  The rotational influence on the eddy-diffusivity tensor D_ij for anisotropic
turbulence fields is considered in order to explain the lithium decay law
during the spin-down process of solar-type stars. Rotation proves to be highly
effective in the transfer of chemicals through the solar tachocline (beneath
the convection zone) which is assumed to contain only turbulence with
horizontal motions. The effect is so strong that the tachocline turbulence must
not exceed a limit of ~10^-(3...4) of the rms velocity in the convection zone
in order to let the lithium survive after Gigayears. Such long depletion times
can also be explained by a very small rotational influence upon the
eddy-diffusion tensor if it is realized with correlation times shorter than 15
min. It is argued that such slow and/or short-living turbulence beneath the
convection zone could hardly drive the solar dynamo. In our theory the
diffusion remains small for rapid rotation due to the rotational quenching of
the turbulence. In young stellar clusters like Pleiades, there should be a
(positive) correlation between rotation rate and lithium abundance, where the
fastest stars should have maximal lithium. First inspections of the data seem
to confirm this finding.
