Roots of most terrestrial plants interact with arbuscular mycorrhizală (AM) fungi and soil protozoa with each individually increasing nitrogenă (N) supply to plants and plant growth. We investigated if AM fungi andă protozoa interactively affect plant N acquisition and growth. We usedă stable isotopes (N-15, C-13) to assess plant N uptake, C fixation and Că partitioning. Shifts in the microbial community structure were evaluatedă by analysing phospholipid fatty acids. Protozoa and AM fungi enhancedă plant N uptake. Protozoa mobilized N from bacterial biomass and AM fungiă increased the translocation of the mobilized N to the host plant; ifă both were present, plant biomass, C fixation and C allocation to rootsă increased twofold. Protozoa alone and in the presence of AM fungiă altered microbial activity and community structure in the rhizosphere.ă The results indicate that plant N uptake via mycorrhizal symbiosisă strongly benefits from the presence of protozoa.