Carrot (Daucus carota L.), a key crop in the Apiaceae family, adapts to environmental changes through its endogenous circadian clock, which coordinates physiological processes over a 24-h cycle. As a central physiological activity of carrot growth, photosynthesis, including parameters such as photosynthetic efficiency and stomatal conductance, is influenced by environmental factors. Among them, photoperiod is one of the main regulatory factors for development and chlorophyll synthesis. In this study, we investigated the effects of three different light cycles (16 h of light/8 h of darkness, 16L/8D, 12 h of light/12 h of darkness, 12L/12D, and 8 h of light/16 h of darkness, 8L/16D) on the expression of circadian rhythm genes in carrot. The core clock genes, DcLNK1, DcLNK3, DcRVEa, DcRVEb, and DcGI exhibited distinct transcriptional responses to these light cycles. Three different photoperiod treatments led to changes in the expression profiles of circadian rhythm related genes, photosynthetic parameters, and stomatal activity in carrot. The results elucidated a potential molecular regulatory network linking photoperiod perception to physiological pathway in carrot, providing potential insight into the intrinsic mechanisms of photo-entrainment within its circadian system.
