POLAR ROCKS: Photosynthetic activity analysis of lichen species Usnea aurantiaco-atra and moss species Andreaea gainii on Livingston Island, 2023

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, as well as of the phyllodes found in mosses belonging to the species Andreaea gainii. Samples of both U. aurantiaco-atra and A. gainii were collected from two 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.), and El Castillo Nunatak (449 m.a.s.l.). A total of 24 samples of U. aurantiaco-atra (12 from each location) and 22 samples of A. gainii (11 from each location) underwent a series of rapid light, induction, and recovery curves. Rapid light curves allow insight into the physiological flexibility with which a photoautotroph organism can adapt its photosynthetic apparatus to fast changes of light intensity and provide information on momentary acclimation states of photosynthesis. Induction curves were performed to study the evolution of photosynthesis 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).