  In our previous papers \cite{Li2008, Li2011}, we proved some martingale
transform representation formulas for the Riesz transforms and the
Beurling-Ahlfors transforms on complete Riemannian manifolds, and proved some
explicit $L^p$-norm estimates for these operators on complete Riemannian
manifolds with suitable curvature conditions. In this paper we correct a gap
contained in \cite{Li2008, Li2011} and prove that the $L^p$-norm of the Riesz
transforms $R_a(L)=\nabla(a-L)^{-1/2}$ can be explicitly bounded by
$C(p^*-1)^{3/2}$ if $Ric+\nabla^2\phi\geq -a$ for $a\geq 0$, and the $L^p$-norm
of the Riesz transform $R_0(L)=\nabla(-L)^{-1/2}$ is bounded by $2(p^*-1)$ if
$Ric+\nabla^2\phi=0$. We also prove that the $L^p$-norm estimates for the
Beurling-Ahlfors transforms obtained in \cite{Li2011} remain valid. Moreover,
we prove the time reversal martingale transform representation formulas for the
Riesz transforms and the Beurling-Ahlfors transforms on complete Riemannian
manifolds.
