S08 - Session P5 - Optimizing light use efficiency and productivity of indoor leafy greens by using different lighting strategies

Authors: Laurent Boucher, Thi Thuy An Nguyen, Frédéric Jobin-Lawler, Annie Brégard, Steeve Pepin, Martine Dorais *

Vertical farming is booming in urban and peri-urban areas and artificial lighting is a crucial growth parameter that must be optimized for high productivity and quality. Indeed, several studies have been conducted during the recent years to determine the optimal spectral quality of LED lighting. In the present study, we hypothesized that for a same day light integral of 18.8 mol m -2 day -1 , the use of a long-fragmented photoperiod and the replacement of the dark period by a low PPFD corresponding to the light compensation point (LCP) improve the light use efficiency, productivity and leaf quality attributes of leafy greens. We also made the assumption that LEDs enriched in green and far-red spectra increase plant height and fresh biomass. To test these hypotheses, we conducted a series of trials in growth chambers with twelve species/varieties of leafy greens where four light treatments were compared: 1- control (18L/6N; 18 h at 289 µmol m -2 s -1 and 6 h of darkness); 2- 5L/1N (5 h at 261 µmol m -2 s -1 + 1 h of darkness); 3- 5L/1LCP (5 h at 256 µmol m -2 s -1 + 1 h of LCP at 20 µmol m -2 s -1 ); 4- 6L/6LCP (6 h at 418 µmol m -2 s -1 + 6 h of LCP at 20 µmol m -2 s -1 ). Regardless of the species/varieties, our results showed that 5L/1N and 5L/1LCP treatments increased plant height, fresh and dry weight, and light use efficiency (expressed in biomass per mole of light received) of leafy greens compared to control (18L/6N) and 6L/6LCP plants. However, there were no advantage in using LCP instead of a dark period. Light treatments did not affect the photosynthetic parameters (SPAD, Fv/Fm, PI,A max , R d , φ), while nitrate leaf content was higher under 6L/6LCP compared with the other treatments. Adding green and far-red light to the LED treatments increased plant dry weight (p=0.09) without affecting their fresh weight or other growth parameters.