  After a review of the many effects of metallicity on the evolution of
rotating and non-rotating stars, we discuss the consequences of a high
metallicity on massive star populations and on stellar nucleosynthesis. The
most striking effect of high metallicity is to enhance the amount of mass lost
by stellar winds. Typically at a metallicity $Z=0.001$ only 9% of the total
mass returned by non-rotating massive stars is ejected by winds (91% by
supernovae explosion), while at solar metallicity this fraction may amount to
more than 40%. High metallicity favors the formation of Wolf-Rayet stars and of
type Ib supernovae. It however disfavors the occurrence of type Ic supernovae.
We estimate empirical yields of carbon based on the observed population of WC
stars in the solar neighborhood, and obtain that WC stars eject between 0.2 and
0.4% of the mass initially locked into stars under the form of new synthesized
carbon. Models give values well in agreement with these empirical yields.
Chemical evolution models indicate that such carbon yields may have important
impacts on the abundance of carbon at high metallicity.
