Experimental studies on cold survival of enchytraeid cocoons

The effect of different culture methods, cold acclimation and desiccation on the supercooling point (SCP), the melting point (MP) of fluids and the quantity of water freezing (osmotically active water) was investigated in individual cocoons of Enchytraeus crypticus and an undescribed Enchytraeus species using differential scanning calorimetry (DSC) techniques. Both species can be easily cultured in the laboratory in agar where the development and hatching of the worms can be observed. Culture methods (agar with nettle leaves or oats as food and wet filter paper without food supply) had a significant effect on fresh weight and SCP of E. crypticus cocoons. The water content (as a proportion of fresh weight) was slightly lower in the cocoons from the wet filter paper cultures. Acclimation at —3 °C did not affect the supercooling ability of E. crypticus cocoons, whereas the SCP of E. sp.1 cocoons was lowered from a mean of —8.7 to —12.4 °C. The supercooling ability of cocoons of E. crypticus was only slightly increased by desiccation and cold acclimation, but the quantity of frozen water was significantly reduced with acclimation and desiccation (2 and 3 min) at room temperature. The MP values of the cocoon fluids reflected these changes in both species. No cocoons of E. crypticus and E. sp.1 survived desiccation and freezing in our experiments and no worms of Enchytraeus albidus, E. crypticus and Henlea perpusilla survived freezing to —10 or —20 °C.     

Population dynamics of Enchytraeidae (Oligochaeta) in different agricultural systems

Organic matter and abiotic conditions seem to influence distribution patterns of Enchytraeidae. In this study effects of changes in management practices on population dynamics of enchytraeids were determined. At two sites (in Athens and Griffin, GA) parts of a fescue (FE) field were converted into conventional tillage (CT) and no-tillage (NT) plots and changes in densities and depth distribution of enchytraeids were followed for 3 years. A site at Watkinsville, containing various soil textures and characterised by very low organic carbon content, which was converted into no-tillage 4 years earlier, was also sampled. Significant reductions in enchytraeid densities, after conversion of fescue into CT, were only found at Griffin. The management practices affected the vertical distribution of enchytraeids. In fescue and NT more enchytraeids were found in the 0–5cm than in the 5–15cm layer. In conventional tillage fields enchytraeids were more evenly distributed over the profile or more abundant in the 5–15cm layer. Management also affected the timing of population dynamics in the different plots. At two sample dates high abundances were found in CT plots only, not in any of the other plots. Enchytraeids were larger at Athens than at Griffin and Watkinsville and contained more soil particles in their gut. At Athens enchytraeids will presumably contribute more to the development of soil structure than at the other sites. We conclude that management affects vertical enchytraeid distributions in soil and changes the timing of population dynamics. Received: 7 January 1996     

Do enchytraeid worms and habitat corridors facilitate the colonisation of habitat patches by soil microbes?

Due to their high abundance and ubiquitous existence, microbes are considered to be efficient colonisers of newly established habitats. To shed light on the dispersal mechanisms of soil microbes, a controlled microcosm experiment was established. In these microcosms, the dispersal of microbes from a source humus patch to originally sterile humus patches (embedded in a mineral soil matrix) was followed for 16 months, applying 16S and 18S ribosomal DNA-based PCR-DGGE molecular methods. Specifically, the role of enchytraeid worms and habitat (humus) corridors as possible facilitators of microbe dispersal was studied. The results showed that enchytraeid worms function efficiently as vectors for horizontal dispersal of saprophytic fungi in soil. Some of the fungi also proved to disperse through the corridors by vegetative growth, although this dispersal was inefficient as compared to dispersal with the enchytraeids. Virtually no saprophytic fungi were able to disperse through the mineral soil matrix in the absence of both enchytraeid worms and corridors. Unlike soil fungi, the dispersal of soil bacteria was not affected by any of the studied factors. The results of the present experiment provide direct evidence of the crucial role of soil fauna in aiding the horizontal dispersal of soil fungi. The role of enchytraeids as a functionally important species in boreal forest soils is further emphasized, since bringing microbes into contact with new resources is likely to enhance the rate of decomposition in soils.     

Communities of Enchytraeidae (Oligochaeta) in planted birch stands as compared with natural forests in central Finland

This study compares the enchytraeid communities in anthropogenous birch (Betula pendula) stands of different origin with each other and with natural forests at the same latitude in Finland. Nine sites were investigated: three birch stands planted ca. 30 years prior to the study after clear-cutting of spruce stands, three birch stands established ca. 30 years earlier on arable soil (cleared from earlier coniferous forest), and three natural deciduous forests. Each site was sampled three times (May, August and October) in 1999, animals were extracted using the wet funnel method, counted and identified. Non-metric multidimensional scaling (NMS) was used to analyse the communities. There were clear differences between the birch stands established after spruce forest and after cultivation, and between these and natural deciduous stands, but even more between replicates of similarly managed forests. Total numbers and populations of most species were lower in birch-after-field than in birch-after-spruce. The superdominant species in coniferous forests, Cognettia sphagnetorum, was dominant in all birch-after-spruce sites and one natural deciduous site. Enchytronia parva was the only species more abundant in birch-after-field than in birch-after-spruce. It is hypothesized that, in addition to soil acidity, accidental transport by man explains the presence of many species on a given locality, and that competition with earthworms plays a role in regulating enchytraeid abundances.     

Dynamics and stratification of Enchytraeidae in the organic layer of a Scots pine forest

In a Dutch Scots pine forest an experiment was conducted to quantify the role of soil biota in the functioning of the soil ecosystem, and the effects of enhanced nitrogen deposition. For this, the site was sampled at 8-week intervals during 2.5 years. This paper reports on the population dynamics of enchytraeids in the field and in stratified litterbags. Mean yearly abundance of the enchytraeid community in the field was 47 600 m^–2, or 0.70 g (dry weight) m^–2. The community consisted mainly of three species: Cognettia sphagnetorum, Marionina clavata and Achaeta eiseni, of which C. sphagnetorum was dominant. The enchytraeid populations showed a marked stratification in the same sequence. Freshly fallen pine needles were colonized by C. sphagnetorum, while other species followed much later. It was found that data from the litterbags were reasonably comparable with field data, when expressed per gram of dry substrate, but less so when expressed per square metre. Multiple regression analysis of the data showed that the population dynamics in the litter layer could largely be explained by temperature and moisture fluctuations; in deeper layers other factors, such as the stage of decomposition, were probably more important. Received: 26 June 1997     

Can differences in soil community composition after peat meadow restoration lead to different decomposition and mineralization rates?

Reducing decomposition and mineralization of organic matter by increasing groundwater levels is a common approach to reduce plant nutrient availability in many peat meadow restoration projects. The soil community is the main driver of these processes, but how community composition is affected by peat meadow restoration is largely unknown. Furthermore, it is unclear whether restoration induced changes could lead to altered decomposition and mineralization rates. We determined soil community composition in restored peat meadows with different groundwater levels and soil pH. This composition was subsequently used in food web model calculations of C and N mineralization rates to assess whether differences in soil community composition may have contributed to differences in decomposition and mineralization rates observed between these meadows.Community composition of micro-organisms, Collembola and Enchytraeidae differed considerably between meadows and were correlated with differences in groundwater levels and soil pH. Collembolan and enchytraeid species from wet and neutral environments were more abundant at meadows with higher groundwater levels. Lower fungal to bacterial PLFA ratios and higher numbers of protozoa indicated an increased importance of the bacterial part of the food web at meadows with higher groundwater levels. Food web model calculations suggested that the observed changes in community composition would lead to higher rates of C and N mineralization at meadows with high groundwater levels. Results from modeling were consistent with field measurements of C mineralization, but not with measurements of N mineralization.We conclude that understanding changes in soil community composition in response to specific restoration measures may help us to better understand ecosystem responses to wetland restoration schemes, especially regarding soil biogeochemical processes.     

Effects of artificial acidification and liming on biomass and on the activity of digestive enzymes in Enchytraeidae (Oligochaeta): Results of an ongoing study

Summary The effects of simulated acid rain and acidification combined with liming on enzymatic activities in the gut of the enchytraied Fridericia sp. were studied under laboratory conditions. Simulated mild (pH 4.4) and strong (pH 3.1) acid rain was applied throughout a 52-day experiment. Liming, at rates of 1500 and 4000 kg CaCO₃ powder ha^-1, was applied once on the 27th day of acid rain. After 52 days, the treatment effects were determined by analysing changes in the fresh body weight of enchytraeids and the activities of amylase (EC 3.2.1.1), xylanase (EC 3.2.1.8), trehalase (EC 3.2.1.28) and C₁-cellulase (EC 3.2.1.91) in the gut. The effects were significant in only a few instances. After acidification, xylanase and trehalase activities decreased. The changes in fresh body biomass were not significant. Amylase and cellulase activities increased slightly, possibly because the acidification had a stimulatory effect on soil amylolytic and cellulolytic microorganisms. After liming, both xylanase activity and the enchytraeid body biomass decreased. This was the only marked evidence of a negative effect on the enchytraeids. The high amylase, trehalase and cellulase activities that were observed might have been caused by intensive digestion of dead acidophilous microflora.     

Interactions between soil micro- and mesofauna and plants in an ecofarming system

Interactions between crops and soil micro- and mesofauna within the root zone were investigated under field conditions on sandy loam on a larger spatial scale and in columns in the laboratory on a smaller spatial scale. During the vegetation period of summer wheat from April to July 1999 soil samples were taken monthly directly from the root zone within plant rows and between plant rows hardly penetrated by roots. Abundances of Enchytraeidae, Collembola, soil flagellates, enzyme activities and contents of total carbon and nitrogen were determined. Additionally, a laboratory experiment was carried out with soil columns. Soil from the field was defaunated and inoculated with soil fauna (Enchytraeidae, Collembola, earthworms) in different combinations. Furthermore, summer wheat was sown. Enzyme activities, soil flagellate abundance and contents of total carbon and nitrogen were measured after 2, 6 and 14 weeks. Our field results revealed considerable interactions between plant roots, sampling date and soil layer affecting Enchytraeidae and Collembola. Within plant rows flagellate numbers correlated higher with N_t and C_t than between plant rows. In the laboratory close relationships between soil fauna as well as enzyme activities and nutrients contents were found within the root zone.