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.