  In-plane Nernst signal and resistivity have been measured for three
$La_{2-x}Sr_xCuO_4$ single crystals (x=0.09, 0.11 and 0.145) with the magnetic
field parallel to c-axis. A quadratic temperature dependence of resistivity,
i.e., $\rho=\rho_0+aT^2$ is observed below a certain temperature $T_R$. It is
found that the upper boundary of the Nernst signal $T_n$ coincides with $T_R$,
which points to an inherent relation between the anomalous Nernst signal and
the nodal quasiparticle transport in the pseudogap region. Finally a phase
diagram together with the pseudogap temperature $T^*$ is presented, which
suggests a second energy scale in the pseudogap region.
