Earthworm Abundance Research Articles

Assessment of Relationships between Earthworms and Soil Abiotic and Biotic Factors as a Tool in Sustainable Agricultural

Earthworms are a major component of soil fauna communities. They influence soil chemical, biological, and physical processes and vice versa, their abundance and diversity are influenced by natural characteristics or land management practices. There is need to establish their characteristics and relations. In this study earthworm density (ED), body biomass (EB), and diversity in relation to land use (arable land—AL, permanent grasslands—PG), management, and selected abiotic (soil chemical, physical, climate related) and biotic (arthropod density and biomass, ground beetle density, carabid density) indicators were analysed at seven different study sites in Slovakia. On average, the density of earthworms was nearly twice as high in PG compared to AL. Among five soil types used as arable land, Fluvisols created the most suitable conditions for earthworm abundance and biomass. We recorded a significant correlation between ED, EB and soil moisture in arable land. In permanent grasslands, the main climate related factor was soil temperature. Relationships between earthworms and some chemical properties (pH, available nutrients) were observed only in arable land. Our findings indicate trophic interaction between earthworms and carabids in organically managed arable land. Comprehensive assessment of observed relationships can help in earthworm management to achieve sustainable agricultural systems.

The effects of soil compaction mitigation on below-ground fauna: How earthworms respond to mechanical loosening and power harrow cultivation

Soils are one of the most biologically diverse habitats within the terrestrial ecosystem. Although soils are vital to the provision of important ecosystem services, their direct protection and sustainable management are often lacking within conservation policy. Many grassland soils have undergone considerable management intensification and are subject to degradation pressures. Soil compaction is an important form of soil degradation that can reduce soil productivity and crop yields, although the impacts can be reversed through natural processes and mitigated through management interventions. While commonly used, substantial knowledge gaps exist regarding the impact of soil compaction mitigation techniques on key soil macrofauna; many of these organisms are essential to soil function. A complete split-plot design was used to investigate the impacts of mechanical loosening (subsurface soil disturbance using tines or radial blades without significant soil mixing or inversion) and power harrow cultivation (shearing and mixing of soil to prepare a seedbed for the establishment of a deep-rooting forb and legume mix) on the abundance and biomass of earthworms up to two years post-treatment. Mechanical loosening was undertaken at two depths, c. 20 cm and c. 35 cm as two separate treatments. There was a negative effect of mechanical loosening at both depths on the abundance and biomass of anecic earthworms, lasting up to two years post-treatment. There was no significant effect of power harrow cultivation on the abundance or biomass of earthworms. These negative effects are consistent with other studies that have shown mechanical loosening to be a source of earthworm mortality. Although these findings resulted from a single episode of power harrow cultivation and mechanical loosening at a single site, the results indicate that the mechanical loosening of grassland soil can have a negative impact on important soil macrofauna and should possibly only be undertaken when the soil is in the most severely degraded conditions. Further work is needed to determine whether the negative impact of mechanical loosening is common to multiple sites and soil types and to link the reduction in earthworm number and biomass to future soil function.

Transcriptomics of sugar beet (Beta vulgaris L.) resistance to Beet necrotic yellow vein virus

Recently detected invertebrate population declines are likely to have far-reaching impacts for ecosystem function. However, very little large-scale monitoring of invertebrates, especially soil invertebrates, has taken place. To address this gap, we established a school-based citizen science project to collect data on soil invertebrate abundance and bird counts across the UK. We examined the association between earthworms (which comprised 93% of the total soil invertebrate biomass in the surface soil) and 15 bird species on school playing fields over three years. We also tested whether simple bird counts of species that rely on earthworms could be used to indicate the earthworm abundance in soil.We found a clear link between earthworm abundance and counts of robins (Erithacus rubecula), blackbirds (Turdus merula) and other thrushes (Turdus pilaris, Turdus viscivorus, Turdus philomelos and Turdus iliacus), all of which rely on earthworms as an important component of their diet. None of these relationships varied with season. There were no correlations found between earthworm abundance and bird counts for species that do not rely on earthworms. We found that the total thrush count (including blackbirds) could be used as a simple indicator of earthworm abundance, explaining up to 20% of the variation in earthworm counts.In spite of the uncertainties associated with the data, these results raise the possibility that existing, robust, long-term bird monitoring data could, with further research, be used to infer changes in soil invertebrates, such as earthworms, and therefore aspects of soil health. We conclude by identifying a series of criteria that would need to be fulfilled in order for such inference to be robust.

Proximal Soil Sensing - A Contribution for Species Habitat Distribution Modelling of Earthworms in Agricultural Soils?

BackgroundEarthworms are important for maintaining soil ecosystem functioning and serve as indicators of soil fertility. However, detection of earthworms is time-consuming, which hinders the assessment of earthworm abundances with high sampling density over entire fields. Recent developments of mobile terrestrial sensor platforms for proximal soil sensing (PSS) provided new tools for collecting dense spatial information of soils using various sensing principles. Yet, the potential of PSS for assessing earthworm habitats is largely unexplored. This study investigates whether PSS data contribute to the spatial prediction of earthworm abundances in species distribution models of agricultural soils.Methodology/Principal FindingsProximal soil sensing data, e.g., soil electrical conductivity (EC), pH, and near infrared absorbance (NIR), were collected in real-time in a field with two management strategies (reduced tillage / conventional tillage) and sandy to loam soils. PSS was related to observations from a long-term (11 years) earthworm observation study conducted at 42 plots. Earthworms were sampled from 0.5 x 0.5 x 0.2 m³ soil blocks and identified to species level. Sensor data were highly correlated with earthworm abundances observed in reduced tillage but less correlated with earthworm abundances observed in conventional tillage. This may indicate that management influences the sensor-earthworm relationship. Generalized additive models and state-space models showed that modelling based on data fusion from EC, pH, and NIR sensors produced better results than modelling without sensor data or data from just a single sensor. Regarding the individual earthworm species, particular sensor combinations were more appropriate than others due to the different habitat requirements of the earthworms. Earthworm species with soil-specific habitat preferences were spatially predicted with higher accuracy by PSS than more ubiquitous species.Conclusions/SignificanceOur findings suggest that PSS contributes to the spatial modelling of earthworm abundances at field scale and that it will support species distribution modelling in the attempt to understand the soil-earthworm relationships in agroecosystems.

Potential effects of tillage and field borders on within-field spatial distribution patterns of earthworms

Earthworms play a key role in regulating soil ecosystem functions and services. The small scale variability in earthworm abundance is often found to be very high, which is a problem for representative sampling of earthworm abundance at larger scales. In agricultural fields, soil tillage may influence both the average earthworm abundance as well as the spatial distribution of earthworms. Therefore we studied the abundance and spatial pattern of the different ecological earthworm types, i.e. endogeic, epigeic and anecic earthworms, in four agricultural fields differing in soil tillage (two fields with regular tillage and two fields with conservation tillage) and surrounding land use (other cropped fields or apple orchard and forest). To this aim we sampled earthworms on a total number of 430 plots (50×50cm2) using a combination of extraction with mustard solution and hand sorting. The results exhibit large differences in average earthworm abundance between the four fields. Only one of the two fields with conservation tillage had a comparatively very high overall abundance of earthworms. Furthermore, we found a high spatial variability of earthworms within the field scale often exhibiting a patchy distribution. We detected a trend of decreasing earthworm abundances from the field border into the field for different earthworm groups on each of the fields. In three fields with low total earthworm abundance (and only very few epigeic earthworms) there was a short scale autocorrelation with ranges varying strongly for the endogeic earthworms (37.9m, 62.6m, and 85.2m) compared to anecic earthworms (19.8m, 22.8m, and 27.4m). In the field with high abundance, after trend removal, the variogram models for anecic and endogeic earthworms were rejected based on their negative explained variances. On this field, we found only a short scale autocorrelation for the epigeic earthworms with a range of 143m.Based on these results it seems that ploughing alone cannot explain the differences in abundance and range of autocorrelation found on the four fields. The trend of strongly decreasing earthworm abundance from the field border into the field in the one field with high abundance does indicate that the field border or surrounding land use may also influence the recolonization of fields, but more research is required to provide further evidence for this hypothesis. Due to the very different patterns of earthworm distributions in the fields it remains difficult to recommend an optimal number and distance of samples to obtain a representative earthworm abundance for the field scale.

Does earthworms density really modify soil's hydrodynamic properties in irrigated systems with recycled water?

Our study has the general objective to understand the impact of the valuation of treated water on earthworm abundance and total porosity of the soil and the effect of the interaction between these two physical-biological components of the hydrological functioning of soils. It was carried out on the meadows soils of the valley of Wadi Bousselam. Although the treated water has high organic and particulate filler, it improved the earthworm abundance, total porosity and hydraulic conductivity of the soil. Keywords: meadows soils; earthworm density; soil morphology; treated water; hydrodynamic soil characteristics

Invasive Asian Earthworms Negatively Impact Keystone Terrestrial Salamanders.

Asian pheretimoid earthworms (e.g. Amynthas and Metaphire spp.) are invading North American forests and consuming the vital detrital layer that forest floor biota [including the keystone species Plethodon cinereus (Eastern Red-backed Salamander)], rely on for protection, food, and habitat. Plethodon cinereus population declines have been associated with leaf litter loss following the invasion of several exotic earthworm species, but there have been few studies on the specific interactions between pheretimoid earthworms and P. cinereus. Since some species of large and active pheretimoids spatially overlap with salamanders beneath natural cover objects and in detritus, they may distinctively compound the negative consequences of earthworm-mediated resource degradation by physically disturbing important salamander activities (foraging, mating, and egg brooding). We predicted that earthworms would exclude salamanders from high quality microhabitat, reduce foraging efficiency, and negatively affect salamander fitness. In laboratory trials, salamanders used lower quality microhabitat and consumed fewer flies in the presence of earthworms. In a natural field experiment, conducted on salamander populations from “non-invaded” and “pheretimoid invaded” sites in Ohio, salamanders and earthworms shared cover objects ~60% less than expected. Earthworm abundance was negatively associated with juvenile and male salamander abundance, but had no relationship with female salamander abundance. There was no effect of pheretimoid invasion on salamander body condition. Juvenile and non-resident male salamanders do not hold stable territories centered beneath cover objects such as rocks or logs, which results in reduced access to prey, greater risk of desiccation, and dispersal pressure. Habitat degradation and physical exclusion of salamanders from cover objects may hinder juvenile and male salamander performance, ultimately reducing recruitment and salamander abundance following Asian earthworm invasion.

Loss of soil (macro)fauna due to the expansion of Brazilian sugarcane acreage

Land use changes (LUC) from pasture to sugarcane (Saccharum spp.) crop are expected to add 6.4Mha of new sugarcane land by 2021 in the Brazilian Cerrado and Atlantic Forest biomes. We assessed the effects of these LUC on the abundance and community structure of animals that inhabit soils belowground through a field survey using chronosequences of land uses comprising native vegetation, pasture, and sugarcane along a 1000-km-long transect across these two major tropical biomes in Brazil. Macrofauna community composition differed among land uses. While most groups were associated with samples taken in native vegetation, high abundance of termites and earthworms appeared associated with pasture soils. Linear mixed effects analysis showed that LUC affected total abundance (X2(1)=6.79, p=0.03) and taxa richness (X2(1)=6.08, p=0.04) of soil macrofauna. Abundance increased from 411±70individualsm−2 in native vegetation to 1111±202individualsm−2 in pasture, but decreased sharply to 106±24individualsm−2 in sugarcane soils. Diversity decreased 24% from native vegetation to pasture, and 39% from pasture to sugarcane. Thus, a reduction of ~90% in soil macrofauna abundance, besides a loss of ~40% in the diversity of macrofauna groups, can be expected when sugarcane crops replace pasture in Brazilian tropical soils. In general, higher abundances of major macrofauna groups (ants, coleopterans, earthworms, and termites) were associated with higher acidity and low contents of macronutrients and organic matter in soil. This study draws attention for a significant biodiversity loss belowground due to tropical LUC in sugarcane expansion areas. Given that many groups of soil macrofauna are recognized as key mediators of ecosystem processes such as soil aggregation, nutrients cycling and soil carbon storage, our results warrant further efforts to understand the impacts of altering belowground biodiversity and composition on soil functioning and agriculture performance across LUC in the tropics.

Farm compost amendment and non-inversion tillage improve soil quality without increasing the risk for N and P leaching

Farmers have to combine several measures to balance carbon contents in the top soil to preserve soil quality but potentially increasing the risk for N and P losses by leaching. We studied the effect of a combination of several measures on topsoil C content, nutrient leaching and soil quality in a multi-year field trial. Soil quality was defined as the result of the interaction between chemical, physical and biological soil characteristics, and included an assessment of disease suppressiveness as well. Initially, the soil had a suboptimal C content (i.e. 0.81%). Soil organic carbon (SOC) levels were maintained and slightly increased by applying slurry and good agricultural practices such as the use of cover crops and the incorporation of cereal straw (on average +0.04 percentage point). Only with a yearly extra plant-based farm compost amendment SOC levels were substantially increased after a period of four years (on average +0.17 percentage point). This application of 8.3 Mg C ha−1 also improved chemical, physical and biological soil quality. Our research demonstrates that farmers can use compost, for at least 4 years, on top of cattle or pig slurry application to soils with suboptimal C levels to increase C content in the top soil, without inducing higher N and P leaching. Repeated compost application increased the microbial biomass (measured by means of PLFA) and disease suppressiveness against Botrytis cinerea on lettuce. There was no effect on the abundance of the plant-parasitic nematode Pratylenchus penetrans in the soil, nor on disease severity caused by Dickeya solani, Streptomyces scabies and Rhizoctonia solani after a potato cropping. Differences between tillage practices were most obvious in the 0–10cm soil layer as non-inversion tillage (compared to ploughing) resulted in an increase in SOC, Total N, hot-water extractable C and P, plant-available P and K, aggregate stability, earthworm abundance and bacterial and fungal populations in this layer.

Biosolids applied to agricultural land: Influence on structural and functional endpoints of soil fauna on a short- and long-term scale

Biosolids have well-documented crop and soil benefits similar to other sources of organic amendment, but there is environmental concern due to biosolids-associated pollutants. The present study investigated two field sites that had received biosolids at commercial-scale rates in parallel to associated field sections which were managed similarly but without receiving biosolids (controls). The investigated endpoints were abundance and diversity of soil organisms (nematodes, enchytraeids and earthworms) and soil fauna feeding activity as measured by the bait lamina assay. Repeated sampling of one of the field sites following the only biosolids application demonstrated an enrichment effect typical for organic amendments, which was mostly exhausted after 44months. After an initial suppression, the proportion of free-living plant-parasitic nematodes tended to increase in the biosolids-amended soil over time. Yet, none of the endpoints at this site indicated significant negative effects resulting from the biosolids until 44months post application. In contrast to the repeatedly tilled first field site, the second one was left fallow after three biosolids applications, and was sampled 96months post last application. It was only at this field site that potential evidence for a long-term impact of biosolids was detected with regard to two endpoints: earthworm abundance and structure of the nematode assemblage. Agricultural management and correlation with abiotic soil parameters explained the observed difference in earthworm abundance. Yet, the development of a highly structured and mature nematode assemblage at the control but not at the biosolids-amended section of this fallow field could not be explained by such correlations nor by soil metal concentrations. Overall, the present study found only weak evidence for negative long-term impacts of biosolids applied at commercial rates on soil fauna. High-level community parameters such as the nematode structure index (SI) appeared more suitable to detect deleterious effects on soil fauna than simple abundance measurements.

The Impact of Invasive Earthworms on Soil Respiration and Soil Carbon Within Temperate Hardwood Forests

Improving current understanding of the factors that control soil carbon (C) dynamics in forest ecosystems remains an important topic of research as it plays an integral role in the fertility of forest soils and the global C cycle. Invasive earthworms have the potential to alter soil C dynamics, though mechanisms and effects remain poorly understood. To investigate potential effects of invasive earthworms on forest C, the forest floor, mineral soil, fine root biomass, litterfall and microbial litter decay rates, and total soil respiration (TSR) over a full year were measured at an invaded and uninvaded deciduous forest site in southern Ontario. The uninvaded site was approximately 300 m from the invaded site and a distinct invasion front between sites was present. Along the invasion front, the biomass of the forest floor was negatively correlated with earthworm abundance and biomass. There was no significant difference between litterfall, microbial litter decay, and TSR between the invaded and uninvaded sites, but fine root biomass was approximately 30% lower at the invaded site. There was no significant difference in total soil C pools (0–30 cm) between the invaded and uninvaded sites. Despite profound impacts on forest floor soil C pools, earthworm invasion does not significantly increase TSR, most likely because increased heterotrophic respiration associated with earthworms is largely offset by a decrease in autotrophic respiration caused by lower fine root biomass.

Transformation of upland meadow’s biogeocenosis during processes of overgrowth by the gray alder (<em>Alnus inсаnа</em> (L.) Moench)

The article presents results of a study of the environmental conditions transformation during the formation of new phytocenoses by the grey alder. Processes of overgrowing meadows by alder entail a change of habitat characteristics, in particular, reduction of brightness and temperature, a significant increase in litter thickness. In addition, abundance and biomass of earthworms per area unit is reduced in upper soil horizons under the alders, compared to the meadow. Conversion of environmental factors significantly affects the development of herbaceous vegetation: species richness and abundance (cover) of herbaceous vegetation plummets under the influence of alder, as well as floristic heterogeneity of the cover. Undergrowth of spruce — indigenous tree species does not develop in the 60-year-old alder. Overgrowing meadows through the gray alder (compared with aspen and birch) inhibits the passage of autogenous succession, aimed at establishing indigenous vegetation type — spruce. Refs 29. Figs 5. Tables 3.

A role for liming as a conservation intervention? Earthworm abundance is associated with higher soil pH and foraging activity of a threatened shorebird in upland grasslands

The relationship between farmland bird populations and agricultural intensification has been well studied. However, the impact of variation in soil conditions and soil management is an exception, especially in upland (sub-alpine) farming systems. In this study, we examined the relationships between liming history, soil pH and patterns of foraging by Northern Lapwing, Vanellus vanellus, chicks in order to test the potential utility of soil amendment as a conservation intervention for shorebirds nesting in agricultural grasslands. Limed fields had higher soil pH than unlimed fields, and soil pH declined with the number of years since a field was last limed. The most important predictor of total earthworm abundance was soil organic matter with very few earthworms in peats of very high organic matter content. However, there was a marked additive effect of soil pH with earthworms more than twice as abundant at high (pH 6.0) as at the low (pH 3.5) extremes of soil pH recorded in the study. Specifically, at Lapwing chick foraging locations, the density of Allolobophora chlorotica, an acid-intolerant species of earthworm found just below the surface of the soil, was significantly higher than at randomly selected locations. These results suggest that liming helped to maintain breeding habitat quality for Lapwings and other species dependent on earthworms. This is of conservation significance in upland agricultural grasslands in the UK, where there has been a long-term reduction in agricultural lime use since the mid-20th century. Field-scale trials of liming would be valuable to test whether targetted amendment of soil pH in agriculturally improved grasslands could retain an important role in conservation management for shorebirds in upland landscapes where geology, high rainfall, and leaching tend to acidify soils over time.

Application of lime (CaCO3) to promote forest recovery from severe acidification increases potential for earthworm invasion

The application of lime (calcium carbonate) may be a cost-effective strategy to promote forest ecosystem recovery from acid impairment, under contemporary low levels of acidic deposition. However, liming acidified soils may create more suitable habitat for invasive earthworms that cause significant damage to forest floor communities and may disrupt ecosystem processes. We investigated the potential effects of liming in acidified soils where earthworms are rare in conjunction with a whole-ecosystem liming experiment in the chronically acidified forests of the western Adirondacks (USA). Using a microcosm experiment that replicated the whole-ecosystem treatment, we evaluated effects of soil liming on Lumbricus terrestris survivorship and biomass growth. We found that a moderate lime application (raising pH from 3.1 to 3.7) dramatically increased survival and biomass of L. terrestris, likely via increases in soil pH and associated reductions in inorganic aluminum, a known toxin. Very few L. terrestris individuals survived in unlimed soils, whereas earthworms in limed soils survived, grew, and rapidly consumed leaf litter. We supplemented this experiment with field surveys of extant earthworm communities along a gradient of soil pH in Adirondack hardwood forests, ranging from severely acidified (pH<3) to well-buffered (pH>5). In the field, no earthworms were observed where soil pH<3.6. Abundance and species richness of earthworms was greatest in areas where soil pH>4.4 and human dispersal vectors, including proximity to roads and public fishing access, were most prevalent. Overall our results suggest that moderate lime additions can be sufficient to increase earthworm invasion risk where dispersal vectors are present.

Nontarget effects of ivermectin residues on earthworms and springtails dwelling beneath dung of treated cattle in four countries.

The authorization of veterinary medicinal products requires that they be assessed for nontarget effects in the environment. Numerous field studies have assessed these effects on dung organisms. However, few studies have examined effects on soil-dwelling organisms, which might be exposed to veterinary medicinal product residues released during dung degradation. The authors compared the abundance of earthworms and springtails in soil beneath dung from untreated cattle and from cattle treated 0 d, 3 d, 7 d, 14 d, and 28 d previously with ivermectin. Study sites were located in different ecoregions in Switzerland (Continental), The Netherlands (Atlantic), France (Mediterranean), and Canada (Northern Mixed Grassland). Samples were collected using standard methods from 1 mo to 12 mo after pat deposition. Ivermectin concentrations in soil beneath dung pats ranged from 0.02 mg/kg dry weight (3 mo) to typically <0.006 mg/kg dry weight (5-7 mo). Earthworms were abundant and species-rich at the Swiss and Dutch sites, less common with fewer species at the French site, and essentially absent at the Canadian site. Diverse but highly variable communities of springtails were present at all sites. Overall, results showed little effect of residues on either earthworms or springtails. The authors recommend that inclusion of soil organisms in field studies to assess the nontarget effects of veterinary medicinal products be required only if earthworms or springtails exhibit sensitivity to the product in laboratory tests. Environ Toxicol Chem 2016;35:1959-1969. © 2015 SETAC.

Effect of abiotic factors on the distribution of earthworms in different land use patterns

The distribution of earthworms is usually diverse and their numbers fluctuate in relation to the different abiotic factors and land use patterns of the soil. The aim of the present study is to determine the biodiversity, distribution and relative abundance of earthworms under different land use pattern and its relation to abiotic factors (physico-chemical properties) of the soil. Earthworms were collected from different sites on the basis of various environment niches like agriculture fields, gardens, nurseries, along the river and road side etc. by hand sorting method. Physico-chemical analysis of the soil was also done to know the important factors affecting earthworm biodiversity and distribution. Total five species of earthworms belonging to the families Megascolecidae and Octochaetidae were identified: Metaphire posthuma, Lampito mauritti, Amynthas morissi, Eutyphoeus waltoni and Eutyphoeus incommodus. M. posthuma was the most abundant species and found in all the collection sites while other four species were abundantly found in gardens and nurseries. Shannon–Wiener diversity index, Margalef species richness and Pielou’s evenness was ranged from 0.11 to 0.37, 0 to 0.6 and 0 to 0.53 respectively. Principal component analysis also proved that the abiotic factors like pH, moisture, soil texture and OC has strong positive effect on the distribution of earthworm. Earthworm biodiversity and distribution have been found to be positively correlated with type of vegetation and moisture content at the different collection sites and also varied according to soil habitat, soil tillage and land used pattern.

Dairy Cattle Manure Effects on Soil Quality: Porosity, Earthworms, Aggregates and Soil Organic Carbon Fractions

AbstractIn the European Union, the maintenance of soil quality is a key point in agricultural policy. The effect of additions of dairy cattle (Bos taurus) manure (DCM) during a period of 11 years were evaluated in a soil under irrigated maize (Zea mays L.) monoculture. DCM was applied at sowing, at wet‐weight rates of 30 or 60 Mg ha−1yr−1 (30DCM or 60DCM). These were compared with a mineral‐N treatment (300 kg N ha−1, MNF), applied at six to eight emerged leaves and with a control (no N, no manure). Treatments were distributed in a randomized block design. Factors analysed were stability against wetting stress disaggregation, porosity, soil organic carbon (SOC) fractions and earthworm abundance, studied eight months after the last manure application. The application rate of 30DCM increased aggregate stability and the light SOC fraction, but not the pore volume, nor the earthworm abundance, compared with MNF. The DCM rates did not result in unbalanced agronomic advantages versus MNF, as high yields (12–16 Mg ha−1 yr−1) were obtained. In Mediterranean environments, the use of DCM should be encouraged mainly because of its contribution to the light SOC fraction which protects dry macro‐aggregates from implosion (slaking) during the wetting process. Thus, in intensive agricultural systems, it protects soil from physical degradation. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Subordinate plant species moderate drought effects on earthworm communities in grasslands

Loss of plant diversity resulting from forecasted drought events is likely to alter soil functioning and affect earthworm communities. Plant-soil interactions are expected to play an important role in mediating climate change effects on soil decomposers. In this study, we test above-belowground linkages after drought by focusing on the effects of subordinate plant species on earthworm communities. Using a combination of subordinate species removal and experimental drought, we show that subordinate species, when present, increased in biomass after drought and induced an increase in total earthworm biomass. These effects were thought to be associated with the maintenance of food quantity and quality (e.g. nitrogen-rich litter) in relation to subordinate species. In support to this hypothesis, we found a positive correlation between the abundance of juvenile earthworms and plant community biomass hence litter quantity, and between the total biomass of earthworms and the abundance of subordinate species. Anecic earthworms were the most benefited by the presence of subordinate species under drought, especially Lumbricus terrestris, which was significantly correlated to the biomass of the nitrogen-rich subordinate species Veronica chamaedrys. Results of a multiple factor analysis (MFA) also highlighted positive associations between earthworm and subordinate species, independently of the drought treatment. Our study highlights how climate change, in this case reduced summer rainfall, can influence plant functional groups, with cascading effects on earthworms. It is therefore crucial, considering forecasted climate change, to understand these processes in order to better predict ecosystem responses and to adapt grassland management.

Distribution and abundance of exotic earthworms within a boreal forest system in southcentral Alaska

Little is known about exotic earthworms (Oligochaeta: Lumbricidae) in Alaska outside its southeastern panhandle. This study documents the distribution of exotic earthworms in the relatively undisturbed Kenai National Wildlife Refuge (KNWR), a large, primarily wilderness refuge in southcentral Alaska. We sampled 69 sites near boat launches, along road corridors, and in low human impact areas > 5 km from the road, finding three species of earthworms ( Dendrobaena octaedra, Dendrodrilus rubidus, and Lumbricus terrestris). Most road sites (90%) and boat launches (80%) contained earthworms; half (50%) of low human impact sites contained earthworms. Distance to roads was the only significant factor in predicting earth worm occurrence; soil pH, soil moisture, leaf litter depth, and vegetation cover were not. The disparate distributions of these three species suggest that within the KNWR road construction and vehicle traffic played a role in dispersal of the widespread, abundant Dendrobaena octaedra and uncommon Dendrodrilus rubidus; bait abandonment appeared to be the primary method of introduction of Lumbricus terrestris. While the distribution of harmful anecic earthworms in KNWR is currently limited, the prohibition of Lumbricus spp. as bait within conservation units in Alaska may be warranted.

Establishment of earthworms on reclaimed lignite mine soils in east Texas

Little is known about earthworm establishment after surface mining of lignite coal in continental climates such as the south central region of the United States. This study examined the abundance and species composition of earthworms in afforested lignite coal mine soils in east Texas. In a 3×3×2 factorial design, earthworms were sampled under two methods of land reclamation, haul-back (n=30) and mixed overburden (n=30). The study was conducted on a chronosequence of 2–28 years since afforestation under pine plantations and mixed pine and hardwood stands. The fieldwork was conducted from January 2012 through March 2014 using hand-sorting field methods. Forest cover type was significant at the mixed overburden sites (p=0.0128); mixed pine and hardwood forest soils (13.7±25.46ind.m−2) contained 43% more earthworms than pine plantation soils (7.6±17.06ind.m−2). The number of earthworm individuals was significantly lower in 2–8 year-old stands than in 12–18 and 22–28 year old stands (p<0.0001) at both haul-back and mixed overburden sites. Regression analysis found percentage of silt to positively influence earthworm abundance. Analysis of the species composition at both Beckville and Oak Hill mines revealed that 83% of earthworms were native earthworms species (from the genera Diplocardia and Bimastos) and 17% were exotic species (Aporrectodea trapezoides, Microscolex dubius, Lumbricus rubellus and Octolasion tytaeum).