Photoprotective strategies in pale versus melanic boreal hair lichens: non-photochemical quenching compensates for less protective fungal pigments.

Hair lichen photoprotection involves algal and fungal strategies while hydrated, with pale lichens compensating weak fungal cortical pigments through high, rapidly induced non-photochemical quenching by the photobiont. Hair lichens play vital roles in boreal forests by influencing nutrient cycles, microclimates, and providing habitats for invertebrates and forage for animals. This study examines two widespread and dominant species, Bryoria fuscescens and Alectoria sarmentosa, which possess different fungal pigments-dark light-absorbing melanin in Bryoria, and pale reflecting usnic acid in Alectoria. These cortical pigments affect species distribution, with Bryoria favoring sun-exposed forest canopies due to its efficient light-protective melanin, while Alectoria thrives in partly shaded, moist environments. By investigating sympatric populations, we explored whether non-photochemical quenching (NPQ) compensates for Alectoria's less-effective sun-screening pigment. Our results reveal that Alectoria exhibits higher and more rapidly induced NPQ compared to Bryoria, along with faster recovery from photoinhibition. The flexibility and rapid response of Alectoria's NPQ help mitigate high-light stress, optimizing growth in fluctuating light environments. These compensatory mechanisms suggest that, despite weaker cortical pigmentation, hydrated Alectoria can sustain photosynthesis and recover from light-induced damage more efficiently. However, because NPQ does not function in the desiccated state-where efficient sun-screening by cortical pigments is essential-Alectoria is confined to humid and sheltered forest canopies in drier macroclimates but not in rainforest climates. This study underscores the adaptive strategies of both photobionts and mycobionts in hydrated hair lichens to manage varying light conditions in boreal forests, highlighting NPQ as a compensating mechanism in lichen photoprotection. It advances our understanding by illustrating how the transition from dry to wet conditions amplifies the algal partner's contribution to overall photoprotection.