In a previous publication we described diel courses of CO 2 exchange and microclimate conditions for characteristic lichens in their natural habitat within upland tundra communities of northern Alaska. The influence of individual environmental factors on net photosynthesis (NP) of Cetraria cucullata, Dactylina arctica, Masonhalea richardsonii, Peltigera aphthosa, Peltigera malacea, Stereocaulon alpinum , and Thamnolia vermicularis was analyzed in the present study. CO 2 exchange measurements were conducted in the laboratory, and clear response characteristics with respect to light, water content (WC), temperature, and external CO 2 concentration were established under controlled conditions. In addition, dependencies of NP on these factors were extracted from field data. These measurements show a high scatter in data points, however, they represent the range of actual performance of the lichens under natural conditions. In general both, field and laboratory data sets, agree well with respect to absolute rates of photosynthetic capacity as well as response characteristics. The combined information from both sources enable us to identify and describe those physiological features which are relevant for photosynthetic production of the lichens at this tundra site. There were large differences in maximal rates of NP attained under natural ambient CO 2 which were expressed more strongly under conditions of CO 2 saturation. Photosynthetic capacity of the cyanobacterial P. malacea is ten times higher than that of the green algal M. richardsonii . In the field, actual photosynthesis often seemed to be depressed due to photoinhibition. Photosynthetic carbon gain occurred even with thallus temperatures of −10°C, while the temperature optimum of NP was between 11 and 22°C. Most of the species responded to supra-optimal degrees of WC with a pronounced depression in NP. Elevated ambient CO 2 concentration prevented this decrease in NP, indicating that it was caused by increased resistance of the thallus to CO 2 diffusion. Depression of NP at high thallus WC regularly occurred under natural conditions, impairing primary production. Response characteristic of the lichens to experimental increase in ambient CO 2 is highly dependent on thallus hydration. At optimal WC some species are already saturated by natural ambient CO 2 at least at lower light intensities. Possible future increase in natural ambient CO 2 concentration will impact lichen NP in particular when the thalli are highly water saturated.