Plant Material
Both adult trees used in long term data and seedlings used in the short term drought trials come from twenty-one seed sources from seven regions across Canada. Long term data was collected from trees planted in May, 1982, at Calling Lake Experimental Area, Lac La Biche Forest, Alberta. Seed sources have been grouped into regions by geographical location, with each region containing two to four sites. Total number of trees planted from each region varies from 100 to 185.
Other seeds from the original seed sources were planted in the summer of 2017. Seedlings were grown in a growth chamber for one year before being separated and placed into drought treatments. After about six months, seedlings were put through a six week dormancy period, to simulate a winter period. Each region had 30-100 individuals.
Other seeds from the original seed sources were planted in the summer of 2017. Seedlings were grown in a growth chamber for one year before being separated and placed into drought treatments. After about six months, seedlings were put through a six week dormancy period, to simulate a winter period. Each region had 30-100 individuals.
Seed Source Climate
Figure 4. Maps indicating location and climate variables for our seed source sites. A) Seeds from twenty one seed sources in seven regions (marked by color), and the long term study site, Calling Lake Experimental Area. B) Map of mean annual precipitation (MAP) measured in mm, across the twenty one source sites. C) Map of mean annual temperature (MAT) across seed sources sites. D) Map of annual heat moisture index (AHM), measured as (MAT+10)/(MAP/1000).
Drought Treatments |
Chlorophyll Fluorescence |
Seedlings were randomly placed in one of two treatments:
Drought was based on needle water potential, so as to control for seedling size differences. Drought treatments lasted 4 weeks, with needle water potential reaching a level of -3.5MPa. |
Chlorophyll fluorescence was measured 3 times a week during the treatment cycle with a handheld chlorophyll fluorometer (Mini-PAM II, Walz). The leaf clip was clamped onto the uppermost clump of needles during measurement.
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