  Let $G$ be a Polish locally compact group acting on a Polish space $X$ with a
$G$-invariant probability measure $\mu$. We factorize the integral with respect
to $\mu$ in terms of the integrals with respect to the ergodic measures on $X$,
and show that $\mathrm{L}^p(X,\mu)$ ($1\leq p<\infty$) is $G$-equivariantly
isometrically lattice isomorphic to an $\mathrm{L}^p$-direct integral of the
spaces $\mathrm{L}^{p}(X,\lambda)$, where $\lambda$ ranges over the ergodic
measures on $X$. This yields a disintegration of the canonical representation
of $G$ as isometric lattice automorphisms of $\mathrm{L}^p(X,\mu)$ as an
$\mathrm{L}^p$-direct integral of order indecomposable representations.
  If $(X^\prime,\mu^\prime)$ is a probability space, and, for some $1\leq
q<\infty$, $G$ acts in a strongly continuous manner on
$\mathrm{L}^q(X^\prime,\mu^\prime)$ as isometric lattice automorphisms that
leave the constants fixed, then $G$ acts on
$\mathrm{L}^{p}(X^{\prime},\mu^{\prime})$ in a similar fashion for all $1\leq
p<\infty$. Moreover, there exists an alternative model in which these
representations originate from a continuous action of $G$ on a compact
Hausdorff space. If $(X^\prime,\mu^\prime)$ is separable, the representation of
$G$ on $\mathrm{L}^p(X^\prime,\mu^\prime)$ can then be disintegrated into order
indecomposable representations.
  The notions of $\mathrm{L}^p$-direct integrals of Banach spaces and
representations that are developed extend those in the literature.
