Showing papers by "Volkmar Wolters published in 2003"

C and N mineralisation in the decomposer food webs of a European forest transect

Abstract: Schro¨ter, D., Wolters, V. and De Ruiter, P. C. 2003. C and N mineralisation in thedecomposer food webs of a European forest transect. – Oikos 102: 294–308.Belowground processes are essential for the overall carbon and nitrogen fluxes inforests. Neither the functioning of the soil food web mediating these fluxes, nor itsmodulation by environmental factors is sufficiently understood. In this study thebelowground carbon and nitrogen mineralisation of four European coniferous forestsites (northern Sweden to north-east France) with different climate and N deposi-tional inputs was analysed by investigating the soil food webs using field observationsand modelling. The soil fauna directly contributed 7–13% to C mineralisation,among which the testate amoebae (Protozoa) made the largest contribution. Micro-bial grazing was suggested to have an important indirect effect by stimulatingbacterial turnover. Due to relatively high C:N ratios of their substrate, bacteriaimmobilized N, while the fauna i.e. testate amoebae, nematodes, microarthropodsand enchytraeids, counteracted this N immobilisation.Despite similar food web biomass, the sites differed with respect to food webstructure and C and N flows. Model calculations suggested a significant influence offood web structure on soil ecosystem processes in addition to environmental factorsand resource quality. Mineralisation rates were lowest at the low N input boreal sitewith a food web dominated by fungal pathways. Further south, as N availabilityincreased, bacterial pathways became more important and the cycling of C and Nwas faster. The bioavailability of degradable C sources is suggested to be a limitingfactor for microbial activity and overall mineralisation rates. In this respect, above-and belowground interactions e.g. transfers of labile C sources from the vegetation tothe decomposer system deserve further attention.Our study revealed the combined effects of climate and nutrient inputs to ecosys-tems and the subsequent changes in the structure and functioning of the systems. Ifdecomposition, and therefore carbon loss, is stimulated as a consequence of struc-tural and/or nutritional changes, resulting for example from continuous industrial Nemission, the storage capacity of forest ecosystems could be altered.

Successional changes of Collembola and soil microbiota during forest rotation

Abstract: Dynamic approaches to forest ecosystems are surprisingly rare. Here we report about successional changes in collembolan community structure and microbial performances during forest rotation. The study was carried out in a chronosequence of four spruce forest stands (5-, 25-, 45-, and 95 years old; Tharandter forest, Germany). CO2 release significantly increased after clear-cutting and the amount of C stored in the organic layer subsequently declined. The early phase of forest rotation was characterized by a very active decomposer microflora, stimulation of both fungi and bacteria as well as by a high abundance of surface-oriented Collembola. In addition, collembolan species turnover was accelerated. While the biomass of fungi further increased at intermediate stages of forest rotation, the metabolic activity of the microflora was low, the functional diversity of bacteria declined and the collembolan community became impoverished. Euedaphic species dominated during this stage of forest development. These changes can be explained by both reduction in microhabitat diversity and depletion of food sources associated with an accumulation of recalcitrant soil organic matter. Results of the General Regression Model procedure indicate a shift from specific associations between collembolan functional groups and microbiota at the early stage of forest rotation to a more diffuse pattern at intermediate stages. Though the hypothesis that Collembola are relatively responsive to changes in environmental conditions is confirmed, consistently high community similarity suggests a remarkable persistence of some components of microarthropod assemblages. Our study provides evidence for substantial ecosystem-level implications of changes in the soil food web during forest rotation. Moreover, correlations between bacterial parameters and Collembola point to the overarching impact of differences in the composition of the microbial community on microarthropods.

Design and evaluation of nematode 18S rDNA primers for PCR and denaturing gradient gel electrophoresis (DGGE) of soil community DNA

Abstract: Consensus nematode 18S ribosomal DNA primers were designed by aligning available 18S sequences and identifying a variable region flanked by highly conserved regions. These primers were then used to amplify nematode 18S rDNA from whole soil community DNA extracted from a range of European grassland types. Cloning of the PCR amplicons (778 bp) followed by restriction digest analysis (RFLP) resulted in the recovery of 34 unique nematode sequences from the four grasslands studied. Comparison of these data with the limited number of 18S rDNA nematode sequences currently held in on-line databases revealed that all of the sequences could be assigned to known nematode taxa albeit tentatively in some cases. Two of the sequences recovered from the site in the Netherlands (wet, hay-grassland) were recovered in a clade that included a sequence of the genus Trichodorus whilst other sequences from this site showed similarity with 18S rDNA sequences of the genus Prismatolaimus (five sequences), Xiphinema (one sequence) and Enoplus (one sequence). Of the remaining sequences, two showed some affinity with Mylonchulus (UK, upland peat), four with Steinernema (UK) and one sequence with Mesorhabditis (Hungary, east European Steppe). Three sequences from the Netherlands and one from Hungary were recovered in a clade that included a sequence of the genus Pratylenchoides whilst three further sequences from the Netherlands and two from Hungary were recovered in a clade encompassing the genus Globodera. Of the remaining nine sequences, two (NL6, NL62) formed a distinct lineage within the Adenophorea with 90% bootstrap recovery in a paraphyletic clade that included sequences of Prismatolaimus and Trichodorus. Seven sequences (three from the Netherlands, three from the UK and one from Greece) were left unassigned though the tree topology suggested some relationship (58% bootstrap recovery) with the genus Cephalobus. To assess whether primers used to amplify 18S rDNA might be used to fingerprint genetic diversity in nematode communities in soil, the environmental sequence data were used to design a second set of primers carrying a GC-clamp. These primers amplified a 469 bp fragment internal to the region flanked by the primer set used to derive the nematode trees and were used to amplify 18S rDNA for subsequent analysis using denaturing gradient gel electrophoresis (DGGE). DGGE analysis of six major European grassland types revealed considerable genetic diversity between sites. However, the relationships seen with the DGGE data were inconsistent with previous studies where the same soils had been characterized with respect to functional and morphological diversity. To confirm that this second set of primers was amplifying nematode sequences, selected bands on the DGGE gels were extracted, PCR amplified and sequenced. The final alignment was 337 bases. These analyses revealed the presence of sequence signatures from the genera Paratrichodorus, Plectus, Steinernema, Globodera, Cephalobus and Pratylenchoides.

Isolation and characterization of microsatellite loci in the ant Myrmica scabrinodis

Abstract: Five polymorphic microsatellite loci were developed for the ant Myrmica scabrinodis using a magnetic bead hybridization selection protocol The number of alleles per locus varied between three and six Cross-species amplification of four of the loci yielded positive amplification products in four Myrmica species, suggesting their general suitability for microsatellite analysis within this taxonomic group