Fig. 5. Evolution of abundance gradients (expressed in dex/kpc) in the Milky Way disk (range: 4-14 kpc from the centre), in the framework of the model presented in Sect. 2 and with the WW95 metallicity dependent yields. Because of the inside-out formation scheme adopted here, gradients were steeper in the past. Because of the metallicity dependence of the yields of WW95, some elements, like N or Mg, have larger abundance gradients (in absolute value) than O. This is also the case for Fe, but the reason is its production mostly by SNIa.