The evaluation of entomopathogenic nematode soil food web assemblages across Switzerland reveals major differences among agricultural, grassland and forest ecosystems

Entomopathogenic nematodes (EPNs) occur in natural and agricultural soils and contribute to the control of soil dwelling insect pests. Ecosystems differ in their soil parameters (pH, moisture, texture, etc.) and microhabitat conditions (presence of roots, plant cover, belowground fauna, etc.), which can affect the EPN soil food web assemblage in an unpredictable manner. By comparing soils that represent different ecological scenarios, we can link the natural distribution of the EPN to abiotic and biotic factors that shape the assemblages of soil food web to unravel the factors that determine EPN abundance and activity. We hypothesized that the EPN soil food web assemblages are affected by agricultural management practices and that this should be reflected when compared to natural ecosystems, such as forests and grasslands. By combining traditional and state-of-the-art molecular tools, we targeted 25 soil organisms to explore EPN food web in 40 Swiss georeferenced sites that can be categorized as "agricultural area", "forest", and "grassland". EPNs abundance, richness and diversity did not vary among the different ecosystems. However, EPN activity (capability to kill insects) was higher in grasslands. Similarly, the free-living nematodes (FLNs) that compete with EPN for the cadavers were much more abundant in grassland, while reduced in the forest soils, suggesting contrasting conditions between these two natural areas. Nematophagous fungi (NF) were more diverse and present in agricultural areas, suggesting that the abiotic conditions in the agricultural areas may favor NF presence. Six soil properties and environmental factors shaped the EPN soil food web in Swiss soils (pH, elevation, clay content, soil water content, temperature, and rainfall), which explained 54% of the community variation in multivariate analysis. These observations were consistent with the key abiotic variables described for subtropical and Mediterranean regions. Identifying the links between the abiotic and biotic factors in very distinct areas can be the basis for predicting EPN soil food web assemblages. Such information can be of value for developing strategies to favour EPN resilience in a changing environment and enhance their capacity as biocontrol agents.