Matrix tree theorem for the net Laplacian matrix of a signed graph

For a simple signed graph G with the adjacency matrix A and net degree matrix D-+/-), the net Laplacian matrix is L-+/-) = D-+/-) - A. We intro-duce a new oriented incidence matrix N +/- which can keep track of the sign as well as the orientation of each edge of G. Also L-+/-) = N-+/-)((NT)-T-+/-). Using this decomposition, we find the number of both positive and negative spanning trees of G in terms of the principal minors of L-+/-) generalizing the Matrix Tree Theorem for an unsigned graph. We present similar results for the signless net Laplacian matrix Q(+/-)) = D-+/-) + A along with a combinatorial formula for its determinant.