Upland Tundra in the Foothills of the Brooks Range, Alaska, U.S.A.: Lichen Long-Term Photosynthetic CO 2 Uptake and Net Carbon Gain

Abstract

Estimates of carbon gain were obtained based upon integration of previously published measurements of diel courses of CO2 exchange of seven lichen species in their natural tundra habitat. Total net photosynthetic CO2 uptake, CO, loss by dark respiration, and the balance between these were calculated. The field measurements (146 observations of lichen sample diel courses on 26 d distributed over the growth periods from July through September in 1988 and 1989) were classed with respect to 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 the cyanobacterial Peltigera malacea, 1.5 times higher than for Dactylina arctica and 5 times higher than for the least productive Masonhalea richardsonii, both being green algal species. There was an essentially linear correlation across species between the sum of carbon uptake and short-term maximal rates of net photosynthesis, stressing the importance of photosynthetic capacity for carbon gain. Mean respiratory carbon loss for all of the species was ca. 33%. Three groups of species were determined with respect to estimated seasonal carbon balance: high productivity (carbon gain of 24.0-21.5% of thallus carbon content) which included D. arctica, P. malacea, P. aphthosa, and Thamnolia vermicularis, lowest productivity (6.8%) for M. richardsonii, and intermediate for Cetraria cucullata (15.9%) and Stereocaulon alpinum (14.6%). Seasonal carbon gain is related to the maximal possible thallus growth. Estimates of annual lichen biomass increase in typical tundra communities ranged from 47.2 gDW m-2 for