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

High growth temperatures decrease black spruce growth and survival, while increasing thermotolerance to transient extreme heat stress.

Way, Danielle^*,1, Sage, Rowan¹, ¹ University of Toronto, Toronto, Ontario, Canada

ABSTRACT- The response of black spruce (Picea mariana (Mill.) B.S.P.) to predicted future warming will have significant effects on the structure and functioning of the North American boreal forest. We investigated the growth and photosynthetic traits of black spruce grown from seed at cool and warm temperature regimes (22:15°C and 30:23°C day:night temperatures, respectively). Cool-grown seedlings were taller and heavier than warm-grown trees and had significantly lower mortality. Warm-grown seedlings had 30-35% lower net CO₂ assimilation rates than cool-grown trees when measured at both 22°C and 30°C, implicating carbon balance as a major cause for the differences. Seedlings from both growth temperatures were also assessed for changes in thermotolerance: trees were heat stressed (ranging from 35°C to 60°C with durations ranging from 1 minute to 40 minutes) and their ability to withstand the stress was measured as the change in the maximum quantum yield (Fv/Fm) by chlorophyll fluorescence. Warm-grown seedlings show an increased ability to cope with short-term heat stress compared to cool-grown trees across a range of temperatures. This study suggests that higher future temperatures will reduce black spruce growth and survival, even though they may also confer the ability to withstand transient extreme heat stresses.

Key words: climate warming, boreal forest, thermotolerance, photosynthesis