The alien A <i>cacia salicina</i> invasive does not infiltrate the native soil rhizobial symbiosis networks

Using <i>Lotus creticus</i>-rhizobia-<i>A. salicina</i> interaction networks, we address first the soil invasion success of <i>A. salicina</i>, and second, we report either <i>A. salicina</i>-rhizobia partnership should form an isolated module within the symbiosis interaction network. Different indexes were used to determine <i>A. salicina</i> model invasion success and the network topology. Our results indicated that <i>A. salicina</i> invasion decreased soil microbial biomass, basal respiration, and enzymatic activities. Housekeeping gene-based phylogeny showed that the invasive <i>A. salicina</i> is exclusively associated with a novel putative nodulating <i>Paraburkholderia</i> sp. not considered, up to now, as a natural symbiont of this species, and the native legume <i>L. creticus</i> nodulating strains, belonged to three new putative undescribed distinct chromosomal lineages within the <i>Rhizobium, Allomesorhizobium,</i> and <i>Mesorhizobium</i> genera. Analysis using <i>nodC</i> gene identified one symbiovar for <i>A. salicina Paraburkholderia</i> symbiont (sv. <i>tropicalis</i>) and three symbiovars for <i>L. creticus</i> endosynbionts (sv. <i>viciae</i>, sv <i>hedysari</i> and sv. <i>loti)</i>. Moreover, <i>L. creticus</i>-rhizobia<i>-A. salicina</i> 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.