Temperature thresholds of shoot elongation in provenances of Pinus contorta

Periodicity of shoot elongation in seedlings of Pinus contorta Dougl. ex Lo ud. was assessed during one growing season in two extremely different envir onments (Cowichan Lake, and Red Rock, British Columbia) for 109 provenances sampled range wide. Analysis of variance of total elongation and growth pa rameters showed significant differences among geographic regions and among provenances within each region. Our study also revealed tremendous genotype -by-environment interaction for growth and phenological traits. The respons e of growth to temperature of each provenance was assessed from their growt h curve using an original methodology. The estimated temperature threshold of the provenance growth responses (i.e., the temperature for which the res ponse reaches half of its maximum) varied between 4.1 and 6.5 degreesC amon g regions. Threshold temperatures showed less variation than total elongati on, and only the northern provenances showed thresholds significantly diffe rent from the other regions. Our results show that, across highly contrasti ng environments, relationship between phenology and growth may not be as im portant as the relationship between growth and number of internode priomord ia. This tempers the results of studies, carried out in one or few similar environments, that have shown that phenological differences were important in determining total height growth in lodgepole pine.