  Exploring the Galactic chemical evolution and enrichment scenarios with open
clusters allows us to understand the history of the Milky Way disk.
High-resolution spectra of OCs are a crucial tool, as they provide precise
chemical information, to combine with precise distances and ages. The aim of
the Stellar Population Astrophysics project is to derive homogeneous and
accurate comprehensive chemical characterization of a number of poorly studied
OCs.Using the HARPS-N echelle spectrograph at the Telescopio Nazionale Galileo,
we obtained high-resolution spectra of giant stars in 18 OCs, 16 of which are
chemically characterized for the first time, and two of which are well studied
for comparison. The OCs in this sample have ages from a few tens of Myr to 4
Gyr, with a prevalence of young clusters. We already presented the radial
velocities and atmospheric parameters for them in a previous SPA paper. Here,
we present results for the alpha-elements O, and the light elements, all
determined by the equivalent width method. We also measured Li abundance
through the synthesis method.We discuss the behaviors of lithium, sodium and
aluminum in the context of stellar evolution. We study the radial, vertical,
and age trends for the measured abundance ratios in a sample that combines our
results and recent literature for OCs, finding significant gradients only for
[Mg/Fe] and [Ca/Fe] in all cases. Finally,we compare O and Mg in the combined
sample with chemo-dynamical models, finding a good agreement for
intermediate-age and old clusters. There is a sharp increase in the abundance
ratios measured among very young clusters, accompanied by a poorer fit with the
models for O and Mg, likely related to the inadequacy of traditional model
atmospheres and methods in the derivation of atmospheric parameters and
abundance ratios for stars of such young ages
