Adaptation of temperate seagrass to Arctic light relies on seasonal acclimatization of carbon capture and metabolism

Whether temperate plant species can immigrate into a warming Arctic depends on their ability to tolerate several weeks of Polar day and night. Plant adaptations to extreme arctic light fluctuations have rarely been studied and are unknown in seagrasses–important ecosystem engineers that could enrich biodiversity and carbon capture potential in shallow coastal regions emerging from under the Arctic ice. Here, we describe for the first time adaptations (resulting from plasticity or genetic changes in response to natural selection) of a temperate seagrass to Arctic light conditions. We identified distinct patterns in photosynthesis and gene-expression of a Norwegian population of eelgrass (Zostera marina), the most widely distributed seagrass in the northern hemisphere, and the only seagrass species growing as far north as 70°N. We show that active carbon capture and metabolic dormancy in winter, driven by functions of the organelles (chloroplast and mitochondrion), dominate the distinct seasonal expression patterns of this population. While our study identified key physiological adaptations that allow eelgrass to endure the dark season at its present northern range limit, experimental research is needed to predict whether and up to which latitude eelgrass can migrate poleward into regions with extreme photoperiods becoming ice-free under projected climate change.