A universe of soil, rhizosphere and endosphere bacteria

I got this cool figure from my postdoc Mike Robeson to contemplate over the weekend. It shows the Bacterial species network (or OTUs as small white squares) we recovered from bulk soil (orange connections), rhizosphere (blue connections) and root endophyte (green connections) samples from 6 sites taken last fall where we sampled Populus deltoides and surrounding tree species on the Caney Fork River in Tennessee (squares of different colors indicate different riparian sites) as part of our Plant Microbial Interfaces project.  Still not sure exactly what it means, except that it is fun to look at and ponder.  Seems to indicate that the effect of habitat (soil, rhizosphere, endosphere) > site location > tree species.  Anyway, kind of mesmerizing.