“…Community assembly processes operate over space and time and influence community structure and eventually microbial metabolisms (Graham, Knelman, et al, ). So far, attempts have been made to understand these processes in a broad range of biomes such as recently deglaciated soils (Castle et al, ; Nemergut et al, ), lake biofilms (Jackson et al, ), water pipes (Martiny et al, ), river sediments (Graham, Crump, et al, ; Stegen, Fredrickson, et al, ; Stegen, Konopka, et al, ; Stegen et al, , ), subseafloor sediments (Starnawski et al, ), and global desert soils (Caruso et al, ). Our study examined a unique system where community assembly processes in an incipient terrestrial system were assessed in a highly controlled and spatially explicit manner.…”