Genetic differences in physiological and morphological characteristics of Sitka alder populations in British Columbia
Creators: name: Benowicz, Andy
Publisher: name: University of British Columbia
Year: 2009

description: Patterns of genetic variations in adaptive and quantitative attributes of Sitka alder, Alnus sinuata Rydb., were examined at the population level. The following traits were studied: germination, frost hardiness, bud break, characteristics related to gas exchange (photosynthesis, dark respiration, stomatal conductance, transpiration, carboxylation efficiency, stomatal sensitivity to vapor pressure deficit and intrinsic water use efficiency) and characteristics related to biomass allocation (height, stem diameter, shoot dry weight, root dry weight, height growth rate and number and size of major stems per plant). The number of examined populations was 29, all but one from British Columbia. There were large genetic differences among the populations in all measured traits except for spring frost hardiness and stomatal sensitivity to vapor pressure deficit. Population genetic structure (variance within and between populations) was investigated: inter-population variations accounted for 13-31% and 26-61%) for gas exchange and biomass related variables, respectively. The populations differed significantly in fall and winter cold resistance, though the differences were less pronounced in maximum hardiness than were found for the timing of frost hardiness development. On 11 November, 1996 65% of the total variation in frost injury index was explained by the differences between the populations, while on 15 December, 1996 33%) of the total variance was due to the population effect. The observed patterns of large genetic variations in Sitka alder populations represent a challenge for gene conservation efforts in high elevation ecosystems. Based on univariate (multiple linear regression) and mulitvariate methods (canonical correlations and cluster analysis), geographic patterns of variation were found for most traits. Variations related to geography were particularly strong in fall frost hardiness (R2 = 0.62), shoot dry weight (R = 0.64), growth rate in July (R = 0.70), ratio of root dry weight to total dry weight (R2 = 0.67) and net photosynthetic rate (R2 = 0.52). Most of the variation was due to latitude and distance from the coast. Seedlings generated from northern seed sources were in general more frost hardy, smaller and allocated more carbon to roots compared to shoots. Plants from the interior wet belt were frost hardy to the same levels as coastal seedlings suggesting that snow cover plays a role in Sitka alder adaptation to low temperatures. Rate of photosynthesis (A) increased largely with the distance from the coast and, to a lesser degree, with elevation and latitude implying that an inverse relationship exists between A and the length of the growing season. Interior populations had higher A due to higher carboxylation efficiency and stomatal conductance (gs). As a result of higher gs, plants from more xeric interior regions tend to have lower water use efficiency. Productivity was negatively correlated with A and positively with water use efficiency. Speed of germination did not affect the plant size after one growing season and was independent from the germination completeness. Strong positive correlation was found between timing of frost hardiness development and spring bud break.