Response of needle dark respiration of Pinus koraiensis and Pinus sylvestriformis to elevated CO2 concentrations for four growing seasons’ exposure

The long-term effect of elevated CO₂ concentrations on needle dark respiration of two coniferous species—Pinus koraiensis and Pinus sylvestriformis on the Changbai Mountain was investigated using open-top chambers. P. koraiensis and P. sylvestriformis were exposed to 700, 500 μmol · mol⁻¹ CO₂ and ambient CO₂ (approx. 350 μmol · mol⁻¹) for four growing seasons. Needle dark respiration was measured during the second, third and fourth growing seasons’ exposure to elevated CO₂. The results showed that needle dark respiration rate increased for P. koraiensis and P. sylvestriformis grown at elevated CO₂ concentrations during the second growing season, could be attributed to the change of carbohydrate and/or nitrogen content of needles. Needle dark respiration of P. koraiensis was stimulated and that of P. sylvestriformis was inhibited by elevated CO₂ concentrations during the third growing season. Different response of the two tree species to elevated CO₂ mainly resulted from the difference in the growth rate. Elevated CO₂ concentrations inhibited needle dark respiration of both P. koraiensis and P. sylvestriformis during the fourth growing season. There was consistent trend between the short-term effect and the long-term effect of elevated CO₂ on needle dark respiration in P. sylvestriformis during the third growing season by changing measurement CO₂ concentrations. However, the short-term effect was different from the long-term effect for P. koraiensis. Response of dark respiration of P. koraiensis and P. sylvestriformis to elevated CO₂ concentrations was related to the treatment time of CO₂ and the stage of growth and development of plant. The change of dark respiration for the two tree species was determined by the direct effect of CO₂ and long-term acclimation. The prediction of the long-term response of needle dark respiration to elevated CO₂ concentration based on the short-term response is in dispute. Supported by the National Natural Science Foundation of China (Grant No. 30400051), the National Basic Research Program of China (Grant No. 2002CB412502) and the Key Program of the National Natural Science Foundation of China (Grant No. 90411020)