© 2000 Heron Publishing—Victoria, Canada
Selection of white spruce families in the context of climate change: heat tolerance
F. J. Bigras (1)
1. Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, 1055 du P.E.P.S., P.O. Box 3800, Sainte-Foy,
Québec G1V 4C7, Canada (bigras@cfl.forestry.ca) / Received May 19, 1999
Summary
To assess the responses and plasticity of white spruce seedlings (Picea glauca (Moench) Voss) to high temperatures, 12 open-pollinated families differing in growth performance were exposed to a 30-min
heat treatment of 42, 44, 46, 48, or 50 °C with or without heat preconditioning at 38 °C for 5 h. Damage was evaluated based
on chlorophyll fluorescence parameters after heat preconditioning, after the heat treatments and during a 7-day recovery period.
Visible needle damage was also evaluated after the heat treatments and 14 days later. Chlorophyll fluorescence parameters
indicated that seedlings subjected to a heat treatment of 42–43 °C lost the ability to phosphorylate and donate water to photosystem
II (PSII). A heat treatment of 44–46 °C severely limited the ability of the seedlings to use NADPH and ATP in the Calvin cycle.
Based on visible needle damage, families with superior height-growth performance were more sensitive to heat stress than families
with intermediate or inferior height-growth performance. Moreover, families with superior height-growth performance had low
photochemical efficiencies in the light (ΔF/Fm′) after heat treatment. Heat preconditioning increased the thermotolerance of the seedlings. However, the data suggest that
white spruce seedlings exhibiting fast-growing characteristics under present conditions may not grow as well at higher temperatures.
Keywords:
chlorophyll fluorescence, global change, global warming, heat damage, heat stress, high temperature, photosystem II, Picea glauca, thermotolerance..
