UPLAND TUNDRA IN THE FOOTHILLS OF THE BROOKS RANGE, ALASKA, USA - LICHEN LONG-TERM PHOTOSYNTHETIC CO2 UPTAKE END NET CARBON GAIN

Estimates of carbon gain were obtained based upon integration of previ ously published measurements of diel courses of CO2 exchange of seven lichen species in their natural tundra habitat. Total net photosynthet ic CO2 uptake, CO2 loss by dark respiration, and the balance between t hese were calculated. The field measurements (146 observations of lich en sample diel courses on 26 d distributed over the growth periods fro m July through September in 1988 and 1989) were classed with respect t o 5 types of weather conditions. The occurrence of these weather types during the growing season was established according to meteorological data. Combination of these data sets permits an estimate of seasonal carbon gain. Integrated photosynthetic carbon uptake was highest for t he cyanobacterial Peltigera malacea, 1.5 times higher than for Dactyli na arctica and 5 times higher than for the least productive Masonhalea richardsonii, both being green algal species. There was an essentiall y linear correlation across species between the sum of carbon uptake a nd short-term maximal rates of net photosynthesis, stressing the impor tance of photosynthetic capacity for carbon gain. Mean respiratory car bon loss for all of the species was ca. 33%. Three groups of species w ere determined with respect to estimated seasonal carbon balance: high productivity (carbon gain of 24.0-21,5% of thallus carbon content) wh ich included D. arctica, P. malacea, P, aphthosa, and Thamnolia vermic ularis, lowest productivity (6.8%) for M, richardsonii, and intermedia te for Cetraria cucullata (15.9%) and Stereocaulon alpinum (14.6%). Se asonal carbon gain is related to the maximal possible thallus growth. Estimates of annual lichen biomass increase in typical tundra communit ies ranged from 47.2 g(DW) m(-2) for dry to 10.8 g(DW) m(-2) per seaso n for moist Cassiope dwarf-shrub heath.