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

Acclimation of photosynthetic activity to irradiance within the canopy of three deciduous broadleaf tree species in northern Japan.

Tobita, Hiroyuki^*,1, Utsugi, Hajime¹, Kitao, Mitsutoshi¹, Kayama, Masazumi¹, Maruyama, Yutaka¹, ¹ Hokkaido Research Center, Forestry and Forest Products Research Institute, Sapporo, Japan

ABSTRACT- The objective of this study was to evaluate photosynthetic acclimation to the canopy light gradient of Betula platyphylla, Kalopanax septemlobus and Quercus mongolica as part of a CO₂ budget simulation in a secondary deciduous broadleaf forest. Vertical and temporal trends in photosynthetic capacity, the maximum rate of carboxylation (V_cmax), leaf nitrogen per area (N_area) and the vertical trends of chlorophyll fluorescence were measured. V_cmax varied extensively among species, by vertical canopy position, and by season. A higher V_cmax in K. septemlobus compared to other species was due to an elevated N_area at higher canopy layers, and by an increased ratio of V_cmax/N_area at lower layers. In general, the vertical variability in V_cmax of each species was closely correlated with the change in N_area. The relationship between N_area and V_cmax, however, varied during the growing season, suggesting that the seasonal physiological changes of V_cmax should be a variable in calculating CO₂ budgets in this forest. In addition, the electron transport rate (ETR) at high light intensities demonstrated a vertical trend similar to V_cmax. The higher ETR of K. septemlobus at each canopy position was associated with elevated photochemical quenching (q_P). The maintenance of a relatively high ETR, even at lower canopy layers, suggests that K. septemlobus has an advantage in the utilization of sunfleck and diffuse solar radiation as well as acclimation to abrupt changes in light conditions.

Key words: chlorophyll fluorescence, electron transport rate, leaf nitrogen per unit leaf area, maximum rate of carboxylation