3.3 | Temperature response of biochemical parameters
In treatment plants the optimum temperature of VCMax was 43.3°C, which was 1.4°C higher than in control plants (Fig. 3) with moderate overlap in credible intervals (Fig. 2; Table 3). Transferring plants from control to treatment conditions increased TOpt of VCMax by 0.8°C, and the posterior distribution overlapped with that of both control and treatment plants (Fig. 2). The transferred plants had lower VCMax at TOpt (Table 3). Plants transferred from treatment to control conditions reduced TOpt by 1.5°C, while VCMax at TOpt was similar before and after the transfer. The activation energy Ha averaged 76.9 kJ mol–1 across treatments, without notable differences between control and treatment plants (Table 3). The median entropy factor ΔS of VCMax tended to be lower in treatment than in control plants, and when conditions were switched ΔS decreased in plants moved to treatment conditions and increased in the plants moved to control conditions; however, the 90% credible intervals of all treatment groups overlapped (Table 3).
JMax peaked at ~2.0°C lower temperatures than VCMax (Table 3). Differences in TOpt of JMax across treatments were small, with treatment plants 1.2°C higher than control plants, and upward and downward shifts of ≤1.6°C following transfer to treatment and control conditions respectively (Fig. 2; Table 3). JMaxat TOpt was lower in treatment than in control plants and decreased when control plants were transferred to treatment conditions (i.e., 90% credible intervals did not overlap), but did not change much when treatment plants were transferred to control conditions (Table 3). Ha and ΔS of JMax did not differ systematically among treatments and had overlapping 90% credible intervals (Table 3).
The JMax to VCMax ratio decreased with increasing measurement temperature in control and treatment plants by on average 21% between 30 and 40°C (Fig. 4). The mean JMaxto VCMax ratio was lower in treatment than in control plants (ANCOVA with Tukey post hoc test, t = −2.76, P = 0.032) and decreased when control plants were transferred to treatment conditions (t = −5.67, P < 0.001) (Fig. 4).