Mutualisms are not constraining cross‐continental invasion success of Acacia species within Australia

Abstract

Aim Studying plant–soil interactions of introduced species in different parts of their global range could assist in managing biological invasions by elucidating the level of host specificity of key mutualists. We assessed the role of the soil microbial community (with an emphasis on symbiotic nitrogen‐fixing bacteria, collectively termed rhizobia) in determining cross‐continental invasion success of five woody legume species. Location Australia. Methods For each species, we compared growth of plants in soils from their native and non‐native ranges using a glasshouse study, a soil dilution method (most probable number) and T‐RFLP to assess rhizobial abundance and community composition, respectively. Results Acacia longifolia was the only species that had significantly larger above‐ground biomass when grown in soils from its non‐native range. Rhizobial abundance was equally high across species and ranges, indicating plants are unlikely to be limited by soil rhizobial abundance in non‐native ranges. Acacia cyclops, A. saligna and Paraserianthes lophantha formed associations with different rhizobial communities in non‐native vs. native range soils. Acacia longifolia and A. melanoxylon associated with similar rhizobial communities in their native and non‐native ranges, suggesting that rhizobia may have been accidentally introduced into their novel range with seeds or seedlings. Main conclusions Invasive success of these five legume species is not constrained by the abundance of rhizobia in novel ranges for established legume populations, at least within Australia. Although differences in rhizobial community composition were evident between the native and non‐native ranges for three of the five species, these were not associated with differences in plant growth. Increased above‐ground biomass of A. longifolia when grown in soil from its non‐native range suggests that invasive success of this species may be associated with differences in the non‐rhizobial components of soil microbial communities in the novel range. This information could assist in management practises by facilitating a more instructive and effective screening for invasiveness.

Reduced availability of rhizobia limits the performance but not invasiveness of introduced Acacia

“…This may partly be due to their ability to establish into nutrient-poor soils, which is facilitated by interactions with rhizobia. Several studies have focused on this genus as a model system with which to study the role of rhizobia in determining invasion outcomes (Rodríguez-Echeverría et al 2009Birnbaum et al 2012).…”

“…Rhizobia with which Acacia can nodulate appear to be widespread in their native Australian range (Barnet & Catt 1991), which may be because congeneric species often share rhizobia (Thrall, Burdon & Woods 2000;Thrall et al 2007;Birnbaum et al 2012) and Acacia are a dominant component of many habitats. Compatible rhizobia also appear to be present in many locations where Acacia have been introduced, with species recorded nodulating in Europe (Rodríguez-Echeverría et al 2009), Asia (Midgley & Vivekanandan 1987;Le Roux et al 2009;Ma et al 2012), Africa (Mohamed et al 2000;Joubert 2002;Rodríguez-Echeverría 2010;Boukhatem et al 2012) and the Americas (Aronson, Ovalle & Avendano 1992), as well as outside their native range in Australia (Birnbaum et al 2012).…”

“…Compatible rhizobia also appear to be present in many locations where Acacia have been introduced, with species recorded nodulating in Europe (Rodríguez-Echeverría et al 2009), Asia (Midgley & Vivekanandan 1987;Le Roux et al 2009;Ma et al 2012), Africa (Mohamed et al 2000;Joubert 2002;Rodríguez-Echeverría 2010;Boukhatem et al 2012) and the Americas (Aronson, Ovalle & Avendano 1992), as well as outside their native range in Australia (Birnbaum et al 2012). Although it is not clear what facilitates nodulation outside the native range, the widespread occurrence of cosmopolitan rhizobia (Weir et al 2004;Birnbaum et al 2012) and the co-introduction of compatible rhizobia from the native range have both been implicated (Rodríguez-Echeverría 2010; Birnbaum et al 2012;Ndlovu et al 2013).…”

Genetic diversity and differentiation of invasive <i>Acacia longifolia</i> in Portugal

“…Marchante et al, 2008;Richardson and Rejmánek, 2011;Ulm et al, 2017). It is known that the invasive capacity of A. longifolia is due to its ability to form a high number of root nodules in different soils and the establishment of a symbiotic relationship with the soil's mutualists (Rodríguez-Echeverría et al, 2008), including the genera Bradyrhizobium and Rhizobium (Rodríguez-Echeverría et al, 2011;Birnbaum et al, 2012), enabling spreading to nutrient-poor soils, such as the dune systems (Ulm et al, 2017). Also, A. longifolia promotes the success of its own offspring (Rascher et al, 2011) and has the ability to control available sunlight to other plants, eventually outcompeting them and occupying their space (Rascher et al, 2011).…”

Invasive Lespedeza cuneata and native Lespedeza virginica experience asymmetrical benefits from rhizobial symbionts

“…Many leguminous plants continue to fix nitrogen after invading a new habitat, by taking advantage of mutualisms with bacteria that were transported with them, or by forming new mutualisms in the invaded range (De Faria et al 1989). Consequently, some invasive legumes do not appear to be limited by the density or community composition of soil rhizobia (Birnbaum et al 2012). However, the legume-rhizobium symbiosis is more effective when invasive Acacia are matched with bacteria from their home range in comparison with native bacteria (Rodriguez-Echeverria et al 2012;Thrall et al 2007).…”