Beta-function of Bruhat--Tits buildings and deformation of $l_2$ on the space of lattices

For the space $La{t}_n$ of all the lattices in a $p$-adic $n$-dimensional linear space we obtain an analog of matrix beta-functions; this beta-function has a degeneration to the Tamagawa zeta-function. We propose an analog of Berezin kernels for $La{t}_n$. We obtain conditions of positive definiteness of these kernels and explicit Plancherel formula.