Trevor G. Piearce

Effects of climate change on soil fauna; responses of enchytraeids, Diptera larvae and tardigrades in a transplant experiment

Abstract A transplant experiment was carried out on the Moor House National Nature Reserve, Cumbria, UK, and two sites with different climatic characteristics were selected for determining how Enchytraeids, Diptera larvae and Tardigrades respond to changes in climate. The soil was a cambic stagnohumic gley, characterized by a high organic matter content and low pH. Vegetated soil cores were taken from near the summit of Great Dun Fell (GDF) and used for the transplant experiment. Cores were then placed back at GDF (845 m) and also transplanted to Sink Beck (SNK, 480 m), providing a mean annual temperature increase of 2.5°C. In order to discriminate between the effects of temperature and rainfall on the size and vertical distribution patterns of the fauna, a further series of lysimeters were established at SNK, and rainfall inputs were manipulated, intending to provide a total input equivalent to the ambient rainfall at the top site. At regular intervals, a number of cores were destructively sampled from each treatment (top site—GDF; lower site—SNK; enhanced rainfall inputs-SNK) and the vertical distribution of the soil fauna determined. Enchytraeidae, Tardigrada and Diptera were commonly found in soil samples at the Reserve and appeared sensitive to the imposed changes in temperature and moisture. Different species of enchytraeids responded differently: numbers of Cognettia sphagnetorum were correlated positively with temperature, whereas their vertical distribution was determined by moisture. Cernosvitoviella atrata was unable to avoid dry conditions which apparently caused severe mortality when exposed to the elevated temperatures; Achaeta eiseni was a more tolerant species, increasing in numbers with increasing temperature. Diptera larvae appeared to be dependent on the moisture status of the upper soil layers and their populations were reduced at higher temperatures and lower moisture contents. By contrast, tardigrades were able to survive adverse conditions by entering an anhydrobiotic stage, recovering when seasonal climate improved. General trends in soil faunal responses to climatological changes in the UK are predicted.

Interactions between earthworms and arsenic in the soil environment: a review

Chemical pollution of the environment has become a major source of concern. In particular, many studies have investigated the impact of pollution on biota in the environment. Studies on metalliferous contaminated mine spoil wastes have shown that some soil organisms have the capability to become resistant to metal/metalloid toxicity. Earthworms are known to inhabit arsenic-rich metalliferous soils and, due to their intimate contact with the soil, in both the solid and aqueous phases, are likely to accumulate contaminants present in mine spoil. Earthworms that inhabit metalliferous contaminated soils must have developed mechanisms of resistance to the toxins found in these soils. The mechanisms of resistance are not fully understood; they may involve physiological adaptation (acclimation) or be genetic. This review discusses the relationships between earthworms and arsenic-rich mine spoil wastes, looking critically at resistance and possible mechanisms of resistance, in relation to soil edaphic factors and possible trophic transfer routes.

Selective consumption of decomposing wheat straw by earthworms

Three species of earthworm, Lumbricus terrestris L., Aporrectodea longa (Ude) and Allolobophora chlorotica (Savigny), were offered a choice of mixtures of soil and small wheat straw fragments which had been inoculated individually with six saprotrophic fungi. All earthworm species showed preferences between the six fungal species offered. Early straw decomposers, capable of utilizing water-soluble sugars and cellulose, were preferred in most cases to the lignin-decomposing fungi characteristic of the later stages of decomposition. The removal of fungal-inoculated straw pieces from the soil surface by L. terrestris followed the same pattern. The palatability of two wheat pathogens to L. terrestris was found to be similar to that of the preferred saprotroph. The implications of these findings for fungal abundance and dispersal in wheat fields are discussed.

Survival and behaviour of the earthworms Lumbricus rubellus and Dendrodrilus rubidus from arsenate-contaminated and non-contaminated sites

Two arsenic- and heavy metal-contaminated mine-spoil sites, at Carrock Fell, Cumbria and Devon Great Consols Mine, Devon, were found to support populations of the earthworms Lumbricus rubellus Hoffmeister and Dendrodrilus rubidus (Savigny). L. rubellus and D. rubidus collected from the Devon site and an uncontaminated site were kept for 28 days in uncontaminated soil and in soil containing sodium arsenate (494 mg As kg−1). The state of the specimens was recorded every 7 days using a semi-quantitative assessment of earthworm health (condition index, C. I.). The C. I. remained high for all specimens except those of L. rubellus and D. rubidus from uncontaminated sites, which displayed 60 and 10% mortality, respectively. L. rubellus collected from the Carrock Fell site, and L. rubellus and D. rubidus from an uncontaminated site, burrowed as rapidly into soil containing up to 1235 mg As kg−1 in the form of sodium arsenate as into uncontaminated soil when placed on the soil surface. When earthworms were allowed a choice between uncontaminated soil and soil contaminated with sodium arsenate in concentrations of up to 1235 mg As kg−1, the threshold concentration for avoidance of contaminated soil was lower for L. rubellus and D. rubidus from uncontaminated soil than for specimens from contaminated soil. There was no significant effect of pH on soil discrimination. The LC50 concentration of As for L. rubellus from Devon Great Consols was significantly higher (P<0.001) than for L. rubellus from the uncontaminated site: 1510 and 96 mg As kg−1, respectively.

Resistance to arsenic-toxicity in a population of the earthworm Lumbricus rubellus

Specimens of the earthworms Lumbricus terrestris L. and L. rubellus Hoffmeister from an uncontaminated site rapidly deteriorated in condition when kept in spoil rich in metal contaminants and arsenic. The site from which the spoil was collected supports several earthworm species, L. rubellus being dominant. Native L. rubellus survived for 12 weeks in spoil in the laboratory. L. rubellus collected from the spoil site and an uncontaminated site were kept for 28 d in uncontaminated soil and in soil containing 2000 mg sodium arsenate heptahydrate kg−1, the state of the specimens being recorded using a semi-quantitative assessment of earthworm condition (condition index, CI). The CI remained high for all specimens except those from the uncontaminated site kept in As-rich soil, for which mortality was 100% after 28 d. Tissue As concentrations in L rubellus from uncontaminated and contaminated sites were <1 mg kg−1 and 230 mg kg−1, respectively. In L. rubellus collected from the uncontaminated site and exposed to contaminated soil containing 2000 mg sodium arsenate heptahydrate kg−1, mean tissue As concentration was 92 mg kg−1.

Temporal changes in earthworm availability and extractability of polycyclic aromatic hydrocarbons in soil.

In this study, the earthworm, Aporrectodea longa, was used as a model soil organism to assess the impact of ageing upon the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in soil. The objectives were to characterise the temporal changes in the extractability/availability of PAHs amended into soil and to examine how the decline in PAH availability to earthworms related to the decline in chemical availability as determined by solvent extraction. Two PAHs (pyrene and benz[a]anthracene) were spiked into sterilised soil and aged in microcosms for up to 240 days. The earthworms were incubated in the PAH spiked soils, at 0, 30, 60, and 240 days after spiking, for a period of 28 days. After exposure, the earthworm-PAH tissue concentrations were measured. Change in chemical extractability of the soil-PAHs was monitored throughout the incubation by employing a sequential extraction technique with two solvents of different polarities. The chemical extractability and bioavailability of both PAHs reduced with increased soil contact time. Pyrene and benz[a]anthracene both displayed biphasic profiles in chemical extractability and earthworm bioavailability, but the rates and extents differed. Thus, chemical extractability does not accurately predict the bioavailable fraction of PAHs in the soil and does not agree with work reported earlier using Eisenia fetida, hence it follows that the earthworm species may be important in determining the bioaccumulation of soil-associated PAHs. Further, the ecological niche occupied by the experimental species will influence feeding behaviour and thus, perhaps, the degree of accumulation. Therefore, the use of the manure earthworm, E. fetida, in screening of contaminated soils (as recommended by the USEPA) may underestimate toxicity or accumulatory potential.

Fate of some fungal spores associated with wheat straw decomposition on passage through the guts of Lumbricus terrestris and Aporrectodea longa.

The effect of passage through the earthworm gut on the viability of spores of saprotrophic fungi was found to vary depending on fungal and earthworm species. Of 5 fungal species fed to Lumbricus terrestris L., the spores of two (Fusarium lateritium Nees, and Agrocybe temulenta (Fries)) failed to germinate after gut passage, while germination of Trichoderma sp. and Mucor hiemalis Wehmer was significantly reduced. A similar fate was recorded for F. lateritium and M. hiemalis spores on passage through the gut of Aporrectodea longa (Ude), however in the case of Chaetomium globosum Kunze there was a significant increase in spore germination after transit through A. longa. The germination of spores of M. hiemalis increased after abrasion by soil particles in a peristaltic pump simulating the mechanical action of the earthworm gut. In contrast germination of this species was significantly reduced when spores were exposed to intestinal fluids from L. terrestris.

Morphology and dynamics of calcium carbonate granules produced by different earthworm species.

Granules of calcium carbonate produced by earthworms are regularly found in soil profiles, but little is known of their origins and dynamics. Pure cultures of a range of species were therefore set up, using artificial soils, and the granules recovered for examination. Species of Lumbricus, Aporrectodea, Octolasion and Allolobophora all produced granules larger than 0.125mm, but Eisenia hortensis did not. For comparison, two compost-dwelling Eisenia species were also cultured. These yielded no granules at all, suggesting that the genus as a whole does not produce granules, consistent with its lack of calciferous sacs. Granules recovered from the other 7 species have a variety of sizes and morphologies, ranging from single calcite crystals to aggregations up to 2.5mm in diameter. SEM photographs of the granules and data on granule concentrations in relation to depth are presented

Decomposition of Pinus sylvestris litter in litter bags: Influence of underlying native litter layer

Abstract Pinus sylvestris (L.) litter confined in 1-mm mesh litter bags was incubated on layers of either P. sylvestris or Picea abies (Dietra.) litter of different origins (native litters) under standard conditions in the laboratory. The decomposition rate of the confined litter was measured both as evolution of CO 2 and as mass loss. The native litter played an important part in governing the rate of decomposition of the confined litter, with the native litters richest in N and Ca resulting in greater decomposition rates (up to 15% more) of the confined litter than the nutrient poor native litters. Both inter- and intra-species effects were observed and these are discussed in terms of chemical and physical interactions between the confined and native litters.

Arsenic-speciation in arsenate-resistant and non-resistant populations of the earthworm, Lumbricus rubellus

Arsenic speciation was determined in Lumbricus rubellus Hoffmeister from arsenic-contaminated mine spoil sites and an uncontaminated site using HPLC-MS, HPLC-ICP-MS and XAS. It was previously demonstrated that L. rubellus from mine soils were more arsenate resistant than from the uncontaminated site and we wished to investigate if arsenic speciation had a role in this resistance. Earthworms from contaminated sites had considerably higher arsenic body burdens (maximum 1,358 mg As kg-1) compared to the uncontaminated site (maximum 13 mg As kg-1). The only organo-arsenic species found in methanol/water extracts for all earthworm populations was arsenobetaine, quantified using both HPLC-MS and HPLC-ICP-MS. Arsenobetaine concentrations were high in L. rubellus from the uncontaminated site when concentrations were expressed as a percentage of the total arsenic burden (23% mean), but earthworms from the contaminated sites with relatively low arsenic burdens also had these high levels of arsenobetaine (17% mean). As arsenic body burden increased, the percentage of arsenobetaine present decreased in a dose dependent manner, although its absolute concentration rose with increasing arsenic burden. The origin of this arsenobetaine is discussed. XAS analysis of arsenic mine L. rubellus showed that arsenic was primarily present as As(III) co-ordinated with sulfur (30% approx.), with some As(v) with oxygen (5%). Spectra for As(III) complexed with glutathione gave a very good fit to the spectra obtained for the earthworms, suggesting a role for sulfur co-ordination in arsenic metabolism at higher earthworm arsenic burdens. It is also possible that the disintegration of As(III)-S complexes may have taken place due to (a) processing of the sample, (b) storage of the extract or (c) HPLC anion exchange. HPLC-ICP-MS analysis of methanol extracts showed the presence of arsenite and arsenate, suggesting that these sulfur complexes disintegrate on extraction. The role of arsenic speciation in the resistance of L. rubellus to arsenate is considered.