Root endophytes and invasiveness: no difference between native and non‐native Phragmites in the Great Lakes Region

Abstract

Microbial interactions could play an important role in plant invasions. If invasive plants associate with relatively more mutualists or fewer pathogens than their native counterparts, then microbial communities could foster plant invasiveness. Studies examining the effects of microbes on invasive plants commonly focus on a single microbial group (e.g., bacteria) or measure only plant response to microbes, not documenting the specific taxa associating with invaders. We surveyed root microbial communities associated with co‐occurring native and non‐native lineages of Phragmites australis, across Michigan, USA. Our aim was to determine whether (1) plant lineage was a stronger predictor of root microbial community composition than environmental variables and (2) the non‐native lineage associated with more mutualistic and/or fewer pathogenic microbes than the native lineage. We used microscopy and culture‐independent molecular methods to examine fungal colonization rate and community composition in three major microbial groups (bacteria, fungi, and oomycetes) within roots. We also used microbial functional databases to assess putative functions of the observed microbial taxa. While fungal colonization of roots was significantly higher in non‐native Phragmites than the native lineage, we found no differences in root microbial community composition or potential function between the two Phragmites lineages. Community composition did differ significantly by site, with soil saturation playing a significant role in structuring communities in all three microbial groups. The relative abundance of some specific bacterial taxa did differ between Phragmites lineages at the phylum and genus level (e.g., Proteobacteria, Firmicutes). Purported function of root fungi and respiratory mode of root bacteria also did not differ between native and non‐native Phragmites. We found no evidence that native and non‐native Phragmites harbored distinct root microbial communities; nor did those communities differ functionally. Therefore, if the trends revealed at our sites are widespread, it is unlikely that total root microbial communities are driving invasion by non‐native Phragmites plants.

Dark septate endophyte improves salt tolerance of native and invasive lineages of Phragmites australis

“…2 ), even though most taxa were present in both lineages and half of them were found at all sites. These results differ from those reported by Bickford et al [ 79 ] who found no differences in root fungal endophytes between P. australis lineages in the Great Lakes, USA. However, soil saturation was a relevant environmental factor in that study, whereas water level did not appear to play a role in endophyte colonization or community structure in our study sites (Fig.…”

Intraspecific and biogeographical variation in foliar fungal communities and pathogen damage of native and invasivePhragmites australis

“…We expand on these earlier findings as one of the first studies conducted outside an agricultural context, by comparing closely related native and invasive taxa over a broad geographical scale and quantifying damage from the fungal pathogen community. For Phragmites , the divergent fungal communities for all lineage comparisons indicate a high degree of specialization of plant–fungal interactions at the lineage level, consistent with previous findings comparing rhizosphere oomycete (Crocker et al, 2015; Nelson & Karp, 2013), bacterial (Bowen et al, 2017) and archaean (Yarwood et al, 2016) communities among Phragmites lineages, but contrasting with a recent study of endophytic root fungal, bacterial and oomycete communities in the Great Lakes region (Bickford et al, 2018). However, our study is the first to examine differences among Phragmites lineages in their foliar microbiome, where leaf tissue provides a substrate different from that of roots or the rhizosphere, which varies among Phragmites lineages in leaf chemistry (Cronin et al, 2015; Pyšek et al, 2019).…”

“…Our results from the field survey and common garden experiment present contrasting evidence for our first prediction and the enemy release hypothesis. Despite divergent foliar fungal communities and pathogen abundance, pathogen damage did not differ among Phragmites lineages in the field, suggesting that release from fungal pathogens does not contribute to the success of invasion by the European lineage (Bickford et al, 2018). However, the common garden experiment identified genetically based differences in susceptibility to some putative pathogens that favoured the European lineage over the Gulf and native lineages.…”

“…The diversity and function of the Phragmites microbiome have been investigated (for review, see Kowalski et al, 2015). Distinct oomycete, archaean and bacterial communities have been reported from rhizosphere soil of native and European Phragmites lineages in North America (Bowen et al, 2017; Crocker, Karp, & Nelson, 2015; Nelson & Karp, 2013; Yarwood, Baldwin, Gonzalez Mateu, & Buyer, 2016), although no differences were detected for fungal, bacterial and oomycete root endophyte communities in the Great Lakes region (Bickford, Goldberg, Kowalski, & Zak, 2018). However, Phragmites foliar fungal communities (i.e., pathogens and non‐symptomatic endophytes) and their impacts have yet to be compared formally among native and invasive lineages (but for a local‐scale survey in New York, see Shearer & Harms, 2012).…”

Differences in rhizosphere microbial communities between native and non‐native Phragmites australis may depend on stand density

“…where we also found no differences between Phragmites lineages across three major microbial groups (Bickford et al, 2018). In exploration of the root microbiome, Bickford et al 2018 The functional implication of this dissimilarity is unresolved in regard to invasive capacity.…”