  Following up our recent analysis devoted to the impact of non steady
accretion on the location of young low-mass stars or brown dwarfs in the
Herzsprung-Russell diagram, we perform a detailed analysis devoted to the
effect of burst accretion on the internal structure of low-mass and solar type
stars. We find that episodic accretion can produce objects with significantly
higher central temperatures than the ones of the non accreting counterparts of
same mass and age. As a consequence, lithium depletion can be severely enhanced
in these objects. This provides a natural explanation for the unexpected level
of lithium depletion observed in young objects for the inferred age of their
parent cluster. These results confirm the limited reliability of lithium
abundance as a criterion for assessing or rejecting cluster membership. They
also show that lithium is not a reliable age indicator, because its fate
strongly depends on the past accretion history of the star. Under the
assumption that giant planets primarily form in massive disks prone to
gravitational instability and thus to accretion burst episodes, the same
analysis also explains the higher Li depletion observed in planet hosting
stars. At last, we show that, depending on the burst rate and intensity,
accretion outbursts can produce solar mass stars with lower convective envelope
masses, at ages less than a few tens of Myr, than predicted by standard (non or
slowly accreting) pre-main sequence models. This result has interesting,
although speculative, implications for the recently discovered depletion of
refractory elements in the Sun.
