  Using a network representation for real soil samples and mathematical models
for microbial spread, we show that the structural heterogeneity of the soil
habitat may have a very significant influence on the size of microbial
invasions of the soil pore space. In particular, neglecting the soil structural
heterogeneity may lead to a substantial underestimation of microbial invasion.
Such effects are explained in terms of a crucial interplay between
heterogeneity in microbial spread and heterogeneity in the topology of soil
networks. The main influence of network topology on invasion is linked to the
existence of long channels in soil networks that may act as bridges for
transmission of microorganisms between distant parts of soil.
