Effects of Different Photoperiods on the Growth and Nutritional Characteristics of Two Celery Cultivars in Plant Factory

Three different photoperiod treatments (8 h/16 h, 12 h/12 h, and 16 h/8 h of light/dark) were implemented to investigate the impact of growth, biomass, and phytochemical accumulation in two celery cultivars, namely 'Zhangqiubaoqin' (BQ) and 'Hongchenghongqin' (HQ), within a plant factory setting. The findings demonstrated that the 12 h/12 h photoperiod stimulated the growth of both celery varieties, while the 16 h/8 h photoperiod hindered their growth. Notably, the root length, shoot fresh and dry weight, plant height, chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid content of both celery cultivars exhibited the highest values under the 12 h/12 h light and dark photoperiod. Furthermore, the effective quantum yields of the electron transfer ratio (ETR) and the photochemical quenching coefficient (qP) displayed superior value under the 12 h/12 h light and dark photoperiod. With the exception of cellulose, the levels of soluble sugar, soluble protein, total phenol, and vitamin C were also highest under the 12 h/12 h photoperiod for both cultivars. BQ demonstrated the highest total apigenin content under the 12 h/12 h (light and dark) photoperiod, whereas HQ exhibited the highest content under the 16 h/8 h (light and dark) photoperiod. In summary, celery plants exhibited optimal performance and biomass production when subjected to the 12 h/12 h (light and dark) photoperiod treatment.