Germinability of arctic plants is high in perceived optimal conditions but low in the field

Sexual reproduction is crucial for plant populations to track and adapt to climate change, but it is uncertain to what degree arctic vascular plants reproduce by seed. Several studies on arctic species show low germination. To re-examine seed germination and evaluate factors limiting sexual reproduction, seeds of 6-22 arctic species were germinated in five different, increasingly more realistic, conditions. Thirteen out of 15 species that were tested in an earlier study in Svalbard, Norway, germinated better in our study. Compared with perceived optimal conditions in a growth chamber, average germination per species was 6%-52% lower in five out of six species germinating at a colder temperature in soil, 36%-64% lower when germinating outdoors in soil, 49%-91% lower when germinating in a moss covered moraine, and 55%-91% lower when germinating in open soil on a moraine. Germination outdoors was below 5% in 10 out of 13 species and not correlated to germination in perceived optimal conditions. The high germination compared with earlier studies suggests that climate warming has already increased seed viability. However, caution should be taken when evaluating species-recruitment potential based on laboratory studies, as germination in the field was limited by species-specific responses to low temperatures, moisture, predation, and safe-site availability.