PARENT SESSION
Poster Session #63: Late Breaking and Newsworthy Papers.
Friday, August 9. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

Temperature and light acclimation of photosynthetic capacity in seedlings and mature grafts of different ponderosa pine genotypes.

Momen, B.^*,1, Anderson, P.², ¹ University of Maryland, College Park, MD² University of Minnesota, Grand Rapids, MN

ABSTRACT- A preliminary step to address the effect of predicted rise in temperature on carbon dynamics of forests is to examine the temperature elasticity of key processes involved in carbon fixation in forest trees. For seedling and mature ponderosa pines of different genetic source, we used a response-surface methodology and ANOVA to determine acclimation of maximum net photosynthesis (A_max), and its corresponding light (_Amax) and temperature (T_Amax) to seasonal changes in ambient temperature. As seasonal ambient temperature decreased: (1) A_max did not change in seedlings or mature trees, (2) _Amax did not change in mature trees, but it decreased for new foliage of seedlings from 964 to 872 mmol photons m^-2 s^-1, and (3) T_Amax did not change in seedlings but it decreased in mature trees for both new and one-yr-old foliage, from 26.8 to 22.2, and 24.6 to 21.7 °C, respectively. Results suggest that the photosynthetic capacity of ponderosa pine was maintained even under cool and short days of mild winter, but the optimal temperature for photosynthesis shifted in the direction of seasonal changes in the ambient temperature. Seasonal adjustment to _Amax in seedlings but to T_Amax in mature trees suggests different adaptation strategy for seedlings and mature trees that might be related to their canoy position.

KEY WORDS: Photosynthetic acclimation, Temperature, Ponderosa pine