“…This suggests that specific host and microbe factors strongly influence the outcome of the interaction and cause the localized proliferation, in space and time, of lowabundance rhizobial species and genotypes. Known rhizobial factors contributing to their dominance in hostassociated habitats include numerical dominance in the bulk soil (Thies et al, 1991;Louvrier et al, 1996), high rhizosphere competence (Albareda et al, 2006;Barr et al, 2008;Ramachandran et al, 2011) or better competitiveness for nodule occupancy (Triplett and Sadowsky, 1992). Additionally, host-specific selection (partner choice) of rhizobial genotypes during the early infection process (Simms and Taylor, 2002;Zanetti et al, 2010;Regus et al, 2014), or host sanctions imposed on poor fixers after nodules have developed (Kiers and Denison, 2008;Marco et al, 2009;Sachs et al, 2010;Akcay and Simms, 2011) are known to affect species and strain abundances in host-associated habitats (Thrall et al, 2011).…”