  We investigate hadron production and attenuation of hadrons with strange and
charm quarks (or antiquarks) as well as high transverse momentum hadrons in
relativistic nucleus-nucleus collisions from 2 AGeV to 21.3 ATeV within two
independent transport approaches (UrQMD and HSD). Both transport models are
based on quark, diquark, string and hadronic degrees of freedom, but do not
include any explicit phase transition to a quark-gluon plasma. From our
dynamical calculations we find that both models do not describe the maximum in
the $K^+/\pi^+$ ratio at 20 - 30 AGeV in central Au+Au collisions found
experimentally, though the excitation functions of strange mesons are
reproduced well in HSD and UrQMD. Furthermore, the transport calculations show
that the charmonium recreation by $D+\bar{D} \to J/\Psi + meson$ reactions is
comparable to the dissociation by 'comoving' mesons at RHIC energies contrary
to SPS energies. This leads to the final result that the total $J/\Psi$
suppression as a function of centrality at RHIC should be less than the
suppression seen at SPS energies where the 'comover' dissociation is
substantial and the backward channels play no role. Furthermore, our transport
calculations -- in comparison to experimental data on transverse momentum
spectra from $pp$, d+Au and Au+Au reactions -- show that pre-hadronic effects
are responsible for both the hardening of the hadron spectra for low transverse
momenta (Cronin effect) as well as the suppression of high $p_T$ hadrons. The
mutual interactions of formed hadrons are found to be negligible in central
Au+Au collisions at $\sqrt{s}$ = 200 GeV for $p_T \geq$ 6 GeV/c and the
sizeable suppression seen experimentally is attributed to a large extent to the
interactions of 'leading' pre-hadrons with the dense environment.
