The AMBRE project: a study of Li evolution in the Galactic thin and
  thick discs
  Recent observations suggest a "double-branch" behaviour of Li/H versus
metallicity in the local thick and thin discs. This is reminiscent of the
corresponding O/Fe versus Fe/H behaviour, which has been explained as resulting
from radial migration in the Milky Way disc. We use a semi-analytical model of
disc evolution with updated chemical yields and parameterised radial migration.
We explore the cases of long-lived (red giants of a few Gy lifetime) and
shorter-lived (Asymptotic Giant Branch stars of several 10$^8$ yr) stellar
sources of Li, as well as those of low and high primordial Li. We show that
both factors play a key role in the overall Li evolution. We find that the
observed "two-branch" Li behaviour is only directly obtained in the case of
long-lived stellar Li sources and low primordial Li. In all other cases, the
data imply systematic Li depletion in stellar envelopes, thus no simple picture
of the Li evolution can be obtained. This concerns also the reported Li/H
decrease at supersolar metallicities.
