Photosynthetic Adjustments Maintain Lettuce Growth Under Dynamically Changing Lighting in Controlled Indoor Farming...

Studies have uncovered delicate mechanisms that enable plant acclimation to fluctuating light. Translating the knowledge to controlled environment agriculture could advance the development of cost-effective dynamic lighting strategies where the light intensity is purposely alternated, mirroring the spot electricity price, but its effects on vegetable crops remain poorly understood. Here, we recorded photosynthetic parameters, metabolic responses, and growth of lettuce (Lactuca sativa L.) cv. "Katusa" under dynamic lighting. The light intensity was altered at different times of the photoperiod with uniform daily light integral. Three different setups, including a plant phenotyping facility, a small-scale vertical farm testbed and a larger-scale vertical farm, were utilized to address the physiological responses and scalability of lighting strategies. The lettuces readily adjusted their photosynthetic light reactions and carbon metabolism according to the changing light intensities. However, the overall metabolic composition of lettuce leaves did not respond to dynamic lighting. Upon simulation of commercial production in the larger-scale vertical farm, constant and dynamic lighting regimes yielded lettuce heads with equal saleable sizes of 87-89 g, even under artificial "Split-Night" regimes where the photoperiod was interrupted by two periods of darkness. These findings suggest that dynamic lighting strategies enable cost-effective lighting via optimization of electricity use in indoor cultivation.