Thermal acclimation as an emergent property of economically optimal photosynthesis
Wenyao Gan, Josef Garen, Sean T. Michaletz, I. Colin Prentice, Sandy P. HarrisonSummary
Leaf‐level photosynthesis acclimates to growth conditions over days to weeks, with the instantaneous optimal temperature for photosynthesis (
T
opt
) increasing with growth temperature (
T
growth
). We investigated how this behaviour emerges in the P model, a primary production model based on eco‐evolutionary optimality hypotheses.
We evaluated the P model estimates against experimental data for three herbaceous species grown at different temperatures and examined mechanisms underlying the responses of
T
opt
and the photosynthetic rate at
T
opt
(
A
opt
).
The model yields a realistic increase in
T
opt
with
T
growth
and a peaked relationship between
A
opt
and
T
growth
. These responses emerge largely from adjustment of the stomatal sensitivity parameter ξ, which determines the internal‐to‐ambient CO
2
ratio (
c
i
:
c
a
) and its sensitivity to vapour pressure deficit. Rubisco kinetics (
K
) does not acclimate in the model, but its temperature dependence enters acclimation through optimality, mainly via ξ, shifting
T
opt
. The decline in
A
opt
at high growth temperatures, often attributed to heat stress, reflects the narrowing gap between
T
opt
and
T
growth
because the
T
opt
shift has a slope below one.
The P model provides a mechanistic explanation for observed trends in
T
opt
and
A
opt
and a scalable approach for representing biochemical and stomatal acclimation in land‐surface models.