Inherited fungal symbionts enhance establishment of an invasive annual grass across successional habitats

Abstract

Plants infected with vertically transmitted fungal endophytes carry their microbial symbionts with them during dispersal into new areas. Yet, whether seed-borne endophytes enhance the host plant's ability to overcome colonisation barriers and to regenerate within invaded sites remains poorly understood. We examined how symbiosis with asexual endophytic fungi (Neotyphodium) affected establishment and seed loss to predators in the invasive annual grass Lolium multiflorum (Italian ryegrass) across contrasting successional plots. Italian ryegrass seeds with high and low endophyte incidence were sown into three communities: a 1-year-old fallow field, a 15-year-old grassland, and a 24-year-old forest, which conformed to an old-field chronosequence in the eastern Inland Pampa, Argentina. We found that endophyte infection consistently increased host population recruitment and reproductive output. Endophyte presence also enhanced aerial biomass production of ryegrass in a low recruitment year but not in a high recruitment year, suggesting that symbiotic effects on growth performance are density dependent. Endophyte presence reduced seed removal by rodents, although differential predation may not account for the increased success of infected grass populations. Overall, there was no statistical evidence for an endophyte-by-site interaction, indicating that the fungal endosymbiont benefitted host establishment regardless of large differences in biotic and abiotic environment among communities. Our results imply that hereditary endophytes may increase the chances for host grass species to pass various ecological filters associated with invasion resistance across a broad range of successional habitats.

Large Shift in Symbiont Assemblage in the Invasive Red Turpentine Beetle

“…Mutualistic symbionts can facilitate invasive species or enhance the damage they cause (i.e., invasional meltdown [5]). For example, successful plant invasions often depend on co-invading or newly adopted mychorrhizae [6] or endophytes [7-9], while plants that lose their mutualists can have lowered fitness in invaded environments [10]. Invasive forest insects can also benefit from microbial symbionts that allow the insects to aggressively colonize naive hosts [11].…”

Does Fungal Endophyte Infection Improve Tall Fescue’s Growth Response to Fire and Water Limitation?

“…Many plant functional traits have been linked to association with bacterial and fungal microorganisms (reviewed in [6]), with fungal endophytes of grasses (in the family Clavicipitaceae) being one of the most studied associations [7], [8], [9]. Association with these fungal endophytes has been linked to success of the invasive annual Italian ryegrass [10], including conferring increased herbicide resistance [11] (but see [12]). In addition, many of the grass functional traits affected by fungal endophytes could be considered traits that make the grasses more competitive [7] and potentially more able to successfully persist and/or invade novel habitats.…”

New pasture plants intensify invasive species risk

“…Widespread establishment of enhanced pasture taxa is likely to exacerbate the current environmental weed problem (17,34,35,37). New taxa may interbreed with existing weed populations, with potential to worsen environmental impacts (37)(38)(39).…”

“…To date, no conventionally bred taxa have been nominated. Notwithstanding Canada's progressive approach, the paucity of regulation surrounding new plant taxa poses serious biosecurity risks (17,34,35,40).…”

“…Pasture breeding organizations actively select for characteristics that might inadvertently lead to environmental impacts outside of pastures, including higher growth rates and tolerance to environmental stress (Table S2) (29). Using polyploidy or endophytes (symbiotic fungi and bacteria; Tables S1 and S2), plant breeders alter features such as growth, reproduction, disease resistance, and risk of seed predation (33)(34)(35). Altering these characteristics has the potential to create forage plants that are more environmentally damaging (35,36).…”