  The plasmoid instability in evolving current sheets has been widely studied
due to its effects on the disruption of current sheets, the formation of
plasmoids, and the resultant fast magnetic reconnection. In this Letter, we
study the role of the plasmoid instability in two-dimensional
magnetohydrodynamic (MHD) turbulence by means of high-resolution direct
numerical simulations. At sufficiently large magnetic Reynolds number
($R_m=10^6$), the combined effects of dynamic alignment and turbulent
intermittency lead to a copious formation of plasmoids in a multitude of
intense current sheets. The disruption of current sheet structures facilitates
the energy cascade towards small scales, leading to the breaking and steepening
of the energy spectrum. In the plasmoid-mediated regime, the energy spectrum
displays a scaling that is close to the spectral index $-2.2$ as proposed by
recent analytic theories. We also demonstrate that the scale-dependent dynamic
alignment exists in 2D MHD turbulence and the corresponding slope of the
alignment angle is close to 0.25.

Plasma Physics;High Energy Astrophysical Phenomena;Solar and Stellar Astrophysics;Fluid Dynamics;Space Physics