The temperature response curves of both net and gross photosynthesis followed a parabolic shape (Fig. 3). The thermal optimum (Topt) of net photosynthesis (An) averaged 19 ± 1.2 °C and was not variable across plantation sites and seed sources (Tables 2 and 3). Net photosynthetic rate (Aopt) at Topt varied significantly among sites (Table 2), with the lowest value of Aopt occurring at the Wendover and Lac Bergeron sites, which were the warmest and coldest sites, respectively (Table 3). Aopt followed a quadratic relationship with mean July temperature of the plantation site (MJT) for the southern seed source but not for the northern one (Fig. 4). Basal rate of Rd (Rd10) and Q10 showed similar responses among seed sources but differed across plantation sites (Table 2). The lowest mean values of Rd10 were measured at the warmest sites, such as Wendover and Dorion (Table 3), while the highest mean values of Q10 occurred at Lac Bergeron, the coldest plantation site (Table 3). Topt and Q10 of dark respiration were not related to climatic variables at the plantation sites (Fig. 4). Rd10 was negatively and linearly related to MJT for the southern seed source (Fig. 4). The temperature response curve of gross photosynthesis (Ag) showed a shape similar to that of An (Fig. 3). The average Topt of Ag, 22.7 ± 1.3 °C, was not affected by either site or seed source (Table 2).