Light-Response Curve and Model Fitting for Berchemiella wilsonii

Objective The study of the photosynthetic adaptation mechanism of Berchemiella wilsonii, a nationally second-class protected wild plant and endangered species, is crucial for revealing its survival strategies and the reasons for its endangerment. This research provides key theoretical foundations for developing scientific conservation and cultivation measures.

Methods Using two-year-old Berchemiella wilsonii seedlings as subjects, photosynthetic light-response curves were measured with an LI-6400 portable photosynthesis system. Five typical light-response models were employed for fitting analysis: the Rectangular Hyperbolic Model (RHM), the Non-Rectangular Hyperbolic Model (NHM), the Exponential Model (EM), the Modified Rectangular Hyperbolic Model (MRHM), and Ye's Model (YM). The fitting performance was evaluated using three parameters: R², RMSE, and MAE.

Results All five models could fit the photosynthetic light-response curves of Berchemiella wilsonii. Among them, the MRHM, through its two-parameter modification mechanism (photoinhibition term β + light saturation term γ), demonstrated the best fitting performance within the photosynthetic active radiation range of 0～2500 μmol/（m²·s） (R² = 0.9760, RMSE = 0.9148, MAE = 0.6263). Particularly in the range of 300～1500 μmol/（m²·s）, the deviation between predicted and measured values was less than 5%. Furthermore, the MRHM was the only model that accurately captured the decline in net photosynthetic rate caused by photoinhibition at light intensities above 1200 μmol/（m²·s）. The estimation accuracy of the maximum net photosynthetic rate (Pnmax) and the light saturation point (LSP) by the MRHM was significantly superior to that of the other models. The RHM provided relatively accurate estimates of the light compensation point (LCP) and dark respiration rate (Rd) at low light intensities but showed significant deviations at high light intensities. The NHM, EM, and YM exhibited varying performance across different light intensity ranges, with overall accuracy lower than that of the MRHM. Berchemiella wilsonii exhibited typical shade-plant light adaptation characteristics, with a light compensation point of approximately 20.00 μmol/（m²·s）.

Conclusion The Modified Rectangular Hyperbolic Model (MRHM) is the most suitable model for fitting the photosynthetic light-response curves of Berchemiella wilsonii. The critical photoinhibition threshold identified by this model is 1200 μmol/（m²·s）. These findings provide essential guidance for light management in the conservation-oriented cultivation of Berchemiella wilsonii.