Abstract:
Photosynthesis, a key process of the terrestrial carbon cycle, is crucial for predicting
ecosystem responses to climate change. Terrestrial biosphere models (TBMs)
commonly use the biochemical model of C3 photosynthesis, which relies on two
primary parameters: Vcmax (maximum Rubisco activity) and Jmax (maximum
electron transport rate). The temperature responses of these parameters are often
modeled using the peaked Arrhenius function, relying on K25 (process rate at 25°C),
Ea (activation energy), Hd (deactivation energy), and ΔS (entropy). To avoid
overfitting, most studies assume a fixed Hd; however, the impact of this assumption
remains untested. In this study, using a global scale dataset of plant photosynthetic
temperature response, we compared the temperature response of Vcmax and Jmax by
fitting with and without assuming a fixed Hd. For Vcmax, found a strong relationship
between the fixed and variable Hd models for K25 (R²=0.85, p<0.001), suggesting that
assuming a fixed Hd moderately captures the observed variability in K25. However,
the relationships were weak for Ea (R²=0.04, p=0.22) and ΔS (R²=0.16, p=0.045),
indicating limited suitability of the fixed Hd assumption for these parameters. For
Jmax, K25 similarly showed a moderate correlation between models (R²=0.66,
p<0.001), whereas Ea (R²= 0.14, p=0.015) and ΔS (R²=0.04, p=0.19) displayed weak
to negligible relationships, highlighting limited applicability of the fixed Hd approach.
These findings suggest that while a fixed Hd assumption may be reasonable for K25
in both Vcmax and Jmax models, it does not adequately capture the temperature
dependence of Ea and ΔS, which could lead to inaccuracies in TBMs. Further
investigation into the variable Hd model’s benefits for temperature response accuracy
is warranted.
