title: Legume-rhizobium symbiotic promiscuity and effectiveness do not affect plant invasiveness.
abstract: The ability to fix atmospheric nitrogen is thought to play an important role in the invasion success of legumes. Interactions between legumes and nitrogen-fixing bacteria (rhizobia) span a continuum of specialization, and promiscuous legumes are thought to have higher chances of forming effective symbioses in novel ranges. Using Australian Acacia species in South Africa, it was hypothesized that widespread and highly invasive species will be more generalist in their rhizobial symbiotic requirements and more effective in fixing atmospheric nitrogen compared with localized and less invasive species.
  
  
  
  To test these hypotheses, eight localized and 11 widespread acacias were examined using next-generation sequencing data for the nodulation gene, nodC , to compare the identity, species richness, diversity and compositional similarity of rhizobia associated with these acacias. Stable isotope analysis was also used to determine levels of nitrogen obtained from the atmosphere via symbiotic nitrogen fixation.
  
  
  
  No differences were found in richness, diversity and community composition between localized and widespread acacias. Similarly, widespread and localized acacias did not differ in their ability to fix atmospheric nitrogen. However, for some species by site comparisons, significant differences in δ15N isotopic signatures were found, indicating differential symbiotic effectiveness between these species at specific localities.
  
  
  
  Overall, the results support recent findings that root nodule rhizobial diversity and community composition do not differ between acacias that vary in their invasiveness. Differential invasiveness of acacias in South Africa is probably linked to attributes such as differences in propagule pressure, reasons for (e.g. forestry vs. ornamental) and extent of, plantings in the country.
authors.affiliation: Department of Botany and Zoology, Stellenbosch University, Matieland 7602, South Africa.
authors.forename: Jan-Hendrik
authors.initials: JH
authors.lastname: Keet
authors.affiliation: Department of Botany and Zoology, Stellenbosch University, Matieland 7602, South Africa.
authors.forename: Allan G
authors.initials: AG
authors.lastname: Ellis
authors.affiliation: Centre for Invasion Biology, Department of Mathematical Sciences, Stellenbosch University, Matieland 7602, South Africa.|Mathematical and Physical Biosciences, African Institute for Mathematical Sciences, Cape Town 7945, South Africa.
authors.forename: Cang
authors.initials: C
authors.lastname: Hui
authors.affiliation: Department of Botany and Zoology, Stellenbosch University, Matieland 7602, South Africa.|Centre for Invasion Biology, Department of Mathematical Sciences, Stellenbosch University, Matieland 7602, South Africa.
authors.forename: Johannes J
authors.initials: JJ
authors.lastname: Le Roux
mesh_terms: D001315:Australia; D007887:Fabaceae / Q000382:microbiology*; D058865:Introduced Species; D009586:Nitrogen Fixation; D012231:Rhizobium / Q000502:physiology*; D013019:South Africa; D013559:Symbiosis
keywords: Acacia; invasive; mutualism; nitrogen fixation effectiveness; rhizobia; root nodule; symbiotic promiscuity