Host promiscuity in symbiont associations can influence exotic legume establishment and colonization of novel ranges

Abstract

Aim Invasive Acacia species have negatively impacted natural areas in multiple regions around the globe. Almost 400 Acacia species have been introduced outside their native ranges in Australia; approximately 6% have become invasive, 12% are naturalized, and 82% have no record of naturalization or invasion. This variation in invasiveness provides a comparative framework in which to examine mechanisms that either promote or constrain establishment and colonization of species in novel regions. Here, we experimentally examine the role that the legume-rhizobia symbiosis plays in the differential invasiveness of acacias introduced outside their native Australian ranges.Location Canberra, Australia.Methods We paired 12 Acacia species ranging in invasiveness globally with 12 rhizobial strains ranging in average symbiotic effectiveness. We measured plant growth and nodulation success and abundance to assess whether invasive acacias were more promiscuous hosts, that is had positive growth and nodulation responses to a broader range of rhizobial strains than naturalized and noninvasive species.Results Invasive acacias had a higher growth response across more rhizobial strains (six of 12 strains) than naturalized and non-invasive species, but invasiveness categories differed only moderately with regard to the percentage of plants with nodules and nodulation abundance.Main conclusion With respect to plant growth, invasive acacias appear to be more promiscuous hosts than naturalized and non-invasive Australian Acacia species. Plant growth response to nodulation, however, is likely more important than nodulation alone in the successful invasion of species in novel ranges. Results from this study help elucidate an important mechanism in the invasive capacity of legumes.

Symbiosis limits establishment of legumes outside their native range at a global scale

“…Inadequate population density of compatible rhizobia or appropriate environmental conditions for effective nitrogen fixation in introduced ranges are viable explanations for our results. This explanation would suggest that symbiotic legume hosts and their compatible symbionts would frequently need to be introduced simultaneously or that introductions would favour legumes that are able to form associations with a broad diversity of rhizobia1718, which is consistent with empirical findings from previous studies examining introduced Acacia species181920.…”

Soil nutritional status and biogeography influence rhizosphere microbial communities associated with the invasive tree Acacia dealbata

“…Bradyrhizobium species are the predominant N 2 -fixing rhizobia associated with acacias (e.g., refs 47 and 48). N 2 -fixing symbionts enhance growth and competitive ability of their host plants 49 , which consequently influences plant invasiveness 50 . Interestingly, it has been reported that seven of nine selected acacia species grew better in association with Bradyrhizobium phylotypes than with members of the genera Burkholderia , Rhizobium and Ensifer 51 .

Figure 5Relative frequency versus relative abundance of biomarker taxa, coloured according to phylum, for bulk and rhizosphere soils (logarithmic LDA score ≥2, P < 0.05).

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Evolutionary dynamics of tree invasions: complementing the unified framework for biological invasions

“…Alternatively, introduced plants can form ‘novel associations’ with native symbionts or co-xenic novel associations (Nuñez and Dickie 2014) can be formed between symbionts from different regions (Klock et al 2015; Le Roux et al 2016). The level of interaction specificity, coupled with chances of co-introduction, may therefore have serious fitness consequences for introduced plants.…”