High-light-intensity damage to the foliose lichen Lobaria pulmonaria within a natural forest: the applicability of chlorophyll fluorescence methods

The annual course of irradiance was recorded at two vertical and even-aged neighbouring Quercus stems, one rich in L. pulmonaria, one without. Irradia nce never exceeded 610 mu mol photons m(-2) s(-1) at the L. pulmonaria sire , whereas the L. pulmonaria-deficient site could experience 2h daily 2000 m u mol photons m(-2) s(-1), and 6 h above 1000 mu mol photons m(-2) s(-1) du ring a clear day in early spring. Thalli oft. pulmonaria were transplanted to these two stems. During the first 40 days (April-May), transplants at th e L. pulmonaria-deficient site developed severe chlorophyll degradation, an d a substantial reduction in maximal PS LT efficiency (F-V/F-M) even when m easured after a 48-h recovery period at low light intensity. Extensive blea ching was formed along light-exposed sides of the tiny ridges on the upper side. Subsequent to this damage, F-V/F-M gradually rose to nearly normal le vels during the following year. This apparent recovery was probably mainly due to irreversible loss of damaged chlorophyll, but also to some level of acclimation. No damage was observed in control transplants on the L. pulmon aria-rich tree, which were the only transplants gaining sufficient growth f or new attachment to the new substratum during the 397-day transplantation period. Nevertheless, a fine-scale, bur highly significant seasonal variati on in F-V/F-M of control transplants reflected variations of even low irrad iance levels. F-V/F-M, as measured after a 48-h recovery period at low ligh t intensity, is an efficient method for recording permanent high light dama ges at and shortly after damage is formed. However, F-V/F-M is nor a useful estimator of chronic long-term damage. (C) 2000 The British Lichen Society .