Earthworms as colonizers of natural and cultivated soil environments

For cultivated soils, the important function of earthworms as ecosystem engineers and their major contribution to the composition and functioning of soil ecosystems with a varying species diversity has been extensively addressed. However, the role of earthworms as colonizers of virgin, uncultivated soil in the process of soil formation has been little researched and long underrated. To better understand this role, the following questions need to be considered: (1) what makes an early colonizer successful, what are its characteristics, and which species are the most successful and under what circumstances are they successful?; (2) what are the limiting factors in these colonization processes with respect to environmental conditions and also to interspecific interactions?; (3) what do earthworms contribute to the further colonization by other soil animals?; and (4) how do they impact the soil itself and what could therefore be the consequences for soil management and restoration?These questions have recently been addressed from the perspective of new (or ‘alien’) earthworm species invading ecosystems, suggesting a massive influx of species, competitive to the originally present fauna. This idea is, however, contrary to colonization, which suggests a gradual exploration of a previously uninhabited area. Unlike recent research, this review approaches colonization primarily as a spatial dispersal process and part of natural succession processes, and is mainly illustrated with examples of Palearctic species, either in Europe or introduced elsewhere. To begin, the various stages of colonization: dispersal, establishment, population growth and interspecies relations are analysed. Next, the colonization processes, the possible limiting environmental factors and the sequence of the appearance and establishment of species are described. Dispersal rates and sequences of colonization by different earthworm species are given for different soil ecosystems. For colonization, limiting environmental factors such as pH, soil type and heavy metal contents as well as the presence of organic matter seem to play a more important role than inherent ecological characteristics like r/K selection. Finally, the role of earthworms in the early colonization of soils that are earthworm-free because of non-cosmopolitan distribution, drained former sea bottom, permanently water-logged soils or anaerobic, acid peaty soils are reviewed. If we understand the role of earthworms in succession, we will be able to improve their role in soil restoration and soil management.     

蚯蚓对土壤温室气体排放的影响及机制研究进展

土壤是温室气体的重要源和汇。蚯蚓是土壤物质循环的重要参与者,能够直接或间接影响土壤CO2、N2O和CH4等温室气体的产生和释放。蚯蚓呼吸产生的CO2,是土壤呼吸的重要组成部分;蚯蚓自身肠道、分泌液、消化物和排泄物等微环境促进反硝化过程释放N2O。蚯蚓还通过取食、掘穴、排泄等活动,改变土壤理化性质、微生物组成和活性及其他土壤动物的组成,影响地上植物生长,调节土壤分解、矿化、硝化、反硝化和甲烷生成及氧化等生态过程,间接影响土壤温室气体的排放。蚯蚓对土壤温室气体排放的影响逐渐受到重视,但目前研究仍以室内培养和单因子环境条件的模拟为主,缺少野外原位实验和多环境因子的交互实验研究。长期监测和同位素示踪技术,是深入探讨蚯蚓影响温室气体排放机制的重要手段。温室气体类型上,CO2和N2O是研究热点,CH4研究比较罕见。未来研究,应重视不同生态类群蚯蚓与土壤理化特征、微生物组成、其他类群土壤动物和地上植物间的交互作用,加强机制研究,并关注土壤污染环境下蚯蚓功能性状的变化;综合评价蚯蚓对土壤温室气体排放和土壤碳氮固定的影响,科学评估蚯蚓活动对土壤碳氮释放的促进或减缓作用。     

Soil fauna feeding activity in temperate grassland soils increases with legume and grass species richness

Edaphic fauna contributes to important ecosystem functions in grassland soils such as decomposition and nutrient mineralization. Since this functional role is likely to be altered by global change and associated shifts in plant communities, a thorough understanding of large scale drivers on below-ground processes independent of regional differences in soil type or climate is essential. We investigated the relationship between abiotic (soil properties, management practices) and biotic (plant functional group composition, vegetation characteristics, soil fauna abundance) predictors and feeding activity of soil fauna after accounting for sample year and study region. Our study was carried out over a period of two consecutive years in 92 agricultural grasslands in three regions of Germany, spanning a latitudinal gradient of more than 500 km. A structural equation model suggests that feeding activity of soil fauna as measured by the bait-lamina test was positively related to legume and grass species richness in both years. Most probably, a diverse vegetation promotes feeding activity of soil fauna via alterations of both microclimate and resource availability. Feeding activity of soil fauna also increased with earthworm biomass via a pathway over Collembola abundance. The effect of earthworms on the feeding activity in soil may be attributed to their important role as ecosystem engineers. As no additional effects of agricultural management such as fertilization, livestock density or number of cuts on bait consumption were observed, our results suggest that the positive effect of legume and grass species richness on the feeding activity in soil fauna is a general one that will not be overruled by regional differences in management or environmental conditions. We thus suggest that agri-environment schemes aiming at the protection of belowground activity and associated ecosystem functions in temperate grasslands may generally focus on maintaining plant diversity, especially with regard to the potential effects of climate change on future vegetation structure.     

Fluorine contamination of soils and earthworms (Lumbricus spp.) near a site of long-term industrial emission in southern Germany

Summary The F contamination of soils and Lumbricus spp. around a site of long-term industrial emission in southern Germany was examined. Among total, water extractable, and HCl-soluble fractions, the latter most appropriately characterized anthropogenic F accumulation. Based on the HCl-soluble fractions from 88 sampling sites, a contamination map consisting of three zones was established. F accumulation in the calcareous soils of the area was restricted to the top 40–50 cm and can be explained by precipitation as CaF₂. Earthworms (Lumbricus spp.) collected from the different zones reflected the F contamination well in the significant correlations found between total F in earthworms with and without gut and the corresponding soils. The bioaccumulation of F in earthworms is obvious, and may become hazardous for the earthworms themselves and for other animals feeding on contaminated soil and/or its fauna. A significantly higher F value was recorded in the linings of earthworm tubes than in the corresponding soil. F translocation by earthworm burrowing may be a mechanism of subsoil contamination.     

The values of soil animals for conservation biology

It has taken time for the international community to accept the idea of biodiversity values, a concept which had previously been restricted to the limited aesthetic and touristic aspects of wildlife. This situation changed following the International Convention on Biodiversity in Rio de Janeiro (1992), which focussed on “the forgotten environmental problem” of biodiversity erosion and made the first clear reference to the values of living species. Biodiversity values refer to direct or indirect, economic or non-economic interest, a given species or ecosystem may represent for human populations. These values are generally split into intrinsic and instrumental (use) values, the last category itself being divided into direct and indirect economic values. Obviously, each of these values carries different weights, and cannot be considered as being weighted equally in terms of justification for species or ecosystem conservation. Soil is probably one of the most species-rich habitats of terrestrial ecosystems, especially if the definition is extended to related habitats like vertebrate faeces, decaying wood, and humus of hollow trees (i.e. epiphytic soils). The diversity of soil communities (sensu lato) thus probably encompasses a large part of terrestrial animals. This highly speciose fauna has been the subject of recent research efforts, and current trends in soil fauna studies include aspects of biology, autecology, ecotoxicology, or functional ecology. During the past 20 years, recognition of the importance of soil fauna in the functioning of soils and by extension of terrestrial ecosystems has been continuously growing, ending in some important applications in agronomy. However, despite the general agreement about the ecological importance of soil fauna and its economic consequences, the absence of concern about this group from conservationists in their studies is conspicuous. This paper aims at presenting soil fauna within the scope of conservation biology concepts, trying to identify the different values of soil fauna and how they participe to the provisioning of key ecosystem services. Finally, the enormous gap between their recognised usefulness and their consideration in protection policies is discussed.     

Chemical manipulation of soil biota in a fescue meadow

Formalin, phorate, and sodium chlorate were used in field enclosures to create artificial habitats in a fescue meadow containing (1) reduced number of earthworms, (2) reduced numbers of earthworms and soil arthropods, and (3) reduction of total soil fauna and rate of microbial decomposition. Under these conditions, confined fescue litter initially decomposed more rapidly where arthropods or earthworms were suppressed than in controls with full complements of soil animals. After one year, reduction in numbers of soil animals had no net effect on litter decomposition, with faunal activity apparently having been compensated for by increased microbial activity. Where animals and microbial activity were reduced, rate of litter loss was depressed initially but recovered after 10 months as the effects of chemical suppression of microbial populations subsided. Contrary to the effects on annual loss of litter, elimination of all or portions of the soil fauna depressed rates of loss of confined and buried roots, reflecting the role of animals in fragmenting roots before their decomposition by microorganisms.Habitat manipulations had pronounced effects on the mobility of ¹³⁴Cs, and loss of the radionuclide from labelled litter was retarded despite an accelerated rate of decomposition. This effect apparently was associated with proliferation of microorganisms on litter and microbial immobilization of the radionuclide. Immobilization of ¹³⁴Cs occurred following chemical perturbations, but only after an initial period of rapid loss resulting from increased microbial activity. Distribution of ¹³⁴Cs in soil beneath tagged litter bags reflected the role of animals in element redistribution within soil. Restricted vertical mobility of the nuclide occurred except where chemical application killed vegetation within the experimental enclosures.     

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.     

Untersuchungen über die toxische Wirkung der in Siedlungsabfällen häufigen Schwermetalle auf die Bodenmikroflora

The toxic effects of heavy metals, commonly found in urban wastes on the soil microflora In several series the influence of soluble salts of Cd, Cr, Zn, Cu, Ni and Hg in various concentrations was tested on the development of bacteria and fungi in cultural studies and in soil model systems. In addition the changes in microbial biomass, in the activity of oxidoreductases and hydrolases, and in nitrification were measured in five soils. Comparison of the results of bacteria-plate-counts in the presence of heavy metals in agar-media and in soils demonstrated that all tested elements have a more toxic effect on isolated soil microorganisms under culture conditions than when tested after heavy metal application to soils. Beside Hg, eucaryotic soil fungi proved to be 10 – 50 fold more resistant to heavy metals in vitro as well as in situ. For calculating the effect of heavy metals on soil microbial activity soil enzymatic methods are not reliable and can be used only to some extent, because some cellfree encymes in the soil are activated or inactivated immediately by heavy metals. In long-term experiments, the microbial biomass and nitrification in soil is not significantly influenced by the elements Cd, Cu and Ni in the concentration range of the tolerable limit content. In contrast, Cr, Zn and Hg reduced these microbiological properties more or less distinctly.     

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 2 mm decreased in contrast to aggregates larger than 5 mm 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.     

传统耕作和免耕的红壤生态系统土壤动物种群的分异

In a field experiment ,the popultions of major soil fauna groups including earthworms,enchytraeids,arthropods and nematodes were examined in conventional tillage(CT) and no-tillage(NT) red soil ecosystems to evaluate their responses to tillage disturbance.Earthworms,macro- and micro-arthropods were stimulated under NT with earthworms showing the highest population increase by four times ,while enchytraeids and nematodes favored CT system predicting certain adaptability of these animals to plow-disturbed soil envi-ronment ,On the basis of relative response index it was found that soil fauna was more sensitive to tillage than soil resource base(C and N pools) and microflora.The population structure of soil fauna was also affected by tillage treatments.Analysis on nematode trophic groups showed that bacteria-feeding and plant parasitic nematodes were more abundant in CT soil whereas the proportions of fungivores and onmivore-predators increased in NT soil.Possible reasons for the differentiaion in both size and structure of the fauna populaion were discussed and the ecological significance involved in these changes was emphasized.     

The combined effects of earthworms and arbuscular mycorrhizal fungi on microbial biomass and enzyme activities in a calcareous soil spiked with cadmium

Earthworms and arbuscular mycorrhizal fungi (AMF) are known to independently affect soil microbial and biochemical properties, in particular soil microbial biomass (SMB) and enzymes. However, less information is available about their interactive effects, particularly in soils contaminated with heavy metals such as cadmium (Cd). The amount of soil microbial biomass C (MBC), the rate of soil respiration (SRR) and the activities of urease and alkaline phosphatase (ALP) were measured in a calcareous soil artificially spiked with Cd (10 and 20 mg Cd kg⁻¹), inoculated with earthworm (Lumbricus rubellus L.), and AMF (Glomus intraradices and Glomus mosseae species) under maize (Zea mays L.) crop for 60 days. Results showed that the quantity of MBC, SRR and enzyme activities decreased with increasing Cd levels as a result of the elevated exchangeable Cd concentration. Earthworm addition increased soil exchangeable Cd levels, while AMF and their interaction with earthworms had no influence on this fraction of Cd. Earthworm activity resulted in no change in soil MBC, while inoculation with both AMF species significantly enhanced soil MBC contents. However, the presence of earthworms lowered soil MBC when inoculated with G. mosseae fungi, showing an interaction between the two organisms. Soil enzyme activities and SRR values tended to increase considerably with the inoculation of both earthworms and AMF. Nevertheless, earthworm activity did not affect ALP activity when inoculated with G. mosseae fungi, while the presence of earthworm enhanced urease activity only with G. intraradices species. The increases in enzyme activities and SRR were better ascribed to changes in soil organic carbon (OC), MBC and dissolved organic carbon (DOC) contents. In summary, results demonstrated that the influence of earthworms alone on Cd availability is more important than that of AMF in Cd-polluted soils; and that the interaction effects between these organisms on soil microorganism are much more important than on Cd availability. Thus, the presence of both earthworms and AMF could alleviate Cd effects on soil microbial life.     

The soil invertebrate contribution to nitrogen mineralisation differs between soils under organic and conventional dairy management

Organic management aims to promote soil biological activity. To test whether organic management stimulates soil biological activity, invertebrates (macrofauna, mesofauna and microfauna) were collected from four paired commercial organically and conventionally managed dairy farms on different soil types (Allophanic, Pallic, Recent and flooded Recent). Food webs were constructed and rates of invertebrate-mediated N mineralisation calculated. The organic dairy operations used fewer nutrient inputs and had lower stocking rates than their paired conventional farms. This translated into lower calculated pasture production and less available plant litter entering the soil food web. Despite the lower plant litter inputs into the organic system, earthworm biomass was higher (particularly in the Recent and flooded Recent soils), suggesting that under conventional management the physical condition of the soil, as influenced by stock treading pressures, was more important for invertebrate activity and their influence on N mineralisation than was food supply. Nitrogen mineralisation was higher in organic systems, with earthworms contributing the most (24–98 kg N/ha/year). As the physical loading on the soil increased under conventional management, the ability of the soil to provide soil services (i.e. N mineralisation and litter decomposition) became compromised. Organic management on four soils stimulated biological activity by reducing the treading pressure on the soil and highlights the need to consider the influence of management practices on the faunal environment (food availability and physical condition) to understand the impacts of organic management and the role of fauna in N mineralisation.     

Earthworms and pH affect communities of nematodes and enchytraeids in forest soil

In northern boreal forests the occurrence of endogeic and anecic earthworms is determined by soil pH. Increasing evidence suggests that large detritivorous soil animals such as earthworms can influence the other components of the decomposer community. To study the effects of earthworms and pH on soil nematode and enchytraeid communities, a factorially designed experiment was conducted with Lumbricus rubellus and/or Aporrectodea caliginosa. Earthworms were added to "mesocosms" containing unlimed (pH 4.8) or limed (pH 6.1) coniferous mor humus with their natural biota of micro-organisms. In the absence of earthworms, nematodes were significantly more abundant in limed than in unlimed humus. Earthworms markedly decreased the numbers of nematodes both in unlimed and limed soils. Earthworm activities eliminated enchytraeids in unlimed soil, but liming improved the survival of some species. It was concluded that liming of soil, either alone or mediated by the earthworm populations, is likely to affect soil nematode and enchytraeid community and mineralisation.     

Einfluß verschiedener Bodeneigenschaften auf die mikrobielle Toxizität von Blei und Cadmium

Effects of different soil properties on the microbial toxicity of lead and cadmium Effects of different soil properties on the microbial toxicity of lead and cadmium were investigated in laboratory experiments on ten arable and nine preserve area soils. Microbial activity was measured by means of the dehydrogenase and the arginine-ammonification tests. The latter was not suitable to show the microbial toxicity of both metals. Effects of lead on dehydrogenase activity were mainly influenced by its concentration in soil solution (r = 0,79). Thus, all soil properties which determined the adsorption of lead correlated significantly with the relative dehydrogenase activities of the contaminated soils. The most important abiotic factors influencing the toxicity of lead were the soil pH and the CEC. Cd solubility and Cd toxicity were influenced by soil pH in a contrary way. Low Cd concentrations caused greater inhibitions of dehydrogenase activity at neutral and slightly alkaline soil reaction than under acidic conditions. Therefore, correlations between Cd concentrations of soil solutions or clay content and dehydrogenase activity were only significant if partial correlation analysis (constant pH) was used.     

Effects of biochar,earthworms, and litter addition on soil microbial activity and abundance in a temperate agricultural soil

Biochar application to arable soils could be effective for soil C sequestration and mitigation of greenhouse gas (GHG) emissions. Soil microorganisms and fauna are the major contributors to GHG emissions from soil, but their interactions with biochar are poorly understood. We investigated the effects of biochar and its interaction with earthworms on soil microbial activity, abundance, and community composition in an incubation experiment with an arable soil with and without N-rich litter addition. After 37 days of incubation, biochar significantly reduced CO₂ (up to 43 %) and N₂O (up to 42 %), as well as NH₄ ⁺-N and NO₃ ^?-N concentrations, compared to the control soils. Concurrently, in the treatments with litter, biochar increased microbial biomass and the soil microbial community composition shifted to higher fungal-to-bacterial ratios. Without litter, all microbial groups were positively affected by biochar × earthworm interactions suggesting better living conditions for soil microorganisms in biochar-containing cast aggregates after the earthworm gut passage. However, assimilation of biochar-C by earthworms was negligible, indicating no direct benefit for the earthworms from biochar uptake. Biochar strongly reduced the metabolic quotient qCO₂ and suppressed the degradation of native SOC, resulting in large negative priming effects (up to 68 %). We conclude that the biochar amendment altered microbial activity, abundance, and community composition, inducing a more efficient microbial community with reduced emissions of CO₂ and N₂O. Earthworms affected soil microorganisms only in the presence of biochar, highlighting the need for further research on the interactions of biochar with soil fauna.     

Einfluß von Herbiziden auf die N2-Fixierung und Atmungsaktivität von Mikroorganismen in Ackerböden

Influence of herbicides on nitrogen fixation and respiration activity of microorganisms in arable soils The influence of pesticides on nitrogen fixation (acetylene reduction test) as well on respiration activity was determined in model experiments. The following soils were used: Chernozem from loess (Boroll), Luvisol from loess (Boralfs), Rendsina (Lithic Rendoll), Pelosol (Fine textured Cambisol) and Humic Podzol (Humod). The tested soils differed considerably in both parameters. The rendsina showed remarkably low fixation rates whereas the podsol reduced acetylene only at higher water contents. The soil herbicides chlortoluron, terbutryne, metabenzthiazuron and chloridazon did not affect the course and the magnitude of the tested parameters even not at higher doses. Only the leaf herbicide dinosebacetate revealed a distinct inhibition of nitrogenase activity in the podsol and in the luvisol from loess. The fungicide carbendazime caused a strong stimulation of the nitrogenase activity in all soils. The respiration activity could not been influenced significantly.     

Mercury methylation,uptake and bioaccumulation by the earthworm Lumbricus terrestris (Oligochaeta)

To date, most studies about mercury (Hg) methylation and bioaccumulation have focused on aquatic ecosystems. In contrast, information regarding the biogeochemical cycle of Hg in terrestrial ecosystems is scarce. Considering the relevance of earthworms in soils, it is very important to study their role in the bioaccumulation and transformation of Hg species (inorganic Hg, IHg, and monomethylmercury, MeHg). The aim of this experimental study was to compare the uptake and bioaccumulation of MeHg and IHg in the earthworm Lumbricus terrestris exposed to soils freshly spiked with inorganic Hg as well as historically contaminated soils. The study consisted of a 28-day uptake phase in Hg (spiked and natural) contaminated and non-contaminated soils followed by a 14-day depuration phase in non-contaminated soils. Soils were characterized by determining not only Hg concentrations (total Hg, MeHg and acid-labile Hg) but also analysed for other physicochemical parameters that can influence the fate of Hg within the earthworm–soil system. Mercury species were determined in earthworms (whole organism) exposed to Hg contaminated and non-contaminated soils. Mercury availability in soils seems to be the main factor controlling the uptake and bioaccumulation of Hg species because, according to kinetic data, the spiked IHg was more readily assimilated and methylated by earthworms. Bioaccumulation factors (BAFs) for MeHg and total Hg were also higher in spiked than in naturally Hg-contaminated soils. In addition, BAFs for MeHg (ranging from 0.8 to 17.3) were higher than those for total Hg (between 0.02 and 0.62) which suggests that MeHg was more easily bioaccumulated by this earthworm species and also that earthworms may actively contribute to MeHg production in soils.     

Earthworms in New Zealand sheep- and dairy-grazed pastures with focus on anecic Aporrectodea longa

Earthworms play an important role as primary decomposers in the incorporation and initial mixing of plant litter. This study explored the response of earthworms to increasing fertiliser inputs, pasture production and livestock numbers (and their influence on food availability and soil physical condition) on six different managements in sheep-grazed and fifteen different managements in dairy-grazed pastures in a variety of New Zealand soils.Native earthworms were only found in some low-fertility pastures. Accidentally introduced peregrine earthworms, when present, dominate pasture soils. Of these, endogeic earthworms dominated the earthworm community and were positively associated with soil types with higher bulk densities. Peregrine anecic earthworms were absent from most hill-country sheep-grazed pastures, however in more fertile and productive dairy-grazed pastures they reached a biomass of up to 2370 kg ha^?1. Only anecic earthworms showed a positive response to the increasing pressures associated with higher potential dry matter inputs and liveweight loadings of grazing livestock on soil, while epigeic earthworms declined. The positive response of anecic earthworms probably reflects the combined effect of the increase in food resources, including dung and plant litter, available on the soil surface, and their lower susceptibility to livestock treading pressure. Anecic species may be a suitable substitute for incorporation of surface litter in those soils where livestock treading limits epigeic earthworm populations.This study confirmed previous observations of limited distribution of the introduced Aporrectodea longa in pastoral hill-country soils in the North Island, and their near absolute absence from the South Island of New Zealand. This would suggest that large areas of New Zealand pastoral farmed soils could benefit from the introduction of anecic species from other parts of New Zealand which already contain A. longa.     

Invertebrate communities (Annelida and epigeic fauna) in three types of Estonian cultivated soils

The abundance and diversity of invertebrate communities (annelids and epigeic fauna) in three types of cultivated soils were studied. Soil biota communities in the three most widespread soil types in Estonia (Calcaric Regosols, Calcaric Cambisols and Stagnic Luvisols) are influenced by environmental conditions, the factors connected to soil texture including moisture, organic matter content and pH being the most essential, and by the intensity of agricultural practice. Potentially high biological activity and low intensity of agricultural human activity of Calcaric Regosols occurs in parameters of communities of organisms not sensitive to soil which dries off, i.e. epigeic fauna living on the soil surface and preferring dry and warm habitat; temporarily dried off soil is not a suitable habitat for Oligochaeta. Both groups of Oligochaeta (earthworms, enchytraeids) appear to prefer Calcaric Cambisols where soil moisture conditions are more stable. The abundance of invertebrate communities is the highest and the diversity is the lowest in Stagnic Luvisols. Some trends occurred in community characteristics along the soil surface following a hypothetical gradient; the number of carabids per trap and diversity of spiders decreased from the edge to the centre of the field. The results presented here on spatial variability in distribution of soil organisms are preliminary.     

Influence of some physicochemical and biological parameters on soil structure formation in alluvial soils

This study examines the role of abiotic (texture, calcium carbonates or iron) and biotic parameters (earthworm and enchytraeid activities) on the initial phases of soil aggregation. Our research focused on humus forms in alluvial soils, which are considered as young and heterogeneous environments. We hypothesized that the soil structure formation is determined by both the nature of the recent alluvial deposits and the soil fauna. For this purpose, six sites were chosen throughout two types of softwood forests (willow and alder forest) representing two stages of vegetation succession. Evidence of soil texture influence on aggregate stability was observed. A dominance of a coarse sand fraction caused a quick colonization of enchytraeids and epigeic earthworms while a silty texture favoured the presence of anecic earthworms, thus increasing the aggregate stabilisation. Iron forms, acting as cementing agents, were observed in the coarse silt, while calcium carbonates were equally distributed among the textural fractions. Active calcium carbonate fraction, binding organic matter with mineral components, was not found in the coarse sand fraction. In conclusion, the tree age cannot alone be used as an indicator of the humus form evolution but biological and physicochemical parameters also influence the initial steps of soil structuration.