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.     

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 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.     

Growth rates of Aporrectodea caliginosa (Oligochaetae: Lumbricidae) as influenced by soil temperature and moisture in disturbed and undisturbed soil columns

Earthworm growth is affected by fluctuations in soil temperature and moisture and hence, may be used as an indicator of earthworm activity under field conditions. There is no standard methodology for measuring earthworm growth and results obtained in the laboratory with a variety of food sources, soil quantities and container shapes cannot easily be compared or used to estimate earthworm growth in the field. The objective of this experiment was to determine growth rates of the endogeic earthworm Aporrectodea caliginosa (Savigny) over a range of temperatures (5–20 °C) and soil water potentials (−5 to−54 kPa) in disturbed and undisturbed soil columns in the laboratory. We used PVC cores (6 cm diameter, 15 cm height) containing undisturbed and disturbed soil, and 1 l cylindrical pots (11 cm diameter, 14 cm height) with disturbed soil. All containers contained about 500 g of moist soil. The growth rates of juvenile A. caliginosa were determined after 14–28 days. The instantaneous growth rate (IGR) was affected significantly by soil moisture, temperature, and the temperature×moisture interaction, ranging from −0.092 to 0.037 d⁻¹. Optimum growth conditions for A. caliginosa were at 20 °C and −5 kPa water potential, and they lost weight when the soil water potential was −54 kPa for all temperatures and also when the temperature was 5 °C for all water potentials. Growth rates were significantly greater in pots than in cores, but the growth rates of earthworms in cores with undisturbed or disturbed soil did not differ significantly. The feeding and burrowing habits of earthworms should be considered when choosing the container for growth experiments in order to improve our ability to extrapolate earthworm growth rates from the laboratory to the field.     

不同提取方法测定的土壤钾的有效性比较研究

以122个油菜钾肥田间试验的籽粒产量和植株吸钾量为标准,分别采用1 mol L-1中性醋酸铵、1 mol L-1沸硝酸和0.2 mol L-1四苯硼钠3种浸提剂测定试验基础土壤的钾素含量,并按浸提剂种类和速效钾、缓效钾将其分类,通过相关性分析探索土壤有效钾的准确测定方法,并建立与之对应的土壤钾素丰缺指标。研究结果表明,不同方法的提取能力有所不同,沸硝酸钾含量四苯硼钠钾含量醋酸铵钾含量。用醋酸铵法和四苯硼钠法测得的土壤钾素的生物有效性均较好,其中又以四苯硼钠法更好。长江流域冬油菜区醋酸铵法浸提的土壤钾素"低"、"中"、"高"和"极高"指标分别为45 mg kg-1、45~115 mg kg-1、115~190mg kg-1和190 mg kg-1;四苯硼钠法浸提的土壤钾素"低"、"中"、"高"和"极高"指标分别为125 mg kg-1、125~415 mg kg-1、415~755 mg kg-1和755 mg kg-1。综合结果表明四苯硼钠法和醋酸铵法测得的土壤钾素含量与油菜相对产量和相对吸钾量间呈极显著相关关系。据此建立的土壤钾素丰缺指标可以用来指导长江流域油菜的测土配方施肥,另外此区域应该重视并合理的施用钾肥。     

Effects of endogeic earthworms on soil processes and plant growth in coniferous forest soil

Summary The effects of the endogeic earthworm, Aporrectodea caliginosa tuberculata (Eisen) on decomposition processes in moist coniferous forest soil were studied in the laboratory. The pH preference of this species and its effects on microbial activity, N and P mineralization, and the growth of birch seedlings were determined in separate pot experiments. Homogenized humus from a spruce stand was shown to be too acid for A. c. tuberculata. After liming, the earthworms thrived in the humus and their biomass increased (at pH above 4.8). In later experiments in which the humus was limed, the earthworms positively influenced the biological activity in humus and also increased the rate of N mineralization. A. c. tuberculata increased the growth of birch seedlings, with increases observed in stems, leaves, and roots. Neither NH ₄ ⁺ -N fertilizer nor mechanical mixing with artificial worms affected seedling growth. No plant-growth-affecting compounds (e.g., hormone-like compounds) due to the earthworms were present in the humus. The shoot: root ratio in the birch seedlings was not affected by either the earthworms or the fertilizer. The experiments revealed the impact of earthworm activity on soil processes and plant growth.     

Influence of earthworms and leaf litter on edaphic variables in sewage-sludge-treated soil microcosms

Summary A series of 48 greenhouse soil microcosms were established and treated with combinations of sewage sludge, Acer saccharum leaves, and the earthworms Eisenia fetida and Lumbricus terrestris. The microcosms were incubated at constant moisture for 110 days. Samples were then taken and analysed for sludge depth, organic-matter content, and waterstable soil aggregates. Weights of surface leaves and weights and numbers of surviving earthworms were determined for each microcosm. L. terrestris significantly reduced sludge depth and the surface organic-matter content of microcosm soil and significantly increased percentages of 4-mm diameter water-stable aggregates. Leaf litter also significantly reduced sludge depth and increased 4-mm water-stable aggregates. E. fetida inhibited surface feeding by L. terrestris, reduced its 110-day survival rate, and inhibited the production of 4-mm water-stable aggregates in L. terrestris treatments. Numbers of E. fetida increased in L. terrestris treatments. Sludge depth, organic-matter content and water-stable aggregates were not significantly different from controls in E. fetida treatments.     

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.     

Population and behavioural level responses of arable soil earthworms to boardmill sludge application

The response of earthworms to soil application of boardmill waste sludge was quantified in field and laboratory experiments. The influence of one application of 6×10⁴ tonnes ha⁻¹ of unamended sludge was tested against no application on silty-clay arable soil. After 2 years, results in stubble-cultivated soil showed a 1.7 times lower density of earthworms where sludge was added, whereas there was no difference in average earthworm fresh weight. In direct-drilled soil, there was an indication of lower average numbers of Lumbricus terrestris middens when sludge was applied. Negative impacts in the field may have been due to indirect negative effects of the sludge application. In the laboratory, habitat choice tests were undertaken with two common species from the field site using sludge-based mulch and fertiliser products. Aporrectodea caliginosa showed no discernible preference between soil and soil mixed with unamended sludge (mulch), but favoured soil over soil mixed with sludge and chicken manure (fertiliser). Tests with L. terrestris showed a similar pattern. The preference of L. terrestris for the two products was compared with that for chopped barley straw by direct observation of foraging behaviour. Differences in foraging time of L. terrestris for different feeds were not significant, but mass of straw collected was significantly greater compared with either type of sludge treatment.     

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.     

The effect of two endogeic earthworm species on zinc distribution and availability in artificial soil columns

The objective of this study was to determine the impact of earthworm bioturbation on the distribution and availability of zinc in the soil profile.Experiments were carried out with Allolobophora chlorotica and Aporrectodea caliginosa in 24 perspex columns (∅ 10 cm), filled with 20-23 cm non-polluted soil (OM 2%, clay 2.9%, pH 0.01 M CaCl₂ 6.4), that was covered by a 3-5 cm layer of aged zinc spiked soil (500 mg Zn/kg dry soil) and another 2 cm non-polluted soil on top. After 80 and 175 days, columns were sacrificed and each cm from the top down to a depth of 15 cm was sampled. Earthworm casts, placed on top of the soil, were collected. Each sample was analyzed for total and CaCl₂-exchangeable zinc concentrations.Effects of earthworm bioturbation were most pronounced after 175 days. For A. chlorotica, total and CaCl₂-exchangeable zinc concentrations in the polluted layers were lower with than without earthworms. Total zinc concentrations in the non-polluted layers were higher in columns with earthworms. Casts of A. chlorotica collected on the soil surface showed slightly higher total zinc concentrations than non-polluted soil. Casts were found throughout the whole column. For A. caliginosa there were no differences in total zinc concentration between columns with and without earthworms. CaCl₂-exchangeable zinc concentrations in the polluted layers were lower for columns with earthworms. Casts were mainly placed on top of the soil and contained total zinc concentrations intermediate between those in non-polluted and polluted soil layers.This study shows that different endogeic earthworm species have different effects on zinc distribution and availability in soils. A. chlorotica transfers soil throughout the whole column, effectively mixing it, while A. caliginosa decreases metal availability and transfers polluted soil to the soil surface.     

Effect of earthworms on molybdenum-depending activities

Pot experiments performed in an alkaline, silty clay soil showed that the presence of Allolobophora caliginosa increased nitrate reductase activity in maize seedlings and nitrogen fixation in the soil, but did not affect photosynthesis and biomass of maize seedlings and oxygen consumption in the soil. The increase in molybdenum-depending activities is ascribed to the greater availability of molybdenum recorded in the presence of earthworms.     

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.     

Effects of earthworms on decomposition and metal availability in contaminated soil: Microcosm studies of populations with different exposure histories

Population-specific differences in the responses of earthworms to simultaneous exposure to Cu and Zn were studied in microcosm experiments. Two populations of Aporrectodea caliginosa tuberculata (Eisen) with different metal exposure histories were chosen for the studies. Microcosms were prepared containing either uncontaminated soil or soils with low or high combined Cu/Zn -concentrations (79/139 or 178/311 mg kg⁻¹ dry mass of soil, respectively). Earthworms from each population were introduced to the microcosm treatments with some microcosms serving as controls without earthworms. One series of microcosms was destructively sampled after 16 weeks incubation in a climate chamber. Survival, growth, reproduction and decomposition by earthworms in each treatment were measured. An additional microcosm series was sampled for soil and earthworm measurements at four weeks intervals to determine temporal changes in the availability of metals in the soils and their accumulation into earthworms. Cu and Zn were sequentially extracted from the soil samples of both microcosm series to estimate mobility and availability of the metals in the soil. Earthworms with long-term exposure history to metal-contaminated soil seemed to tolerate higher soil metal concentrations than earthworms without earlier exposure. Both earthworms and metals affected soil respiration (CO₂ production) and nitrogen mineralization. In addition, earthworms seemed to decrease the mobility and bioavailability of metals in the soil through their burrowing activity.     

Microcosm investigations into the influence of sheep manure on the behaviour of the geophagous earthworms Aporrectodea trapezoides and Microscolex dubuis

A series of experiments was conducted over 96 h in 240-mm-deep soil microcosms, to assess the effect of the presence and distribution of sheep manure over the soil surface on the vertical and horizontal distribution of burrows and numbers of the earthworms Aporrectodea trapezoides and Microscolex dubius. Within some microcosms the dung was placed on half of the soil surface and this caused aggregation, with over two-thirds of the earthworms being found in the soil directly under the manure. The presence of surface-applied sheep manure caused both species to aggregate in the surface soil. In contrast, without manure, A. trapezoides was evenly distributed throughout the soil profile while M. dubius aggregated in the deeper soil. The pattern of burrow construction was also influenced by the presence of surface manure. In the absence of manure, burrows of both species were evenly distributed through the soil, but in the presence of surface manure M. dubius constructed proportionally more burrows close to the surface. Both species constructed approximately twice the burrow area in the absence than in the presence of surface manure. For both species the daily rate of burrow construction decreased over the experimental period. From these data we inferred that there was more widespread and active foraging behaviour in both species when organic food material was scarce. M. dubius differed from A. trapezoides in that it more strongly concentrated foraging activity in the vicinity of the manure food source.     

Growth of Lumbricus terrestris and Aporrectodea caliginosa in an acid forest soil, and their effects on enchytraeid populations and soil properties

A laboratory experiment was carried out to test the hypothesis that the earthworms Lumbricus terrestris and Aporrectodea caliginosa are able to maintain their populations and reproduce in the acid forest soil of a deciduous forest where no lumbricids were found in the field. The experiment was conducted in 45-l containers in which layers of mineral subsoil, humus and organic topsoil collected from the site were established. Both species survived and at least L. terrestris reproduced during the 60 weeks’ incubation. Burrows and middens of L. terrestris were recorded and quantities of litter were consumed. The presence of lumbricids increased the organic matter content of humus, reduced the acidity of the topsoil and humus layers, and suppressed the population of the enchytraeid Cognettia sphagnetorum. A dense population of Enchytraeus albidus was found in L. terrestris middens. It is concluded that edaphic factors do not explain the absence of earthworms, but isolation from cultural landscapes and lack of opportunity to colonize the site from the surroundings is the decisive factor.     

The effects of earthworms on the demography of annual plant assemblages in a long-term mesocosm experiment

Earthworms have been shown to influence plant growth, survival and fecundity. They can therefore affect plant demography in plant communities changing their composition. A long term mesocosm experiment was set-up to test the effects of an endogeic (Aporrectodea caliginosa) and an anecic (Lumbricus terrestris) earthworm species on assemblages of four species of annuals: one grass (Poa annua), two forbs (Veronica persica and Cerastium glomeratum) and one legume (Trifolium dubium). The number of individuals and the biomass of each species were investigated. A. caliginosa and L. terrestris affected the density of T. dubium at each of the three monitored census dates. The other plant species responded to A. caliginosa and L. terrestris at the second and third generations. The presences of A. caliginosa and L. terrestris reduced the total number of plant individuals from the second to the third generation. At harvest (3rd generation), T. dubium and V. persica had more and larger individuals in the presence of A. caliginosa. When both earthworm species were present, T. dubium had few but larger individuals. Our study confirms that earthworms affect plant demography and plant community structure. Our results also show that accurate prediction of long-term effects of earthworms on plant communities cannot be achieved using results on their short-term effects on plant growth. This is due to the poor understanding of the effects of earthworms on plant resource allocation and demography, and also the possibility that earthworms may exert the opposite effect on the short and long-term availability of nutrients.     

Earthworm effects on the use of C sources by microorganisms: Non-linear response to temperature alteration

A microcosm was used to study the effect of the endogeic earthworm Aporrectodea caliginosa (Savigny) on the use of C by microorganisms in a calcareous beech forest soil and its dependence on temperature (5–25%C). Inclusion of ¹⁴C-labelled beech leaf litter made it possible to differentiate between C use by litter-colonizing microflora and by autochthonous soil microflora. The effect of temperature on the soil microbial biomass ¹²C was confined to a significant increase at 15 and 20°C. The size of the ¹⁴C-labelled microbial biomass, in contrast, was positively correlated with temperature. The ¹²C mineralization increased exponentially with temperature. The relationship between ¹⁴C mineralization and temperature, in contrast, followed a logistic curve. Significant main effects of A. caliginosa were confined to ¹²C mineralization, reflecting an increase in ¹²CO₂–C production in the earthworm treatments. The earthworm effects on ¹²CO₂–C production and on ¹⁴C incorporation of the microflora were not linear. The effect of A. caliginosa on ¹²CO₂–C production was most pronouned at intermediate temperatures. It is concluded that temperature alterations affect the microbial use of different C sources in different ways and that the temperature effects can be significantly modified by endogeic earthworms.     

Mucus excretion and carbon turnover of endogeic earthworms

Summary Mucus excretion of endogeic earthworms, by the body surface to burrow walls and by the intestine to casts, was investigated using uniformly ¹⁴C-labelled adult or subadult specimens of Octolasion lacteum (Örley) in laboratory incubations in soil from a beechwood on limestone. The daily loss of C due to mucus excretion from the body surface and in casts was calculated as 0.2 and 0.5% of total animal C, respectively. The C loss due to mucus excretion by subadult or adult individuals of O. lacteum is assumed to account for 63% of total C losses (including mucus excretion and respiration) of the earthworms. In a second experiment we studied the incorporation of ¹⁴C from labelled soil, again from a beechwood on limestone, into the tissue of the endogeic earthworm species Aporrectodea caliginosa (Savigny). The results of this experiment indicate the existence of two C pools, one more labile and one more stable, in earthworms. It is assumed that the C investment for respiration and mucus excretion is derived from the labile C pool of endogeic earthworms.