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
DI0/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 DI0/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.
