Nitrogen‐fixing bacterial communities in invasive legume nodules and associated soils are similar across introduced and native range populations in Australia

Abstract

Methods 42NifH genes were amplified from rhizosphere soils collected from beneath each species 43 (multiple populations) within their native and introduced range and directly from 44 nodules collected from plants previously grown in the glasshouse using field-collected 45 soil as inoculum. NifH gene sequences from soils and nodules were 454 46 pyrosequenced and assigned to taxonomic groups based on nifH consensus taxonomy. 47 48 Results 3We found no difference in the NFB community of soils or nodules between native and 50 introduced ranges across the five species, suggesting that these legumes encounter 51 similar NFB communities in soils across Australia. Bradyrhizobium was the most 52 abundant rhizobial genus present in both soils and nodules. Bradyrhizobium species 53 found in nodules were significantly different across the ranges for A. longifolia. 54 55 Main conclusions 56The results indicate that these invasive legumes have similar nitrogen fixing bacterial 57 communities in their rhizosphere and nodules across Australia, with the exception of 58A. longifolia. This species has diverse Bradyrhizobium genotypes in its nodules 59suggesting that A. longifolia may be a more generalist host compared to the other four 60 legumes. Thus it is unlikely that the invasive success of these legumes is constrained 61 Soil microbes are increasingly acknowledged to play significant roles in invasion 68 outcomes for many plant species (Inderjit & Cahill, 2015;Vestergård et al., 2015). (Wandrag et al., 2013). 92Broad symbiotic promiscuity and ability to nodulate at low rhizobial abundance have 93 been described as significant advantages for invading legumes (Parker, 2001; Perez-94 Fernanndez & Lamont, 2003;Rodríguez-Echeverria et al., 2011). Previous studies 95 have shown that some invasive woody legumes are able to readily nodulate (Lafay & 96 Burdon, 2006) and associate with novel bacterial communities in their exotic ranges 97 (Marsudi et al., 1999; Amrani et al., 2010; Callaway et al., 2011; Ndlovu et al., 98 2013). 99Despite the evidence for promiscuity for some host species, there are also reports 100showing that some invasive legumes in their invasive range have specificity towards 101 rhizobia from their native range (Chen et al., 2005). Such results were reported for A. 102 longifolia in Portugal which was found to associate with rhizobial communities that 103 were very similar to those from A. longifolia's native range in south-east Australia 104 (Rodríguez-Echeverria, 2010). Thus, there appears to be considerable variation 105 between legume hosts and their symbiotic associations across introduced and native 106 ranges. 107There is evidence to suggest that invasive acacias (sensu Richardson et al. 2011) 108 could be more promiscuous, i.e., they are able to associate with more diverse rhizobia, 109 than non-invasive acacias (Klock et al., 2015). However, there is also evidence to 110 suggest that some acacias (e.g., A. cyclops, A. pycnantha) are able to non-specifically 111 nodulate with both fast-and...

Cointroductions of Australian acacias and their rhizobial mutualists in the Southern Hemisphere

“…These observations also support the notion that, while acacias mainly associate with bradyrhizobia, they show some level of interaction promiscuity to strains within this genus (Birnbaum et al, ; 1). Introduced acacias are known to share rhizobial strains in places like South Africa (Keet et al, ) and in their non‐native distributions in Australia (Birbaum et al, ). These findings imply that a single cointroduction can facilitate symbiont associations and invasion of other acacias, at least for the four species we investigated.…”

Biotic and abiotic plant–soil feedback depends on nitrogen‐acquisition strategy and shifts during long‐term ecosystem development

“…As such, to detect a significantly greater investment in growth by N‐fixing plants in young soils that will achieve the predicted positive PSF, a substantially greater amount of plant‐available soil [N] than that measured in young soils beneath N‐fixing plants may be required. Furthermore, the absence of biotic PSF experienced by N‐fixing plant species in young soils from heterospecific N‐fixing plants is in line with previous studies (e.g., Birnbaum, Bissett, Thrall, & Leishman, ; Birnbaum & Leishman, ). Together, our results showing differences in biotic and abiotic PSF responses between N‐fixing plants and co‐occurring non‐N‐fixing plants from the young dune system demonstrate the dependency of PSF on the type of plant functional group or trait (Baxendale et al, ; Cortois, Schröder‐Georgi, Weigelt, van der Putten, & de Deyn, ; Teste et al, ).…”

Availability of soil mutualists may not limit non‐native Acacia invasion but could increase their impact on native soil communities

“…This interest has generated a series of studies investigating the ability of non‐native Acacia to access rhizobia, and the performance implications of doing so. These include: six studies that examine differentially invasive Acacia species in both native and non‐native locations (Birnbaum, Barrett, Thrall, & Leishman, ; Birnbaum, Bissett, Thrall, & Leishman, ; Birnbaum & Leishman, ; Klock, Barrett, Thrall, & Harms, ; Wandrag et al, ; Warrington et al, ), two that examine only one species but do so in both the native Australian and non‐native (Portugal and South Africa) range (Crisóstomo, Rodríguez‐Echeverría, & Freitas, ; Ndlovu, Richardson, Wilson, & Le Roux, ), and one that examines differentially invasive Acacia in only the non‐native (South Africa) range (Keet et al, ). These studies cover 22 Acacia species that range from only casually occurring in a few locations, to those that are widespread invaders in almost all non‐native locations (Table ), and five geographic ranges: Australia (both native and non‐native ranges), New Zealand, South Africa, the US (California) and Europe (Portugal).…”

“…Rhizobia associated with Acacia in New Zealand (Warrington et al, ), Portugal (Crisóstomo et al, ; Rodríguez‐Echeverría, ) and the non‐native Australian range (Birnbaum et al, ) were all similar to their native Australian range. There is only one clear example of differences between the rhizobial communities in native and non‐native locations, with Acacia longifolia forming novel associations with rhizobia in its non‐native Australian range (Birnbaum et al, ).…”