Combination of dehydration and high light exposure effects on PSII photochemistry in three Antarctic moss species

Mosses stand out for their ability to sustain photosynthetic activity even when exposed to extreme stress. They 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.

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 (GAMMs).

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. B. 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 to the other species. It was observed that high light can strongly affect the photosynthesis by enhancing the rate at which the photosynthetic efficiency declines and, at the same time, induces a faster increase of photoinhibition related quenching (i.e. qI).

This study highlighted inter-specific 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 inter-specific variability and the molecular and physiological mechanisms driving stress tolerance and adaptation in these species.