  We combine simultaneous constraints on stellar evolutionary status from
asteroseismology, and on nitrogen abundances derived from large spectroscopic
surveys, to follow nitrogen surface abundances all along the evolution of a
low-mass star, comparing model expectations with data. After testing and
calibrating the observed yields from the APOGEE survey, we first show that
nitrogen surface abundances follow the expected trend after the first dredge-up
occurred, i.e. that the more massive is the star the more nitrogen is enhanced.
Moreover, the behaviour of nitrogen data along the evolution confirms the
existence of non-canonical extra-mixing on the RGB for all low-mass stars in
the field. But more surprisingly, the data indicate that nitrogen has been
depleted between the RGB tip and the red clump. This may suggest that some
nitrogen has been burnt near or at the He flash episode.
