Seed germination and invasion success of Poa annua L. in Antarctica

One of the first steps to successful invasion of plant species that reproduce sexually is seed germination, which may be highly influenced by climatic conditions. We studied Poa annua, a cosmopolitan species found across all climatic zones and the only alien species that has successfully colonized the Antarctic. Our research questions were: (i) if harsh polar conditions restrict seed germination of P. annua and (ii) if the germination capacity of the Antarctic population of the species is due to high germination aptitude in the source population. We compared germination of seeds collected from eight populations around the world (maritime Antarctica, S Chile, W Argentina and E Argentina, NE USA, SW Croatia, C Poland and S Poland). We followed germination of seeds collected in the field and acquired from plants cultivated under unified optimal conditions. We found significant differences between populations in germination characteristics of seeds collected in the field. These could be associated with seed ripening in different locations. Seeds obtained under favorable conditions differed in stratification requirements. The germination potential of the Antarctic population is lowered by unfavorable polar conditions impacting seed maturation. Thus, the species’ invasion in the Antarctic seems highly restricted by the harsh environment. Environmental unsuitability may restrict invasions of other species in the same way potentially. However, this environmental barrier protecting Antarctica from invasions may be broken under a climate warming scenario.