Plants produce organic resources of different quantity and quality for soil organisms. In turn, the plant receives nutrients from soil organisms which mediate the nutrient remobilization by their decomposing activities. Thus, the plant links above and belowground ecosystem processes. This work aimed to demonstrate how rhizosphere microbial communities of different complexity can mediate plant foraging for light (Carbon, C) and nutrients (Nitrogen, N). Nitrogen mineralization and fluxes of C and N within the plant and between soil and plant compartments were quantified with 13C and 15N stable isotopes. We established model systems of different trophic level in planted microcosms. Our results (a) confirm the plant growth promoting effect of protozoa in showing that protozoan grazing on the bacterial community in the rhizosphere increased root and shoot surface area; (b) show that morphological effects and N uptake from soil vary among plant species; (c) demonstrate that plant N uptake from decomposing organic patches and net CO2 assimilation were stimulated when arbuscular mycorrhiza fungi and protozoa interact. Thus, we conclude that protozoa play a key role in plant nutrition through their interactions with microbial communities, highlighting the importance of biotic interactions in the rhizosphere for the productivity of both natural- and agro-ecosystems.