EFFECTS OF NEEDLE AGE, LONG-TERM TEMPERATURE AND CO2 TREATMENTS ON THE PHOTOSYNTHESIS OF SCOTS PINE

Naturally regenerated 20-25-year-old Scots pine (Pinus sylvestris L.) trees were grown in open-top chambers in the presence of an elevated t emperature or CO2 concentration, or both. The elevated temperature tre atment was administered year-round for 3 years. The CO2 treatment was applied between April 15 and September 15 for 2 years. The photosynthe tic responses of 1- and 2-year-old needles to varying photon flux dens ities (0-1500 mu mol m(-2) s(-1)) and CO2 concentrations (350, 700 and 1400 mu mol mol(-1)) during measurement were determined. The CO2 trea tment alone increased maximum photosynthetic rate and light-use effici ency, but decreased dark respiration rate, light compensation and ligh t saturation regardless of needle age. In contrast, the temperature tr eatment decreased maximum photosynthetic rate and photosynthetic effic iency, but increased dark respiration rate, light compensation and lig ht saturation. The aging of needles affected the photosynthetic perfor mance of the shoots; values of all parameters except photosynthetic ef ficiency were less in 2- than in I-year-old needles. The CO2 treatment decreased and the temperature treatment enhanced the reduction in max imum photosynthesis due to needle aging.