Radial abundance profiles of the main N-bearing volatile molecules in the gas phase (dotted lines) and in the ice phase (solid lines) in the disc midplane after 3 Myr of evolution with the time-dependent model (full model). The results are shown for the four chemical scenarios and the three investigated grain sizes assuming α = 10^-3. The horizontal small arrows indicate the initial abundance of N₂ and NH₃ in the gas phase in the inheritance scenario (see also Table 2).