PARENT SESSION
Poster Session 2: Forest Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Effects of elevated [CO₂] and nutrient on photosynthetic functions of birch seedlings.

Zhang, Shouren¹, Dang, Qing-Lai^*,1, ¹ Faculty of Forestry and the Forest Environment, Thunder Bay, Ontario, Canada

ABSTRACT- To investigate the interactive effects of elevated [CO₂] and nutrition on photosynthesis, white birch seedlings were exposed to the factorial combinations of two nutrient regimes (high vs. low N-P-K) and two [CO₂] levels (ambient vs. doubled) for four months in the greenhouse. Large pots were used to eliminate pot size limitation on root growth. Photosynthesis and related variables were measured 2.5 and 3.5 months after the start of treatment. We found that the CO₂ elevation enhanced Pn, IWUE, Vcmax, Jmax, F/Fm′ and Jc, but suppressed gs, E and J_O/J_T. However, the effects on Vcmax, Jmax, F/Fm′ and Jc became insignificant after 3.5 months of treatment. The CO₂ elevation increased Pn by 41 % and 43%, respectively, after 2.5 and 3.5 months of treatment. The stimulation of Pn, Vcmax, Jmax, F/Fm′ and Jc by the CO₂ elevation was much greater under the high than the low nutrient regime. The CO₂ effects on g_s and E were similar under the two different nutrient regimes. The high nutrient treatment significantly increased Pn, Vcmax, Jmax, TPU, (Fm′-F)/Fm′ and Jc, but decreased J_O/J_T (Pn increased by 59% and 93 %, respectively, after 2.5 and 3.5 months of treatment). Jmax was less sensitive to the nutrient treatment than Vcmax. The low nutrient suppression of Pn was mainly attributed to increases in mesophyll resistance rather than stomatal limitation. The CO₂ elevation reduced the total leaf nitrogen concentration, particularly under low nutrient, but had no significant effect on leaf P and K concentration. Among the three nutrient elements, leaf K concentration was the least sensitive to the nutrient treatment.

Key words: photosynthesis up-regulation, boreal trees, ecophysiology, paper birch