Differential selection of photobionts and ecophysiological acclimation by the bipolar lichen Cetraria aculeata

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Lichens are highly specialized symbioses between heterotrophic fungi and autotrophic green algae or cyanobacteria. Polar and alpine habitats are mostly dominated by lichens, which successfully outcompete vascular plants and bryophytes in terms of biodiversity and often also biomass. Previous results by the applicant show that (sub)antarctic and arctic populations of Cetraria aculeata select different strains of the green algal photobiont Trebouxia jamesii s. lat. than temperate populations. However, it is so far unknown, whether this is just a phlogeographic pattern or whether genetic differences between the photobionts are associated with differences in physiological traits (ecotypic differentiation). In this project, we propose (1) to genotype mycobionts and photobionts from six antarctic, arctic and temperate populations, (2) to measure photosynthetic parameters for these genotyped lichens and their isolated photobionts, and (3) to transplant temperate individuals to arctic populations and vice versa in a common garden design to measure changes in dry weight over three years. The ultimate goal is to investigate whether differential association with ecotypically differentiated photobionts allows widely distributed lichen fungi to inhabit climatically hostile polar regions. The results of our study will strongly influence our ability to predict the impact of global climate change on polar terrestrial ecosystems.