  Chemical abundances and abundance ratios measured in galaxies provide
precious information about the mechanisms, modes and time scales of the
assembly of cosmic structures. Yet, the nucleogenesis and chemical evolution of
elements heavier than helium are dictated mostly by the physics of the stars
and the shape of the stellar mass spectrum. In particular, estimates of CNO
isotopic abundances in the hot, dusty media of high-redshift starburst galaxies
offer a unique glimpse into the shape of the stellar initial mass function
(IMF) in extreme environments that can not be accessed with direct observations
(star counts). Underlying uncertainties in stellar evolution and
nucleosynthesis theory, however, may hurt our chances of getting a firm grasp
of the IMF in these galaxies. In this work, we adopt new yields for massive
stars, covering different initial rotational velocities. First, we implement
the new yield set in a well-tested chemical evolution model for the Milky Way.
The calibrated model is then adapted to the specific case of a prototype
submillimeter galaxy (SMG). We show that, if the formation of fast-rotating
stars is favoured in the turbulent medium of violently star-forming galaxies
irrespective of metallicity, the IMF needs to be skewed towards high-mass stars
in order to explain the CNO isotope ratios observed in SMGs. If, instead,
stellar rotation becomes negligible beyond a given metallicity threshold, as is
the case for our own Galaxy, there is no need to invoke a top-heavy IMF in
starbursts.
