Impact of ecologically different earthworm species on soil water characteristics

A laboratory experiment was performed to assess the impact of ecologically different earthworm species on soil water characteristics, such as soil tension, water content, and water infiltration rate. Three earthworm species (Lumbricus rubellus, Aporrectodea caliginosa, Lumbricus terrestris) were exposed in soil columns (diameter 30 cm, height 50 cm) for 100 days with a total fresh earthworm biomass of 22.7 ± 0.4 g per column, each in duplicate. Each column was equipped with tensiometers at 10 and 40 cm and FD-probes at 10 cm depth, to continuously measure the temporal development of soil tension and soil moisture. Additionally, 30 g of sieved and rewetted horse manure was placed on the soil surface as a food source. Precipitation events (10 mm) were simulated at day 28 and day 64. At the end of the experiment the water infiltration rate and the runoff at 55 cm depth were determined.The results showed considerable evidence, that ecologically different earthworms modify soil water characteristics in different ways. The anecic L. terrestris and the endogeic A. caliginosa showed the tendency to enhance the drying of the topsoil and subsoil. Their intensive and deep burrowing activity might enhance the exchange of water vapor due to a better aeration in soil. In contrast, the epigeic L. rubellus tended to enhance the storage of soil moisture in the topsoil, which might be linked to lower rates of litter loss from soil surface and thus a thicker litter layer remaining. A. caliginosa led to considerable higher water infiltration rates and faster water discharges in the subsoil, relative to the other species, probably due to a high soil dwelling activity.     

Impact of landspread sewage sludge and earthworm introduction on established earthworms and soil structure

Summary Sewage sludge was applied to twelve 4-m² plots in two forest (mixed hardwood, Norway spruce plantation) site and one old field site. The earthworm Eisenia fetida was introduced to half the control and half the treated plots. Earthworm populations were sampled by formalin extraction and hand-sorting five times in the year following treatment. One year after treatment, soil samples were wet-sieved and water-stable aggregate size-class arrays were determined.The dominant earthworm in the study site, Lumbricus terrestris, increased in density and mean individual biomass in response to sludge treatment in mixed hardwood and old field plots. In the Norway spruce plots, L. terrestris increased in individual biomass but decreased in density following sludge application. The density of the introduced E. fetida rapidly declined in all control plots. One year after introduction, E. fetida was found only in the sludge-treated Norway spruce plot. The introduction of E. fetida with sludge decreased the density and biomass of L. terrestris in the hardwood plots.Sludge treatment increased the percentages of 4-mm diameter water-stable aggregates in old field and hardwood plots. The addition of E. fetida with sludge in the hardwood plots generated no increase in 4-mm water-stable aggregates. In the old field, sludge + E. fetida increased the 4-mm water-stable aggregates. Little change in water-stable aggregates in response to either treatment combination was seen in the Norway spruce site.     

Impact of irrigation water quality on soil nitrifying and total bacterial communities

Disturbance induced by two contrasting irrigation regimes (groundwater versus urban wastewater) was evaluated on a sandy agricultural soil through chemical and microbial analyses. Contrary to wastewater, groundwater displayed very high nitrate contents but small amounts of ammonium and organic matter. Despite these strong compositional shifts, soil organic carbon and nitrogen, nitrate and ammonium contents were not significantly different in both types of irrigated plot. Moreover, neither microbial biomass nor its activity, determined as fluorescein diacetate hydrolysis activity, was influenced by irrigation regimes. Bacterial community structure, assessed by denaturing gradient gel electrophoresis (DGGE) of 16S ribosomal DNA fragments, was also weakly impacted as molecular fingerprints shared an overall similarity of 85%. Ammonia-oxidizing bacterial community (AOB) was monitored by DGGE of the functional molecular marker amoA gene (alpha subunit of the ammonia monooxygenase). Surprisingly, no amoA signals were obtained from plots irrigated with groundwater, whereas signal intensities were high in all plots under wastewater. Among the last, compositional shifts of the AOB community were weak. Overall, impact of irrigation water quality on soil chemistry could not be evidenced, whereas effects were low on the total bacterial compartment but marked on the AOB community.     

Effects of different land use on soil chemical properties, decomposition rate and earthworm communities in tropical Mexico

The effects of land use on soil chemical properties were evaluated, and earthworm communities and the decomposition rate of three typical land use systems in tropical Mexico, namely banana plantations (B), agroforestry systems (AF) and a successional forest (S) were compared.The study was carried out from November 2005 to April 2006. A completely randomized sampling design was established in six sites (B1, B2, AF1, AF2, S1 and S2). Soil properties and chemical characteristics (texture, pH, organic carbon (Corg), nutrients, and available Zn and Mn), earthworm communities and the decomposition of Bravaisia integerrima and Musa acuminata litter were analyzed over a period of 8 weeks.All soils were loamy clays with a medium to high content of nutrients. Three principal clusters were generated with the soil chemical properties: a first cluster for forest soils with high Corg and Ntot and low available Zn content, a second cluster for AF1 and a third cluster for B1, B2 and A2.The decomposition of B. integerrima litter was significantly faster (half-life time: 1.8 (AF2)–3.1 (B1) weeks) than that of M. acuminata (4.1 (AF2)–5.8 (S2) weeks). However, the decomposition rates did not differ significantly among the different sites.The greatest earthworm diversities were observed in AF2 and B1. Native species were dominant in the forest soils, whereas exotic species dominated in AF and in the banana plantations. The abundance and biomass of certain earthworm species were correlated to physical and chemical soil parameters. However, litter decomposition rates were not correlated with any of the soil physical–chemical parameters.While none of the land use systems studied led to a decrease in nutrient status, earthworm biodiversity and abundance, or in litter decomposition rate, they did result in a change in earthworm species composition.     

Impact of root herbivory by insect larvae on soil microbial communities

Bentgrass (Agrostis capillaris) and clover (Trifolium repens) were grown as pure swards and mixtures in pots containing soil from the NERC Soil Biodiversity field site located in Scotland. Six weeks after plant establishment leatherjacket larvae (Tipula paludosa) were added at field density to half the pots and the impacts of their feeding on plant shoot and root biomass and soil microbial communities was determined after 10 days. Plate counts and community level physiological profiles (CLPP) were used to characterise the microbial communities. Larval herbivory had a significant negative effect on shoot growth of both grass and clover and root biomass of grass. In mixed swards, larvae preferentially fed on clover. Soil microbial community structure was altered in the presence of larvae with populations of pseudomonads being significantly increased. These community differences may be attributed to increased quantity and qualitative changes in carbon flux to the soil as a result of root herbivory, as indicated by differences in the CLPPs of microbial communities in the presence and absence of larvae. This was mainly due to increased utilisation of some sugars, carboxylic and amino acids in the presence of larvae.     

Impact of soil compaction on earthworm burrow systems using X-ray computed tomography: preliminary study

This study is a first approach of the impact of soil compaction due to trafficking by machinery on earthworm burrow systems. To this end, two experiments were established. In the first one, microcosms were incubated in the laboratory for 70 d with Lumbricus terrestris or Aporrectodea giardi. In the second experiment, soil cores were excavated from a sugar beet field mainly colonised by L. terrestris and Aporrectodea caliginosa. The cores were then artificially compacted at 0.12 MPa or 0.25 MPa (which corresponds to the compaction due to trafficking by machinery in the field) or remained non-compacted. The whole cores were submitted to an X-ray computed tomography scan. This method allowed to compare the characteristics of the entire burrow system (total and mean burrowed length, mean length and number of burrows) and of the burrows themselves (number, area and roundness of pores constituting the burrows) in the compacted and non-compacted cores. The results showed that soil compaction contributes to close numerous pores, reduce mean length of burrows and increase the number of fragmented burrows. We concluded that soil compaction affects to a large extent the functionality of burrow systems by fragmenting them and affecting their continuity. This impact increases with the intensity of compaction. The applied soil compaction mainly affected the burrows located in the upper part of the soil. From a general point of view and especially for the upper part of the cores, horizontal burrows seemed to be more affected by compaction than vertical or oblique ones. Globally, the effects of soil compaction were especially observed at the greatest applied pressure (0.25 MPa). At 0.12 MPa, the damage to the burrows was less obvious.     

Impact of litter species diversity on decomposition processes and communities of soil organisms

The effect of plant species diversity and the C/N ratio of litter on soil processes were analysed in mesocosms in a three year field experiment. Plots 0.5 × 0.5 m with a depth of 15 cm containing sand mixed with loam were used to compare five natural and one artificial litter type (polypropylene string). Natural litters were either monospecific (I: Dactylis glomerata; II: Festuca rubra and III: Trifolium pratense) or were species mixtures (IV: mixture of three species I, II and III; V: mixture of twelve species, IV and nine other meadow plants). Differences among treatments in the litter decomposition rate, humic acid content and nematode density depended on the litter quality (C:N ratio) in most cases. By contrast, most of the differences among treatments found in the substratum below the litter cover resulted from litter diversity. The largest increase of carbon and nitrogen amount during growing season was found under litter mixtures (IV, V) and the highest fulvic acid content under the most diverse litter (V). Similarly, the production of algae in the substratum also significantly increased with litter diversity. Higher taxonomic diversity of Nematoda and Collembola and the most mature community of nematodes were observed under the most complex litter. Epigeic macrofauna, both dwelling in and penetrating the litter, did not differ significantly between experimental treatments. However, the highest share of predators was found in the treatment with the richest plant species diversity. In general, the results suggest that the decomposition of diverse plant litter enhances humus acid accumulation in soils. It is likely that algae participate in the process of humus formation.     

Impact of heavy metals on the degradative capabilities of soil bacterial communities

The degradative capabilities of six heavy-metal-affected and six unaffected bacterial communities from Canadian and German soils were determined by enumerating colony-forming units on 20 specific media. Each of these contained an aromatic substrate as the sole source of C and energy. Comparisons of plate counts revealed that heavy metal stress caused a decrease in the eveness of the distribution of the 20 degradative capabilities This suggests that in heavy-metal-affected bacterial communities, relatively rare degradative capabilities, irrespective of their nature, are even rarer than in unaffected communities, while the reverse is true for more common capabilities. The results are discussed with respect to the ease with which aromatic substrates can serve as C and energy sources.     

Influence of mulch and soil compaction on earthworm cast properties

The effects of different mulch materials applied to compacted and uncompacted soil on the quantity and the quality of deposited earthworm casts were investigated. Biochemical properties and water stability of soil aggregates were compared with the corresponding properties of worm casts. This short-time experiment was conducted in the laboratory, simulating field conditions of mulch management in temperate agricultural systems. In microcosms Lumbricus terrestris and Octolasion cyaneum were inoculated separately. Barley, lupin, maize, or sugar-beet as straw or leaves were applied as mulch in amounts comparable to those usually found in the field. The soil was compacted artificially to a bulk density of 1.0 or 1.5 Mg m⁻³. In general, plant material and to a lesser extent soil compaction influenced the dynamic processes in the soil affecting microbial activity and water stable aggregation. Higher values of phosphatase activity was measured in compacted soil, while the corresponding enzyme activities in the casts were less affected by compaction. The worm species and the nutritional quality of the food source were factors strongly influencing water stable aggregation. Mulch as well as soil compaction had consequences for the burrowing activity of the worms, which resulted in different rates of cast production depending on the species.     

The interactions between soil type and earthworm species determine the properties of earthworm casts

Earthworms are recognized to increase soil porosity, reorganize soil structure, and stimulate soil microflora and nutrient mineralization. The properties of earthworm casts should depend both on earthworm species or ecological group and on soil properties. Interactions between earthworm species and soil types have been suggested, but only poorly demonstrated. In order to better understand those interactions, two hypotheses led our study: (1) Soil type has a greater influence on cast properties than earthworm; (2) Earthworms from different species influence cast properties differently; (3) The intensity and direction of the impact of each earthworm species on cast properties vary with soil properties. Fifteen physical and chemical variables (N–NH₄⁺, N–NO₃⁻, total organic C and N, C/N ratio, CaCO₃, pH, P, K⁺, Mg²⁺, Mn²⁺, Na⁺, CEC, moisture, wettability) were measured in casts of three earthworm species (Lumbricus terrestris, Allolobophora chlorotica and Aporrectodea rosea) produced in three temperate soils. Univariate and multivariate analyses showed that earthworm species and soil types significantly impacted cast properties. pH, N_t, K and Mg contents were interactively altered by both factors. Multivariate analysis showed that a difference of soil type had a major impact on casts properties (62%) compared to the impact of a difference of earthworm species (10%). Cast properties were most impacted by L. terrestris, then by A. chlorotica and last by A. rosea. The response ratio (ratio of the properties of the casts to the properties of the bulk soil) was used to quantify the effect of earthworm species compared to the control soil. It showed a higher response of variables in casts in nutrient-rich soils, especially in casts of L. terrestris. The interactions between earthworm species and soil types on cast properties were discussed with regards to earthworm ecology, properties of the soil, and earthworm modifications of cast microflora.     

Influence of reduced tillage on earthworm and microbial communities under organic arable farming

Although reduced tillage is an agricultural practice reported to decrease soil erosion and external inputs while enhancing soil fertility, it has still rarely been adopted by European organic farmers. The objective of this study was to assess the long-term interactive effects of tillage (conventional (CT) vs. reduced (RT)) and fertilization (slurry (S) vs. composted manure/slurry (MCS)) on earthworms and microbial communities in a clay soil under spelt in an organic 6-year crop rotation. Earthworm populations (species, density and biomass, cocoons) were investigated by handsorting the soil nine years after initial implementation of the treatments. Soil microbial carbon (C_mic) and nitrogen (N_mic) were measured by chloroform-fumigation extraction and a simplified phospholipid fatty acid (PLFA) analysis was used to separate for populations of bacteria, fungi and protozoa. Significantly increased total earthworm density in RT plots was mainly attributed to increased numbers of juveniles. Moreover, we found five times more cocoons with RT. Species richness was not affected by the treatments, but tillage treatments had differentially affected populations at the species-level. In addition, cluster analysis at the community level revealed two distinct groups of plots in relation to tillage treatments. In RT plots C_mic increased in the 0–10 cm and 10–20 cm soil layers, while PLFA concentrations indicative of Gram-negative bacteria, fungi and protozoa only increased in the topsoil. Lower bacteria-to-fungi ratios in the upper soil layer of RT plots indicated a shift to fungal-based decomposition of organic matter whereas a higher C_mic-to-C_org ratio pointed towards enhanced substrate availability. Slurry application decreased microbial biomass and enhanced density of juvenile anecic earthworms but overall fertilization effect was weak and no interactions with tillage were found. In conclusion, tillage is a major driver in altering communities of earthworms and microorganisms in arable soils. The use of reduced tillage provides an approach for eco-intensification by enhancing inherent soil biota functions under organic arable farming.     

A review of earthworm impact on soil function and ecosystem services

Biodiversity is responsible for the provision of many ecosystem services; human well‐being is based on these services, and consequently on biodiversity. In soil, earthworms represent the largest component of the animal biomass and are commonly termed ‘ecosystem engineers’. This review considers the contribution of earthworms to ecosystem services through pedogenesis, development of soil structure, water regulation, nutrient cycling, primary production, climate regulation, pollution remediation and cultural services. Although there has been much research into the role of earthworms in soil ecology, this review demonstrates substantial gaps in our knowledge related in particular to difficulties in identifying the effects of species, land use and climate. The review aims to assist people involved in all aspects of land management, including conservation, agriculture, mining or other industries, to obtain a broad knowledge of earthworms and ecosystem services.     

Combined effects of zinc and earthworm density on soil ecosystem functioning

In traditional environmental risk assessment for soils, interactions between biota, contaminants and soil functioning are seldom taken into account. Also, single species toxicity tests are conducted with a fixed number of test animals. The objective of this study was to investigate effects of zinc (0–620 mg Zn kg^?1 dry soil) on soil ecosystem processes at different densities of the earthworm Lumbricus rubellus. Experiments were conducted using 1-liter microcosms equipped with respirometers. The presence of L. rubellus stimulated relevant soil processes and parameters: litter fragmentation, leaf litter mass loss from the soil surface, soil organic matter (SOM) content and soil respiration. Zinc was not lethal to L. rubellus, but negatively impacted soil respiration at the highest concentrations. Litter mass loss from the soil surface was also decreased by zinc and there was a significant interaction with worm density. The results of the study demonstrate that the impact of zinc on soil processes depends on the presence and densities of key soil organisms such as earthworms that influence decomposition and SOM content. The outcome of this research can be used to make existing models for site-specific risk assessment more ecologically relevant, linking effects of contaminants on soil fauna populations with effects on ecosystem functioning.     

Impact of a no-till with mulch soil management strategy on soil macrofauna communities in a cotton cropping system

Systematic exportation, burning of crop residues and decreases in fallow periods have led to a large-scale depletion of soil organic matter and degradation of soil fertility in the cotton (Gossypium hirsutum L.) cropping systems of Cameroon. The present study tested whether soil management systems based on a no-till with mulch approach intercropped with cereals, which has been shown to restore cotton production, could boost the biological activity of soil macrofauna. The impacts of no tillage with grass mulch (Brachiaria ruziziensis Germain and Eward) (NTG) and no tillage with legume mulch (Crotalaria retusa L. or Mucuna pruriens Bak.) (NTL) on the abundance, diversity and functional role of soil invertebrates were evaluated during the third year of implementation in northern Cameroon (Windé and Zouana), compared to conventional tillage (CT) and no tillage (NT) without mulch. Macrofauna were sampled from two 30 cm × 30 cm soil cubes (including litter) at the seeding stage of cotton, and 30 days later. The collected organisms were grouped into detritivores, herbivores and predators. Examination of the soil macrofauna patterns revealed that the abundance and diversity of soil arthropods were significantly higher in NTG and NTL than in CT plots (+103 and +79%, respectively), while that of NT plots was in-between the no tillage groups and CT (+37%). Regarding major ecological functions, herbivores and predators were significantly more abundant in NTG and NTL plots than in CT plots at Windé (+168 and +180%, respectively), while detritivores, predators and herbivores were significantly more abundant in the NTG plots than in CT plots at Zouana (+92, +517 and +116%, respectively). Formicidae (53.6%), Termitidae (24.7%) and Lumbricidae (9.4%) were the most abundant detritivores while Julidae (46.1%), Coleoptera larvae (22.1%) and Pyrrhocoridae or Reduviidae (11.8%) were the dominant herbivores. The major constituents of the predatory group were Araneae (33.8%), Carabidae (24.6%), Staphylinidae (15.7%) and Scolopendridae (10.3%). Direct seeding mulch-based systems, NTG and NTL, favoured the establishment of diverse macrofaunal communities in the studied cotton cropping system.     

Influence of earthworm middens on the distribution of soil microarthropods

Summary Earthworm middens and non-midden soil were sampled for microarthropods in a mowed recreational field and and adjacent woodlot site. Samples were taken in fall 1983 and spring 1984. The earthworm middens of the mowed field supported a higher density of micrarthropods (especially Collembola and prostigmatid mites) than adjacent non-midden soil. This positive midden effect in the mowed field was more pronounced in the fall than in the spring. Woodlot earthworm middens examined in the fall had lower densities of microarthropods (especially oribatid mites) than adjacent non-midden soi, but in the spring woodlot middens supported greater densities of microarthropods (especially Collembola) than adjacent, non-midden soil.     

Impact of organic amendments on the dynamics of soil microbial biomass and bacterial communities in cultivated land

In the course of a 1 year study on agricultural plots (mustard-beet) the impact of organic materials and soil management on soil microbial communities was assessed after amendment with three types of organic materials (sewage sludge, turkey manure and compost made of turkey manure and ligneous waste) and a mineral fertilizer. Transient impacts on potential metabolic activity, on genetic structure and on quantities of soil microorganisms, measured with three different methods (C_mic, total DNA content and CFU enumeration), were observed. The extent of these impacts depended on the composition of the amendment. The proportions of mineralisable carbon and lignin in organic materials seemed to influence the behaviour of the bacterial communities during the first 3 months after amendment. After a period of 6 months, no effect specific to the type of organic materials was detected. The dynamics of microbial biomass was assessed by both microbial carbon and by total DNA, but no correlation was found between the results; DNA seemed to be more sensitive to time-related variations in microbial biomass. Finally, although the bacterial functional and genetic structures were strongly modified between 3 and 6 months, this modification was not related to the type of amendment. This result suggests that organic amendments have less effect than seasonal variations or others anthropic factors such as the mechanical management of the soil.     

EM对连作大蒜根际土壤微生物和酶活性的影响

采用盆栽试验,研究了EM (Effective Microorganisms)对连作大蒜不同发育期干物质累积量,土壤微生物数量和酶活性的影响。结果表明,与对照相比,EM对土壤细菌、真菌和过氧化氢酶活性促进率随大蒜发育期均呈现先升后降的趋势,在蒜薹伸长期达到最大值;对硫化细菌和酚分解菌促进率最大值均出现在鳞茎膨大期;对氨化细菌和硝化细菌的促进率最大值分别出现在分化期和幼苗期。EM对放线菌、土壤多酚氧化酶、脲酶和磷酸酶活性促进率随发育期的延长而呈现持续上升的趋势。EM处理有利于改善土壤微生物群落结构,提高土壤微生物数量和土壤酶活性,增加干物质的累积量。