Résumé
Context: Identifying traits that enhance canopy photosynthesis is particularly crucial for sustaining maize productivity under high plant densities. Utilizing a model-assisted approach is an effective strategy to achieve this goal. Objective: The objectives of this study were to (i) integrate a biochemical model of C4 photosynthesis into the existing GreenLab to enhance its capacity for simulating canopy photosynthesis under varying plant densities; (ii) evaluate the model's performance through simulations under different plant densities; and (iii) utilize the model to identify key physiological and structural targets that can enhance productivity under high plant densities. Method: In this study, a two-year field trial of maize (Zea mays L.) was conducted under four plant densities i.e. 3, 6, 9, 12 plants m−2. Simultaneously, the Functional-Structural Plant Model ‘GreenLab’ was extended by replacing its existing module for calculating canopy photosynthesis with an update of the C4 photosynthesis model by von Caemmerer (2021). Model parameters (i.e., leaf photosynthesis; sink strength, the capacity of each organ receives biomass; sink variation, each sink strength varies during the duration of organ expansion) governing maize growth and development were estimated using field data collected in 2022. The revised GreenLab was subsequently validated by demonstrating good agreement between independent simulations and experimental observations of maize growth and development across various plant densities in 2023. Results: Leaf photosynthetic and organ sink strength parameters decreased linearly with increasing plant density, while organ sink variation parameters linearly increased. Notably, maximal linear electron transport rate and reproductive organs sink strength and sink variation parameters were quite sensitive to plant density. Modelling trials using only the C4 photosynthetic model revealed that canopy photosynthesis was limited by maximum Rubisco activity, maximal linear electron transport rate, and light distribution under high plant densities. Furthermore, additional modelling studies with the revised GreenLab suggested that synergistically modifying both maximal linear electron transport rate and leaf angle can maximize canopy photosynthesis, thereby improving maize productivity under high plant density. Conclusion: Overall, this study successfully quantified the impact of modifying molecular targets through modelling on enhancing maize canopy photosynthesis under high plant density conditions.