Differential plant invasiveness is not always driven by host promiscuity with bacterial symbionts

• Published in: AoB plants 2016-01, Vol.8
• Main Authors: Klock, Metha M., Barrett, Luke G., Thrall, Peter H., Harms, Kyle E.
• Format: Article
• Language: English
• Subjects: Acacia; Biomass; Community composition; Congeners; Indigenous species; Introduced species; Invasive species; Invasiveness; Legumes; Life history; Nodulation; Nonnative species; Strains (organisms); Survival; Symbionts; Symbiosis
• ISSN: 2041-2851; 2041-2851
• DOI: 10.1093/aobpla/plw060

Acacias have been widely introduced outside their native range, with a subset of species becoming invasive in multiple parts of the world. Our study examined whether a key mechanism in acacia life history, the legume-rhizobia symbiosis, influences invasiveness of these species. We determined whether more invasive acacias formed symbioses with a wider diversity of rhizobial strains (i.e. are more promiscuous hosts) and found that acacias introduced to California are promiscuous hosts regardless of invasive status. Our results highlight the importance of examining mechanisms driving species invasions on different scales and in their native and introduced ranges. Identification of mechanisms that allow some species to outcompete others is a fundamental goal in ecology and invasive species management. One useful approach is to examine congeners varying in invasiveness in a comparative framework across native and invaded ranges. Acacia species have been widely introduced outside their native range of Australia, and a subset of these species have become invasive in multiple parts of the world. Within specific regions, the invasive status of these species varies. Our study examined whether a key mechanism in the life history of Acacia species, the legume-rhizobia symbiosis, influences acacia invasiveness on a regional scale. To assess the extent to which species varying in invasiveness correspondingly differ with regard to the diversity of rhizobia they associate with, we grew seven Acacia species ranging in invasiveness in California in multiple soils from both their native (Australia) and introduced (California) ranges. In particular, the aim was to determine whether more invasive species formed symbioses with a wider diversity of rhizobial strains (i.e. are more promiscuous hosts). We measured and compared plant performance, including aboveground biomass, survival, and nodulation response, as well as rhizobial community composition and richness. Host promiscuity did not differ among invasiveness categories. Acacia species that varied in invasiveness differed in aboveground biomass for only one soil and did not differ in survival or nodulation within individual soils. In addition, acacias did not differ in rhizobial richness among invasiveness categories. However, nodulation differed between regions and was generally higher in the native than introduced range. Our results suggest that all Acacia species introduced to California are promiscuous hosts and that ho