  We studied near-infrared disk fractions of six young clusters in the
low-metallicity environments with [O/H$] \sim -0.7$ using deep $JHK$ images
with Subaru 8.2\,m telescope. We found that disk fraction of the
low-metallicity clusters declines rapidly in $<$1\,Myr, which is much faster
than the $\sim$5--7\,Myr observed for the solar-metallicity clusters,
suggesting that disk lifetime shortens with decreasing metallicity possibly
with an $\sim$$10^Z$ dependence. Since the shorter disk lifetime reduces the
time available for planet formation, this could be one of the major reasons for
the strong planet--metallicity correlation. Although more quantitative
observational and theoretical assessments are
  necessary, our results present the first direct observational evidence
  that can contribute to explaining the planet--metallicity correlation.
