Adaptive variation in fall cold hardiness of aspen from northwestern Ontario
Y. H. Weng (1, 2) and W. H. Parker (3)
1. New Brunswick Department of Natural Resources, Kingsclear Forest Nursery, Island View, NB E3E 1G3, Canada / 2. Corresponding author () / 3. Faculty of Forestry and Forest Environment, Lakehead University, Thunder Bay, ON P7B 5E1, Canada / Received February 9, 2007; accepted April 18, 2007; published online October 15, 2007
Summary
We investigated adaptive variation in fall cold hardiness development based on the electrical conductivity of tissue diffusates
(EC) among 20 aspen provenances from northwestern Ontario. Provenance accounted for over 40% of the total variation in cold
injury for seven dates from September through November in three provenance trials. Principal component analysis was performed
to summarize the combinations of results for all sampling sites, dates and temperatures (traits). Principal component (PC)-1
represented fully developed cold hardiness differences among provenances; PC-2 represented differences in the timing of the
onset of cold hardiness development; and PC-3 represented a site-related difference in cold hardiness development. Heat sum
in early summer and late summer precipitation together were the best predictors of absolute degree of cold hardiness (PC-1),
whereas temperatures for mid- to late summer were best for predicting onset of cold hardiness development (PC-2).
In a second study, we assessed the efficacy of chlorophyll fluorescence (CF) as a simpler technique for determining the cold
hardiness of aspen stem samples. Fall cold hardiness of stem samples of 12 of the original 20 provenances was estimated by
CF, and the results were evaluated by a visual scoring (VS) method. Correlations between EC and CF measurements from the two
studies were moderately strong based on the extent of cold hardiness in October of each year, but were negative for September
dates because of a later onset of cold hardiness in the EC study year. Although the EC and CF methods gave similar cold hardiness
values for stem samples from 12 provenances, the CF method may be preferred to the EC or VS method for species with chlorophyllous
stems because of its greater ease of use.
Keywords:
chlorophyll fluorescence, electrical conductivity, Populus tremuloides, principal component analysis, provenance trial, visual scoring.
