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.     

Axial pressures generated by the earthworm Aporrectodea rosea

Summary The axial forces generated by the earthworm Aporrectodea rosea were measured by directing the earthworm to tunnel into soil discs mounted on an electronic balance connected to a datalogger. The area over which the force acted was estimated from the size of the hole created by the tunnelling. The maximum force recorded by an individual worm was 0.760 N and the mean maximum value was 0.465 N. The maximum pressures recorded was 116.5 kPa, while the mean maximum pressure was 72.8 kPa. These axial pressures are approximately one-tenth of the maximum axial pressure recorded for plant roots. The statistical distribution of activity as the worms tunnelled through the soil discs was analysed. Pressures recorded were well in excess of physiologically measured pressures and the generation of forces within muscles to achieve these pressures was calculated by some assumptions. It was estimated that there is a maximum tension in the circular muscles of 0.15 N per segment of the worm.     

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.     

Radial pressures generated by the earthworm Aporrectodea rosea

Summary The radial pressures generated by the earthworm Aporrectodea rosea were measured in a study of the conditions under which the worms were able to crack soil discs into which they were encouraged to tunnel. The tensile strength of replicate discs was determined by indirect tension tests and by expansion of rubber membranes in soil discs. Simple engineering theory was used to relate the stress required to fracture a disc with the applied internal stress. Mean values for the radial stress applied by the earthworms in tunnelling through the discs was 230 kPa. With some assumptions about the distribution of muscles across the worm diameter, it was estimated that the mean maximum force generated by all the longitudinal muscles in any segment was 3.2 N.     

Ability of the earthworms Aporrectodea rosea and Aporrectodea trapezoides to increase plant growth and the foliar concentration of elements in wheat (Triticum aestivum cv. spear) in a sandy loam soil

In a greenhouse study, the ability of the earthworms Aporrectodea rosea and A. trapezoides to influence the foliar concentration of elements and the growth of wheat plants was assessed 27 days after sowing in a sandy loam soil. The presence of A. rosea and A. trapezoides (at densities equivalent to 314 and 471 m^-2, respectively) caused a significant increase in the shoot dry weight of wheat. The presence of A. rosea and A. trapezoides (at densities equivalent to 314 and 157 m^-2, respectively) was also associated with a significant increase in the root dry weight of wheat. The presence of A. rosea caused a significant increase in the foliar concentration of Ca, Cu, K, Mn, N, Na, and P, but did not influence the foliar concentration of Al, B, Fe, Mo, Mg, S, and Zn. The presence of A. trapezoides was associated with a significant increase in the foliar concentration of Al, Ca, Fe, K, Mn, N, and Na, but did not influence the foliar concentration of B, Cu, Mo, Mg, P, S, and Zn. These results demonstrate the potential of A. rosea and A. trapezoides to increase the growth of wheat in a sandy loam soil and suggest that the mechanism by which they increased plant growth was, in part, through increasing the availability and uptake of nutrients from this soil.     

Factors affecting surface casting behaviour in several species of earthworm

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

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.     

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.     

Structural parameters and functional patterns of simulated earthworm burrow systems

Summary Earthworm burrow systems have been simulated by modelling, from field observations, five main characteristics of burrow units: density (number of burrows per unit volume), mean length, angular orientation, middle coordinates and diameter. The functional properties of the burrow systems have been analysed using structural parameters, i. e. number of full perforations, mean available burrow surface and minimal burrow spacing, and by estimating the shortest pathway through the burrow system. The simulations are used to study the effects of each of the main characteristics on structural parameters and the shortest pathway. This work reveals that the specific role of density is to lead to a threshold by determining an optimal horizontal distance, and that the mean length governs the vertical critical dimension of the system. These simulations may be applied to explain the nature of field burrow systems.     

Changes in active microbial biomass by earthworms and grass amendments in agricultural soil

The influence of the earthworm Aporrectodea caliginosa on the biomass and the proportion of active and dormant soil microorganisms after the addition of cut perennial ryegrass (Lolium perenne) to upper soil from agricultural field was studied in a microcosm experiment. During a 2-month period, soil samples were taken 1, 8, 22, 36, 50, and 64 days after cut grass addition. A substrate-induced respiration (SIR) method was used to analyse the samples for total microbial biomass and the distribution of active and dormant microbial biomass. It was found that the addition of grass increased the microbial biomass (SIR) because of an increase in the active microbial biomass. After the initially high values, the active microbial biomass decreased slowly, and at day 64, it was still higher in the grass-amended soils than in the control treatment without grass addition. After 1 day, the active microbial biomass was higher in the soil with A. caliginosa than without the earthworm. At the subsequent samplings, there were no differences in microbial biomass or the proportion of dormant vs active microorganisms between the grass-amended soils. The average from all sampling occasions of SIR was higher in earthworm-treated soil.     

The earthworm population of a winter cereal field and its effects on soil and nitrogen turnover

The earthworm population in a winter cereal field in Ireland was studied over a 3-year-period and its effects on soil and N turnover were assessed. The mean annual population density was 346–471 individuals m^-2 and the mean biomass was 56.9–61.2 g m^-2. Twelve species were recorded, the most abundant being Allolobophora chlorotica followed by Aporrectodea caliginosa, and 242 mg at 5°C to 713 mg at 10°C in the case of juvenile Lumbricus terrestris. Gut contents (dry mass of soil) comprised 6.7–15.5% of the A. caliginosa live mass, and 9.7–14.7% of the Lumbricus terrestris mass. Annual soil egestion by the field population was estimated as 18–22 kg m^-2. Tissue production ranged from 81.7 to 218.5 g m^-2, while N turnover resulting from mortality was calculated as 1.5–3.9 g m^-2 depending on the year and the method of calculation. Earthworms were estimated to contribute an additional 3.4–4.1 g mineral N to the soil through excretion, mucus production, and soil ingestion. Independent estimates of N output via mucus and excretion derived from ¹⁵N laboratory studies with Lumbricus terrestris were 2.9–3.6 g m^-2 year^-1.     

Destabilization of soil during the production of earthworm (Lumbricidae) and artificial casts

The mechanisms by which soil is destabilized in the digestive tract of endogéic earthworms were investigated with artificial casts, which were moulded with a syringe from slurries of a silty loam with or without gypsum and organic matter treatments, and compared to casts produced by Aporrectodea rosea (Lumbricidae). Both types of casts generally had the same levels of mechanical dispersion, observations of slaking, and particle size distribution when the casts were fresh, aged-moist for 30 days, or air-dried. Fresh casts were significantly more dispersive than the uningested soil despite the addition of gypsum or organic matter to the soil. However, the dispersion from aged-moist or air-dried casts was not substantially greater than that of uningested soil. Air-drying was more effective than moist-ageing in increasing the stability of casts and uningested soil. The concentration of soluble carbohydrate was greater in artificial casts produced from soil treated with sheep dung or xanthan gum, and in earthworm casts produced from soil treated with xanthan, than in the uningested soil of the same treatments. An increase in the concentration of soluble carbohydrate was related to an increase in dispersion. An attempt was made to simulate the addition of mucus to soil in the digestive tract of earthworms, by the addition of sucrose or xanthan gum to the slurry during the production of artificial casts. The addition of xanthan, but not sucrose, to the slurry increased mechanical dispersion relative to that of the uningested soil in the fresh treatment. Although the production of artificial casts destabilized soil to the same degree as earthworm casts, the artificial casts did not simulate all chemical, biochemical, and microbiological aspects of digestion. Received: 24 November 1995     

The response of Aporrectodea rosea and Aporrectodea trapezoides (Oligochaeta: Lubricidae) to moisture gradients in three soil types in the laboratory

The question of whether the response of earthworms to soil moisture is governed by their reaction to soil wetness (moisture content) or to soil water energy (matric suction) was examined in two species of earthworm using moisture gradients in three contrasting soil types with clay contents varying from 4 to 39%. Gravimetric moisture gradients ranging over 5–30% were established in horizontal cores comprising 12 or 14 sections containing loosely packed soil. Earthworms were introduced to each section at the beginning of each experiment. The earthworms moved from sections containing dry soil into adjacent sections containing moister soil. Clear effects were evident after 6 h but these became more obvious after 96 h. For the earthworm Aporrectodea rosea, the threshold soil mositure level at which earthworms were induced to move away from dry soil was a matric suction of about 300 kPa (pF 3.4) and was independent of soil type. In contrast, for A. trapezoides, the threshold soil moisture varied with soil type (sandy loam 15 kPa, loam 25 kPa, clay 300 kPa). We conclude that, for the earthworm A. rosea, matric suction and not water content of soil provided the cue by which the earthworm recognized dry soil. For A. trapezoides, there was an interaction between matric suction and soil type in which the response of A. trapezoides to soil moisture varied with soil texture and the threshold for avoidance of dry soil ranged from a matric suction of 300 kPa (20% w/w) in clay to 15 kPa (10% w/w) in sandy loam.     

A method of extracting earthworms from cores of soil with minimum damage to the soil

 Lumbricid earthworms have often been shown to increase the growth of plants. The earthworms and plants were generally grown together in the same soil, although sometimes earthworms were reluctant to enter the soil. It was not possible to isolate the mechanism for the increased growth, as no method was available to extract the earthworms with no damage to the soil before the plants were grown. A method is described which enabled Aporrectodea caliginosa, but not A. trapezoides, to enter all cores, and which extracted A. caliginosa from the cores probably with minimum damage to the soil. Received: 20 October 1998     

Reproduction and growth of three deep-burrowing earthworms (Lumbricidae) in laboratory culture in order to assess production for soil restoration

Laboratory experiments were conducted to examine the growth and reproduction of three deep-burrowing lumbricids, Aporrectodea longa, Lumbricus terrestris, and Octolasion cyaneum. The reproductive output was recorded as 18.8, 38.0, and 32.3 cocoons per worm per year for A. longa, L. terrestris, and O. cyaneum, respectively. For the same species, maturity was reached at a mean mass of 3.9, 5.0 and 2.4 g, within 3 months from the hatchling stage by L. terrestris and within 4 months by the other two species. The hatching success of cocoons at 15 and 20°C was within the range of 70–80% for each species, except A. longa at the higher temperature, where a viability of 47% was recorded. Twenty percent of viable O. cyaneum cocoons produced twin hatchlings, compared with only one percent for A. longa and L. terrestris. A combination of these results suggests that a complete life-cycle for each species could be achieved within 6 months (L. terrestris and A. longa) or 7–8 months (O. cyaneum). Each species has particular life-cycle strategies that would aid survival and colonisation, under field conditions, if inoculated into restored soils.     

Distribution of earthworms and influence of soil properties across a successional sand dune ecosystem in NW England

An investigation of earthworms across a sand dune system in NW England examined species distribution and abundance with respect to soil physico-chemical conditions and management. Replicated 0.1 m² quadrats were examined every 50 m along 700 m transects across areas of vegetation succession and samples were then taken every 10 m where earthworms were first encountered. A translocation of Aporrectodea longa assessed the ability of this species to live in soils with a high sand content and laboratory work examined growth, maturation and survival of this species in soils with increasing proportions of sand (0–100%). Nine earthworm species were found on the dunes, but none in yellow dunes where organic matter (OM) content was <1%. Dendrobaena octaedra and Lumbricus rubellus were located 300 m from the strand line in grey dunes with an OM content of 3.9%. Allolobophora chlorotica and Lumbricus castaneus occurred within a wet dune slack at 340 m (OM content 11%). In areas of human disturbance (dune car park), A. longa, Aporrectodea caliginosa and Lumbricus terrestris were present, and in soil below pine trees L. castaneus and L. rubellus were present in litter. Laboratory growth of A. longa demonstrated significant (p < 0.05) increases in growth (2–2.75 g) with 25 and 50% sand compared with 0, 75 and 100% over 24 weeks and a greater rate of maturation. Initial results show earthworm colonisation to be influenced by dune successional stage. Laboratory findings suggested A. longa could exist in higher sand content areas but experimental design needs development. The translocation was unsuccessful. Future investigations could examine soil properties more closely and undertake monitoring on site throughout the year.     

Microbial activity and nutrient dynamics in earthworm casts (Lumbricidae)

Summary Microbial respiration, microbial biomass and nutrient requirements of the microflora (C, N, P) were studied in the food substrate (soil taken from the upper 3 cm of the mineral soil of a beech wood on limestone), the burrow walls and the casts of the earthworm Aporrectodea caliginosa (Savigny). The passage of the soil through the gut caused an increase in soil microbial respiration of about 90% over a 4-week period. Microbial biomass was increased only in freshly deposited casts and decreased in aging faeces to a level about 10% lower than in soil. Microbial respiration of the burrow walls was only increased over a shorter period (about 2 weeks). The microflora of the soil and the burrow walls was limited by P, whereas in earthworm casts, microbial growth was limited by the amount of available C. In aging faeces the P requirement of the microflora increased and approached that of the soil. Immobilization of phosphate in earthworm casts is probably caused by mainly abiotic processes. C mineralization by soil microflora fertilized with glucose and P was limited by N, except in freshly deposited casts. Ammonium, not nitrate, was responsible for this process. N dynamics in earthworm casts are discussed.     

Soil partitioning effect of an earthworm burrow system

Summary Through the simulation of an earthworm burrow system and the calculation of the shortest pathway from the bottom of the system to the surface, using a succession of burrows, it is shown that the borrow system leads to a partition of soil space. The characteristics of the resulting heterogeneity, the size of this partitioning and the length of the shortest pathways are discussed with regard to the functional relationship between the burrow system and the soil.Dedicated to the late Prof. Dr. M. S. Ghilarov