Aspect-dependent high-irradiance damage in two transplanted foliose forest lichens,Lobaria pulmonariaandParmelia sulcata

Abstract

High-irradiance damage in two epiphytic lichens was recorded as reduction in predawn photosystem II quantum yield (Fv/Fm) measured at the end of a night with full hydration. Measurements were repeated during a 29-day transplantation in early summer at defined aspects (north, east, south, west, perpendicular to the sun at noon, and shade) in an open site at 60°N. These treatments included the contrasts that remaining lichens adjacent to clear-cut areas could experience subsequent to logging. The Fv/Fmvalues declined linearly with the mean irradiance during the previous day, with the old-forest epiphyte Lobaria pulmonaria (L.) Hoffm. being consistently more severely photoinhibited than the ubiquitous Parmelia sulcata Taylor. Both irradiance levels and predawn Fv/Fmvalues decreased in the following direction: shaded controls > transplants facing north > south, east, west > transplants perpendicular to the sun. Since the transplantation period happened to be very rainy with favorable conditions for recovery, all transplants survived. Nevertheless, photoinhibition was sustained from one day to the other, especially in the old-forest species L. pulmonaria, implying a long-lasting strain, which could affect long-term performance and survival of thalli. The results are discussed in a wider context including confounding effects of irradiance in forests, with implications to facilitate lichen conservation in managed forests.