The long-term effect of removing the UV-protectant usnic acid from the thalli of the lichen Cladonia foliacea

Abstract

Terricolous lichens are abundant in semi-arid areas, where they are exposed to high irradiation. Photoprotection is essential for the algae as the photobiont provides the primer carbon source for both symbionts. The UV-protectant lichen metabolites and different quenching procedures of the alga ensure adequate photoprotection. Since the long-term effect of diminishing UV-protectant lichen metabolites is unknown, a major part of lichen secondary metabolites was removed from Cladonia foliacea thalli by acetone rinsing, and the lichens were then maintained under field conditions to investigate the effect on both symbionts for 3 years. Our aim was to determine if the decreased level of UV-protectant metabolites caused an elevated photoprotection in the algae and to reveal the dynamics of production of the metabolites. Photosynthetic activity and light protection were checked by chlorophyll a fluorescence kinetics measurements every 6 months. The concentrations of fumarprotocetraric and usnic acids were monitored by chromatographic methods. Our results proved that seasonality had a more pronounced effect than that of acetone treatment on the function of lichens over a long-term scale. Even after 3 years, the acetone-treated thalli contained half as much usnic acid as the control thalli, and the level of photoprotection remained unchanged in the algae. However, the amount of available humidity was a more critical limiting environmental factor than the amount of incoming irradiation affecting usnic acid production. The lichenicolous fungus Didymocyrtis cladoniicola became relatively more abundant in the acetone-treated samples than in the control samples, indicating a slight change caused by the treatment.

Effect of light stress on maximum photochemical efficiency of photosystem II and chloroplast structure in cryptogams Cladonia mitis and Pleurozium schreberi

“…On the contrary, bryophytes are better suited for occupying moist habitats, often those that are only available seasonally, but have slower recovery times after experiencing dehydration (Green and Proctor, 2016). The higher the PAR energy, the faster the drying of the thallus (Tobias and Niinemets, 2010;Veres et al, 2022b), which in turn leads to photoinhibition and confirms the first research hypothesis that photosynthetic activity varies over time depending on the amount of PAR energy supplied. The response to high PAR is observed in both C. mitis and P. schreberi, and is more pronounced in lichens (Kappen et al, 1996).…”

“…This observation may indicate that chloroplast degradation or its avoidance reaction is occurring. As noted by other authors (Beckett et al, 2021;Derks et al, 2015;Veres et al, 2022b), high light intensity leads to progressive changes in the cell, which in most cases are irreversible. However, lichens in the sample of natural light showed very high photosynthetic activity and thus were accompanied by intense fluorescence, which informed about the normal state of chloroplast behavior.…”

Cryptogamic Biomass in Pannonic Acidic Sand Steppes Subject to Changing Land-Use

“…Knowledge of the conservation status of bryophytes and lichens is still scarce, and usually their distribution is less well documented than that of the vascular plants. In the last 20 years, in the European dry habitats, numerous projects studied the biodiversity patterns and functional role of lichens and bryophytes [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. Lichen- and bryophyte-rich dry habitats, in spite of being fragmented by anthropogenic activities, can still reach a rather large extent [ 33 , 34 ].…”

“…Since the pioneering works of Verseghy [ 63 , 64 , 65 , 66 , 67 ], cryptogamic biomass and productivity have not been analyzed in Hungary, except for a recent study of the production of the lichen secondary metabolites of a few steppe species [ 31 , 32 ]. Phytosociological studies tend to neglect or discuss only partly the cryptogams.…”