Canadian Forest Service Publications
Selection of white spruce families in the context of climate change: heat tolerance. 2000. Bigras, F.J. Tree Physiology 20: 1227-1234.
Issued by: Laurentian Forestry Centre
Catalog ID: 20437
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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.