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

Introduction Atmospheric CO 2 elevation significantly impacts plant carbon metabolism, yet accurate quantification of respiratory parameters—photorespiration rate (R p ) and mitochondrial respiration rate in the light (R d )—under varying CO 2 remains challenging. Current CO 2 -response models exhibit limitations in estimating these parameters, hindering predictions of crop responses under future climate scenarios. Methods Low-oxygen treatments and gas exchange measurements, calculating CO 2 recovery/inhibition ratio in of wheat ( Triticum aestivum L. ) and bean ( Glycine max L. ) were employed to elucidate the biological significance and interrelationships of R p and R d . Model-derived estimates of R p and R d were compared with measured values to assess the accuracy of three CO 2 -response models (biochemical, rectangular hyperbola, modified rectangular hyperbola). Furthermore, the effects of ambient CO 2 concentration (0~1200 μmol·mol -1 ) on the measured R p and R d were quantified through polynomial regression. Results The A/C a model achieved superior fitting performance over the A/Ci model. However, significant disparities persisted between A/Ca-derived R p /R d estimates and measurements ( p < 0.05). CO 2 concentration exhibited dose-dependent regulation of respiratory fluxes: R p-measured ranged from 4.923 ± 0.171 to 12.307 ± 1.033 μmol (CO 2 ) m -2 s -1 (wheat) and 4.686 ± 0.274 to 11.673 ± 2.054 μmol (CO 2 ) m -2 s ⁻ ¹ (bean), while R d-measured varied from 0.618 ± 0.131 to 3.021 ± 0.063 μmol (CO 2 ) m -2 s -1 (wheat) and 0.492 ± 0.069 to 2.323 ± 0.312 μmol (CO 2 ) m -2 s -1 (bean). Polynomial regression revealed strong non-linear correlations between CO 2 concentrations and respiratory parameters (R ² > 0.891, p < 0.05; except bean R p- C a : R ² = 0.797). Species-specific CO 2 thresholds governed peak R p (600 μmol·mol -1 for wheat vs. 1,000 μmol·mol -1 for bean) and R d (400 μmol·mol -1 for wheat vs. 200 μmol·mol -1 for bean). Discussion These findings expose critical limitations in current respiratory parameter quantification methods and challenge linear assumptions of CO 2 -respiration relationships. They establish a critical framework for refining photosynthetic models by incorporating CO 2 -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 CO 2 , with implications for climate-resilient agricultural practices.