  Let $\mathfrak A$ be a type 1 subdiagonal algebra in a $\sigma$-finite von
Neumann algebra $\mathcal M$ with respect to a faithful normal conditional
expectation $\Phi$. We consider a Riesz type factorization theorem in
noncommutative $H^p$ spaces associated with $\mathfrak A$. It is shown that if
$1\leq r,p,q<\infty$ such that $\frac1r=\frac1p+\frac1q$, then for any $h\in
H^r$, there exist $h_p\in H^p$ and $h_q\in H^q$ such that $h=h_ph_q$. Beurling
type invariant subspace theorem for noncommutative $L^p(1< p<\infty)$ space is
obtained. Furthermore, we show that a $\sigma$-weakly closed subalgebra
containing $\mathfrak A$ of $\mathcal M$ is also a type 1 subdiagonal algebra.
As an application, We prove that the relative invariant subspace lattice
$Lat_{\mathcal M}\mathfrak A$ of $\mathfrak A$ in $\mathcal M$ is commutative.
