The Effects of Temperature Treatment on Photosynthesis of Pitch Pine from Northern and Southern Latitudes

Abstract

Pitch pine (Pinus rigida Mill.) seedlings were grown at constant temperatures of either 21.degree. C or 29.degree. C. Photosynthetic temperature and light response curves were determined after 59, 107 and 153 days. Rates of CO2 uptake decreased with age, and the response to changes in light and temperature became less pronounced. Growth temperatures had no effect on the photosynthetic temperature optimum, and populations from Quebec [Canada], New Jersey and Tennessee [USA] all had the same temperature optimum and response pattern. For the Tennessee population, growth at 21.degree. C depressed the rate of photosynthesis at all temperatures at both 59 and 107 days, but stimulated it at 153 days. The Quebec population showed no effect of premeasurement temperature at 59 or 153 days, and the New Jersey population was intermediate in this respect. Photosynthetic plasticity, defined as the difference between photosynthetic rates of seedlings grown at 21.degree. C and those grown at 29.degree. C, was related inversely to the degree of seasonal variation under which the populations had evolved.