  This paper is aimed at exploring implications of velocity dispersion scalings
on high-mass star formation in molecular clouds, including the scalings of
Larson's linewidth--size ($\sigma$--$R$) and ratio--mass surface density
($\cal{L}$--$\Sigma$; here $\cal{L}$$=\sigma/R^{0.5}$). We have systematically
analyzed the $\sigma$ parameter of well-selected 221 massive clumps,
complemented with published samples of other hierarchical density structures of
molecular clouds over spatial scales of 0.01--10 pc. Those massive clumps are
classified into four phases: quiescent, protostellar, HII region, and PDR
clumps in an evolutionary sequence. The velocity dispersion of clumps increases
overall with the evolutionary sequence, reflecting enhanced stellar feedback in
more evolved phases. The relations of $\sigma$--$R$ and $\cal{L}$--$\Sigma$ are
weak with the clump sample alone, but become evident when combined with others
spanning a much wider spatial scales. For $\sigma$--$R$, its tight relation
indicates a kinematic connection between hierarchical density structures,
supporting theoretical models of multiscale high-mass star formation. From the
$\cal{L}$--$\Sigma$ relation, cloud structures can be found to transition from
over-virial state ($\alpha_\mathrm{vir} > 2$) to sub-virial state
($\alpha_\mathrm{vir} < 2$) as they become smaller and denser, indicating a
possible shift in the governing force from turbulence to gravity. This implies
that the multiscale physical process of high-mass star formation hinges on the
self-gravity of sub-virial molecular clouds. However, the influence of
turbulence may not be dismissed until large-scale clouds attain a sub-virial
state. This is pending confirmation from future multiscale kinematic
observations of molecular clouds with uniform observing settings.
