Photosynthesis of Sphagnum fuscum at long-term raised CO 2 concentrations

Rate of net photosynthesis in Sphagnum fuscum (Schimp.) Klinggr. was measured during long-term (50–122 days), and subsequently during short-term (/2 h), exposure to 350, 700, 1 000 or 2 000 ppm CO2 concentrations. Raised CO2 concentrations caused a general increase in the rate of net photosynthesis, increasing the rate of photosynthesis at light saturation and causing a given rate of net CO2 exchange to be reached at lower light fluxes. The relative increase in the rate of net photosynthesis by increasing radiation fluxes was independent of the CO2 treatment. The rates of net photosynthesis at enhanced CO2 concentrations gradually decreased compared to rates found with the 350 ppm treatment and this acclimation was also noticed during short-term exposure to all four CO2 concentrations. At 2 000 ppm of CO2, the depression of net photosynthesis at high water contents, found at lower CO2 concentrations, was removed. Observed rates of net photosynthesis indicated that water-use efficiency of Sphagna was not coupled with constant long-term CO2 concentrations.