Nematodes are by far the most abundant fauna in agricultural soil, but despite their putative crucial role for soil functions, our fundamental knowledge on soil nematode functions is extremely limited. Building on our expertise from the past decade, we will investigate how bacterivorous, herbivorous and fungivorous nematodes impact nitrogen mineralization and plant growth. We will test the hypothesis that the impact of nematodes is mainly indirect, through their effects on root morphology (architecture), root exudation, and on the composition of the soil microbial community. This will be done using a highly original combination of state-of-the-art techniques (dedicated soil microcosms, selective removal of metazoa using precisely administered gamma-irradiation, X-ray µCT visualization of root traits, metagenome sequencing and 16S and ITS amplicon sequencing), within a unique multidisciplinary consortium.