  Magnetohydrodynamic (MHD) turbulence is pervasive in astrophysical systems.
Recent high-resolution numerical simulations suggest that the energy spectrum
of strong incompressible MHD turbulence is $E(k_{\perp})\propto
k_{\perp}^{-3/2}$. So far, there has been no phenomenological theory that
simultaneously explains this spectrum and satisfies the exact analytic
relations for MHD turbulence due to Politano & Pouquet. Indeed, the
Politano-Pouquet relations are often invoked to suggest that the spectrum of
MHD turbulence instead has the Kolmogorov scaling -5/3. Using geometrical
arguments and numerical tests, here we analyze this seeming contradiction and
demonstrate that the -3/2 scaling and the Politano-Pouquet relations are
reconciled by the phenomenon of scale-dependent dynamic alignment that was
recently discovered in MHD turbulence.
