Both Multi-Segment Light Intensity and Extended Photoperiod Lighting Strategies, with the Same Daily Light Integral, Promoted Lactuca sativa L. Growth and Photosynthesis

With the rise of plant factories around the world, more and more crops are cultivated under artificial light. Studies on effects of lighting strategies on plant growth, such as different light intensities, photoperiods, and their combinations, have been widely conducted. However, research on application of multi-segment light strategies and associated plant growth mechanisms is still relatively lacking. In the present study, two lighting strategies, multi-segment light intensity and extended photoperiod, were compared with a constant light intensity with a 12 h light/12 h dark cycle and the same daily light integral (DLI). Both lighting strategies promoted plant growth but acted via different mechanisms. The multi-segment light intensity lighting strategy promoted plant growth by decreasing non-photochemical quenching (NPQ) of the excited state of chlorophyll and increasing the quantum yield of PSII electron transport (PhiPSII), quantum yield of the carboxylation rate (PhiCO2), and photochemical quenching (qP), also taking advantage of the circadian rhythm. The extended photoperiod lighting strategy promoted plant growth by compensating for weak light stress and increasing light-use efficiency by increasing chlorophyll content under weak light conditions.