Light is both the primary energy source for photosynthesis and a key regulator for circadian rhythms, influencing the comprehensive quality and the production cycle of plants. Light quality is a critical parameter of light parameters, and the response patterns of photosynthesis and circadian rhythm to different light qualities remain to be explored. Here, white (broad-spectrum), red, blue and purple lights were each applied to celery for two days (light/dark: 12 h/12 h), and stomatal openness, photosynthetic parameters, photosynthetic pigments contents, and the expression levels of photoreceptor-related genes were measured. The results showed, narrow-spectrum treatments outperformed white light in both photosynthetic parameters and pigments accumulation red light most effectively promoted stomatal openness and net photosynthetic rate (P), reached the maximum levels after 4 h of illumination. Compared with white light, the average contents of photosynthetic pigments were improved 1.12, 1.25 and 1.37 times higher under the red, blue, and purple light, respectively. Furthermore, within the two days, narrow-spectrum treatments upregulated the maximal relative expression of most photoreceptor genes (especially AgPHYB and AgPHOT2). The expression of circadian rhythm genes previously established under white light were disrupted, leading to disordered expression, complex uncoupling or loss of rhythmicity. This research provided references for light quality response mechanism researches and facility-based light supplementation in celery cultivation. n
