Accuracy of photorespiration and mitochondrial respiration in the light fitted by CO2 response model for photosynthesis

Huajing Kang^1*Zheng-wen Niu¹Zi-Wu-Yin Ye²Qi Huang¹Chunju Peng¹

• ¹Wenzhou Vocational College of Science and Technology, Wenzhou, China
• ²Guangdong Baiyun University, Guangzhou, Guangdong, China

This study presents a systematic evaluation of photorespiration rate (Rp) and mitochondrial respiration rate in the light (Rd) estimation accuracy across three CO₂response models-the biochemical model, rectangular hyperbola model, and modified rectangular hyperbola model-using photosynthetic CO₂-response curves in wheat (Triticum aestivum L.) and common bean (Phaseolus vulgaris L.). Through gas exchange measurements and low oxygen method under variable CO₂ conditions (0~1200 μmol•mol⁻¹), we compared intercellular (A/Ci) and ambient (A/Ca) CO₂ concentration frameworks. Results demonstrated that the A/Ca model achieved superior fitting performance over the A/Ci model. However, significant disparities persisted between A/Ca-derived Rp/Rd estimates and empirical measurements (p < 0.05), exposing critical limitations in current respiratory parameter quantification methods.CO₂ concentration exhibited dose-dependent regulation of respiratory fluxes: Rp-measured 2 ranged from 4.923 ± 0.171 to 12.307 ± 1.033 μmol (CO₂) m⁻² s⁻¹ for wheat and 4.686 ± 0.274 to 11.673 ± 2.054 μmol (CO₂) m⁻² s⁻¹ for bean, while Rd-measured varied from 0.618 ± 0.131 to 3.021 ± 0.063 μmol (CO₂) m⁻² s⁻¹ for wheat and 0.492 ± 0.069 to 2.323 ± 0.312 μmol (CO₂) m⁻² s⁻¹ for bean. Polynomial regression revealed strong non-linear correlations between CO₂ concentrations and respiratory parameters (R² > 0.891, p < 0.05; except bean Rp-Ca: R² = 0.797), challenging linear assumptions of CO₂-respiration relationships. Notably, species-specific CO₂ thresholds governed peak Rp (600 μmol•mol -1 for wheat vs. 1,000 μmol•mol -1 for bean) and Rd (400 μmol•mol -1 for wheat vs. 200 μmol•mol -1 for bean). These findings establish a critical framework for refining photosynthetic models through CO₂-responsive respiratory mechanisms. The identified non-linear regulatory patterns and model limitations provide actionable insights for advancing carbon metabolism theory and optimizing crop carbon assimilation strategies under rising atmospheric CO₂ scenarios, with implications for climateresilient agricultural practices.