  We demonstrate tuning of two-dimensional (2D) plasmon spectrum in
modulation-doped AlAs quantum wells via the application of in-plane uniaxial
strain. We show that dramatic change in the plasma spectrum is caused by
strain-induced redistribution of charge carriers between anisotropic $X_x$ and
$X_y$ valleys. Discovered piezoplasmonic effect provides a tool to study the
band structure of 2D systems. We use piezoplasmonic effect to measure how the
inter-valley energy splitting depends on the deformation. This dependency
yields the AlAs deformation potential of $E_2 = (5.6 \pm 0.3)$~eV.
