3.2 | Net photosynthesis
Net photosynthesis at 400 ppm CO2 (P400) peaked at 32.2°C in treatment plants, which was almost 5°C higher than TOpt in control plants (Fig. 1), with limited overlap of the credible intervals (See Fig. 2 for the full posterior distributions of TOpt with highlighted 50, 90, and 99% credible intervals, and Table 2 for 10–90 percentiles of the posterior distribution). Median P400 at TOpt was lower for the treatment plants than for the controls (Table 2). Transfer of control plants to treatment conditions increased TOptof P400 from 27.3 to 31.2°C (Fig. 2) and decreased P400 at TOpt by 41% to 11.3 µmol m–2 s–1 (Table 2). Transfer of treatment plants to control conditions decreased TOptfrom 32.2 to 28.9°C (Fig. 2) with minimal change in P400at TOpt (Table 2). When fitting the data with the peaked Arrhenius function (Eqn 3), the activation energy (Ha) was higher in treatment plants than in control plants, and transferring plants resulted in adjustments in Ha towards the values of plants grown under the conditions plants were transferred to, while not quite reaching those values (Table S3). Estimates of Ha tended to have right-skewed posterior distributions.
The optimum temperature of photosynthesis at 800 ppm (P800) differed by 3.6°C between control and treatment plants, with moderate upward and downward adjustments in TOpt of plants transferred to warmer and cooler conditions, respectively (Figs. 2, 3; Table 2). Control plants achieved higher rates of P800 than treatment plants, and P800 was reduced by 35% in control plants transferred to treatment conditions (Table 2). Ha of P800 was higher in treatment plants than in control plots (Table S3). P800 of treatment plants was considerably higher than P400 of controls, indicating higher net photosynthesis rates at their respective conditions.