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

Abstract

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.

Continuous Lighting and High Daily Light Integral Enhance Yield and Quality of Mass-Produced Nasturtium (Tropaeolum majus L.) in Plant Factories

“…In Experiment 1, under the same DLI (17.28 mol m −2 d −1 ), the dry mass of the nasturtium plant was significantly enhanced by extending the light period from 16 to 24 h, rather than increasing the light intensity from 200 to 300 µmol m −2 s −1 (Figure 2). A similar trend has been reported in several leafy vegetables, such as lettuce and mizuna [8][9][10]. It is reported that, under the same DLI, the plant growth could be better with a longer photoperiod and lower PPFDs, because the photosynthetic efficiency would be driven higher under such a lighting environment than otherwise [9].…”

“…For the accumulation of a plant biomass, extending the photoperiod with a low light intensity level is more effective than increasing the light intensity with a short photoperiod under the same DLI [7]. For instance, under the same DLI of 8.64 mol m −2 d −1 , the total FW and the total dry weight (DW) of hydroponic lettuce were heavier for the extended light period of 16 h than for the shorter light period of 12 h by 8.6% and 8.5%, respectively [8]. Weaver and van Iersel [9], who tested four different light periods (12,15,18, and 21 h) with the same DLI at 17 mol m −2 d −1 on lettuce grown in a greenhouse, found that the DW of lettuce was positively correlated with the photoperiod, and the highest DW was attained under 21 h. For lettuce and mizuna cultured under the DLI of 16 mol m −2 d −1 provided by white LED in a walk-in growth chamber, the shoot biomass of these crops grown under the photoperiod of 20 h was more than that of 10 h by 16.0% and 18.7%, respectively [10].…”

Effect of Daily Light Integral on Cucumber Plug Seedlings in Artificial Light Plant Factory

“…The plant height, shoot dry mass, root dry mass and chlorophyll content index of rudbeckia seedlings were larger with longer photoperiods [18]. A longer photoperiod with the same DLI increased the light interception, chlorophyll content index, quantum yield of photosystem II, and aboveground biomass of lettuce and mizuna [31,32].…”

Analysis of Metabolomic Changes in Lettuce Leaves under Low Nitrogen and Phosphorus Deficiencies Stresses

“…The EC and pH of the nutrient solution were adjusted to 1.6 dS m −1 and 6.0, respectively. Air temperature, relative humidity, and CO 2 concentration were maintained at 20 ± 5 • C, 60-80%, and 400 ± 10 µmol mol −1 , respectively [26]. After two weeks, eighteen plants having similar growth from each treatment were harvested between 10:00 and 12:00 to minimize diurnal effects on metabolite concentration.…”