Regulation of Rhythmic Photosynthesis by Photoperiod and Light Intensity in Non-Heading Chinese Cabbage: A Computational Approach

Abstract

Light is a key environmental factor regulating plant photosynthesis, yet the coordinated effects of photoperiod and light intensity on photosynthetic dynamics in non-heading Chinese cabbage remain unclear. Using experimental data, we developed a circadian clock-controlled photosynthesis model integrating photoperiod and light-intensity inputs. The model was calibrated and evaluated against experimental observations and was then used to analyze circadian gene expression, diurnal net photosynthetic rate (Pn), light-period net CO2 assimilation, and the marginal carbon benefit of increasing daily light integral (DLI). Under a constant DLI of 9.216 mol·m−2·d−1, extending the photoperiod from 8 to 20 h while reducing light intensity from 320 to 128 µmol·m−2·s−1 lowered and delayed the instantaneous Pn peak but progressively increased light-period net CO2 assimilation. Among the treatments examined, 20L:4D produced the highest net CO2 assimilation. Moreover, across the simulated DLI range of 5–19 mol·m−2·d−1, the 20-h photoperiod consistently produced the highest net assimilation, whereas the marginal carbon benefit of additional light declined by approximately 62%. The results suggest that distributing a fixed daily light input over a longer photoperiod at lower instantaneous light intensity can enhance daily carbon gain within the tested range, whereas increasing DLI produces progressively diminishing photosynthetic returns. This study provides a modeling framework for evaluating photoperiod–light intensity coordination and provides a quantitative basis for optimizing light–environment management in controlled-environment agriculture.