High-light damage in air-dry thalli of the old forest lichen Lobaria pulmonaria - interactions of irradiance, exposure duration and high temperature

High-light damage in air-dry thalli of Lobaria pulmonaria were measured in the laboratory as reductions in maximal PSII efficiency (F-V/F-M) after a 4 8 h recovery in a hydrated state at low light to account for permanent dama ge. Thalli treated with the lowest light dose (90 mol photons m(-2)) recove red normal F-V/F-M-values with increasing irradiances (400-700nm) up to 100 0 mu mol photons m(-2) s(-1). Doubling this dose lowered the threshold leve l for damage from 1000 to 320 mu mol photons m(-2) s(-1), and reduced F-V/F -M at 1000 pmol photons m(-2) s(-1) by more than 50%. A second doubling of the dose to 360 mol photons m(-2) caused damage at 200 mu mol photons m(-2) s(-1), and a nearly complete cessation of PSII efficiency occurred at 1000 mu mol photons m(-2) s(-1). No reciprocity of irradiance and duration of i llumination for PSII function was found. The measured time-dependent decrea se in F-V/F-M was remarkably similar for the naturally coupled, but artific ially separated, light and temperature factors. Therefore, the damage of hi gh light on desiccated L. pulmonaria seemed to be an additive effect of hig h irradiance and high temperatures. Air-dry thalli were highly heat suscept ible, being affected already at temperatures around 40 degrees C. Logging o perations in forests are likely to raise the solar radiation at remaining l ichen sites to destructive levels.