Evaluating Photosynthetic Models and Their Potency in Assessing Plant Responses to Changing Oxygen Concentrations: A comparative Analysis of A n -C a and A n -C i Curves in Lolium perenne and Triticum aestivum

Zi-Piao Ye ^1,2 Xiaolong Yang ^3,4 Zi-Wu-Yin Ye ⁵ Ting An ⁶ Duan Shihua ⁷ Huajing Kang ⁸ Fubiao Wang ^2*

• ¹ New Quality Productivity Research Center, Guangdong ATV College of Performing Arts, Deqing, Guangdong, China
• ² The Institute of Biophysics in College of Mathematics and Physics, Jinggangshan University, Jiangxi, China
• ³ School of Life Sciences, Nantong University, Nantong, Jiangsu Province, China
• ⁴ State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, Beijing, China
• ⁵ Guangdong Baiyun University, Guangzhou, Guangdong, China
• ⁶ College of Bioscience and Bioengineering, Jiangxi Agricultural University, Nanchang, Jiangxi Province, China
• ⁷ College of Life Science, Jinggangshan University, Jinggangshan, China
• ⁸ Key Laboratory of Crop Breeding in South Zhejiang, Wenzhou Academy of Agricultural Sciences, Wenzhou, Zhejiang, Zhejiang, China

Accurate determination of photosynthetic parameters is essential for understanding how plants respond to environmental changes. In this study, we evaluated the performance of the Farquhar-von Caemmerer-Berry (FvCB) model and introduced a novel model to fit photosynthetic rates against ambient CO₂ concentration (An–Ca) and intercellular CO2 concentration (An–Ci) curves for Lolium perenne and Triticum aestivum under 2% and 21% O₂ conditions. We observed significant discrepancies in the FvCB model's fitting capacity for An–Ca and An–Ca curves across different oxygen regimes, particularly in estimates of key parameters such as the maximum carboxylation rate (Vcmax), the day respiratory rate (Rday), and the maximum electron transport rate for carbon assimilation (JA-max). Notably, under 2% and 21% O2 conditions, the values of Vcmax and Rday derived from An–Ca curves using the FvCB model were 46.98%, 44.37%, 46.63%, and 37.66% lower than those from An–Ci curves for L. perenne, and 47.10%, 44.30%, 47.03%, and 37.36% lower for T. aestivum, respectively. These results highlight that the FvCB model yields significantly different Vcmax and Rday values when fitting An–Ca versus An–Ci curves for these two C3 plants. In contrast, the novel model demonstrated superior fitting capabilities for both An–Ca and An–Ci curves under 2% and 21% O2 conditions, achieving high determination coefficients (R2 ≥ 0.989). Key parameters such as the maximum net photosynthetic rate (Amax) and the CO₂ compensation point (Γ) in the presence of Rday, showed no significant differences across oxygen concentrations. However, the apparent photorespiratory rate (Rpa0) and photorespiratory rate (Rp0) derived from An–Ci curves consistently exceeded those from An–Ca curves for both plant species. Furthermore, Rpa0 values derived from An–Ca curves closely matched observed values, suggesting that An–Ca curves more accurately reflect the physiological state of plants, particularly for estimating photorespiratory rates. This study underscores the importance of selecting appropriate CO₂-response curves to investigate plant photosynthesis and photorespiration under diverse environmental conditions, thereby ensuring a more accurate understanding of plant responses to changing environments.