  Motivated by recent simulations of sunspot formation, we extend the theory of
the pressure difference between magnetized and non-magnetized gas by Dicke to
include rotating turbulence. While the (vertical) background field provides a
positive-definite magnetic pressure difference between the magnetized and the
unmagnetized gas, Reynolds stress and Maxwell stress of turbulence strongly
modify this result. With the quasilinear approximation we demonstrate that the
influence of the turbulence differs between the high-conductivity and the
low-conductivity limits. Sufficiently small magnetic Reynolds numbers lead to
magnetic pressure suppression where indeed the pressure excess can even assume
negative values. Box simulations of magnetoconvection subject to a vertical
magnetic field carried out with the Nirvana code confirm this overall picture.
They also demonstrate how a global rotation {\em reduces} the negative magnetic
pressure effect. For rapid rotation the total magnetic pressure difference
caused by large-scale magnetic fields { and} turbulence even fully disappears
for small field strengths. Magnetic fields of moderate strength thus neither
reduce nor enhance the turbulence pressure of rapidly rotating convection.
Consequences of this phenomenon for the star formation efficiency are shortly
discussed.
