Abstract
Epiphytic lichens are vital to tropical biodiversity, their distribution shaped by light. Parmotrema tinctorum and Usnea barbata, common in open Cerrado, endure high radiation, necessitating photoprotection. This study tested the hypothesis that the primary photochemistry of P. tinctorum and U. barbata responds differentially to light conditions across distinct landscapes of the Brazilian Savanna, to the height at which lichens were sampled, and to radiation levels from different components of the visible spectrum. Our results demonstrate that P. tinctorum and U. barbata possess efficient photoprotective mechanisms, such as energy dissipation as heat, which enable their survival in the dry and highly illuminated landscapes of the Brazilian Savanna. In particular, stressful environments such as Cerrado and Cerrado Ralo exhibited high DI(0)/RC values, leading to lower photochemical performance in lichen thalli. However, U. barbata showed greater resilience to light stress than P. tinctorum, likely due to the presence of antioxidant metabolites such as usnic acid. Lichens sampled at higher stem positions and exposed to elevated levels of photosynthetically active radiation (PAR) dissipated less energy as heat and exhibited lower photochemical performance, suggesting photosystem II (PSII) damage under these conditions. Conversely, when different components of the visible spectrum were analyzed separately, increasing light intensities reduced DI(0)/RC and enhanced Pi_ABS in the thalli, highlighting photodamage resistance in P. tinctorum and U. barbata. The ability of both species to adapt to high-light environments, combined with their physiological plasticity, supports their broad distribution in these tropical ecosystems.