Seed fungal endophytes promote the establishment of invasive Poa annua in maritime Antarctica

Abstract

Background: Invasive plants may displace native species. This is the case for Poa annua, theonly non-native plant species successfully established in Maritime Antarctica. Nonetheless, it is uncertain which factors drive the competitive success of P. annua in the harsh environmentalconditions of the region. The ability of this plant species to establish novel mutualistic interactions with resident soil fungi may be crucial for its invasiveness. Such ability may be linked to the vertical transmission of fungal endophytes via seeds.Aims: We undertook a study to assess the role of seed fungal endophytes as promoters of theestablishment and invasion of Poa annua in Maritime Antarctica.Methods: We explored the composition and diversity of fungal communities associated withdifferent P. annua tissues (seeds, leaves and roots) and the soil. We also measured parametersincluding germination rate, above-ground biomass, reproductive structures, and the survival ofinvasive P. annua as well as of the native Colobanthus quitensis and Deschampsia antarcticagrown from seeds with and without endophytes. Furthermore, we conducted inter- andintraspecific competition experiments among native and invasive plants, where chemicallymediated plant-to-plant interference (allelopathy) and plant growth rate were measured tocalculate a relative competition index.Results: We found that fungal endophyte taxa associated with P. annua tissues were verydifferent from those in the soil. Fungal endophytes in P. annua differed among seed, root andshoot tissues, which suggests low transmission among different organs. The removal ofendophytes from P. annua seeds was associated with reduced seed germination, plant growthand survivorship, while the competitive ability of P. annua (assessed by accumulated biomass)relative to native species, as well as levels of allelochemicals in soils, were higher in thepresence of seed fungal endophytes.Conclusion: Our results suggest that fungal endophytes, maternally inherited through seeds,improve host fitness and may contribute to the invasive success of P. annua in Antarctica.