Detailed mapping of spatial distribution patterns of terrestrial nematodes at landscape scale reveals distinct, ecologically relevant patterns

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 mainly technical reasons; the microscopic analysis of nematode assemblages is labour intensive and requires extensive expertise. With the availability of relatively large molecular frameworks, it became possible to design molecular assays that allow for the quantitative analysis of individual taxa against complex DNA backgrounds. Quantitative (q) PCR assays were used to explore spatial distribution patterns of 45 individual taxa (at family, genus and species level) across the Netherlands at mesoscale (plot or field – scale dimensions: 1 – 1,000 m). Fields were located in two systems (nine arable fields and three grasslands with high plant diversity) and three soil types (marine clay, river clay and sand). In each field 100 composite samples were collected by using a sampling grid (100 x 100m) optimized for geostatistic analysis. Each sample (n >1,200) was analyzed with about 25 - 30 nematode taxon specific molecular assays. In total over 35,000 qPCR reactions were run. Spatial patterns of nematode taxa were mapped by using Integrated Nested Laplace Approximation (INLA) in combination with geostatistical modeling. Patchiness might be related to either nematode traits, such as feeding strategy, body size and colonizer-persister (c-p) scale, or the characteristics of the environment, such as system, soil type and other abiotic conditions. The results that will be presented show a great variation in distribution patterns among nematode taxa, not only on the basis of their traits but also based on environmental characteristics. These data are essential for the design of scientifically sound sampling schemes for nematodes in agricultural and natural soil at hectare scale and above.