Genetic variation among paper birch (Betula papyrifera MARSH.) populations in germination, frost hardiness, gas exchange and growth

Patterns of genetic variation in paper birch (Betula papyrifera MARSH.) were evaluated at the population level. A sample of 18 populations from the south interior, central interior and north coast of British Columbia were examined in a number of traits related to germination (germination capacity, germination speed, peak value and germination value), fall and winter frost hardiness, gas exchange (transpiration rate, stomatal conductance, net photosynthesis, instantaneous water use efficiency and mesophyll conductance) and biomass accumulation after the first and the second growing season. Analysis of variance or covariance revealed significant differences among the populations in all studied attributes except for stomatal conductance and height after the second growing season. Proportion of total variance attributed to population effect was up to 92% for germination parameters, 63% for fall frost hardiness, 22% for winter frost hardiness, 63% for biomass after the first growing season, 20% for biomass after the second growing season, and 5% for gas exchange variables. Germination speed and capacity were positively correlated and were higher in populations from colder climates. Central interior populations had the highest level of fall frost hardiness and were the most uniform with respect to that trait. There were large variations in fall frost hardiness within north coastal and south interior populations. Revealed patterns of variations have implications for paper birch genetic resources management and conserva