The Antarctic lichen, Xanthoria elegans, in its hydrated state has several physiological mechanisms to cope with high light effects on the photosynthetic processes of its photobionts. We aim to investigate the changes in primary photochemical processes of photosystem II in response to a short-term photoinhibitory treatment. Several chlorophyll a fluorescence techniques: (1) slow Kautsky kinetics supplemented with quenching mechanism analysis; (2) light response curves of photosynthetic electron transport (ETR); and (3) response curves of non-photochemical quenching (NPQ) were used in order to evaluate the phenomenon of photoinhibition of photosynthesis and its consequent recovery. Our findings suggest that X. elegans copes well with short-term high light (HL) stress due to effective photoprotective mechanisms that are activated during the photoinhibitory treatment. The investigations of quenching mechanisms revealed that photoinhibitory quenching (qIt) was a major non-photochemical quenching in HL-treated X. elegans; qIt relaxed rapidly and returned to pre-photoinhibition levels after a 120 min recovery. We conclude that the Antarctic lichen species X. elegans exhibits a high degree of photoinhibition resistance and effective non-photochemical quenching mechanisms. This photoprotective mechanism may help it survive even repeated periods of high light during the early austral summer season, when lichens are moist and physiologically active.

Supplementary lighting of specific wavelengths can be used for inducing morphological and physiological responses in different crops, ultimately improving yield and quality. Based on this approach, new greenhouse covering materials are being developed in order to improve the use of sunlight in horticulture. These new-generation greenhouse coverings may incorporate light spectrum modulation agents or fluorescent additives which convert solar UV radiation into visible light. In this work, we tested the agronomical and physiological response of lettuce grown under a greenhouse covered with poly-methyl-methacrylate (PPMA) panels doped with a blend of the rare-earth inorganic material with a photo-luminescent effect. The doped greenhouse elicited a 36% increase in lettuce yield compared to the undoped greenhouse. Chlorophyll and carotenoid content, as well as antioxidant activity and ascorbic acid content, were not affected by greenhouse cover, but the doped panels induced a 22% reduction in total phenolics and a 14% increase in nitrate content in leaves. The greenhouse covering materials also affected the photochemistry of photosynthesis, as the daily fluctuations in both the effective quantum yield (ΦPSII) and the electron transport rate (ETR) were attenuated under the doped greenhouse. Non-photochemical quenching (NPQ) was closely related to the light environment in all experimental conditions, with the highest values at 14:00 h. Our results showed that the red-supplemented light spectrum under the doped greenhouse cover contributed to increased plant growth and yield, with a corresponding effect on the physiology of photosynthesis.

Background and Aims: Mosses stand out for their ability to sustain photosynthetic activity even when exposed to extreme stress. They have developed intricate protective strategies that safeguard photosynthesis from dehydration, excessive light and oxidative stress. While considerable progress has been made in understanding how dehydration and high light each affect PSII photochemistry, their combined influence on Antarctic mosses is still not well characterized. The present study examines how simultaneous dehydration and high light exposure influence PSII function in three Antarctic moss species: Bryum pseudotriquetrum, Hypnum revolutum and Sanionia uncinata. Methods: Chlorophyll fluorescence parameters, including FV/FM, ΦPSII, RFd, NPQ, qE and qI, were measured under controlled dehydration and high light treatments at the Mendel Polar Station on James Ross Island in the Antarctic peninsula; the obtained curves were analysed with generalized additive mixed models. Key Results: The results showed species-specific responses to the combined stress, displayed as a difference in curve shape, and a strong influence of high light on the desiccation curves’ shapes. Bryum pseudotriquetrum exhibited higher PSII performances under low light while S. uncinata showed a less rapid decline in photosynthetic efficiency under high light exposure and a lower NPQ decline in response to high light compared with the other species. It was observed that high light can strongly affect photosynthesis by enhancing the rate at which photosynthetic efficiency declines and at the same time induces a faster increase in photoinhibition-related quenching (i.e. qI). Conclusions: This study highlights interspecific differences among Antarctic mosses in their sensitivity to photoinhibition during thallus desiccation. Thus, light exposure during desiccation is an important factor to be considered in future ecophysiological studies. Finally, this study also emphasizes the need to examine both intra- and interspecific variability and the molecular and physiological mechanisms driving stress tolerance and adaptation in these species.