Effect of soil warming on growth and physiology of aspen seedlings from Alberta, Canada

Boreal tree species are migrating northwards due to rising temperatures, and differences in heat tolerance can impact the range limits of boreal species. Soil warming may benefit tree growth by promoting root development, or harm growth by creating a high-stress environment, increasing root respiration rates. We assessed the impact of soil warming on the growth of 2-year-old trembling aspen seedlings from 10 families. These families originated from Peace River, in central Alberta, and Camrose, near the southern boreal fringe in Alberta, Canada. We correlated growth traits with climatic data from each region and analyzed the effect of soil warming on the gas exchange of seedlings from Camrose. Families from Peace River exhibited greater growth overall, regardless of warming treatment, while families from Camrose showed a positive growth response under soil warming. Camrose families exposed to soil warming showed greater total leaf area and total leaf biomass compared to those without warming. A Principal Component Analysis (PCA) showed that, regardless of region, some families displayed stronger positive responses and appeared better adapted to soil warming than others. The overall positive response of the Camrose families to soil warming suggests that they have the capacity to take advantage of warmer environmental conditions. Our results indicate regional growth differences in aspen families in Alberta and variation in performance between families within a region, indicating there is differential capacity within local populations to acclimate under rapid climate change.