  Let X be a normal affine algebraic variety with regular action of a torus \TT
and T\subset\TT be a subtorus. We prove that each root of X with respect to T
can be obtained by restriction of some root of X with respect to \TT. This
allows to get an elementary proof of the description of roots of the affine
Cremona group. Several results on restriction of roots in the case of subtorus
action on an affine toric variety are obtained.
