Free‐living nematodes as prey for higher trophic levels of forest soil food webs

Abstract

Nematodes are the most abundant invertebrates in soils and are key prey in soil food webs. Uncovering their contribution to predator nutrition is essential for understanding the structure of soil food webs and the way energy channels through soil systems. Molecular gut content analysis of consumers of nematodes, such as soil microarthropods, using specific DNA markers is a novel approach for studying predator–prey interactions in soil. We designed new specific primer pairs (partial 18S rDNA) for individual soil‐living bacterial‐feeding nematode taxa (Acrobeloides buetschlii, Panagrellus redivivus, Plectus velox and Plectus minimus). Primer specificity was tested against more than 100 non‐target soil organisms. Further, we determined how long nematode DNA can be traced in the gut of predators. Potential predators were identified in laboratory experiments including nine soil mite (Oribatida, Gamasina and Uropodina) and ten springtail species (Collembola). Finally, the approach was tested under field conditions by analyzing five mite and three collembola species for feeding on the three target nematode species. The results proved the three primer sets to specifically amplify DNA of the respective nematode taxa. Detection time of nematode DNA in predators varied with time of prey exposure. Further, consumption of nematodes in the laboratory varied with microarthropod species. Our field study is the first definitive proof that free‐living nematodes are important prey for a wide range of soil microarthropods including those commonly regarded as detritivores. Overall, the results highlight the eminent role of nematodes as prey in soil food webs and for channelling bacterial carbon to higher trophic levels.

Roots rather than shoot residues drive soil arthropod communities of arable fields

“…Further, similar high incorporation of maize C into predator and decomposer taxa suggests that in arable fields the flow of C is not only channelled from meso-and macrofauna decomposers to predators but also via prey groups not included in our analyses, presumably nematodes. Supporting this assumption, herbivorous nematodes reached high densities at our study site in July 2010 (Scharroba et al 2012), and the studied predators were dominated by Gamasida and Collembola which have been shown to prey heavily on nematodes (Read et al 2006;Klarner et al 2013;Heidemann et al 2014).…”

“…and P. crassipes preferentially incorporated root-as compared to shoot-derived maize C, suggesting that their prey taxa predominantly live on root-derived resources. Nematodes contribute substantially to the diet of predatory Collembola and Gamasida (Klarner et al 2013;Heidemann et al 2014); therefore, the high proportions of root-derived C in these species suggest predation on nematodes, in particular those feeding on roots. In addition, large-bodied predators such as Carabidae larvae presumably preyed heavily on Collembola or other small soil arthropods that rely on root-derived resources.…”

Trophic consistency of supraspecific taxa in below‐ground invertebrate communities: Comparison across lineages and taxonomic ranks

“…The stronger correlation between taxonomic and Δ 15 N dissimilarity as compared to Δ 13 C dissimilarity suggests that switching between prey of different trophic levels is evolutionary difficult resulting in taxa being conserved within their trophic level. Despite there are examples of predatory species in detritivore lineages such as Collembola (Hopkin, ; Potapov et al, ) and Oribatida (Heidemann et al, ; Maraun et al, ), they likely represent only a minority of the species of these groups. Notably, isotopic dissimilarity increased steadily from the species to the class level, but decreased thereafter, suggesting that the differences in trophic level between taxa were established early in the evolution of these lineages, that is during the colonization of land by the major arthropod lineages, and diversification within these lineages was associated by refinement of trophic niches (Rota‐Stabelli, Daley, & Pisani, ; Schaefer, Norton, Scheu, & Maraun, ).…”

Effects of environmental warming and drought on size‐structured soil food webs

“…These communities provide essential functions for primary production in general and agriculture in particular including nutrient cycling, carbon sequestration, and litter decomposition. Despite their importance, soil organisms and their interactions are still poorly understood (Wolters , Ruess and Chamberlain , but see Digel et al , Ferlian and Scheu , Günther et al , Heidemann et al ) and mechanistic insights on climate change effects are scarce (Brose et al ).…”