A comparison of growth and physiology in Picea glauca and Populus tremuloides at different soil temperatures

Trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss) seedlings were grown at uniform air temperatures but different soil temperatures (5, 15, and 25°C), and gas-exchange and growth characteristics were examined during active growth and early dormancy. At 5°C, Populus tremuloides had no root growth and limited growth in leaf area and shoot mass compared with the large increases in leaf and shoot mass at 25°C. In contrast, Picea glauca had some root growth at 5°C and moderate growth of roots at 15 and 25°C; however, there were no differences in aboveground mass at the different soil temperatures. Net assimilation and stomatal conductance in Populus tremuloides were reduced with decreasing soil temperatures, while in Picea glauca soil temperatures did not affect these gas-exchange variables. In both species, root mass was higher in the dormant period than during the growing period, while root volume remained constant. Generally, the growth variables of Populus tremuloides were more suppressed by cold soils than in Picea glauca. Root total nonstructural carbohydrates (TNC) decreased between the active growth and dormancy period by nearly 50% in Populus tremuloides, while there was no change in TNC in Picea glauca. Results suggest a more conservative use of TNC reserves in Picea glauca combined with a tolerance to cold soil temperatures compared with Populus tremuloides