  We study the production of hadrons in nucleus-nucleus collisions within the
Parton-Hadron-String Dynamics (PHSD) transport approach that is extended to
incorporate essentials aspects of chiral symmetry restoration (CSR) in the
hadronic sector (via the Schwinger mechanism) on top of the deconfinement phase
transition as implemented in PHSD. The essential impact of CSR is found in the
Schwinger mechanism (for string decay) which fixes the ratio of strange to
light quark production in the hadronic medium. Our studies provide a
microscopic explanation for the maximum in the $K^+/\pi^+$ ratio at about 30 A
GeV which only shows up if in addition to CSR a deconfinement transition to
partonic degrees-of-freedom is incorporated in the reaction dynamics.
