Significance of earthworms in stimulating soil microbial activity

 The stimulatory effect of earthworms (Lumbricus terrestris L.) on soil microbial activity was studied under microcosm-controlled conditions. The hypothesis was tested that microbial stimulation observed in the presence of a soil invertebrate would be due to the utilization of additional nutritive substances (secretion and excretion products) that it provides. Changes in microbial activity were monitored by measuring simultaneously CO₂ release and protozoan population density. The increase in CO₂ released in the presence of earthworms was found to result from both earthworm respiration and enhanced microbial respiration. The stimulation of microbial activity was confirmed by a significant increase in protozoan population density, which was 3–19 times greater in the presence of earthworms. The respiratory rate of L. terrestris was estimated to be 53 μl O₂ g^–1 h^–1. Earthworm respiration significantly correlated with individual earthworm weight, but there was no correlation between the increase in microbial respiration and earthworm weight. This finding does not support the hypothesis given above that enhanced microbial respiration is due to utilization of earthworm excreta. A new hypothesis that relationships between microbial activity and earthworms are not based on trophic links alone but also on catalytic mechanisms is proposed and discussed. Received: 26 August 1997     

Biological and physical effects of non-native earthworms on nitrogen cycling in riparian soils

Global nitrogen cycling is being altered by anthropogenic disturbances including invasion by non-native species. European and Asian earthworms have invaded northern temperate forests in North America with dramatic consequences for litter thickness, forest floor plant diversity, and soil nitrogen cycling. Invasive earthworms present at the boundary of terrestrial and aquatic ecosystems (i.e., riparian zones) may alter the flux of nitrogen into adjacent aquatic ecosystems. We examined how nitrogen cycling in riparian soil responds to amendments of invasive earthworms or artificial earthworm burrows. In earthworm-free riparian plots (0.25 m²), we established treatments of invasive earthworms (60 g fresh mass·m⁻²), artificial burrows (120 m⁻²), or control plots and sampled the plots after 30 days. Before and after treatment application we measured major soil characteristics (water-filled pore space, organic matter, and pH), nitrogen pools (exchangeable NH₄⁺ and NO₃⁻), and nitrogen transformation rates (net N-mineralization, net nitrification, and denitrification). Exchangeable NH₄⁺ and NO₃⁻ changed through time but did not differ among treatments. Net N-mineralization and net nitrification rates did not change through time and were similar across all treatments. However, denitrification rates in plots with added earthworms were 4 times greater than rates in control and burrow-only plots, which represents a large rapid increase in gaseous nitrogen flux out of these riparian soils. For all response variables, artificial burrows responded similarly to control plots, suggesting that earthworm biological activity (i.e., feeding, excretion, and mucus production) rather than physical effects (i.e., burrowing and soil aeration) drove the changes in nitrogen cycling. Examination of soil nitrogen pool and flux measurements suggest that this increase in denitrification was coupled with NH₄⁺ consumption by nitrifying bacteria, but future studies are needed to confirm this hypothesis. We conclude that the activity of invasive earthworms in riparian zones can increase the flux of N out of riparian zones, but the hydrologic context of the riparian zone (e.g., pore-water residence time) ultimately controls whether denitrification or nitrate leaching is the dominant flux of N.     

The effect of earthworms (Lumbricidae) on nitrogenase activity in soil

Summary Nitrogenase activity associated with earthworms, their faeces and activity in soil was measured by the acetylene reduction technique. A clear increase in nitrogenase activity was found in field-deposited casts of Aporrectodea caliginosa in comparison with surrounding soil, although potential nitrogenase activity was significantly higher in soil than in casts. Nitrogenase activity associated directly with earthworms (Lumbricus rubellus ) was detected, indicating the presence of active N₂-fixing bacteria on the body surface and/or in the gut. Laboratory experiments showed that nitrogenase activity in the casts of L. rubellus was higher than in unmodified soil, and that nitrogenase activity in soil was significantly increased by the burrowing and feeding activity of these worms. This paper discusses the possible causes of these earthworm effects on soil nitrogenase activity and some methodological problems of determining the nitrogenase activity.     

The effect of earthworm coprolites on the soil water retention curve

The effect of earthworm coprolites on the water retention curves in soils of different geneses and textures was investigated by the method of equilibrium centrifuging. Coprolites sampled in the field were compared with the surrounding soil. The effect of earthworms on a soddy-podzolic light loamy soil (from Moscow oblast) was comprehensively analyzed in the course of a special model experiment in a laboratory. This experiment was necessary because it was difficult to separate the coprolites from the soil, in which additional coprolites could appear under natural conditions. In all the variants of the experiment, the differences between the water retention curves of the coprolites and the surrounding soil (or control substrates unaffected by earthworms) were statistically significant. The development of coprolites favored a considerable increase (up to 20 wt.% and more) of the soil water retention capacity upon equivalent water potentials within the range from 0 to ?1000 kPa. In most cases, the soil water retention capacity increased within the entire range of the soil moisture contents. This could be explained by the fact that strongly swelling hygroscopic plant remains (detritus) were included into the coprolites and by the formation of a specific highly porous aggregate structure.     

Biological activity of acetylated phenolic compounds

In recent years an effort has been made to isolate and identify biologically active compounds that are included in the Mediterranean diet. The existence of naturally occurring acetylated phenolics, as well as studies with synthetic ones, provide evidence that acetyl groups could be correlated with their biological activity. Platelet activating factor (PAF) is implicated in atherosclerosis, whereas its inhibitors seem to play a protective role against cardiovascular disease. The aim of this study was to examine the biological activity of resveratrol and tyrosol and their acetylated derivatives as inhibitors of PAF-induced washed rabbit platelet aggregation. Acetylation of resveratrol and tyrosol was performed, and separation was achieved by HPLC. Acetylated derivatives were identified by negative mass spectrometry. The data showed that tyrosol and its monoacetylated derivatives act as PAF inhibitors, whereas diacetylated derivatives induce platelet aggregation. Resveratrol and its mono- and triacetylated derivatives exert similar inhibitory activity, whereas the diacetylated ones are more potent inhibitors. In conclusion, acetylated phenolics exert the same or even higher antithrombotic activity compared to the biological activity of the initial one.     

Biological activity of chernozems in the center of the Russian Plain

Specific features of the microbiological and enzymatic activity of chernozems are considered in genetically associated and technogenic series. The biological processes in chernozems follow the main soil-geographical regularities inherent to the Central Chernozemic region. The biological characteristics of the chernozems reflect the dynamic properties of the microorganisms habitat and are indicators of their technogenic degradation. Plowing of chernozems and their intense agricultural use is accompanied by changes in their biological activity. The disturbances revealed in the biosystem of the chernozems caused by plowing and fertilization were of a functional, i.e., reversible character. The changes in the intensity of the biochemical processes in the chernozems were observed only under the long-term application of fertilizers (for not less than 10 years). A single application of fertilizers caused temporary changes.     

Biological activity of alpine mountain-meadow soils in the Teberda Reserve

The intensity of the actual and potential CO₂ emissions, nitrogen fixation, denitrification, and methane production were determined by gas chromatography in alpine mountain-meadow soils under different types of phytocenoses at the Teberda State Reserve. The main factors that control the intensity of these processes in the mountain-meadow soils are moisture and accumulation of biophilous elements related to the position of the soils on the biogeochemical catena. The CO₂ emission and intensity of the nitrogen fixation in the soils under Geranium-Hedysarum meadows that occupy transit-accumulative positions were 2–3 times higher that these parameters in the soils under the alpine heathlands and Festuca meadows. The soils under the carpet-like alpine meadows, accumulating moisture and mineral nitrogen, were characterized by the highest intensity of denitrification and methane production.     

Biological activity of ant nests in the middle taiga zone

Ants are the most widespread social insects. Many species of ants influence a range of soil properties when building their nests in soil. The paper discusses the effects of ants on soil biological activity (nitrogen fixation, denitrification), as well as on biomass and the diversity of microorganisms. In many cases, these processes were more active in anthills. Changes in soil pH caused by nest-building activity of ants were also. There were no patterns in the distribution of pH values. Specific differences between microbial complexes of anthills and corresponding reference soils were revealed.     

Identifying earthworms through DNA barcodes

With almost 3000 species, earthworms provide important model systems for studying soil fauna. However, species identification of earthworms is difficult and therefore limiting. The use of DNA barcodes, which are short sequences from standardized regions of the genome, has been regarded as a promising approach to resolve this taxonomic dilemma. We evaluated sequence diversity in the mitochondrial cytochrome-c oxidase I (COI) gene as a tool for resolving differences among species of Chinese earthworms. Members of six genera and 28 species were examined, and species were successfully discriminated in all cases. Sequence divergence within species was generally less than 1%, whereas divergence between species was greater than 15% in all cases. Divergence among individuals of Eisenia fetida were much higher (up to 7.8%); however, this may represent the presence of unrecognized sibling species or subspecies. We conclude that although it cannot completely replace taxonomy, the DNA barcode is a powerful tool for identifying species of earthworms and provides a useful complement to traditional morphological taxonomy.     

Effect of earthworms on molybdenum-depending activities

Pot experiments performed in an alkaline, silty clay soil showed that the presence of Allolobophora caliginosa increased nitrate reductase activity in maize seedlings and nitrogen fixation in the soil, but did not affect photosynthesis and biomass of maize seedlings and oxygen consumption in the soil. The increase in molybdenum-depending activities is ascribed to the greater availability of molybdenum recorded in the presence of earthworms.     

Effects of earthworms on nitrogen mineralization

The influence of earthworms (Lumbricus terrestris and Aporrectodea tuberculata) on the rate of net N mineralization was studied, both in soil columns with intact soil structure (partly influenced by past earthworm activity) and in columns with sieved soil. Soil columns were collected from a well drained silt loam soil, and before the experiment all earthworms present were removed. Next, either new earthworms (at the rate of five earthworms per 1200 cm³, which was only slightly higher than field numbers and biomass) were added or they were left out. At five points in time, the columns were analyzed for NH ₄ ⁺ , NO ₃ ^– , and microbial biomass in separate samples from the upper and lower layers of the columns. N mineralization was estimated from these measurements. The total C and N content and the microbial biomass in the upper 5 cm of the intact soil columns was higher than in the lower layer. In the homogenized columns, the C and N content and the microbial biomass were equally divided over both layers. In all columns, the concentration of NH ₄ ⁺ was small at the start of the experiment and decreased over time. No earthworm effects on extractable NH ₄ ⁺ were observed. However, when earthworms were present, the concentration of NO ₃ ^– increased in both intact and homogenized cores. The microbial biomass content did not change significantly with time in any of the treatments. In both intact and homogenized soil, N mineralization increased when earthworms were present. Without earthworms, both type of cores mineralized comparable amounts of N, which indicates that mainly direct and indirect biological effects are responsible for the increase in mineralization in the presence of earthworms. The results of this study indicate that earthworm activity can result in considerable amounts of N being mineralized, up to 90 kg N ha^–1 year^–1, at the density used in this experiment.     

Distribution of earthworms in soils of Yakutia

The distribution of earthworms in 18 types of tundra, middle-taiga, alas, and floodplain soils of Yakutia has been studied. The species Eisenia nordenskioldi is typical of Yakutian soils. The area, population density, and seasonal dynamics of earthworms in permafrost-affected soils have been determined. It is shown that earthworms are absent in excessively moist peat-muck permafrost-affected soils, excessively dry soddy soils of alases (thermokarst depressions), and soddy alluvial soils under steppe communities. The best living conditions for earthworms are associated with meadow floodplain, meadow alas, and mucky calcareous soils.     

Burial of soil-surface artifacts in the presence of lumbricid earthworms

Rings of wire placed on the soil surface of two pastures containing populations of Lumbricidae were recovered after 52 months. They had been buried at the rate of 9–10 mm per year. At a forest site where only Megascolecidae were present there was no burial. At the pasture sites, populations of Lumbricidae in tubes of soil sterilized with methyl bromide 52 months earlier were indistinguishable from those in untreated soils.     

The use of resource patches by earthworms

A field experiment was established to assess the effects of additional organic matter on earthworm populations. Bags of soil (15 cm deep) were placed in a pasture at Balhannah, South Australia, at the beginning of autumn 1991. The bags were initially seeded with five individuals ofAporrectodea trapezoides, and 250 g dried sheep manure was added to most bags. Manure was added either in pellet or milled form, and applied either on the surface, in the 5–10 cm layer, or evenly dispersed over 15 cm. In harvests during weeks 7,9, and 11 after the start of the experiment,A. trapezoides and three other species,A. caliginosa, A. rosea, andMicroscolex dubius, were recovered from the bags. Bags with added manure had significantly higher numbers of each species than bags with no manure. During the 4-week sampling period (weeks 7–11) the numbers ofM. dubius recovered per bag decreased, whileA. rosea increased. Total earthworm numbers were not influenced by either the form or the location of application of the manure. Earthworms were sampled from three depths, 0–5, 5–10, and 10–15 cm. Both numbers and biomass of earthworms were positively correlated with the location of the manure. Cocoons ofAporrectodea spp. were more abundant when the manure was milled and evenly dispersed, and were consistently located in the lower soil layers, regardless of the form or location of manure.     

Inoculation of earthworms into reclaimed soils: the UK experience

Earthworms have positive effects on soil structure, therefore their incorporation during the process of soil reclamation is a sensible route towards the final restoration of a site. Over the past 20 years, 16 documented field trials have been conducted in the United Kingdom. These trials took place at locations with a number of previous uses, for example, landfill sites, steelworks and opencast mines. The species of earthworm used varied, as did the techniques used for introducing them into the soil. This paper assessed the suitability of the earthworms chosen for each trial and, more importantly, trial outcomes. The most appropriate species were not always selected (possibly due to availability) and the introduction technique was not always the most appropriate for the site. Monitoring of trials generally occurred over relatively short periods of time (possibly due to limited funding). It is evident that more recent trials were not always informed by previous events. It is suggested that work of this nature may only be viable if brought about through site-related legal obligations. Copyright © 1999 John Wiley & Sons, Ltd.     

Biological activity of chernozem on different elements of microtopography

A pedogenetic stratification of the physicochemical and biological properties has been studied in the profiles of chernozemic soils on different elements of the paleocryogenic microtopography under a shelterbelt within the Kamennaya Steppe Reserve. The biological activity of soil samples was determined in laboratory from the amount of CO₂ produced by the soil upon its incubation. It is shown that the soil properties vary considerably both in the vertical (along the soil profile) and horizontal (along the elements of the microtopography) directions. The methods of correlation and factor analyses have been applied to group the soil properties according to the three major factors and to study the relationships between these groups. A quantitative assessment of the particular factors of soil formation under given pedoclimatic conditions is suggested. The dominant role belongs to the biological factor (50% of the total factor load). This factor is reflected in the soil properties with the maximum degree of differentiation in the soil profile. The paleocryogenic microtopography (17% of the total factor load) specifies the differentiation of soil acidity and the content of carbonates.     

Effects of earthworms on soil enzyme activity in an organic residue amended rice–wheat rotation agro-ecosystem

The effect of earthworms on soil hydrolases (protease, urease, invertase, and alkaline phosphatase) and dehydrogenase activities was investigated in maize residue amended rice–wheat rotation agro-ecosystem. Experimental plots in the rotation had five treatments, i.e. incorporation or mulching of maize residues with or without added earthworms and an untreated control. The application of maize residues to soil without earthworms significantly enhanced the five soil enzyme activities compared with the control treatment during rice and wheat cultivation. The presence of earthworms further significantly enhanced protease activity in the soils with both incorporated and mulched maize residues during two cultivation seasons, but only significantly increased alkaline phosphatase activity in the soil with incorporated maize residue during the rice cultivation season. Invertase activity was significantly enhanced by the presence of earthworms in the soil with maize residue incorporation during two cultivation seasons. There were no changes in dehydrogenase activity when earthworms were present. Additionally, the five enzyme activities in earthworm casts were significant higher than those in the surrounding soil, especially dehydrogenase and invertase activities. Whatever the treatment, the values obtained for the enzyme activities in both soil and casts, except for dehydrogenase activity in earthworm casts, were significantly higher under wheat than those in rice-cultivated soil. These results indicate that the presence of earthworms strongly affected soil enzyme activities, depending on the method of organic residue application, and the enhanced enzyme activities of earthworm casts probably contributed to the surrounding soil enzyme activities.     

Impact of earthworms on decomposition of garden refuse

Summary Decomposition of garden refuse was studied in containers with and without the earthworm species Eisenia andrei and Lumbricus rubellus. The reduction of cellulose and hemicellulose was greater where earthworms were present. Respiration was similar regardless of the presence of earthworms, whereas dry matter reduction, on average, was greatest without earthworms. The earthworm biomass decreased during the 58 days of the experiment; E. andrei increased in biomass, whereas L. rubellus died out.     

Vertical distribution of earthworms in grassland soils of the Colombian Llanos

 The vertical distribution of native earthworm species from natural and disturbed savannas in the Oxisols of the Colombian Llanos was assessed in a native savanna and in a 17-year-old grazed grass-legume pasture during a period of 17 months. Different patterns of vertical stratification were observed for all species with a strong migration of populations to deeper layers in the dry season. The correlation between the size of the earthworms and the average depth at which they were found was not significant (P>0.05), despite the fact that bigger species are located deeper in the soil. The living habits and adaptive strategies of the smallest species, Ocnerodrilidae n. sp., found in both ecosystems studied are responsible for this pattern. This endogeic species is associated with organic pools generated by an anecic species and further studies should assess the role of this species in ecosystem functioning. Mature worms of one anecic species were located deeper than immature ones in the soil (P<0.01). Soil moisture had an important effect on the vertical distribution of earthworms, although differences between immature and mature worms of the anecic Martiodrilus carimaguensis are likely to be of biotic origin. New data on the biology and ecology of these Neotropical species are shown. Received: 24 November 1999