c4_temperature_param_vc: C4 temperature response parameters from von Caemmerer

In PhotoGEA: Photosynthetic Gas Exchange Analysis

C4 temperature response parameters from von Caemmerer

Description

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) [\Sexpr[results=rd]{tools:::Rd_expr_doi("10.1093/jxb/erab266")}].

PhotoGEA documentation built on April 11, 2025, 5:48 p.m.