The photosynthetic irradiance-response of Norway spruce exposed to a long-term elevation of CO2 concentration

During an open-top chamber experiment performed in a mountain stand of young (12-year-old) Norway spruce (Picea abies [L.] Karst.), the trees were exposed to one of two CO2 concentrations (ambient CO2, AC, or AC + 350 mu mol mol(-1) = elevated CO2, EC) continuously over three growing seasons. To evaluate the EC influence, measurements of the relations between the rate of net CO2 uptake (P-N) and incidental photosynthetically active photon flux density (PPFD), as well as the content of photosynthetic pigments and chlorophyll (Chl) a fluorescence were taken in the third growing season. The short-term response to EC was evident mainly on ribulose-1,5-bisphosphate carboxylase/oxygenase kinetics without any significant change to the utilization of radiant energy. The long-term effect of EC was responsible for a decrease in P-N, Content of Chl a + b, F-v/F-m ratio, quantum yield of fluorescence, and photochemical quenching. Changes of stoichiometry between the electron transport, Calvin cycle and the end-product synthesis were confirmed for responses to the longterm import of EC and led to a definition of the photosynthetic acclimation to EC an Norway spruce.