  The generic form of spacetime dynamics as a classical gauge field theory has
recently been derived, based on only the action principle and on the Principle
of General Relativity. It was thus shown that Einstein's General Relativity is
the special case where (i) the Hilbert Lagrangian (essentially the Ricci
scalar) is supposed to describe the dynamics of the "free" (uncoupled)
gravitational field, and (ii) the energy-momentum tensor is that of scalar
fields representing real or complex structureless (spin-$0$) particles. It
followed that all other source fields---such as vector fields representing
massive and non-massive spin-$1$ particles---need careful scrutiny of the
appropriate source tensor. This is the subject of our actual paper: we discuss
in detail the coupling of the gravitational field with (i) a massive complex
scalar field, (ii) a massive real vector field, and (iii) a massless vector
field. We show that different couplings emerge for massive and non-massive
vector fields. The \emph{massive} vector field has the \emph{canonical}
energy-momentum tensor as the appropriate source term---which embraces also the
energy density furnished by the internal spin. In this case, the vector fields
are shown to generate a torsion of spacetime. In contrast, the system of a
\emph{massless} and charged vector field is associated with the \emph{metric}
(Hilbert) energy-momentum tensor due to its additional $\mathrm{U}(1)$
symmetry. Moreover, such vector fields do not generate a torsion of spacetime.
The respective sources of gravitation apply for all models of the dynamics of
the `free' (uncoupled) gravitational field---which do not follow from the gauge
formalism but must be specified based on separate physical reasoning.
