Estimating C₄ photosynthesis parameters by fitting intensive A/C_i curves

Area of Science:

• Plant Physiology
• Photosynthesis Research
• Biochemistry

Background:

• A/Ci curves are standard for C3 photosynthesis parameter estimation.
• Limited methods exist for estimating C4 plant photosynthetic parameters.
• Understanding C4 photosynthesis is crucial for crop improvement.

Purpose of the Study:

• To adapt A/Ci curve estimation methods for C4 plants.
• To develop new tools for assessing C4 photosynthetic parameters.
• To investigate the role of carbonic anhydrase in C4 photosynthesis.

Main Methods:

• Fitting intensive A/Ci curves using three photosynthesis models.
• Employing simulation analysis, out-of-sample tests, in vitro, and chlorophyll-fluorescence measurements for validation.
• Extending C3 plant A/Ci curve frameworks for C4 species.

Main Results:

• Identified robust parameters: maximal Rubisco carboxylation rate, electron transport rate, maximal PEP carboxylation rate, and carbonic anhydrase activity.
• Mesophyll conductance and day respiration showed variability.
• Developed a novel method to estimate carbonic anhydrase activity from A/Ci curves.

Conclusions:

• The new methods enable robust estimation of key C4 photosynthetic parameters.
• Models without explicit carbonic anhydrase provide approximate results.
• Optimized C4 traits include low Rubisco specificity, high catalytic rate, low bundle sheath leakage, and high PEPC affinity for enhanced efficiency.