Contrasting response to cropping of populations of earthworms and predacious nematodes in four soils

The activities of many soil animals make a positive contribution to soil processes and they should be considered for inclusion in indices of ‘soil quality'. To assess the potential use of nematodes and earthworms as indicators, the relationships between populations of earthworms (Lumbricidae), total number of nematodes and predacious nematodes (Mononchoidea) and six soil physical factors, soil carbon and pH were investigated in four New Zealand soils. In each, soil treatments ranged from 5–90 year pastures to cropping with maize or barley for 11–29 years. With increasing cultivation, trends in bulk density, total porosity, aggregate stability and concentration of total carbon were similar in all four soils. In Manawatu (Dystric Fluventic Eutrochrept) and Kairanga (Typic Endoaquept) soils earthworm populations were negligible under continuous cropping while Mononchoidea were abundant (11 600 and 34 100 m⁻²). In contrast, in Moutoa (Fluvaquentic Endoaquoll) and Wakanui (Aquic Ustochrept) soils earthworms persisted under cultivation, while Mononchoidea were less abundant (300 and 2500 m⁻²). At these two latter sites, aggregate stability was higher (1.14 and 0.92 mm mean weight diameter (MWD)) than in Manawatu and Kairanga soils (0.38 and 0.35 mm MWD). These relationships between aggregate stability, earthworm abundance and predacious nematodes show not only that some potential indicators may have a local rather than national application, but also that there are important interactions between soil physical properties and soil fauna which require further investigation.     

Community structure of Lumbricidae in beech woodland of the Bieszczady National Park, Southeast Poland

As ecosystem engineers, earthworms play a key role in the soil environment. However, due to increasing anthropogenic pressure, soil organisms,including earthworms, are being threatened by habitat loss. In this study, we undertook a qualitative and quantitative investigation of earthworms of the family Lumbricidae in four types of Carpathian beech woodland(Fagetum carpaticum), characterized by their understory vegetation(I, F. c. festucetosum drymejae; II, F. c. typicum; III, F. c. lunarietosum; and IV, F. c. allietosum), in the Bieszczady National Park(Eastern Carpathians, Southeast Poland). At each investigated site, soil monoliths(25 cm × 25 cm × 25 cm) were examined by hand sorting. Earthworms were expelled from deep soil layers using a weak formalin solution(0.4%). Depending on the phytocoenosis, 7 species of Lumbricidae were identified at each of the sites I, II, and III and 10 at site IV. Site IV(F. c. allietosum) differed significantly(P 0.05) from the other three sites with respect to earthworm biomass(59.71 ± 39.53 g m~(-2))and the Shannon-Wiener diversity index(0.52 ± 0.12). Although present three decades ago, the deep-burrowing species Octodrilus transpadanus and the litter-dwelling species Dendrobaena octaedra were not found at site IV in the present study. We suspect that these two species may have been displaced by the invasive Lumbricus terrestris, which was not found at the same site in the 1980 s. Such observations warrant further investigation to verify the predicted effects of an invasive earthworm, including the potential effects on soils and other fauna and flora, which have been documented in numerous countries.     

Quantification of the effects of rotation breaks on soil biological properties and their impact on yield decline in sugarcane

Three contrasting rotation breaks (sown pasture, alternate crops and bare fallow) were established at five sites in Queensland, Australia, on land that had been under sugarcane monoculture for at least 20 years. The breaks were in place for 30-42 months at four sites and for 12 months at the fifth site. The effects of the breaks on selected soil biological properties were assessed following the removal of the breaks and before the area was re-planted with sugarcane. At the four sites with the long-term breaks, microbial biomass increased under the pasture break, declined under the bare fallow break and did not change significantly under the crop break, compared to microbial biomass under continual sugarcane. At these sites, populations of the root lesion nematode (Pratylenchus zeae) declined under all three breaks whereas populations of free-living nematodes increased under the pasture and crop breaks but declined under the bare fallow break. At the site with the 12 month breaks, a forage legume pasture increased microbial biomass, reduced lesion nematodes and together with the crop break increased populations of free-living nematodes. At the four sites with the long-term breaks there was an increase in the ratio of fungal:bacterial fatty acids and an increase in fatty acid 16:1ω5c (used as a biomarker for mycorrhizal fungi) under the pasture and crop breaks. Also at these sites, the soil microbial community under the pasture, crop and bare fallow breaks, respectively, showed increased, no change or diminished capacity to utilize carbon substrates compared to the soil microbial community under continual sugarcane. The yield of the sugarcane crop following all three breaks was significantly higher than the yield of the crop following continual sugarcane at each of the sites with the long-term breaks. Examination of the longevity of the effect of the rotation breaks on soil biological properties at the sites with the long-term breaks, suggested that effects on some soil organisms (e.g. lesion nematodes) maybe short-lived.     

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

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

Indication of soil heavy metal pollution with earthworms and soil microbial biomass carbon in the vicinity of an abandoned copper mine in Eastern Nanjing,China

Mining activities can cause severe soil pollution in mining area and its surroundings. Nevertheless, very little is known about the local environmental risk after the mining activities are ended in China. Earthworms and soil microbial biomass carbon (SMBC), which are often used as bioindicators of soil pollution, were studied in order to support chemical analyses in assessing the status of soil heavy metal pollution around an abandoned copper mine in eastern Nanjing, China. Seven earthworm species belonging to three families (Megascolecidae, Moniligastridae, and Lumbricidae) were present. Correlations between earthworm densities or biomass and a range of soil physical and chemical parameters were generally poor; however, several linear regression models based on the soil physicochemical characteristics and metal concentrations in earthworm bodies were established for each metal (Cu, Cd, and Zn) and each earthworm family. Therefore, metal bioaccumulation by soil-dwelling earthworms can be used as an ecological indicator of metal availability for this area. The SMBC, which varied from 83.9 to 499 g kg^?1, did not correlate with the soil heavy metal concentrations, and SMBC is not proposed as a sensitive indicator for evaluating the environmental effects of soil heavy metal pollution in this area.     

Effect of the herbicide fluazifop-butyl on fungal populations and activity in soil

The side effects of fluazifop-butyl on soil fungal populations and oxygen uptake were studied by incubating soil samples with a range of fluazifop-butyl concentrations (0, 0.6, 3 and 6 μg g^?1) over 8 weeks. Cellulose decomposition in soil was also studied in laboratory experiments with the herbicide which was either incorporated in soil or sprayed onto calico squares which were buried in soil. The mycelial dry weight of six fungal species under the effect of the herbicide was also examined. Fluazifop-butyl had no significant effect on total fungal propagule populations at 0.6 μg g^?1. At 3 and 6 μg g^?1, it caused temporary reduction in fungal populations observed after 1 and 2-wk of incubation. The herbicide had no significant effect on OZ uptake. The decay of calico buried in herbicide-treated soil was generally stimulated, while the decomposition of herbicide-treated calico, buried in untreated soil, was temporary delayed. The mycelial dry weight yields of Aspergillus favus (at 2 and 12 μg mL^?1 of fluazifop-butyl) and Cunninghamella echinulata (at 12 μg mL^?1) were significantly increased. At 24 μg mL^?1 the mycelial dry weight of A. flavus and Alternaria alternata was significantly reduced.     

Reduction in viability of sclerotia of Macrophomina phaseolina with polyethylene mulching of soil

Mulching of Macrophomina phaseolina-inksted soil (moist or dry) with transparent polyethylene sheets during the hot days of May increased temperature of wet soil at 5 cm from 37°C (unmulched) to 52°C (mulched) and of dry soil from 52°C (unmulched) to 65°C (mulched). At 20 cm mulching increased temperature from 30°C to 41°C (wet) and from 38°C to 42°C (dry). In artificially-infested soil. the sclerotia of M. phaseolina were eradicated at 5 cm by a mulch treatment for 1 week and at 20 cm depth 50% sclerotia lost viability in wet soil but were not affected in dry soil. In a naturally infested soil (5–7 sclerotia g^?1), which gave 20% infection on Vigna, the sclerotia were reduced to such an extent that after 1 week mulching no disease was observed on Vigna.     

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     

Effect of solid waste compost on microbiological and physical properties of a burnt forest soil in field experiments

 The restoration of soil microbial activities is a basic step in the reclamation of burnt soils. For this reason, the ability of municipal solid waste compost to accelerate the re-establishment of bacterial and fungal populations, as well as to re-establish physical properties in a burnt soil, was evaluated in a field experiment. Four treatments were performed by adding different doses of compost (0, 0.5, 1 and 2 kg compost m^–2 soil) to a burnt Calcic Rodoxeralf soil, and the changes in microbial populations, salt content, aggregate stability and bulk density were evaluated for 1 year. Initially, the addition of compost had a negative effect on soil microbial populations, but 3 months after compost addition, the number of viable fungal propagules increased in all the amended soils. This positive effect lasted until the end of the experiment. From 30 days onwards, all the amended soils showed a greater total number of bacterial cell forming units than the unamended burnt soil. Organic amendment increased the percentage of 2- to 4-mm aggregates, although the effect on the stability of the 0.2- to 2-mm aggregates and on bulk density was less noticeable. Received: 24 November 1999     

Survival and plasmid stability of rhizobia introduced into a contaminated soil

The behaviour of Rhizobium strains introduced separately into soil from a contaminated site with high concentrations of heavy metals (mainly Zn and Hg), and the role of plasmids in the ecology of these rhizobia strains were studied. Six Rhizobium leguminosarum biovar trifolii strains, from different sources and with different plasmid contents, were selected. Two of them were isolated from nodules of subterranean clover plants (Trifolium subterraneum) grown in the contaminated soil and four were from an uncontaminated soil. After inoculation with approximately 10⁷ cells g⁻¹ soil, of each strain, survival and plasmid stability were assessed over a period of 12-18 months. Differences in survival of Rhizobium strains were only detected more than 12 months after inoculation. After 18 months it was clear that survival in contaminated soil was greatest in the two strains originally isolated from that contaminated soil, and also by two of the strains originally isolated from uncontaminated soil. The latter two strains were also the only ones that showed changes in their plasmid profiles. The remaining isolates had the lowest populations, and their plasmid profiles were unchanged and similar to the parent strains.     

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.     

Populations of Pseudomonas solanacearum biovar 3 in naturally infested soil

Populations of Pseudomonas solanacearum biovar 3 were monitored in a clay loam soil sampled from the root zone of infected tomato plants during 1978, 1979 and 1980. Soil numbers increased during symptom development and declined with the death of infected plants. The decline in population size in the soil was continuous where no cover crop was planted between the autumn and spring crops. This decline in population size was interrupted, however, following the planting of an oats cover crop numbers decreased with the ploughing under of the oats. Rainfall was associated with high soil numbers but soil temperature did not appear to directly affect population size. Soil populations in the root zone of susceptible tomato plants cultivar Floradel reached a maximum 1000-fold greater than in soil from the root zone of a resistant line. P. solanacearum survived in bare fallow soil for 21 months. Tomatoes planted 2 months later wilted rapidly.     

Cocomposting of Cattle Manure and Hydrocarbon Contaminated Flare Pit Soils

The potential of using composting technology to remediate clayey soils with high levels of crude oil contamination was evaluated. An open air windrow comprised of flare pit soil, manure and wood chips was constructed at Olds College, Composting Technology Centre. Aeration and mixing were carried out by a skid steer loader and composting parameters were monitored for ten months. Temperature profile of this windrow gave cyclic patterns of high and low temperature recordings corresponded to the turning events. Most of the microbial metabolic activity occurred within the mesophilic temperature range and the hydrocarbon degrading microorganism populations remained high throughout the trial. Complete removal of BTEX compounds was achieved within six months and extractable carbons from C₅ to C₁₀ were reduced by 98.7% compared to the initial contaminated soil. Vegetative growth on the composted soil was also evaluated. Barley and timothy plants grown in the composted soil were compared to the control off-lease soil, contaminated soil, and other treatments of varying salinity and organic matter levels. Plant germination, survival, and biomass production was significantly better in the composted soil than in the contaminated soil. Furthermore, barley plants grown in the composted soil were more resilient than those grown in the control off-lease soil.     

Short-term effects of earthworm activity and straw amendment on the microbial C and N turnover in a remoistened arable soil after summer drought

Short-term effects of actively burrowing Octolasion lacteum (Örl.) (Lumbricidae) on the microbial C and N turnover in an arable soil with a high clay content were studied in a microcosm experiment throughout a 16 day incubation. Treatments with or without amendment of winter wheat straw were compared under conditions of a moistening period after summer drought. The use of ¹⁴C labeled straw allowed for analyzing the microbial use of different C components. Microbial biomass C, biomass N and ergosterol were only slightly affected by rewetting and not by O. lacteum in both cases. Increased values of soil microbial biomass were determined in the straw treatments even after 24 h of incubation. This extra biomass corresponded to the initial microbial colonization of the added straw. O. lacteum significantly increased CO₂ production from soil organic matter and from the ¹⁴C-labeled straw. Higher release rates of ¹⁴C-CO₂ were recorded shortly after insertion of earthworms. This effect remained until the end of the experiment. O. lacteum enhanced N mineralization. Earthworms significantly increased both mineral N content of soil and N leaching in the treatments without straw addition. Moreover, earthworms slightly reduced N immobilization in the treatments with straw addition. The immediate increase in microbial activity suggests that perturbation of soil is more important than substrate consumption for the effect of earthworms on C and N turnover in moistening periods after drought.     

Fate of prions in soil: Longevity and migration of recPrP in soil columns

Research into transmissible spongiform encephalopathy (TSE) diseases has become a high priority worldwide in recent years yet remarkably little is known about the behaviour of TSE infectivity in the environment. The resilience and stability of prion proteins could lead to soils becoming a potential reservoir of TSE infectivity as a result of contamination from activities such as infected carcass burial or the dispersion of effluents from slaughter houses, or by contamination of pastures by infected animals, (e.g. scrapie in sheep). Knowledge of the fate of prion proteins in soils, and associated physico-chemical conditions which favour migration, can be used to help prevent re-infection of animals through grazing, to protect watercourses and develop good management practices. In two consecutive experiments of 9 and 6 months, the migration of recombinant ovine PrP (recPrP) in soil columns was followed under contrasting levels of microbial activity (normal versus reduced), under varying regimes of soil water content and redox potential, and in two different soil types (loamy sand and clay loam). At each analysis time (1, 3, 6 or 9 months), in both soil types, full-length recPrP was detected in the original contaminated layer, indicating the resilience and stability of recPrP under varied soil conditions, even in the presence of active soil microbial populations. Evidence of protein migration was found in every soil column at the earliest analysis time (1 or 3 months), but was restricted to a maximum distance of 1 cm, indicative of limited initial mobility in soils followed by strong adsorption over the following days to weeks. The survival of recPrP in the soil over a period of at least 9 months was demonstrated. In this study, recPrP was used as an indicator for potential TSE infectivity, although infectivity tests should be carried out before conclusions can be drawn regarding the infection risk posed by prions in soil. However, it has been demonstrated that soil is likely to act as a significant barrier to the dispersion of contaminated material at storage or burial sites.     

Schwermetallbelastung von Aporrectodea caliginosa (Oligochaeta,Lumbricidae) im Raum Kiel

Heavy metal content in Aporrectodea caliginosa (Oligochaeta, Lumbricidae) in the city of Kiel (Germany, Schleswig-Holstein) In November 1995 the content of lead, cadmium, copper and zinc in earthworms of the Aporrectodea caliginosa species was investigated at 28 sites of the Kiel area, as well as at one reference site (Belauer See, ca. 20 kilometres south of Kiel), and compared with the heavy metal content in the soil taken from all those sites. As for the lead and copper content, a positive correlation could be established between the earthworms and the soil. However, the lead content in the earthworms did not depend only on its amount in the soil, but also on soil pH and calcium content. Their copper content decreased exponentially as weight increased. The content of lead, cadmium and copper in A. caliginosa suggested an influence of urban soil pollution on the heavy metal content in earthworms. According to the grouping of heavy metal content in the earthworms, which was done in the course of the research work, the city of Kiel ranges among a minor to a medium degree of pollution caused by the investigated heavy metals.     

RHIZOSPHERE MICROBIAL POPULATIONS IN CONTAMINATED SOILS

Rhizosphere microbial populations may increase bioremediation of soil contaminated with organic chemicals. A growth chamber study was conducted to evaluate rhizosphere microbial populations in contaminated and non-contaminated soil. Alfalfa (Medicago sativa L.) and alpine bluegrass (Poa alpina L.) were grown in soil containing a mixture of organic chemicals for 14 weeks. The equal millimolar mixture of hexadecane, (2,2-dimethylpropyl)benzene, cis-decahydronaphthalene (decalin), benzoic acid, phenanthrene, and pyrene was added at levels of 0 and 2000 mg/kg. Organic chemical degrader (OCD) populations were assessed by a Most-Probable-Number technique, and bacteria and fungi were enumerated by plate count methods. Different methods for expressing OCD rhizosphere populations were investigated to determine the effect it had on interpretation of the results. At 9 weeks, the OCD numbers were significantly higher in rhizosphere and contaminated soils than in bulk and non-contaminated soils, respectively. Alfalfa rhizosphere OCD levels were 4 × 10⁷/g for contaminated and 6 × 10⁶/g for non-contaminated soils. Bluegrass rhizosphere OCD levels were 1 × 10⁷/g and 1 × 10⁶/g in contaminated and non-contaminated soils, respectively. Selective enrichment of OCD populations was observed in contaminated rhizosphere soil. Higher numbers of OCD in contaminated rhizospheres suggest potential stimulation of bioremediation around plant roots.     

The effects of organic residue quality on growth and reproduction of <Emphasis Type="Italic">Aporrectodea trapezoides</Emphasis> under different moisture conditions in a salt-affected agricultural soil

We studied the effects of organic residues with different C/N ratios and soil moisture contents on the growth and reproduction of the earthworm Aporrectodea trapezoides to investigate potential measures to increase its population in a salt-affected agricultural soil. The experiment consisted of eight treatments in a fully factorial design: low or high C/N ratio organic residue, soil moisture at 75 or 95% field capacity (FC), and salinity (as electrical conductivity (EC)) of 3.07 or 4.77 dS m^?1. It was carried out under controlled laboratory conditions for 4 months. In the low C/N ratio organic residue application, there was a significantly greater mean total dry weight and number of clitellate individuals of A. trapezoides, regardless of the soil moisture and salinity content, which may be due to the greater soil microbial biomass and dissolved organic N (DON) derived from the low C/N ratio organic residue. Generally, more cocoons were found in the application of low C/N ratio clover residue at months 2 and 4. At an EC of 3.07 dS m^?1 and moisture content of 75% field capacity (FC), significantly more hatchlings were found when low C/N ratio clover residue was applied compared to the high C/N ratio wheat residue. High soil moisture content (95% FC) resulted in a significantly greater mean total dry weight of A. trapezoides at months 2 and 4 and significantly more clitellate individuals and cocoons at month 4 compared to the low soil moisture content (75% FC), but only when the low C/N ratio residue was applied. In contrast, high soil moisture content (95% FC) resulted in significantly less hatchling numbers at an EC of 3.07 dS m^?1, only when the low C/N ratio residue was applied. These results suggest that the organic residue type and soil moisture content can regulate the growth and reproduction of the earthworm A. trapezoides, which should help to improve the recovery of their populations in salt-affected agricultural soil.     

Effect of heptachlor on numbers of bacteria,actinomycetes and fungi in soil

Growth of many soil microorganisms was inhibited on culture media containing heptachlor. At a concentration of 25 mg/l., heptachlor killed 63 per cent of the bacteria transferred from soil dilution plates. Heptachlor, at 100 mg/1. in agar media used for isolating microorganisms from soil, prevented the development of 89 per cent of the bacteria, 81 per cent of the actinomycetes, and 50 per cent of the fungi that appeared on isolation plates without heptachlor. After heptachlor was added to soil, fungal populations declined and bacterial populations increased. Numbers of bacteria were related to amount of heptachlor added; higher concentrations of heptachlor in soil resulted in larger populations. A selective increase in numbers of fungi which would grow on media containing heptachlor at 100 mg/l. occurred in soils amended with heptachlor in amounts ordinarily used in field practices, but a similar increase of heptachlor-resistant bacteria occurred only in soils amended with higher amounts of heptachlor.