  We report a significantly tighter trend between gaseous N/O and $M_*/R_e$ (a
proxy for gravitational potential) than has previously been reported between
gaseous metallicity and $M_*/R_e$, for star-forming galaxies in the MaNGA
survey. We argue this result to be a consequence of deeper potential wells
conferring greater resistance to metal outflows while also being associated
with earlier star-formation histories, combined with N/O being comparatively
unaffected by metal-poor inflows. The potential-N/O relation thus appears to be
both more resistant to short-timescale baryonic processes and also more
reflective of a galaxy's chemical evolution state, when compared to
previously-considered relations.
