CHLOROPHYLL-A FLUORESCENCE AND CO2 EXCHANGE OF UMBILICARIA-APRINA UNDER EXTREME LIGHT STRESS IN THE COLD

A lichen growing in a continental Antarctic region with low temperatur es and strong irradiance in summer was investigated for evidence of ph otoinhibition. Field experiments with Umbilicaria aprina from a shelte red site with heavy snowpack showed no effects of photoinhibition when the lichen was exposed to strong sun irradiance for nearly 11 h a day . This was evident from CO2 exchange and simultaneous chlorophyll a fl uorescence measurements. CO2 exchange was also not affected if quartz glass allowing greater UV penetration, was used as a lid for the cuvet te. The dependency of net photosynthesis on photosynthetic photon flux density suggests that the lichen is photophilous.