Investigating pulsed LED effectiveness as an alternative to continuous LED through morpho-physiological evaluation of baby leaf lettuce (Lactuca sativa L. var. Acephala)

Abstract

Photoperiod, light intensity, and spectral quantum distribution (SPD) affect plant development and physiology. Light determines morphological signals, influences plant behavior and regulates metabolism in addition to providing energy for photosynthesis. In this experiment, lettuce (Lactuca sativa) was grown in an indoor LED-equipped chamber, operated in a pulsed and continuous mode, with an average photosynthetic photon flux density (PPFD) at a seedling level of 150 µmole s¯¹ m¯², photoperiod of 16 h for growing cycle of 30 days. The primary aim of this study was to observe the effects of varying LED on the growth and quality of the produce. Regardless of the treatments, in both continuous and pulsed LED, an increment in the yield, leaf length and leaf width of lettuce was recorded in comparison to the control, which was managed in a glasshouse under controlled environmental conditions using a winter cropping cycle. In-vitro physiological analysis of lettuce revealed the outperformance of the continuous LED treatment over the pulsed LED as well as the control in terms of total sugars, chlorophyll concentration, carotenoids, phenolic index, and sucrose accumulation. Continuous LED treatment has also resulted in a significant reduction in nitrate content, a commercially vital parameter, making it the most advantageous and effective of all the treatments performed. However, the production of anthocyanins, an antioxidant released during stress, was enhanced under pulsed LED which requires further investigation and improvements to achieve an improved metabolite profile of lettuce with a minimal energy usage and cost.