  We address the in-plane pressure-dependent electrodynamics of graphite
through synchrotron based infrared spectroscopy and ab initio Density
Functional Theory calculations. The Drude term remarkably increases upon
pressure application, as a consequence of an enhancement of both electron and
hole charge densities. This is due to the growth of the band dispersion along
the k_z direction between the K and H points of the Brillouin zone. On the
other hand, the mid-infrared optical conductivity between 800 and 5000 cm-1 is
almost flat, and very weakly pressure dependent, at least up to 7 GPa. This
demonstrates a surprising robustness of the graphene-like universal quantum
conductance of graphite, even when the interlayer distance is significantly
reduced.
