The alien Acacia salicina invasive does not infiltrate the native soil rhizobial symbiosis networks

Using Lotus creticus-rhizobia-A. salicina interaction networks, we address first the soil invasion success of A. salicina, and second, we report either A. salicina-rhizobia partnership should form an isolated module within the symbiosis interaction network. Different indexes were used to determine A. salicina model invasion success and the network topology. Our results indicated that A. salicina invasion decreased soil microbial biomass, basal respiration, and enzymatic activities. Housekeeping gene-based phylogeny showed that the invasive A. salicina is exclusively associated with a novel putative nodulating Paraburkholderia sp. not considered, up to now, as a natural symbiont of this species, and the native legume L. creticus nodulating strains, belonged to three new putative undescribed distinct chromosomal lineages within the Rhizobium, Allomesorhizobium, and Mesorhizobium genera. Analysis using nodC gene identified one symbiovar for A. salicina Paraburkholderia symbiont (sv. tropicalis) and three symbiovars for L. creticus endosynbionts (sv. viciae, sv hedysari and sv. loti). Moreover, L. creticus-rhizobia-A. salicina interaction networks are significantly modular with high levels of specialization. Network topology remained consistent over the invasion gradient, whereas native legume-associated rhizobia underwent significant change as acacias took over more the landscape. The absence of mutual overlapping networks emphasizes the importance of the simultaneous invasion of rhizobia–acacia species complexes in successful acacia invasion, suggesting unique interactions that often arise and evolve.