Updating the steady state model of C₄photosynthesis

Abstract

C4 plants play a key role in world agriculture. For example, C4 crops such as maize and sorghum are major contributors to both first and third world food production and the C4 grasses sugarcane; miscanthus and switchgrass are major plant sources of bioenergy. In the challenge to manipulate and enhance C4 photosynthesis, steady state models of leaf photosynthesis provide and important tool for gas exchange analysis and thought experiments that can explore photosynthetic pathway changes. Here the C4 photosynthetic model by von Caemmerer and Furbank (1999) has been updated with new kinetic parameterisation and temperature dependencies added. The parameterisation was derived from experiments on the C4 monocot, Setaria viridis, which for the first time provides a cohesive parametrisation. Mesophyll conductance and its temperature dependence have also been included, as this is an important step in the quantitative correlation between the initial slope of the CO2 response curve of CO2 assimilation and in vitro PEP carboxylase activity. Furthermore, the equations for chloroplast electron transport have been updated to include cyclic electron transport flow and equations have been added to calculate electron transport rate from measured CO2 assimilation rates.

Mesophyll conductance response to short-term changes in CO2 is related to leaf anatomy and biochemistry in diverse C4 grasses

“…Our study advances understanding about CO 2 response of g m in diverse C 4 species and identifies the key leaf anatomical and biochemical traits related to this response. This understanding is essential for improving C 4 photosynthetic models (von Caemmerer, 2021) and in attempts to improve water-use efficiency of C 4 crops through modification of g m (von Caemmerer & Furbank, 2016). Values in each panel represent mean ± SE with n = 3-6.…”

“…g m varies across plant groups due to variation in leaf anatomy and biochemistry, changes dynamically in response to environmental stimuli and has a significant impact on the plant and ecosystem-level photosynthetic CO 2 uptake and water-use efficiency (Evans et al, 2009;Flexas et al, 2014;Knauer et al, 2019b;Pathare et al, 2020a). Despite its importance for photosynthetic CO 2 uptake and water-use at both plant and ecosystem levels and its variation across diverse plants groups, g m is only beginning to be explicitly implemented into global models which upscale leaf-scale photosynthetic processes to canopy and global scales (Rogers et al, 2017;Knauer et al, 2019a;Knauer et al, 2019b;von Caemmerer, 2021).The implementation of g m is complicated because there is a lack of detailed information about responses of g m to short and long-term changes in environmental conditions (e.g., light, precipitation, temperature, and CO 2 concentration) across diverse plant groups (Rogers et al, 2017;Knauer et al, 2019a;Knauer et al, 2019b). Most investigations on the responses of g m to changes in environmental conditions focus on C 3 species (von Caemmerer & Evans, 2015;Xiong et al, 2015;Carriqui et al, 2018;Shrestha et al, 2018), but there is less information about the response of g m to changing environmental conditions in diverse C 4 species (Ubierna et al, 2017;Kolbe & Cousins, 2018;Ubierna et al, 2018;Sonawane et al, 2021).…”

“…Most investigations on the responses of g m to changes in environmental conditions focus on C 3 species (von Caemmerer & Evans, 2015;Xiong et al, 2015;Carriqui et al, 2018;Shrestha et al, 2018), but there is less information about the response of g m to changing environmental conditions in diverse C 4 species (Ubierna et al, 2017;Kolbe & Cousins, 2018;Ubierna et al, 2018;Sonawane et al, 2021). A better understanding of how C 4 -g m responds to changing environmental conditions is essential for improving the models of C 4 photosynthetic at both the leaf and global scales (Rogers et al, 2017;Knauer et al, 2019a;Knauer et al, 2019b;von Caemmerer, 2021) as well as for potentially increasing water-use efficiency of C 4 crops through manipulation of g m (Cousins et al, 2020;Pathare et al, 2020a).…”

A Model of C4 Photosynthetic Acclimation Based on Least‐Cost Optimality Theory Suitable for Earth System Model Incorporation

“…A P is defined in terms of the mesophyll reactions (Von Caemmerer, 2021): $$${A}_{P}={A}_{P\text{gross}}-L$$$ where A P gross is the rate of PEP carboxylation and L is the rate of CO 2 leakage from the bundle sheath to the mesophyll. This assumes that the steady state rate of PEP carboxylation and the rate of C 4 acid decarboxylation are equal.…”

Expression of a CO2-permeable aquaporin enhances mesophyll conductance in the C4speciesSetaria viridis

“…c. Data from a and b compared to the C4 biochemical model predictions 36 . The model relates the initial slope of the ACi curve (dA/Ci) to gm by:= ( + ) ⁄, where Vpmax and Kp denote the maximum PEPC activity and the Michaelis Menten constant for CO2 taken here as 250 µmol m -2 s -1 and 82 µbar65,66 . Azygous plants of line 44 were used as control.…”