Das Projekt "Gas exchange in Twings of Mature Coniferous Trees in the Subalpine Zone, influenced by elevated CO2 Concentrations in the Air" wird/wurde gefördert durch: Eidgenössische Forschungsanstalt für Wald, Schnee und Landschaft. Es wird/wurde ausgeführt durch: Eidgenössische Forschungsanstalt für Wald, Schnee und Landschaft.Over several years, photosynthesis and transpiration in shoots of mature coniferous trees at natural subalpine sites (Seehornwald and Stillberg, Davos) have been measured using thermoelectrically climatized gas exchange chambers with different CO2 concentrations (ambient and ambient + 350ppm CO2). Maximum photosynthetic capacity of the shoots has been estimated periodically. In addition to the gas exchange measurements at ambient CO2 concentration, past measurements, taken at the same places, will serve as controls. Leading Questions: Are the photosynthetic rates of mature coniferous trees different at elevated CO2 concentrations? Are there changes in the water relations (transpiration, stomatal conductance) of shoots of mature coniferous trees exposed to elevated CO2 concentrations? In short-term experiments with elevated CO2 concentration, an increase in CO2 assimilation is observed. Is there, with time, an adaptation back to the present photosynthetic rates? Is the temperature optimum in shoots grown under elevated CO2 concentration different?