Endogeic Species Research Articles

Different impacts of native and exotic earthworms on rhizodeposit carbon sequestration in a subtropical soil

Earthworms are known to regulate the sequestration of soil and leaf litter carbon (C). However, their impacts on the more accessible rhizospheric C, which represents a major energy source for soil food webs and an essential factor for C sequestration, are still unclear. Previous studies indicate that earthworms regulate the dynamics of SOC and leaf litter-C by increasing C accessibility to microbiota. However, in the case of labile rhizodeposit-C, microbiota might not require any pre-conditioning by earthworms and may rapidly metabolize most of this root-derived C. Consequently, potential pathways by which earthworms may affect the fate of rhizodeposit-C would be to regulate the biomass and/or activity of rhizosphere microbiota and, further, to mineralize/stabilize microbial products. A 13CO2 labelling experiment was performed to determine the impacts of four different earthworm species on the fate of tree rhizodeposit-C in a subtropical soil. We hypothesized that endogeic earthworm species, representing primarily geophagous species, would closely interact with soil microbiota and sequester the microbially metabolized rhizodeposit-C more efficiently than epigeic and anecic earthworm species. We found that irrespective of ecological group affiliation, the three native earthworms did not affect rhizodeposit-C sequestration. In contrast, the exotic endogeic species stimulated the immobilization of rhizodeposit-C in the biomass of root-associated bacteria and/or arbuscular mycorrhizal fungi and, further, accessed the microbiota-metabolized rhizodeposit-C more efficiently. As a consequence, the exotic endogeic earthworm species transiently tripled rhizodeposit-C retention in soil. We propose that the weak linkages between native earthworms and rhizodeposits-related microbiota limit earthworm impacts on rhizodeposit-C sequestration. However, the exotic endogeic species Pontoscolex corethrurus may potentially alter rhizodeposit-C dynamics in invaded areas by shifting rhizosphere microbial community composition. This work highlights a distinct mechanism by which earthworms can regulate C dynamics and indicates a significant contribution of invasive earthworm species to belowground processes.

Morphological and functional characterisation of the burrow systems of six earthworm species (Lumbricidae)

Earthworm burrow systems are generally described based on postulated behaviours associated with the three eco- logical types. In this study, we used X-ray tomography to obtain 3D information on the burrowing behaviour of six very common anecic (Aporrectodea nocturna and Lumbricus terrestris) and endogeic (Aporrectodea rosea, Allolobophora chlorotica, Aporrectodea caliginosa, Aporrectodea icterica) earthworm species, introduced into repacked soil cores for 6 weeks. A simple water infiltration test, the Beerkan method, was also used to assess some functional properties of these burrow systems. Endogeic worms make larger burrow sys- tems, which are more highly branched, less continuous and of smaller diameter, than those of anecic worms. Among the anecic species, L. terrestris burrow systems are shorter (9.2 vs 21.2 m) with a higher number (14.5 vs 23.5) of less branched burrows (12.2 vs 20.2 branches m �1 ), which are also wider (7.78 vs 5.16 mm) than those of A. nocturna .I n comparison, the burrow systems made by endogeic species appeared sim- ilar to each other. However, A. rosea burrows were short and narrow, whereas A. icterica had a longer burrow system (15.7 m), more intense bioturbation intensity (refilled macropores or soil lateral compaction around them) and thus a greater number of burrows. Regarding water infiltration, anecic burrow systems were far more efficient due to open burrows linking the top and bottom of the cores. For endogeic species, we observed a linear relationship between burrow length and the water infiltration rate (R 2 =0.49, p<0.01). Overall, the three main characteristics significantly influenc- ing water infiltration were burrow length, burrow number and bioturbation volume. This last characteristic highlighted the effect of burrow refilling by casts.

Burrowing and casting activities of three endogeic earthworm species affected by organic matter location

Abstract Earthworms are crucial for production and maintenance of soil structure and their activities can strongly impact soil functioning ( e.g. water regulation, nutrient dynamics). This laboratory study investigated the bioturbation activity of three endogeic species, Allolobophora chlorotica , Allolobophora icterica and Aporrectodea caliginosa , as affected by different locations of organic matter (OM) in the soil profile: OM scattered on the soil surface (surface-OM) or homogeneously mixed into the soil (mixed-OM). Microcosms, each containing a combination of one species (three individuals) and one OM location, were subjected to controlled environmental conditions (temperature, humidity and day/night cycle) for 60 days. At the end of the experiment, microcosms were cut into multiple horizontal cross-sections every centimetre and bioturbation activities were analyzed based on the number of burrows, the burrowed area and the percentage of burrowed area totally refilled with casts. Results showed that regardless of species, there was significantly fewer burrows and a greater percentage of burrowed area refilled with casts under mixed-OM than under surface-OM. A. chlorotica and A. caliginosa had a significantly greater burrowed area under mixed-OM than under surface-OM. Regardless of OM location, as depth increased, burrow number and area decreased for A. chlorotica and generally increased for A. icterica . In contrast, burrowing activity of A. caliginosa was affected by OM location as depth increased: under mixed-OM, burrow number decreased but burrowed area remained constant, whereas under surface-OM, burrow number remained constant and burrowed area increased. These results improve understanding of effects of endogeic species on soil structure and highlight effects of OM location on earthworm bioturbation. Especially this study gives information about the burrowing activity of A. icterica which has so far been little documented, and also informs about refilled burrows which is a major parameter for soil functioning.

Deforestation effects on biological and other important soil properties in an upland watershed of Bangladesh

Deforestation occurs at an alarming rate in upland watersheds of Bangladesh and has many detrimental effects on the environment. This study reports the effects of deforestation on soil biological properties along with some important physicochemical parameters of a southern upland watershed in Bangladesh. Soils were sampled at 4 paired sites, each pair representing a deforested site and a forested site, and having similar topographical characteristics. Significantly fewer (p≤0.001) fungi and bacteria, and lower microbial respiration, active microbial biomass, metabolic and microbial quotients were found in soils of the deforested sites. Soil physical properties such as moisture content, water holding capacity, and chemical properties such as organic matter, total N, available P and EC were also lower in deforested soils. Bulk density and pH were significantly higher in deforested soils. Available Ca and Mg were inconsistent between the two land uses at all the paired sites. Reduced abundance and biomass of soil mesofauna were recorded in deforested soils. However, soil anecic species were more abundant in deforested soils than epigeic and endogeic species, which were more abundant in forested soils than on deforested sites.

Impact of soil engineering by two contrasting species of earthworms on their dispersal rates

By burrowing galleries and producing casts, earthworms are constantly changing the structure and properties of the soils in which they are living. These changes modify the costs and benefits for earthworms to stay in the environment they modify. In this paper, we measured experimentally how dispersal behaviour of endogeic and anecic earthworms responds to the cumulative changes they made in soil characteristics. The influence of earthworm activities on dispersal was studied in standardised mesocosms by comparing the influence of soils modified or not modified by earthworm activities on earthworm dispersal rates.The cumulative use of the soil by the earthworms strongly modified soil physical properties. The height of the soil decreased over time and the amount of aggregates smaller than 2mm decreased in contrast to aggregates larger than 5mm that increased. We found that: (i) earthworm activities significantly modified soil physical properties (such as bulk density, soil strength and soil aggregation) and decreased significantly the dispersal rates of the endogeic species, whatever the species that modified the soil; (ii) the decreasing in the dispersal proportion of the endogeic species suggests that the cost of engineering activities may be higher than the one of dispersal; (iii) the dispersal of the anecic species appeared to be not influenced by its own activities (intra-specific influences) or by the activities of the endogeic species (inter-specific influences). Overall these results suggest that the endogeic species is involved in a process of niche construction, which evolved jointly with its dispersal strategy.

Carbon food resources of earthworms of different ecological groups as indicated by 13C compound-specific stable isotope analysis

One of the challenges in soil ecology is to determine which organisms utilise stable forms of carbon in soil. Recent studies have indicated that endogeic earthworms are able to mobilise such stable carbon compounds. However, it remains unclear which particular compounds of stabilised carbon in soil are utilised by earthworms. Furthermore, current knowledge on ecological groups and food resources of earthworms is mainly based on direct observations, hence only reflecting what was ingested but not what was actually assimilated. We analysed seven earthworm species in beech and spruce forests and the associated litter, earthworm middens and soils, and employed compound-specific 13C stable isotope analysis of fatty acids (FAs) to identify the origins of carbon resources of the earthworms. To relate food resources to carbon compounds of different stability, we analysed 13C signatures of FAs of different particle size fractions. FA δ13C profiles of epigeic and endogeic earthworm species indicated assimilation of recently-fixed and recalcitrant carbon resources, respectively, whereas anecic earthworms assimilated a mixture of resources of different stability. Utilisation of carbon resources did not differ between beech and spruce forests. Endogeic species were associated with neutral lipids of soil particle size fractions with δ13C signatures of the bacterial marker a15:0 in earthworms resembling those of the clay fraction. This suggests that they assimilated carbon associated with small particle size fractions attached to clay–humus complexes. The results showed that earthworms of different ecological groups utilise carbon pools of different origin and stability. As indicated by neutral lipids of bacterial origin, physically-stabilised organic matter appears to contribute to the nutrition of endogeic earthworms in forest systems.

Livestock grazing activities and wild boar rooting affect alpine earthworm communities in the Central Pyrenees (Spain)

In alpine areas, shifts in traditional grazing activities are globally affecting ecosystem properties and rural livelihoods. The ongoing decrease in extensive husbandry, with a decline in sheep numbers and a relative increase in cattle stocking rates, has resulted in the abandonment of large alpine grazing areas. This pastoral change has been recently associated with increased disturbances of wild boar (Sus scrofa), mainly within cattle-stocked ranges. In turn, cattle areas favor earthworm communities, a preferred trophic resource for wild boars in mountain environments. However, it is unknown whether wild boar disturbances, together with grazing activities, can affect earthworm communities. Our aim is to analyze the abundance, richness and ecological categories of earthworms and soil parameters (soil C and N concentrations, moisture, and C:N ratio) in relation to the occurrence of wild boar disturbances and grazing activities at different stocking pressures. We sampled two different grazing scenarios differing in the distribution of cattle along a grazing gradient, which was represented by three levels of stocking pressure (high, intermediate and low). Our results showed a complex effect of grazing activities and disturbances on the abundance and richness of earthworms, along with variations in C:N ratio and soil moisture, especially with increasing cattle presence. At high-stocking pressures differences in earthworm abundance and richness between disturbed and undisturbed areas were limited, whereas at intermediate-stocking pressures earthworms were favored by wild boar disturbances. Ecological categories of earthworms responded differently; endogeic species were the most affected by grazing pressures and wild boar rooting, with highest occurrence at high-stocking pressures and within boar disturbed areas. In sum, pastoral use and soil disturbances affected earthworm community structure and composition in complex ways. These results indicate an interaction of processes that is relevant to understand current changes in alpine ecosystems.

Burrow systems of endogeic earthworms: Effects of earthworm abundance and consequences for soil water infiltration

Abstract By creating burrows, earthworms influence the transfer properties of soils. The effects of endogeic species on soil transfer properties, however, are not yet well understood because these earthworms generally create burrows that are refilled by casts and have no preferential vertical orientation. Thirty soil cores were incubated for various periods (1–3 or 4 weeks) at different earthworm densities (70, 210, 345 or 480 individuals m −2 ). The cores were then scanned using X-ray tomography and the burrow systems were characterised by measuring the total burrow volume, bioturbation volume (refilled burrows and lateral compaction around the burrows), the number of branches, tortuosity and continuity (assessed by computing the number of burrows with a vertical extension greater than 15, 20 and 25% of the core). We also computed the mean geodesic distance, i.e. the mean distance from the bottom to the top of the core assuming that distances inside burrows are null. Rainfall simulations were carried out on 17 cores chosen to encompass the variations observed in the burrow systems. The water transfer efficiency of each core was estimated by measuring two parameters: breakthrough volume and the percentage of water transmitted after 1 h of rain. Burrow and bioturbation volume increased significantly and steadily with time and earthworm density. We estimated that on average Allolobophora chlorotica burrowed 22 cm per week. All other burrow system characteristics also increased with time and earthworm density except the mean geodesic distance, which decreased significantly. This suggests that intraspecific interactions had no significant effect on burrow system geometry. Univariate PLS regressions were used to understand which burrow system characteristics had the strongest influence on water transfer. These regressions showed that the mean geodesic distance was the most important parameter. This means that in addition to individual burrow characteristics, the spatial arrangement of the whole burrow system also had a major effect on transfer properties.

The action of an anecic earthworm (Aporrectodea longa) on vertical soil carbon distribution in New Zealand pastures several decades after their introduction

Anecic earthworms have the ability to incorporate carbon (C) from the surface to depth in the soil. This study aimed to quantify the rate of spread of Aporrectodea longa, and their influence on the amount of C stored, in two contrasting soils where this earthworm was introduced in the 1980s. The rate of spread of A. longa at both sites (5.3–12.5 m/y) is similar to endogeic species. Over several decades there was a decrease in soil C in the presence of A. longa in the Pallic soil (78 912 vs. 85 796 kg C/ha for 0–300 mm) while soil C tended to increase in the Allophanic soil (141 845 vs. 111 076 kg C/ha at 0–300 mm). In the Pallic soil, bulk density tended to be lower in the presence of anecic earthworms at 150–300 mm depths and may have encouraged the decomposition of more stable C. Further, the interaction with higher abundances of endogeic earthworms and lower organic matter inputs in the Pallic soil than the Allophanic soil may help explain the lower soil C in the Pallic soil. The conflicting results in the two soils highlight the influence of the earthworm community and soil properties on C dynamics.

Effect of tillage on earthworms over short- and medium-term in conventional and organic farming

Earthworms play an important role in many soil functions and are affected by soil tillage in agricultural soils. However, effects of tillage on earthworms are often studied without considering species and their interactions with soil properties. Furthermore, many field studies are based on one-time samplings that do not allow for characterisation of temporal variation. The current study monitored the short (up to 53 days) and medium term (up to 4 years) effects of soil tillage on earthworms in conventional and organic farming. Earthworm abundances decreased one and three weeks after mouldboard ploughing in both conventional and organic farming, suggesting direct and indirect mechanisms. However, the medium-term study revealed that earthworm populations in mouldboard ploughing systems recovered by spring. The endogeic species Aporrectodea caliginosa strongly dominated the earthworm community (76%), whereas anecic species remained <1% of all earthworms in all tillage and farming systems over the entire study. In conventional farming, mean total earthworm abundance was not significantly different in reduced tillage (153m−2) than mouldboard ploughing (MP; 130m−2). However, reduced tillage in conventional farming significantly increased the epigeic species Lumbricus rubellus from 0.1m−2 in mouldboard ploughing to 9m−2 averaged over 4 years. Contrastingly, in organic farming mean total earthworm abundance was 45% lower in reduced tillage (297m−2) than MP (430m−2), across all sampling dates over the medium-term study (significant at 3 of 6 sampling dates). Reduced tillage in organic farming decreased A. caliginosa from 304m−2 in mouldboard ploughing to 169m−2 averaged over 4 years (significant at all sampling dates). Multivariate analysis revealed clear separation between farming and tillage systems. Earthworm species abundances, soil moisture, and soil organic matter were positively correlated, whereas earthworm abundances and penetration resistance where negatively correlated. Variability demonstrated between sampling dates highlights the importance of multiple samplings in time to ascertain management effects on earthworms. Findings indicate that a reduction in tillage intensity in conventional farming affects earthworms differently than in organic farming. Differing earthworm species or ecological group response to interactions between soil tillage, crop, and organic matter management in conventional and organic farming has implications for management to maximise soil ecosystem functions.

Controls on wood and leaf litter incorporation into soil fractions in forests at different successional stages

In this study, we examined the response of surface soils to increased leaf and wood litter input within adjacent successional forests recovering from agricultural disturbance at the Smithsonian Environmental Research Center (SERC), Maryland, USA. Previous studies at this site demonstrated an arrested development of O-horizon, even after 130 years of forest growth, and an annual loss of leaf litter in forests with the highest abundance of invasive earthworms. Biogeochemical indices of plant biopolymer dynamics, i.e. extractable lignin and substituted fatty acids (SFAs), were applied to soil physical fractions in order to assess the fate of 5 years of increased Tulip poplar (Liriodendron tulipifera L.) wood and leaf litter into O-horizon and mineral soil particles of purportedly different protection levels in this recovering forest system. Our results showed that in this continuously-disturbed recovering system the pattern of litter incorporation into soil varied with both litter type and forest age. For example, young successional forests, that also contained higher abundances of soil feeding endogeic earthworms, incorporated wood amendments deeper into soils and in a predominantly particulate organic matter (POM) form than older successional systems with predominantly litter and surface dwelling earthworms. Soil lignin concentration increased sharply with wood amendments in both forest stages, but young successional forests exhibited incorporation of fresher lignin into both POM and silt and clay (SC) fractions over 0–5 cm and 5–10 cm depths while old forests only increased in POM in the 0–5 cm depth. We attribute these differences to the higher rates of physical mixing from soil feeding endogeic species and potentially lower fungal activity in young successional forests. However, despite nearly 2.5 times of background annual leaf litter input over 5 years, neither total C content nor SFA concentration in soil fractions increased, a phenomenon we attribute to full decomposition of leaf litter amendments. These results demonstrate how the chemical trajectory of soils and litter layers in recovering forests can be a function of both legacy and current disturbance.

Slow recovery of earthworm populations after heavy traffic in two forest soils in northern France

To determine the role of earthworms in regenerating compacted zones, it is essential to consider their capacity to colonise these zones. This study aimed to determine the short-term (3–4 years) response of earthworm populations to heavy traffic in two forest soils, at Azerailles (AZ) and Clermont-en-Argonne (CA) in north-eastern France. Earthworm populations were recorded immediately and for 3–4 years after heavy traffic by a 8-wheel drive forwarder with a load of about 23 Mg at AZ and 17 Mg at CA. To test the capacity of earthworms to recolonise traffic plot from the edges, an extra sampling was performed at the border of the traffic plots at AZ. Heavy traffic had a detrimental impact on the density and biomass of three earthworm functional groups. At AZ, earthworm populations, dominated by endogeic species, followed by anecic and epigeic species, had not fully recovered four years after compaction. The absence of statistically significant colonisation by the three functional groups from control to traffic plots indicated that the soil habitat was not yet favourable. At CA, earthworm populations, represented exclusively by epigeic species, had fully recovered three years after compaction, suggesting that the soil habitat was already suitable for them. This strong dependence on soil habitat quality is discussed and may be one reason for variation in the recovery rate of earthworms after compaction reported in the literature. In conclusion, this study did not support the hypothesis that earthworms play a role in regenerating soil structure the first few years following forest-soil compaction.

Cadmium and Lead Accumulation in Three Endogeic Earthworm Species

The objective of this study was to assess the capability of earthworms from the same ecological group as heavy metal bioindicators. Three earthworm species from the endogeic group were studied: Aporrectodea caliginosa (Savigny, 1826), Perelia kaznakovi (Michaelsen, 1910) and Octolasion lacteum (Örley, 1885). Their accumulation of the heavy metals lead (Pb) and cadmium (Cd) were studied from three stations in Tehran province, Iran. O. lacteum was used to compare metal accumulations in two sites located next to a highway. A. caliginosa and P. kaznakovi were used at a third site located near the edge of a sewage system to compare metal accumulations between the two endogeic species in this area. At both locations, the concentrations of Cd and Pb in earthworms were higher than in the surrounding soil. The results of the study revealed that P. kaznakovi and A. caliginosa were better bioindicators for Pb, but O. lacteum was a better bioindicator for Cd. These earthworms can therefore be used as Cd and Pb bioindicators in environmental assessment.

Are dispersal behaviours of earthworms related to their functional group?

Dispersal plays a key role in the dynamics of ecological communities as it strongly determines the potential of individuals to colonize new habitats. Understanding and predicting species dispersal behaviour is therefore central to any effort at managing or even understanding the formation of communities. In this context, it is essential to understand the influence of environmental and biotic determinants of dispersal. In this work, we assessed these questions using earthworms as model organisms.We assessed the dispersal behaviour of six earthworm species belonging to two different functional groups (i.e. three anecics and three endogeics) in response to three key environmental factors: habitat quality, intraspecific density, and environment homogeneity. We found that habitat quality significantly influenced the dispersal rates of all species. Intraspecific density increased the dispersal rate of the three anecic species but only of one endogeic species. In a homogeneous environment, anecics dispersed further and in greater proportion than the majority of endogeics. Moreover, few anecic species have shown a tendency to follow conspecifics. Overall, anecic species seemed to have a higher active dispersal inclination than most endogeic ones. We found a high variability of our results within each functional groups, which suggests that this classification cannot be used to explain or predict the dispersal behaviour of earthworms.

Landscape and site effects on Collembola diversity and abundance in winter oilseed rape fields in eastern Austria

Soil animals are rarely considered in landscape ecology although recent findings show that landscape composition and habitat fragmentation may exert a strong influence on their communities. We assessed the relationships between landscape parameters and the species richness of Collembola (springtails) in agricultural eastern Austria, hypothesizing that the richness of surface active (epigeic) species are more significantly correlated with landscape-scale parameters than soil living (endogeic) species. We used pitfall traps and soil samples to measure species richness and abundance of the two life forms in 29 oilseed rape fields in differently structured landscapes.Epigeic species richness was positively correlated to landscape parameters like landscape diversity, habitat richness, isolation of open habitats and area of oilseed rape fields at small to medium (250–1000m) and at larger (1000–1750m) landscape scales around the investigated sites. Endogeic species richness was also significantly correlated with landscape parameters like landscape diversity and road-side strip length. Total species richness was significantly correlated with landscape diversity at a larger scale, isolation of open habitats and proportion of woody area at a smaller spatial scale. Landscape diversity measures explained a higher percentage of the diversity of epigeic (42%) than of endogeic diversity (32%). Epigeic abundance was not significantly correlated to any of the site parameters, but with landscape parameters like oilseed rape area, woody area and minimum distance to dry grassland. Endogeic abundance was only correlated to oilseed rape cover.Our results suggest that parameters associated with landscape diversity can be good predictors of Collembola diversity at two spatial scales: At small scales probably due to active migration from bordering hedges, forests or grasslands; and at larger scales possibly due to passive wind dispersal. Soil ecologists rarely take landscape-scale variables into account, and our findings may contribute to broader recognition of the importance of landscape parameters in investigations of soil biota.

Occurrence and distribution of earthworms in agricultural landscapes across Europe with regard to testing for responses to plant protection products

Within the regulatory framework for authorisation of plant protection products (PPPs) (EU Directive 91/414/1991/EEC replaced by Regulation (EC) 1107/2009), higher tier risk assessments and earthworm field tests are conducted in different countries across Europe. This paper describes dominant earthworm species for regulatory and biogeographical regions in agricultural landscapes across Europe and examines regional differences in earthworm communities and densities and their respective response to a toxic reference. For the assessment of earthworm abundance and species distribution, data of untreated control plots from 30 earthworm field studies were analysed; each conducted according to the ISO 11268–3 (1999) guideline by European Crop Protection Association member companies in the context of registration of PPPs. For the evaluation of the response to PPPs under different regional and climatic conditions, the effect on earthworm abundance was assessed by comparing plots treated with toxic references with untreated control plots. Additionally, a comparative literature review was included providing an overview of earthworm species composition and densities in agricultural crops from 14 European countries. The assessment of earthworm field studies from six different European countries revealed that common earthworm species of anecic and endogeic ecological groups are present at most field sites. Dominant species groups of endogeic and anecic earthworms can be defined that are abundant in all assessed countries. These are the endogeic species Aporrectodea caliginosa, Aporrectodea rosea and Allolobophora chlorotica, and the anecic species Lumbricus terrestris (Northern and Central Europe) and Lumbricus friendi (Southern Europe). Taking into account the high variability in total earthworm abundances, it can be concluded that the variability within regions was larger than the variability between regions. Analysis of the earthworm community and data of toxic references lead to the conclusion that testing in different zones is not considered necessary.

Acoustic emission monitoring of the effect of temperature on activity rhythms of the subterranean termite Reticulitermes speratus

Daily activity rhythms are widespread characteristics among many organisms and are usually related to one or more physical environmental variables, such as light and temperature. Even organisms that are not obviously exposed to wide fluctuations in environmental variables, such as troglodytic and endogeic species, exhibit some daily activity patterns. Termites inhabit underground areas or tree trunks where little or no fluctuation in light occurs. In the present study, the activity rhythms of field colonies of the subterranean termite Reticulitermes speratus Kolbe (Blattodea: Termitidae) are examined, during all four seasons, by monitoring their acoustic emissions using a newly‐modified method. Nest temperature affects termite activity significantly during all four seasons. By contrast, no significant effect of time is observed during the different seasons, with the exception of autumn. Activity and nest temperature are negatively correlated in summer and autumn, although thay are are positively correlated during winter and spring. The greatest activity occurs at 23–25 °C. The experimental observations suggest that the activity of R. speratus termite colonies is affected mainly by ambient temperature, in a manner that is based on optimum temperature.

Isolation of polymorphic microsatellite markers in Aporrectodea icterica (Savigny 1826)

Earthworms play a major role in soil dynamics acting as modifiers of properties and soil characteristics. Although population genetics is a promising approach to get a better understanding of their ecology, the use of molecular tools in earthworm studies is still scarce. Here, we developed and analyzed seven microsatellite loci for Aporrectodea icterica, a common endogeic species of most temperate natural and agricultural soils, with the aim to investigate its dispersal capacity in further researches. Although sequences of a fragment of the mitochondrial gene cytochrome oxidase subunit I (COI) showed the existence of two mitochondrial lineages within the species, with a mean divergence between them of 10%, microsatellite data proved that these two COI lineages are interbreeding and form part of a single species.

Short-term effects of ploughing on the abundance and dynamics of two endogeic earthworm species in organic cropping systems in northern France

An understanding of the effects of ploughing on earthworm dynamics is required for the design of organic cropping systems maximising the beneficial effects of earthworms. Earthworms are often reported to be disturbed by ploughing, which is frequently used for weed control in organic farming. In this preliminary study, we investigated the effect of ploughing on the dynamics of two common endogeic species: Aporrectodea caliginosa and Aporrectodea rosea, to test the assumption that the sensivity to ploughing is species dependant. Two field trials were set up in October 2009 and November 2010, at two locations on a haplic luvisol, located in northern France. For comparison, part of each field was left unploughed, with the rest being ploughed. Earthworms were sampled at ten dates between October 2009 and July 2010 at Vi and six dates between November 2010 and March 2011 at Fa. Seven species were found in these two fields, with more than 88% of the earthworms belonging to two endogeic species, A. caliginosa and A. rosea. Ploughing had contrasting effects on the two species. A. caliginosa was more sensitive than A. rosea to tillage. In the unploughed part of the field, in 2009, the population remained small (less than 100 individuals m−2) and it was assumed that the two species were in competition for food. In 2010, the carrying capacity was higher, and A. caliginosa abundance reached 300 individuals m−2, whereas the abundance of A. rosea remained below 90 individuals m−2. In 2009, the effect of ploughing on A. caliginosa was immediate and persisted throughout the experiment, from October 2009 to June 2010, with an 80% decrease in abundance in June 2010. In 2010, the effect was delayed, but populations decreased during the winter following ploughing, with a 60% decrease in January 2011. Concerning A. rosea, the differences between the ploughed and the unploughed treatments were lower than for A. caliginosa. Our results confirm that endogeics earthworms may adapt themselves to the disturbance caused by tillage. Our observations suggest that A. caliginosa is more sensitive to ploughing than previously reported. These preliminary findings were obtained under favourable climatic conditions. They may help to define the optimal scheduling of tillage for earthworm conservation.

Does the influence of earthworms on water infiltration, nitrogen leaching and soil respiration depend on the initial soil bulk density? A mesocosm experiment with the endogeic species Metaphire posthuma

Soil compaction has a negative impact on both earthworm abundance and diversity. Recent studies, however, suggest that earthworm cast properties are not influenced by the initial soil bulk density. With time, earthworms could therefore transform soils with different bulk densities into a soil with the same physical state and thus with a similar ecological functioning. This study aimed to test this hypothesis in two laboratory incubation experiments. First, we measured the influence of soil bulk density (1.1 or 1.4 g cm−3) on the production of cast by the endogeic earthworm species Metaphire posthuma. In a second experiment, we investigated the effect of M. posthuma on water infiltration, NH4+, and NO3− leaching and soil respiration at the same two soil bulk densities. Although initially higher, earthworm casting activity in soil at 1.4 g cm−3 decreased until it reached the same level of activity as earthworms in soil at 1.1 g cm−3. This behavioral plasticity led to a transformation of compacted and loose soils, with their own functioning, to a third and similar state with similar hydraulic conductivity, nitrogen leaching, and soil respiration. The consequences for soil organization and soil functioning are discussed.