The carbon (C) and nitrogen (N) cycles in soil are tightly coupled, but research on N cycling has largely ignored the role of microfauna and their interactions with plant roots, bacteria and fungi in the flow of rhizodeposits in soil. We will set up unique multitrophic experiments controlling for the presence of specific trophic groups of nematodes and their combinations, to assess how herbivorous nematodes control rhizodeposition, the cascading of this root derived carbon to the microbial community, bacterivorous and fungivorous nematodes, and the feedback mechanisms on plant (roots). To this end, we will use 13C stable isotope labelling to track the rhizodeposition as a function of time, and its redistribution over the soil decomposer community. We will monitor the evolution of root trait development using both destructive and non-destructive methods, and assess how the activity of microfauna controls this development, both directly and indirectly. We will also investigate for the first time how specifically designed nematode trophic groups affect soil N cycling and plant performance in field conditions. Finally, this project will produce unique data that should allow to critically evaluate existing soil food web models, and propose new concepts for such models, and that may allow to increase our prediction of N dynamics in biogeochemical simulation models.