COMBINED EFFECTS OF CO2 CONCENTRATION AND NUTRIENT STATUS ON THE BIOMASS PRODUCTION AND NUTRIENT-UPTAKE OF BIRCH SEEDLINGS (BETULA-PENDULA)

Birch seedlings (Betula pendula) were grown for four months in a green house at three nutrient levels (fertilization of 0, 100 and 500 kg ha( -1) monthly) and at four CO2 concentrations (350, 700, 1050 and 1400 p pm). The effect of CO2 concentration on the biomass production depende d on the nutrient status. When mineralization of the soil material was the only source of nutrients (0 kg ha(-1)), CO2 enhancement reduced t he biomass production slightly, whereas the highest production increas e occurred at a fertilization of 100 kg ha(-1), being over 100% betwee n 350 and 700 ppm CO2. At 500 kg ha(-1) the production increase was sm aller, and the production decreased beyond a CO2 concentration of 700 ppm. The CO2 concentration had a slight effect on the biomass distribu tion, the leaves accounting for the highest proportion at the lowest C O2 concentration (350 ppm). An increase in nutrient status led to a lo nger growth period and increased the nutrient concentrations in the pl ants, but the CO2 concentration had no effect on the growth rhythm and higher CO2 reduced the nutrient concentrations.