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.