Ultraviolet radiation affects growth and photosynthesis in the old forest lichens Lobaria pulmonaria and L. virens
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- Master's theses (INA) 
Depletion of the ozone layer and human activities such as logging may increase ultraviolet (UV) radiation-exposure of forest lichen habitats. Previous studies show that some forest lichens are highly susceptible to high light exposure. Studies on the effect of UV radiation on lichen viability and growth are rare. This study assesses how UV radiation affects growth, melanic pigment formation and photosynthesis in the old forest lichens Lobaria pulmonaria and L. virens. The lichens were exposed to different radiation treatments by screening specific wavelength ranges of natural solar radiation. Lichen thalli were placed under three different screens in a fully exposed site in Ås, southeastern Norway, for four weeks during early autumn. Three radiation treatments were used: 1. Photosynthetic active radiation (PAR), 2. PAR + UV-A and 3. PAR + UV-A + UV B. UV exposure reduced relative growth rates (RGR) in Lobaria pulmonaria and L. virens, compared to the PAR treated thalli. In L. pulmonaria, UV exposure reduced relative thallus area growth rate (RTAGR) more than the RGR reduction. All treatment groups of both species experienced an increase in specific thallus mass (STM). Both UV A and UV-B induced melanic pigment synthesis in L. pulmonaria, evidenced by a darker colour, lower mean reflectance and higher browning reflectance index (BRI) compared to the PAR treated thalli. The highest pigment production occurred in UV-B-exposed L. pulmonaria, in which no indication of photoinhibition was detected. PAR treated L. pulmonaria had significantly lower photosynthetic CO2 uptake at high irradiances compared to the control, but no significant differences were found between the UV treated thalli and the control. There was no evidence that UV exposure induced melanic pigment production in L. virens. All treatment groups of L. virens experienced photoinhibition. These results indicate that L. pulmonaria has the ability to acclimate to high light conditions, if additionally exposed to UV radiation and sufficiently hydrated. No clear evidence indicated high light-acclimation in L. virens. The high growth rates observed in L. pulmonaria and L. virens show that growth is a highly useful parameter in short-term experiments assessing the ecophysiology of lichens.