POLAR ROCKS: Photosynthetic activity analysis of lichen species Usnea aurantiaco-atra on Livingston Island, 2022

A MINI-PAM-II photosynthesis yield analyser (Heinz Walz GmbH, Germany) was used to evaluate the activity status of the photosystem II (PSII) of the photobionts within thalli of Usnea aurantiaco-atra. Samples were collected from three locations in the vicinity of the Spanish Antarctic Station Juan Carlos I on Livingston Island (South Shetland Islands, Antarctica): Punta Polaca (50 m.a.s.l.), Mount Reina Sofía (278 m.a.s.l.), and El Castillo Nunatak (449 m.a.s.l.). At each of the selected sampling sites five thalli were collected, making it a total of 15 thalli. Induction curves were performed to study the evolution of photosynthetic yield values during actinic illumination. All the studied samples underwent three fluorescence induction curves each, at three actinic light intensities: 190, 625 or 1500 µmol m-2 s-1. Recovery curves are a useful tool to obtain information on post-actinic-illumination reactions, in particular on the recovery of various components of nonphotochemical quenching and on the extent of photoinhibition. Each of the induction curves was immediately followed by a recovery curve.

These curves offer a more in-depth understanding of potential adaptation mechanisms adopted by photosynthetic organisms, since they allow for the measurement of certain photosynthetic activity parameters that cannot be analysed in the field (e.g., quenching parameters).