Adaptive variation in growth, phenology, cold tolerance and nitrogen fixation of red alder (Alnus rubra Bong.)

Abstract

Red alder (Alnus rubra Bong.) is the most abundant deciduous tree on the Pacific coast of North America and its use as a timber species is increasing. To explore adaptive variation and genotype×environment interactions in this species, we examine the pattern and degree of variation in physiological and growth traits among 59 families of red alder, and relate this variation to the climates of family origin. Red alder families from coastal British Columbia were grown in common garden experiments at two contrasting test sites. We determined the degree of local adaptation among red alder families and the major climatic variables driving adaptive variation in this species. Significant genetic variation among regions was detected in height, diameter, canopy cover, cold hardiness and nitrogen concentration of red alder families. Differences in continentality and available moisture of the climate of origin explained most of the among-family variation in autumn canopy cover, bud burst, and cold hardiness, whereas temperature and length of the growing season of origin was associated with among-family differences in cold hardiness and growth. Families from northern, moist, coastal regions had earlier bud burst at the southern test site, and less autumn canopy cover, lower nitrogen concentrations but higher nitrogen fixation, on average, at both test sites. A trade-off between growth and cold hardiness of red alder families was clearly evident, and family height at the southern test site was negatively correlated with cold hardiness, whereas there was a positive correlation at the northern test site. Red alder families vary in the degree of phenotypic plasticity; however, our results show that most red alder families tested are relatively tightly adapted to their climate of origin and may perform sub-optimally if planted in a contrasting climate. Phenology, cold hardiness, survival and height of tightly adapted families will be most affected by assisted migration or long-term climate change, but some families do not show strong adaptation to their climate of origin and will be more able to acclimate to deviations in climate.