Earthworm burrowing in laboratory microcosms as influenced by soil temperature and moisture

Earthworm burrows contribute to soil macroporosity and support diverse microbial communities. It is not well known how fluctuations in soil temperature and moisture affect the burrowing activities of earthworms. The objective of this experiment was to evaluate the maximum depth and length of burrows created by the endogeic earthworm Aporrectodea caliginosa (Savigny) and the anecic earthworm Lumbricus terrestris L. for a range of temperatures (5–20 °C) and soil water potentials (−5 and −11 kPa). The laboratory microcosm was a plexiglass chamber (45 cm high, 45 cm wide) containing 0.14 m² of pre-moistened soil and litter, designed to house a single earthworm for 7 days. Earthworm mass, surface casting and burrowing activities were affected significantly by soil temperature, moisture and the temperature×moisture interaction. Burrow length and maximum burrow depth increased with increasing temperature, but there was less burrowing in wetter soil (−5 kPa) than drier soil (−11 kPa). Weight gain and surface casting, however, were greater in soil at −5 kPa than −11 kPa. Our results suggest more intensive feeding and limited burrowing in wetter soil than drier soil. Earthworms inhabiting the non-compacted, drier soil may have pushed aside particles without ingesting them to create burrows. The result was that earthworms explored a larger volume of soil, deeper in the chamber, when the soil was drier. How these burrowing activities may affect the community structure and activity of soil microorganisms and microfauna in the drilosphere remains to be determined.     

Earthworm primers for DNA-based gut content analysis and their cross-reactivity in a multi-species system

Specific primers can be used in polymerase chain reactions (PCR) to amplify prey DNA from the gut content of generalist predators at high specificity and sensitivity. A prerequisite for applying this approach to field studies, however, is to confirm that primers are actually targeting specific prey species or prey groups and do not produce false positive results by amplifying DNA either from predator species or from the wide range of potential alternative prey found under natural conditions. Here, we report on a new group-specific primer pair for earthworms designed from cytochrome oxidase c subunit 1 (COI) sequences of 11 earthworm species found in Central Europe that can be used to detect consumption of earthworms by invertebrate predators. Besides inter-specific also considerable intra-specific variation was found for COI sequences among most of the earthworm species. We, therefore, combined a universal forward primer with an earthworm-specific reverse primer which amplified a 523 bp product from all 11 species tested. Earthworm DNA amplification was also successful in the presence of excess DNA of a predator species. The primer pair was tested against 82 non-target invertebrate species commonly found in the same habitats, including potential prey for generalist predators and predators themselves. The earthworm primer was highly specific: only one of the non-target species showed a product of similar length as the earthworms, whereas PCR with 12 non-target species produced amplicons whose length differed from that of earthworms. We conclude that the new primer will be a useful tool to investigate the role earthworms play as a food resource in soil food-webs. Moreover, we suggest that future studies utilizing DNA-based approaches for prey detection should select non-target species for cross-reactivity tests according to their abundance and importance rather than choosing representatives of taxonomic units; this will help validate the results achieved using species- or group-specific primers and guarantee their meaningful ecological interpretation.     

Earthworm burrowing activity of two non-Lumbricidae earthworm species incubated in soils with contrasting organic carbon content (Vertisol vs. Ultisol)

The aim of this study was to investigate the burrowing activity of two earthworm species: the endogeic Drawida sinica and one undescribed Amynthas species incubated in Vertisol and Ultisol presenting different soil organic C content. Because of their contrasting feeding behaviours, we hypothesised that soil type would have a bigger influence on the burrowing activity of the endogeic than the anecic species. Repacked soil columns inoculated with earthworms for 30 days were scanned using X-ray tomography and the compiled images used to characterise the burrow systems. After scanning, the saturated hydraulic conductivity (K _sat) was also measured. The Amynthas species burrows were less numerous (30 vs. 180), more vertically oriented (57 vs. 37°), more connected from the surface to the bottom of the columns (73 vs. 5 cm³) and had a higher global connectivity index (83 vs. 28%) than those of D. sinica. The K _sat was threefold faster in columns incubated with Amynthas and was linked to the volume of percolating burrows (R ² = 0.81). The soil type did not influence Amynthas burrow characteristics. In contrast, there were 30% more D. sinica burrows in the Vertisol than in the Ultisol while other burrow characteristics were not affected. This result suggests that these burrows were more refilled with casts leading to shorter and discontinuous burrows. The K _sat was negatively related to the number of burrows (R ² = 0.44) but was not statistically different between the Vertisol and the Ultisol, suggesting a constant impact of this species on the K _sat. We found that a decrease in the amount of soil organic C by 50% had only a small influence on earthworm burrowing activity and no effect on the K _sat.     

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     

Sublethal effects of imidacloprid on the burrowing behaviour of two earthworm species: Modifications of the 3D burrow systems in artificial cores and consequences on gas diffusion in soil

Earthworms have been termed ‘ecosystem engineers’ (sensu [Jones, C.G., Lawton, J.H., Shachak, M., 1994. Organisms as ecosysem engineers. Oikos 69, 373-386.]) because of the important roles they play in the soil. As a consequence, it is assumed that if earthworms change their behaviour following exposure to pesticides or pollutants this could have a drastic impact on soil functioning. To test this assumption under laboratory conditions, we studied the burrow systems made by two earthworm species (the anecic Aporrectodea nocturna and the endogeic Allolobophora icterica) in artificial soil cores containing imidacloprid, a widely used neonicotinoid insecticide. After 1-month incubation period, the macropores created in the soil core were analyzed by tomography. In order to further characterize transfer properties associated with burrow systems gas diffusion measurements were also carried out. The burrow systems made by the two earthworm species were very different: A. nocturna made more continuous, less branched, more vertical and wider burrows than A. icterica. Some changes to A. nocturna burrow systems were observed after exposure to imidacloprid (they made a smaller burrow system and burrows were more narrow), but only at the highest concentration of imidacloprid used (0.5 mg kg⁻¹). A. icterica worms were more sensitive to imidacloprid and many differences in their burrow systems (length, sinuosity, branching rate and number of burrows) were observed at both concentrations tested (0.1 and 0. 5 mg kg⁻¹). As a consequence, the continuity of the burrow systems made by both species was altered following imidacloprid treatment. Gas diffusion through the A. nocturna soil cores was reduced but no difference in gas diffusion was observed in the A. icterica soil cores.     

Earthworm communities in grasslands and horticultural soils

 In a survey of 42 farm sites, comprising grassland and two types of horticultural farms (growing vegetables or flower bulbs), earthworm communities were sampled by hand-sorting and a number of soil physico-chemical characteristics recorded. For heavy metals the availability in the soil solution was estimated based on the measured absolute content. Abundance, biomass and species richness were significantly higher in grassland soils than in horticultural soils, and within the horticultural farms significantly higher in vegetable than in flower-bulb farms. No epigeic species were found in horticultural soils. The differences between the various farm types were probably related to the intensity of management practices, such as soil tillage, harvesting and crop protection measures, that result in less soil organic matter of lower quality. The data from the grassland farms were analyzed in conjunction with the physico-chemical soil characteristics, applying canonical correspondence analysis. Community parameters such as species richness and diversity apparently were not related to soil characteristics, but an appreciable part of the variation in abundance and biomass of several individual species could be explained by factors such as lutum content (particles <16 μm), pH, bio-availability of metal ions and geographical position of the sample site. It is concluded that repeated surveys of this type may become a valuable tool for monitoring soil quality. Received: 16 March 2000     

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.     

Earthworm communities in birch stands with different origin in central Finland

The aim of the study was to compare earthworm communities in anthropogenous birch stands with different origin in Finland. A total of nine forest sites were investigated: three birch stands (Betula pendula) planted ca. 30 years prior to the study after clear-cutting of spruce stands (“Birch after Spruce”, BS), three birch stands planted ca. 30 years earlier on arable soil that had been under normal cultivation until forestation (“Birch after Field”, BF), and three “Natural Deciduous” forests (D). Earthworms were sampled in May and October 1999 using a combination of formaline extraction and modified wet funnels. There were conspicuous differences between replicates of similarly managed forests. Earthworms were totally lacking in one of the D sites, while another had an abundant and diverse community. Only Dendrobaena octaedra was present in one BS site, while the two others harboured also Aporrectodea caliginosa and three Lumbricus species. All these species were also present in the BF sites, where their total biomass (ranging from 70 to 138 g (f.w.)/m²) was 2.6 times the average in BS, and of the same magnitude as the average in natural deciduous stands. A separate experiment revealed that L. terresris and A. caliginosa, which are not found in the surrounding coniferous forest, are able to live and reproduce in the soil of the D site where they were absent. It was concluded that earthworm species survive and reproduce in birch stands established on arable soil, where they have invaded during the long cultivation. On the other hand, their possibilities to disperse from cultural landscapes determine their presence not only in birch stands established in earlier coniferous forests, but also in “natural deciduous” forests where source populations are not present in the surroundings.     

Microbiological Properties in Earthworm Cast and Surrounding Soil Amended with Various Organic Wastes

Abstract

Changes produced in the microbiological properties of earthworm Lumbricus terrestris casts and surrounding soil by the addition of various organic wastes such as wheat straw (WS), tea production waste (TEW), tobacco production waste (TOW), cow manure (CM), and hazelnut husk (HH) were evaluated in an incubation experiment. Twenty‐one days after organic waste treatment, analyses of microbial biomass (Cmic), basal soil respiration (BSR), metabolic quotient (qCO₂), and enzyme activities (dehydrogenase, catalase, β‐glucosidase, urease, alkaline phosphatase, and arylsulphatase) were carried out on collected cast and soil samples. Addition of organic wastes to the soil increased values of Cmic, BSR, and enzyme activities in soil and earthworm casts, indicating activation by microorganisms. Except for catalase activity, these values of microbiological parameters in casts were higher than in surrounding soil at all waste treatments and control. The addition of organic wastes caused a rapid and significant increase in organic carbon, total nitrogen, and microbiological properties in both soils; this increase was especially noticeable in soils treated with TEW.     

Earthworm communities and soil properties in shaded coffee plantations with and without application of glyphosate

In central Veracruz, Mexico, many coffee plantations are managed using agrochemicals for weed control, with glyphosate-based herbicides (GBH) the most commonly used. To date, however, no studies in this region have characterized the soil biological and physicochemical properties in coffee plantations under such glyphosate application. In this study, earthworms were used as bioindicator organisms by measuring differences in the earthworm community in plots within shaded coffee plantations, with and without repeated applications of glyphosate. Differences in earthworm-induced soil processes, such as water infiltration rates, potential net carbon mineralization rates and soil physicochemical properties were also evaluated. Eight plots were selected in shaded coffee plantations; four had received regular applications of GBH over the preceding 22 years, while the other four had received no herbicides over the preceding 7 years. The earthworm species found in plots with no GBH treatment were Pontoscolex corethrurus (99%) and Amynthas corticis (1%), while A. corticis was absent in plots that had been treated with GBH. Significant differences (P < 0.01) in earthworm density (168 ± 16 and 353 ± 37 ind m⁻²) and biomass (22.7 ± 1.1 and 45.4 ± 6.9 g m⁻²) were observed in soils with and without GBH, respectively. No significant difference (P = 0.08) was observed in the water infiltration rate (2 × 10⁻⁴ ± 4 × 10⁻⁵ and 4 × 10⁻⁴ ± 1 × 10⁻⁴ cm s⁻¹ with and without GBH, respectively). Soil carbon flow was greater in plots with GBH (76 ± 7 μg dry soil⁻¹ d⁻¹) than in those without GBH (62 ± 1 μg dry soil⁻¹ d⁻¹, P < 0.005). Significant differences (P < 0.05) were found in pH and in the clay, silt and Ca content of the soil. Our findings indicated reduced species number, density and biomass of earthworms, and increased net carbon mineralization rate in plots with GBH. The plots managed with glyphosate presented a negative effect on the earthworm parameters measured, and we conclude that the earthworms therefore acted as indicators of perturbation. It is also possible that this effect could be due to factors unrelated to the glyphosate that were not considered in this study, such as chemical fertilization or legume litter spatial variability, among others.     

Experiences with Novel Approaches in Earthworm Testing Alternatives (7 pp)

Goal, Scope and Background   The earthworm avoidance test is a sensitive screening test. Currently, two test designs, a two-chamber system and a six-chamber system, are under standardization. In the scope of the present study, the two test systems are compared. To assess the results, two procedures are applied, which are based on a threshold value and a statistical method. Moreover, the sensitivity of the avoidance test is compared with the sensitivity of the reproduction test. Methods   The avoidance behaviour of E. fetida towards five chemicals (Cd, Cu, PCP, TBT, TNT) was tested in a sandy and a loamy soil. The ecotoxicological test was performed according to the draft guideline ISO/DIS 17512-1. The results were compared with the number of offspring determined in the reproduction test carried out according to ISO 11268-2. Results and Discussion   The results demonstrate that the avoidance behaviour towards organic chemicals and heavy metals is a suitable screening method showing first tendencies of a chemical's effects on the habitat function of soils. Effects caused by chemical substances become visible at low concentrations and within short test periods. The sensitivity of the reproduction test and the avoidance test is principally comparable; in some cases, the avoidance test showed more sensitive reactions. The dose-response-relationships were more pronounced in the two-chamber test than in the six-chamber-system. Recommendation and Outlook   The two-chamber-system proved to be more feasible than the six-chamber-system. As the sensitivity of the avoidance test and the reproduction test is comparable, the avoidance test can be considered as a suitable screening test as well. A possible field of application may be the selection of soil samples for which the reproduction assay seems necessary. To assess contaminated or remediated soils, the earthworm reproduction test is recommended as an indicator for the habitat function of the soils. To reduce costs, the labour intensive reproduction test could be largely replaced by the avoidance test in performing the earth-worm reproduction test only for relevant samples. Before the Draft International Standard of the guideline will be adopted as an ISO Guideline, there will be sufficient time left to gain further international experience required to finalize the method.     

Earthworm channels in cultivated clayey and loamy Norwegian soils

Studies of earthworm species and their activity, expressed as channels, on cultivated loamy (Humic Cryaquept) and clayey soils (Typic Endoaqualf and Typic Cryaquept) were conducted in southern and central Norway before conversion from conventional to organic cropping systems. At all the three study areas: Landvik (Grimstad), Voll (Ås) and Kvithamar (Stjørdal), the earthworm species Aporrectodea caliginosa, Aporrectodea rosea, Allolobophora chlorotica and Lumbricus rubellus were found. At Landvik, where the deep-burrowing species Aporrectodea longa, A. caliginosa and Lumbricus terrestris dominated, medium (4–6 mm) and coarse (>6 mm) earthworm channels were most numerous below the plough layer. Almost no coarse pores were found at Voll and Kvithamar. The volume of earthworm channels below the plough layer was 0.6–0.8% of total soil volume at Landvik and Voll and 0.3–0.4% at Kvithamar. Earthworm channels >6 mm below the plough layer were useful to identify present and previous activity of deep-burrowing earthworms such as L. terrestris. Below the plough layer, roots were almost entirely restricted to earthworm channels and interaggregate spaces.     

Assessment of earthworm burrowing efficiency in compacted soil with a combination of morphological and soil physical measurements

Summary Column experiments were carried out to quantify the effect of earthworms on compacted soil. The earthworms (Lumbricus terrestris) were able to burrow into soil which was artificially compacted to a pore volume as low as 40%; they may also penetrate an artificial plough pan deep in the soil. The effect of the burrowing activity of Lumbricus terrestris was quantified by measuring hydraulic conductivities and infiltration rates through the whole soil column (19 cm wide, 40 cm long). Morphological parameters, mainly the vertically projected burrow depth, were correlated with the saturated hydraulic conductivity. The amount of casts deposited by Lumbricus terrestris on the soil surface increased with the degree of soil compaction. The bulk density of casts was always less than that of the original soil.     

Enhanced Lead Uptake by an Association of Plant and Earthworm Bioaugmented with Bacteria

Lead (Pb) is recorded as the second most hazardous pollutant of the environment. Previous cases of Pb bioremediation has been reported using single biosystem, but very few reports are available in biological approaches using multi-biosystems to achieve an enhanced bioremoval of Pb. The present study evaluated the capacity of a unique association of Pennisetum purpureum, a hyperaccumulator plant, and Lumbricus terrestris (earthworm) bioaugmented with a Pb-resistant bacterium, obtained from an industrially contaminated site and identified as isolate VITMVCJ1 Klebsiella variicola, to bioremediate Pb. The Pb-resistant gene was amplified in the bacterial isolate VITMVCJ1. The study was conducted for 60 d. Results verified that the bioaugmentation process enhanced 1) root and shoot length of the plants, 2) chlorophyll content of the plants, and 3) biofilm-producing ability of the microbes from the rhizosphere region of the plants. The total phenolic and flavonoid contents were found to be lower in the plants in the bioaugmented setup. The study also observed a reduction in the toxic effects of Pb on earthworm and plant. The earthworm was used to assess the Pb-induced stress syndrome after exposure to sublethal concentrations of Pb in the soil. A reduction in the content of malondialdehyde, a potential biomarker, on exposure to Pb demonstrated the role of the inoculum to alleviate heavy metal-induced stress in earthworms. All three symbionts accumulated Pb; Pb was accumulated mainly in the root of the plant, and poorly in the shoot of the plant and body mass of the earthworm. The bioaugmentation system exhibited stable and excellent uptake of Pb from the contaminated soils. The results of the present study suggest the positive effect of the synergistic association of the plant and earthworm with appropriate microbes for the bioremoval of Pb.     

Early decomposer assemblages of soil organisms in litterbags with vetch and rye roots

The assemblages of microbial (bacteria and fungi), microfaunal (protozoa and nematodes) and mesofaunal (microarthropods) populations were studied in decomposing root residues from hairy vetch (Vicia villosa Roth) and rye (Secale cereale L.) in a litterbag field experiment. Litterbags containing vetch or rye root residues were buried in soil at the same day as either vetch or rye winter catch crops were incorporated into the field soil from which the materials were gathered. The litterbags were sampled after 6 weeks in the field. In vetch, bacterial and fungal biomasses were similar whereas fungi dominated microbial biomass in rye. The biomass of the bacterial consuming fauna dominated by nematodes and microarthropods was similar to the biomass of bacteria in vetch as opposed to in rye where bacterivore biomass was lower than bacterial biomass. This suggests a much higher bacterial production in vetch compared to rye. Furthermore, in vetch dauer larvae of bacteria feeding nematodes prevailed, which is also a sign of high bacterial production followed by food shortage for the bacterivores. Bacterivorous and predatory nematodes with capability of consuming protozoa showed an inverse relationship to flagellated protozoa. This suggests that these nematodes controlled the protozoan biomass constituting a lower fraction of the bacterivore biomass in vetch compared to in rye. Such intraguild predator-prey relationship is therefore indicated for microbivorous organisms among bacterivorous and predatory nematodes (the intraguild predator) protozoa (the intraguild prey) and bacteria (the common prey). The much higher fungal biomass in rye than in vetch litterbags was not reflected in the biomass of the fungal feeders. Due to the generally lower intrinsic rate of increase of the fungivores, as well as of the omnivores and predators, in comparison with the bacterial feeders, they were not able to generate dense populations at this early stage of decomposition.     

Earthworm response to rotation and tillage in a Missouri claypan soil

 Agricultural management practices affect earthworm populations. A field experiment was conducted to determine the effect of two rotations and two tillage systems on earthworm population density and biomass in a claypan soil. The rotations were soybean/corn and wheat/corn, and the tillage systems were conventional tillage (chisel plowed and disked) and no-tillage. Earthworm and soil samples were collected in fall 1995, spring 1996, and fall 1996. Aporrectodea trapezoides and Diplocardia singularis were the species identified at the site. A. trapezoides accounted for 92–96% of the total earthworm population density and D. singularis accounted for only 4–8%. In a no-till system, soybean/corn rotation resulted in significantly greater population density of A. trapezoides compared with the wheat/corn rotation. Crop residue quality (low C:N ratio) and quantity were important factors in increasing A. trapezoides population density and biomass. Conventional tillage markedly decreased population density and biomass of both earthworm species. Our results suggest that rotation and tillage significantly affect earthworm population density and biomass. Received: 6 June 1998     

Bioaccumulation of Total Mercury and Monomethylmercury in the Earthworm Eisenia Fetida

Bioaccumulation factors (BAFs) for inorganic mercury in earthworms are usually < 1; however, factors up to ～10 have been reported. Little information is available concerning the bioaccumulation of organic mercury in earthworms from actual contaminated soils and thus there has been uncertainty in the risk characterization phase of ecological risk assessments of mercury-contaminated sites. This study was initiated to determine the rate of uptake and bioaccumulation of total mercury (T-Hg) and monomethylmercury (MMHg) in Eisenia fetida from soils which have been contaminated with mercury for approximately 30 years. The study consisted of a 28-day uptake phase in three mercury-contaminated soils and one soil with background concentrations of mercury followed by a 14-day depuration phase in background soil only. Total mercury concentrations in the study soils ranged from 85 to 11,542 μg kg^?1 dry weight soil; MMHg concentrations ranged from 1.12 to 7.35 μg kg^?1 dry weight soil. Time to 90% steady states for T-Hg ranged from 36 to 42 days. A steady state did not occur for any of the MMHg exposures during the 42-day study; estimated time to 90% steady state varied from 97 to 192 days. BAFs for T-Hg ranged from 0.6 to 3.3. BAFs for MMHg ranged from 175 to 249. The BAFs for T-Hg and MMHg were larger in earthworms exposed to the lower contaminated soils and smaller in the higher mercury-contaminated soils. The absolute concentrations of T-Hg and MMHg bioaccumulated in E. fetida, however, were higher in the earthworms exposed to the higher mercury soils and lower in the less mercury-contaminated soils.     

不同土地利用方式下的蚯蚓种群特征及其与土壤生物肥力的关系

采用样方法对华北平原(河北曲周)盐渍化改造区7种土地利用方式下的蚯蚓种群进行详细调查,并通过培养实验研究了蚯蚓种群特征对若干土壤生物学指标的影响。结果表明:(1)在7种土地利用调查样地中共存在蚯蚓有3个科,5个属,5个种,其中赤子爱胜蚓(Eisenia fetida)占调查样地总个体数的60%以上,梯形流蚓(Aporrectodea trapezoides)和赤子爱胜蚓两个种在本地区广泛分布,样点出现频率分别为74%和44%,为该地区的优势种;(2)不同土地利用方式的蚯蚓种群密度及生物量变化趋势是:庭院菜地>直立免耕>清茬免耕>商品菜地>传统玉米地>果园>原貌地。其中庭院菜地蚯蚓种群的平均密度和生物量分别达到272 Ind.m-2和68.04gm-2;(3)蚯蚓种群密度和物种数等种群特征与土壤基础呼吸强度、微生物生物量碳含量成显著正相关(p<0.01),与土壤基础呼吸商成显著负相关(p<0.01);(4)不同土地利用方式下,蚯蚓的种群密度、生物量等种群特征对土壤中微生物群落的影响作用显著。蚯蚓生物量越大、种群越丰富的土壤有机质、氮、磷、钾等有效成分越高,反之则相反。室内培养实验表明,随着蚯蚓个体数量增加土壤原生动物总丰度、微生物生物量碳、氮也存在升高的趋势,与用土壤生物学特性指标及土壤化学特性指标评价的结果基本一致。     

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.