C4 temperature response parameters from von Caemmerer

Temperature response parameters describing the temperature response of important C4 photosynthetic parameters, intended to be passed to the calculate_temperature_response function.

Usage

c4_temperature_param_vc

Format

List with 10 named elements that each represent a variable whose temperature-dependent value can be calculated using either an Arrhenius or Gaussian equation:

• Vcmax_norm: The maximum rate of rubisco carboxylation (Vcmax) normalized to its value at 25 degrees C.

• Vpmax_norm: The maximum rate of PEP carboxylase activity (Vpmax) normalized to its value at 25 degrees C.

• RL_norm: The respiration rate (RL) normalized to the value of Vcmax at 25 degrees C.

• Kc: The Michaelis-Menten constant for rubisco carboxylation.

• Ko: The Michaelis-Menten constant for rubisco oxygenation.

• Kp: The Michaelis-Menten constant of PEP carboxylase.

• gamma_star: Half the reciprocal of rubisco specificity.

• ao: The ratio of solubility and diffusivity of O2 to CO2.

• gmc_norm: The mesophyll conductance to CO2 diffusion normalized to its value at 25 degrees C.

• J_norm: The electron transport rate J normalized to its value at 25 degrees C.

The J_norm parameter is calculated using a Gaussian function and hence its corresponding list element is itself a list with 4 named elements:

• type: the type of temperature response ('Gaussian')

• optimum_rate: the largest value this parameter can take.

• t_opt: the temperature where the optimum occurs in degrees C.

• sigma: the width of the Gaussian in degrees C.

• units: the units of the corresponding variable.

Each of the remaining elements is a list with 4 named elements:

• type: the type of temperature response ('Arrhenius')

• c: the (dimensionless) Arrhenius scaling factor.

• Ea: the activation energy in kJ / mol.

• units: the units of the corresponding variable.

Source

Some of these parameters (Vcmax, Vpmax, RL, gmc, and J) are normalized to their values at 25 degrees C. These variables include _norm in their names to indicate this.

The remaining parameters (Kc, Ko, Kp, gamma_star, and ao) are not normalized because they are assumed to not vary significantly between species.

Here, the Arrhenius scaling factors (c; dimensionless) and activation energy values (Ea; kJ / mol) are obtained from von Caemmerer (2021). In that publication, the overall scaling for each parameter is specified by its value at 25 degrees C; the scaling factors are determined from this information as described in the documentation for calculate_temperature_response_arrhenius.

The Gaussian parameters (t_opt and sigma) for J_norm are also obtained from von Caemmerer (2021), assuming that J and Jmax follow the same temperature response. The value of optimum_rate is chosen such that J_norm is equal to 1 at a temperature of 25 degrees C.

References:

• von Caemmerer, S. "Updating the steady-state model of C4 photosynthesis" Journal of Experimental Botany 72, 6003–6017 (2021) [doi:10.1093/jxb/erab266 ].