Fit for the future? Alpine plant responses to climatic stress over two decades of seed bank storage

Climate warming is occurring in high mountain areas faster than the global average, making cold-adapted alpine specialists vulnerable. Ex situ seed conservation is a solution, but little is known about how plants from stored seeds will cope with the altered climate. We grew plants from seeds of the artic-alpine specialist Viscaria alpina, collected from the same location at different time points and held under seed bank conditions over the last 20 years. During this time the site has warmed by 0.3 °C per decade and it has been drier than average. For three old (‘ancestor’) and three recent (‘descendant’) accessions, we exposed juvenile plants to temperature and/or soil moisture stress for one month. To determine plant fitness we measured vegetative traits (above ground biomass, specific leaf area), reproductive performance (flower number, stalk height) and seed traits (number, mass). Descendants had lower above ground biomass than ancestors and produced heavier seeds. In response to drought, compared to the control, ancestors had lower biomass whereas descendants did not, though the actual biomass did not vary between ancestors and descendants. Ancestors had higher seed production under drought than descendants, but the variation was large. We show plant traits in an alpine specialist have changed over 20 years, with plants originating from recent accessions apparently better adapted to drought. These findings indicate that alpine species have adjusted to the changed climate, implying older seed bank stored seeds may be unsuitable for use in plant conservation. Seed banks should therefore increase the frequency of seed collection.