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Aim: Poa annua L. (annual bluegrass) is presently the sole invasive vascular plant species to have successfully established in Maritime Antarctica, where it poses a significant conservation threat to native plant species. However, the reasons for its success in the region have yet to be established. Here, we determined whether the invasiveness of P. annua, and its competitiveness with the native Antarctic hairgrass Deschampsia antarctica, is influenced by symbioses formed with seed fungal endophytes, and whether plants derived from seeds from four global regions differ in their performance. Locations: Four regions (Maritime Antarctica, sub‐Antarctica, South America and Europe). Methods: Endophyte frequency was measured in P. annua seeds collected from the four regions. The germination, survival, biomass accumulation, flowering and competitiveness with D. antarctica of P. annua plants grown from endophyte‐uncolonised and uncolonised seeds was determined in the laboratory. The effects of endophytes on P. annua seed germination and survival and seedling osmoprotection were also assessed in the Maritime Antarctic natural environment using locally‐sourced seeds. Results: Endophytes were at least twice as frequent in seeds from Maritime Antarctica than in those from other regions. A higher proportion of endophyte‐colonized seeds germinated and survived than did uncolonised seeds, but only when they originated from Maritime Antarctica. Seed endophytes increased the competitiveness of P. annua with D. antarctica, but only for plants grown from Maritime Antarctic seeds. In the field, endophyte‐colonized seeds from Maritime Antarctica germinated and survived more frequently than uncolonised seeds, and osmoprotection was higher in seedlings grown from colonized seed. Main Conclusions: The findings indicate beneficial effects of seed endophytes on invasion‐related traits of P. annua, such as survival, germination success and flowering. Together with vegetative and reproductive traits facilitating the colonization process, the seed‐fungal endophyte symbiosis can be invoked as an important factor explaining the invasiveness of P. annua in Maritime Antarctica. [ABSTRACT FROM AUTHOR]

For plants, reactive oxygen species (ROS) and ultraviolet B radiation (UV-B) stand out as important genotoxic agents. Hence, the genetic damage among the Antarctic vascular flora, whose individuals frequently experience these abiotic stresses, might be recurrent among their populations. To respond this, the genetic damage associated with these stress factors was evaluated in Colobanthus quitensis and Deschampsia antarctica for the first time in the field and compared with those showed by plants grown at laboratory under less stressful conditions. Fifteen individuals per species from Admiralty Bay populations at King George Island (Maritime Antarctica) were used to semi-quantitatively estimate the genetic damage at the whole genome level by the single-cell gel electrophoresis (SCGE) assay, revealing by means of specific enzymatic treatments the damage generated by oxidative stress (oxidized purines and pyrimidines) and UV-B radiation (pyrimidine dimmers). Compared with laboratory control individuals, the basal genetic damage observed in both species was significantly higher under field conditions. However, while for C. quitensis, oxidative stress (Ox) was more relevant than UV-B radiation (field relative revealed damage: Ox = 29% vs. UV-B = 25%), in D. antarctica, it was UV-B radiation the most relevant genotoxic factor (Ox = 10% vs. UV-B = 33%). This first approach to the genetic damage of the Antarctic vascular flora suggests that the conditions experienced on their natural ecosystems would constitute a genotoxic environment for these species, yet with differential impact between them. [ABSTRACT FROM AUTHOR]