  There is an intriguing discrepancy between \alpha_s(M_Z) values measured
directly at the CERN $Z_0$-factory and low-energy (at few GeV) measurements
transformed to $Q=M_{Z_0}$ by a massless QCD \alpha_s(Q) evolution relation.
There exists an attempt to reconcile this discrepancy by introducing a light
gluino $\gl$ in the MSSM.
  We study in detail the influence of heavy thresholds on \alpha_s(Q)
evolution. First, we consruct the "exact" explicit solution to the
mass-dependent two-loop RG equation for the running \alpha_s(Q). This solution
describes heavy thresholds smoothly. Second, we use this solution to
recalculate anew \alpha_s(M_Z) values corresponding to "low-energy" input data.
Our analysis demonstrates that using {\it mass-dependent RG procedure}
generally produces corrections of two types: Asymptotic correction due to
effective shift of threshold position; Local threshold correction only for the
case when input experiment lies in the close vicinity of heavy particle
threshold: $Q_{expt} \simeq M_h $.
  Both effects result in the effective shift of the \asmz values of the order
of $10^{-3}$. However, the second one could be enhanced when the gluino mass is
close to a heavy quark mass. For such a case the sum effect could be important
for the discussion of the light gluino existence as it further changes the
$\gl$ mass.
