plants and earthworm contribution to nitrogen (N) mineralization and micronutrient mobility are discussed.     

Effect of food type and placement on earthworm (Aporrectodea tuberculata) burrowing and soil turnover

Subsurface-dwelling Aporrectodea tuberculata, a common earthworm in Upper-Midwest (USA) agricultural fields, may be a significant component of agroeco-systems with regard to soil mixing and preferential transport of water and chemicals. In this study we looked at effects of food residue placement and food type on A. tuberculata burrowing and soil turnover in two-dimensional Evans box microcosms. Four food residue placements mimicked patterns induced by primary tillage and two food types, readily available and natural food sources, with no food as a control. An average earthworm population of 100 earthworms m^-2 was calculated to generate 1058 km ha^-1 of new burrows and turnover 7.9 Mg ha^-1 of soil in 1 week of activity at 20°C. Burrowing was random until food sources were encountered, at which time burrowing appeared to center around the food source.     

Burrow systems made by Aporrectodea nocturna and Allolobophora chlorotica in artificial cores: morphological differences and effects of interspecific interactions

Burrow systems of earthworms contained in artificial cores were analysed through X-ray computed tomography and 3D skeleton reconstructions. Gas diffusion experiments were carried out on these cores to characterize soil transfer properties associated with the different burrow systems. Three types of cores were studied: cores in which Aporrectodea nocturna, an anecic earthworm was introduced (treatment 1), cores in which Allolobophora chlorotica, an endogeic earthworm was introduced (treatment 2) and cores that contained both species (treatment 3). Comparisons of the characteristics of the burrow systems of treatment 1 and 2 show important differences: the burrow system of A. nocturna comprises fewer burrows, which are longer, less branched, more vertical and have a lower sinuosity. The burrow system of A. chlorotica is characterized by lower continuity, which however did not result in a lower soil diffusivity. To study the burrow systems made by the two species in the same core (treatment 3), a separation that was based on differences in pore diameter between the two species and that takes into account the burrow orientation was designed. This separation was proven to be efficient since it resulted in low percentages of errors (around 10%) when applied to the burrow systems of treatments 1 and 2. Comparison of the burrow systems from treatments 1 and 3 demonstrated that the burrow system of A. nocturna was influenced by the presence of A. chlorotica: in treatment 3, A. nocturna made burrows that were smaller, more vertical and less branched. However, these interactions have to be confirmed under natural conditions.     

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

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

Three-dimensional visualization and quantification of soil macroporosity and water flow patterns using computed tomography

Abstract. Efforts to assess the role of soil structure in soil and water processes have been limited by data based on two dimensional geometry or disturbed samples. Computed tomography (CT) is a non-invasive technique that allows for the three dimensional, non-destructive examination of heterogeneous materials. X-ray CT scanning was used to acquire serial images of contrasting soil types that could be used to render, and hence, quantify important soil constituents in three dimensions. By repeating the scanning techniques after an infiltration period, it was also possible to examine the nature of water movement in real time. Macropore architecture between different soil types was highly variable and generally appeared as unconnected pore segments at the resolution examined. As expected, water flow characteristics were similar to macropore structure, with wetting patterns resembling both Darcian and preferential flow identified in different soils. From this, it was found that in the sandy clay soil c . 90% of macropore space was active following infiltration, compared with c . 50% for the sandy loam soil. In addition, it was possible to visualize the three dimensional distribution of stones and other mineral material. The results illustrated the benefits of computed tomography over more conventional analyses of soil structure, and its potential as a tool for examining dynamic soil processes. However, problems associated with accessibility, resolution and artefacts still provide limitations of the technique.     

Population dynamics of the earthworm Aporrectodea trapezoides (Annelida: Lumbricidae) in a Western Australian pasture soil

Summary The changes in size and age-composition of an earthworm population were studied in a Western Australian pasture developed since 1912. The population size in the surface 10 cm was estimated by handsorting during the cool wet season (19 weeks from May to September). Two species, both exotic, were found, Aporrectodea tranpezoides (Lumbricidae) and Microscolex dubius (Acanthodrilidae). Of the 615 individual speciemens collected, 99.7% were A. trapezoides. The abundance of A. trapezoides increased from 58 m^-2 at the time of the opening rains to 170 m^-2 (88.6 g live weight m^-2) after 10.5 weeks. Near the end of the wet season (in October) the density was 37 m^-2. At the time of the opening rains the population consisted of juvenile and semimature individuals. Clitellate earthworms were found 1 month later and predominated from August (10.5 weeks) to the end of the season. Egg capsules were found from August through October. Egg capsules incubated in the laboratory at 16°C hatched on average after 42 days and produced two juveniles. Juvenile and immature earthworms collected from a quiescent state at the end of summer matured within 1 month when reared in moist soil in the laboratory.     

蚯蚓对电刺激的响应及其与蚯蚓粪胁迫分离的参数量化

蚯蚓与蚯蚓粪快速高效分离是规模化蚯蚓生物消解农业废弃物的关键技术环节。针对目前电刺激分离蚯蚓方法在实际生产应用中缺乏相关定量参数等问题,该研究探讨了蚯蚓分离率对电刺激方式、强度、通断电循环周期时长、通电时长及电刺激耦合物料含水率、物料厚度等因子的响应关系,并分析了电刺激对蚯蚓生理生化指标的影响。结果表明,电刺激可促进蚯蚓与蚓粪分离,间歇式电刺激方式较持续式电刺激具有更好的分离效果;间歇式电刺激方式下,蚯蚓分离率与电刺激强度、通断电循环周期时长、通电时长均呈显著的开口向下一元二次抛物线关系,蚯蚓生长的物料含水率适宜值为52.60%,物料厚度越小,越有利于电刺激分离率的提高;电刺激处理对蚯蚓体内过氧化氢酶、超氧化物歧化酶、乙酰胆碱酯酶、纤维素酶、可溶性蛋白含量无显著影响,但显著提高了丙二醛含量,蚯蚓经过5 d的恢复性驯养后,丙二醛含量可恢复至对照处理水平;综合蚯蚓分离率、技术参数易操作性等,采用间歇式电刺激方式分离蚯蚓,设计电刺激强度2 mA、通断电周期时长30 s、通电时长1 s,控制物料含水率50%左右、物料厚度20～25 cm,辅助210 lx白光光照,电刺激作业时间30 min,蚯蚓分离效率可达85%左右。研究可为快速高效分离蚯蚓活体与蚯蚓粪的设备研发与应用提供参考。     

C and N turnover of fermented residues from biogas plants in soil in the presence of three different earthworm species (Lumbricus terrestris,Aporrectodea longa,Aporrectodea caliginosa)

A soil microcosm experiment was performed to assess (1) the C- and N- turnover of residues from biogas plants in soils in the presence of three earthworm species (Lumbricus terrestris, Aporrectodea longa and Aporrectodea caliginosa) and (2) the resulting changes in soil chemical and microbiological properties when using these residues as fertilizer in comparison to conventional slurry. Earthworms were exposed in soils, fertilized with an equivalent amount of 120 kg of NH₄-N ha^?1 from: (1) conventional cattle slurry and (2) a fermented residue derived from cattle slurry, grass (silage) and maize. Additional treatments without slurry and earthworms were used as controls.There was considerable evidence that soils fertilized by fermented slurry comprised fewer amounts of readily available nutrients for microbial C and N turnover. We observed significant stimulation of microbial biomass, basal respiration and nitrification in treatments with conventional slurry, especially in the presence of earthworms. However, the stimulation of microbial activity by manure and earthworms were significantly lower in treatments with fermented slurry. Moreover, the results showed clear interactions between different earthworm species and manures. While the biomass of the anecic species (L. terrestris and A. longa) increased in both slurry treatments, the biomass of A. caliginosa (endogeic) decreased, with a significantly stronger biomass decline in treatments with fermented slurry. The metabolic quotients revealed microbial stress metabolism in fermented slurry treatments, predominantly in treatments with A. caliginosa. We conclude that particularly A. caliginosa and soil microorganisms competed for labile C sources in treatments with fermented slurry. An application of these residues as fertilizer might result in a reduction of microbial activity in agricultural soils and in a decline of endogeic earthworms.