Robert Rauschkolb, Lisa Henres, Caroline Lou, Sandrine Godefroid, Lara Dixon, Walter Durka, Oliver Bossdorf, Andreas Ensslin, J F Scheepens

Plant populations must continuously adapt to ongoing global climate change, including warmer temperatures and more extreme weather events. One way to detect such evolutionary changes within plant populations is through historical comparisons where plants grown from seeds collected in the past (“ancestors”) are compared to freshly collected seeds from the same populations (“descendants”) in common garden experiments. Here, we used 21-26 year old seeds stored in seed banks for two multi-species experiments that investigated changes in phenotypic traits and their plasticity conferring drought tolerance in early life stages of European plant species from two biogeographic regions. In the first experiment we used seedlings of four Mediterranean species, ceased watering and recorded their day of mortality. In one of four species descendant seedlings survived significantly longer without watering and were smaller than the ancestral seedlings. In the second experiment we studied phenotypic responses to drought in juvenile plants of nine species originating from temperate regions in Europe. We found that descendant plants were generally taller under well-watered conditions but smaller under drought than their ancestors, thus showing stronger plasticity. Our historical comparisons thus suggest that some populations have likely evolved, through changes in trait means and plasticity, within the last decades, and in ways consistent with adaptation to increased drought. Using seed bank material for historical comparisons has several weaknesses, such as unknown sampling protocols or invisible fractions. However, we show how accurately sampled and stored seed bank collections can be used similar to the resurrection approach for investigating rapid evolutionary processes in plants under climate change, opening up a vast amount of available ancestral seed material worldwide for similar studies.