PARENT SESSION
Contributed Oral Session 154: Photosynthesis and Water Relations: Climate Effects
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 515 A, Level 5, Palais des congrès de Montréal

Acclimation of photosynthesis and respiration to growing season temperatures in Loblolly pine.

Nedlo, Jason^*,1, Teskey, Robert ¹, ¹ University of Georgia, Athens, GA, U.S.A.

ABSTRACT- Plants may be able to adjust rates of photosynthesis and respiration for optimum carbon gain under changing temperature regimes. As air temperatures increase, acclimation of photosynthesis and respiration may be a major component of the plant response to changing temperatures. Understanding these responses is essential for predicting plant growth and performance under global warming scenarios. We hypothesized that tree seedlings grown in warmer environments, compared to those grown in cooler environments, would: (1)have higher rates of photosynthesis and lower rates of respiration, (2) add more biomass due to the ability to gain more carbon, and (3) achieve larger heights and diameters. To test this, we grew loblolly pine seedlings for one season in four locations along a North/South gradient from NC to FL. Coweeta, NC, located beyond the Northern range of loblolly pine, has an average growing season temperature of 17.6⁰C. Athens and Macon, GA are both centrally located in loblolly pine′s natural range and have average growing season temperatures of 22.5 and 23.9⁰C, respectively. In Gainesville, FL, beyond the southern limit of loblolly pine, temperatures averaged 26.3⁰C during the growing season. Plant height and diameter were measured monthly, gas exchange temperature response curves were performed, and in November, all sites were harvested and final biomass measurements were taken. Measured at the same temperatures, seedlings from FL averaged 67% lower respiration rates and slightly higher photosynthetic rates than those grown in cooler NC. Athens seedlings (near the middle of the species native range) produced 10%, 38% and 44% more biomass than those from Macon, Gainesville and Coweeta, respectively. While the root to shoot ratio was similar at the Gainesville and Macon sites, the ratio was 16% and 24% higher than Athens and Coweeta, respectively. This evidence of acclimation to growing season temperatures indicates that loblolly pine may have reduced sensitivity to increasing growing season temperatures associated with climate change but acclimation was not enough to counter the effects of suboptimal and supraoptimal temperatures encountered at the northern and southern extremes of its range.

Key words: Pinus taeda, climate change, temperature response curves, photosynthesis/respiration