Column density profiles of HCN and HNC, as well as their ratio profiles, for disk models with different levels of C and O initial abundances: the fiducial model with C/O = 0.3 close to the ISM level (in purple), C and O abundances reduced by a factor of 10 (in blue) and 100 (in cyan) from fiducial values, thus with the same ISM C/O, and the C abundance reduced by a factor of 100 from fiducial values with enhanced O depletion to reach a high C/O = 1.5 (in orange).