2.3 | Experimental setup
After collecting the P. britannica specimens, they were exposed to a 12-hour light/12-hour dark cycle (13.3 µmol m-2s-1) in a cold room at 4 °C for five days in a closed Petri dish. At this temperature, they were first sampled (Fig. 2): pieces of thallus (ca. 1 cm² each) of the cyanomorph and the tripartite morph were cut off from all four specimens (treatment “4 °C_1”). The lichens were kept for 14 days at 4 °C and were watered regularly with deionized water to prevent desiccation. Once a week, Petri dishes were left open for the thalli to dry out to simulate the conditions in nature where they regularly dry out, and to avoid damages associated with permanent hydration. After this two-week period, the lichens were sampled again as before (treatment “4 °C_2”). Then, the fully hydrated lichens were transferred to a plant growth chamber (TOP-version KK-700 625-liter Climatic Chamber manufactured by POL-EKO-APARATURA; 13.1 µmol m-2 s-1) set to 15 °C, where they were left for two hours before additional samples were taken (treatment “15 °C”). In the last step, the lichens were exposed to 25 °C for two hours before sampling (treatment “25 °C”). At the higher temperatures, the specimens desiccated rapidly, therefore, they were sprayed with deionized water of the respective temperatures so they were fully hydrated during incubation and sampling. Immediately after harvest, samples were shock frozen in liquid nitrogen and stored at -80 °C until processing.