Impact of Different Red/Far-Red Light Ratios on the Morphological Changes and Nutritional Profile of Green Leafy Vegetable Choy Sum

The impact of far-red light on crop development and plant nutrition is controversial. Choy sum, a commonly consumed Asian leafy vegetable, was cultivated under four different ratios of red/far-red (R/FR) light, set at R/FR of 10, 2, 1, and 0.5, and compared with the control plants grown in the absence of FR light. Our results showed that increasing FR intensity (i.e., lower R/FR) elongated the edible parts, promoted flowering, and increased the fresh weight of flowers but decreased the fresh weight of leaves and roots. Furthermore, most of carotenoids and flavonoids, especially total kaempherols, were found to be 40–50% lower under R/FR 2, 1, and 0.5, although zeaxanthin increased to 175% under R/FR 0.5. In contrast, several quercetins and isorhamnetins showed a reverse trend. These results suggest that FR enhances the shift from the vegetative phase to the reproductive phase, leading to early flowering, but affects various plant nutrients in the choy sum.