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The current study explores the influence of soil organic matter content on abundance and biomass of earthworm communities. The observation was carried out on three type of soils: Pellic Vertisols (very fine texture), Cromi-Vertic Luvisols (fine texture) and Calcaric Fluvisols (medium texture) from the Balkan Peninsula (Bulgaria). The field experiment was provided on uncultivated plots. In the studied area earthworm fauna comprises of four species: Aporrectodea rosea, Aporrectodea caliginosa, Lumbricus terrestris and Octolasion lacteum. We found peregrine lumbricid taxa, which are widely distributed in European soils. Our study demonstrated that soil organic matter has a positive effect on lumbricid populations. It was revealed that augmentation of soil organic matter favours characteristics of earthworm communities. The soil organic matter content and earthworm abundance are in strong positive correlation (r > 0.981). The same relationship was revealed between the biomass of lumbricid fauna and amount of soil organic matter (r > 0.987). In sum, the soil organic matter could be used as an indicator for earthworm communities in uncultivated soils. [ABSTRACT FROM AUTHOR]

The factors regulating soil animal communities are poorly understood. Current theory favors niche complementarity and facilitation over competition as the primary forms of non-trophic interspecific interaction in soil fauna; however, competition has frequently been suggested as an important community-structuring factor in earthworms, ecosystem engineers that influence belowground processes. To date, direct evidence of competition in earthworms is lacking due to the difficulty inherent in identifying a limiting resource for saprophagous animals. In the present study, we offer the first direct evidence of interspecific competition for food in this dominant soil detritivore group by combining field observations with laboratory mesocosm experiments using 13C and 15N double-enriched leaf litter to track consumption patterns. In our experiments, the Asian invasive species Amynthas hilgendorfi was a dominant competitor for leaf litter against two European species currently invading the temperate deciduous forests in North America. This competitive advantage may account for recent invasion success of A. hilgendorfi in forests with established populations of European species, and we hypothesize that specific phenological differences play an important role in determining the outcome of the belowground competition. In contrast, Eisenoides lonnbergi, a common native species in the Eastern United States, occupied a unique trophic position with limited interactions with other species, which may contribute to its persistence in habitats dominated by invasive species. Furthermore, our results supported neither the hypothesis that facilitation occurs between species of different functional groups nor the hypothesis that species in the same group exhibit functional equivalency in C and N translocation in the soil. We propose that species identity is a more powerful approach to understand earthworm invasion and its impacts on belowground processes. [ABSTRACT FROM AUTHOR]

Effects of leaf litter of beech ( Fagus sylvatica L.) and stinging nettles ( Urtica dioica L.) and of the endogeic earthworm species Octolasion lacteum (Örley) on carbon turnover and nutrient dynamics in soil of three beechwood sites on a basalt hill (Hesse, Germany) were investigated in a laboratory experiment lasting for about 1 year. The sites were located along a gradient from basalt (upper part of the hill) to limestone (lower part of the hill) with an intermediate site in between (transition zone). At the intermediate site U. dioica dominated in the understory whereas at the other sites Mercurialis perennis L. was most abundant. The amount and composition of organic matter was similar in soil of the basalt (carbon content 5.9%, C/N ratio 13.8) and intermediate site (carbon content 5.6%, C/N ratio 14.3) but the soil of the intermediate site produced more CO2 (in total +17.5%) and more nitrogen (as nitrate) was leached from this soil (in total +55.6%). It is concluded that the soil of the intermediate site contains a large mobile carbon and nitrogen pool and the formation of this pool is ascribed to the input of U. dioica litter. Leaf litter of U. dioica strongly increased NO3 –-N leaching immediately after the litter had been added, whereas nitrogen was immobilized due to addition of beech litter. Despite the very fast initial decomposition of nettle litter, the increase in CO2 production due to this litter material was only equivalent to 20.1% of the amount of carbon added with the nettle litter; the respective value for beech litter was 34.8%. Earthworms altered the time course of carbon and nitrogen mineralization in each of the treatments. In general, earthworms strongly increased mineralization of nitrogen but this effect was less pronounced in soil of the intermediate site (treatments without litter), which is ascribed to a depleted physically protected nitrogen and carbon pool. In contrast, their effect on the total amount of nitrogen mobilized from nettle litter was small. Earthworms significantly reduced CO2 production from soil of the intermediate site (treatments without litter) and it is concluded that earthworm activity contributes to the restoration of the depleted physically protected carbon pool at this site. [ABSTRACT FROM AUTHOR]

C mineralization of three different C-14-labelled lignin substrates (Klason-lignin, dioxane-lignin, lignocellulose) was investigated in four microcompartments, consisting of white-rotted beechwood ( Fagus sylvatica L)., brown-rotted beechwood, earthworm [ Octolasion lacteum (Örley)] faecal particles mixed with white-rotted beechwood, and earthworm feacal particles mixed with brown-rotted beechwood, incubated at 10°C for 193 days. Conversion of the labelled substrates to CO was low in both white-rotted and brown-rotted wood without faecal particles. Overall C mineralization followed the order Klason-lignin > dioxane-lignin > lignocellulose, indicating that there were different amounts of labelled contaminants in the lignin substrates. Lignin degradation was more pronounced in earthworm faeces mixed with wood materials, and overall C mineralization ranged between 4.4% and 6.3% of the inital C content. C mineralization of the lignin substrates increased considerably in faecal particles after about 90 days, presumably due to nutrient immobilization and microbial succession. The usefulness of the three lignin substrates in monitoring the time-course and extent of lignin degradation in soil microcompartments is discussed. [ABSTRACT FROM AUTHOR]

Mucus excretion of endogeic earthworms, by the body surface to burrow walls and by the intestine to casts, was investigated using uniformly C-labelled adult or subadult specimens of Octolasion lacteum (Örley) in laboratory incubations in soil from a beechwood on limestone. The daily loss of C due to mucus excretion from the body surface and in casts was calculated as 0.2 and 0.5% of total animal C, respectively. The C loss due to mucus excretion by subadult or adult individuals of O. lacteum is assumed to account for 63% of total C losses (including mucus excretion and respiration) of the earthworms. In a second experiment we studied the incorporation of C from labelled soil, again from a beechwood on limestone, into the tissue of the endogeic earthworm species Aporrectodea caliginosa (Savigny). The results of this experiment indicate the existence of two C pools, one more labile and one more stable, in earthworms. It is assumed that the C investment for respiration and mucus excretion is derived from the labile C pool of endogeic earthworms. [ABSTRACT FROM AUTHOR]

The physiological activity and C and N allocation of beech seedlings planted in two different beech forest soils (acid brown earth, rendzina) were studied over 80 days. One adult earthworm Octolasion lacteum (Örley) was placed in half of the containers. Transpiration, CO, assimilation, chlorophyll synthesis and N incorporation were higher in the acid brown earth than in the rendzina. Fine root production was also higher in the acid brown earth. Production of stems and total N incorporation were higher in the O. lacteum treatments than in the controls. Burrowing activity of O. lacteum did not affect total root production but stimulated the transfer of C and N towards aboveground parts of the plants and shifted the large root to fine root ratio towards large roots. O. lacteum effects were similar in both soils. It is concluded that endogeic earthworms significantly affect resource allocation patterns of beech seedlings over a wide range of soils. This effect can be partly explained by an increased availability of N in soils worked by earth-worms. [ABSTRACT FROM AUTHOR]