Investigations on the CO2 exchange of lichens in the alpine belt. II. Comparative patterns of net Co-2 exchange in Cetraria islandica and Flavocetraria nivalis

The CO2 exchange of two fruticose alpine lichen species was compared with r espect to their thallus water content, light, temperature and moisture in t he field and in the laboratory. Maximum net photosynthesis in both lichens was similar in the field, but in the laboratory Cetraria islandica had high er net CO2 uptake rates than Flavocetraria nivalis. The light compensation point of Cetraria islandica was lower than those of Flavocetraria ia nivali s and increased with increasing temperature. The upper temperature compensa tion point was higher in Cetraria islandica than in Flavocetraria nivalis. Both lichens had similar moisture compensation point in the field and in th e laboratory. The maximal and minimal thallus water content was lower in Ce traria islandica in comparison with Flavocetraria nivalis. In the field hydration is the most important factor which determines the pa ttern of CO2 exchange. CO2 exchange was detected during the daytime and no nocturnal respiration was recorded. Total period of NP was ca. 52% and ca. 45% of time the lichens were inactive. Less but still positive NP was found when the lichens were frozen respectively when air temperature was far bel ow the freezing point.