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).