Variation in bud phenology, frost tolerance and non-structural carbohydrates among white spruce seed sources on climate-contrasted test sites: implications for assisted migration
To assess the potential impacts of climate change on white spruce local adaptation, six seed sources were evaluated seven years after plantation on two test sites with contrasting growing conditions and latitude in Quebec. Bud set, frost tolerance and analysis of non-structural carbohydrates (NSC) content showed important effects of test sites, seed sources, and their interactions on bud set phenology and growth. The average bud set initiation occurred one week later in the southern site compared to the northern site, whereas the late stage of bud set was similar between sites. Significant differences were observed between seed sources for some phenological stages. Frost tolerance was significantly lower in the southern site and below -12 {degrees}C for all seed sources sampled at the beginning of October. The trend in fructose and glucose content was opposite between sites in September. It decreased from September to October in the southern site and increased in the northern site, while sucrose content showed an opposite pattern, with the southwestern seed source harboring the lowest sucrose content. NSC content was also correlated to frost tolerance. Our study highlighted the crucial role of NSC in cold hardiness to early fall frosts and local adaptation. Implications for assisted migration are discussed.