Geostatistical analysis of nematode taxa on hectare scale provide essential knowledge to monitor the ecological impact of bio-based crops and residues

Because of their abundance, their trophic diversity and their relatively straightforward extractability, nematodes have a potential as a proxy for the biological condition of soils and sediments. So far the potential of this group is underexploited for technical reasons; the microscopic analysis of nematode assemblages is labour intensive and requires extensive expertise. With the availability of a relatively large molecular framework, it became possible to design molecular assays that allow for the quantitative analysis of individual taxa against complex DNA backgrounds (Vervoort et al. 2012). The availability of high throughput tools to monitor nematode assemblages makes it possible to investigate the spatial distribution of nematode taxa at field level. In order to assess the degree of patchiness of individual nematode taxa (and this relates directly to the strategy that should be used to sample them), 12 fields (4 from each marine clay, river clay and sandy soils) of a single hectare each were investigated in great detail. Using a sampling grid optimized for geostatistic analysis, 96 composite samples were taken from each of these fields. Each of these samples were analysed with 24 molecular assays (corresponding to 23 nematode taxa and one internal control). In total over 30,000 qPCR reactions were run, a preliminary results (visualized as semi-variograms and surface maps) show a great variation in distribution patterns not only on the basis of nematode taxa but also based on soil type. The data that will be presented are essential for the design of scientifically sound sampling schemes to monitor the ecological impact of bio-based crops and residues on arable field scale.