  Dwarf stars with debris discs and planets appear to be excellent laboratories
to study the core accretion theory of planets formation. These systems are
however, insufficiently studied. In this paper we present the main metallicity
and lithium abundance properties of these stars together with stars with only
debris discs and stars with only planets. Stars without detected planets nor
discs are also considered. The analysed sample is formed by main-sequence FGK
field single stars. Apart from the basic stellar parameters, we include the use
of dusty discs masses. The main results show for the first time that the dust
mass of debris disc stars with planets correlate with metallicity. We confirm
that these disc dust masses are related to their central stellar masses.
Separately, the masses of stars and those of planets also correlate with
metallicity. We conclude that two conditions are necessary to form giant
planets: to have a sufficient metallicity and also a sufficient protoplanetary
mass of gas and dust. The debris discs masses of stars without giant planets do
not correlate with metallicity, because they do not fulfil these two
conditions. Concerning lithium, by adopting a stellar model for lithium
depletion based on a strong interaction between the star and a protoplanetary
disc, we found that in agreement with the model predictions, observations
indicate that the main lithium depletion occurs during this initial
protoplanetary evolution stage. We show that the ultimately lithium depletion
is independent of the presence or absence of planets and appears to be only age
dependent.
