  The spin and quasiparticle relaxation dynamics in
La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ and LaMnO$_{3}$ single crystals and thin films
is investigated as a function of temperature and magnetic field by pump-probe
spectroscopy. The unusually slow spin-lattice relaxation dynamics is governed
by the temperature- and magnetic field- dependent pseudogap in
La$_{0.67}$Ca$_{0.33}$MnO$_{3}$, and by the temperature-independent Jahn-Teller
gap in LaMnO$_{3}$. Our results show that the coupled dynamics of charge, spin
and lattice is strongly correlated with the distinct gap structures in these
manganites.
