Abstract
Plant factories using artificial light to produce vegetables have high energy costs due to the high demand for electricity for lighting. Compared to conventional light sources, light-emitting diodes (LEDs) offer the possibility of tailoring the light spectrum and regulating light intensity and are more energy-efficient in terms of energy conversion regardless of the levels of lighting intensity. Optimal light intensity and daily light integral (DLI) requirements are key factors for plant growth; however, their values vary among species and varieties. Our experiment aimed to identify the best light intensity to produce lettuce plants in controlled environment. Lettuce plants of the type Batavia cv ‘Blackhawk’ were grown in plastic pots filled with perlite and peat (20:80 v/v) for 33 days in a growth chamber under blue (B, 20%) and red (R, 80%) LED light at a photosynthetic flux density of 130 µmol m−2 s−1 (BR 130, DLI 7.49 mol m−2 d−1), 259 µmol m−2 s−1 (BR 259, DLI 14.92 mol m−2 d−1), and 389 µmol m−2 s−1 (BR 389, DLI 22.41 mol m−2 d−1). Our results showed that increasing light intensity and DLI promotes net photosynthesis, sustains the electron transport rate (ETR), and stimulates the synthesis of anthocyanins and carotenoids, with positive results for plant photoprotection. Furthermore, the decreases in vegetation indexes (photochemical reflectance index (PRI), greenness, and modified chlorophyll absorption in reflectance index (MCARI1)) also indicate changes in photosynthetic pigment content in response to plant acclimation to different DLIs. Among the three light intensities, 389 µmol m−2 s−1 (DLI 22.41 mol m−2 d−1) gave the best results for growing Batavia red lettuce cv ‘Blackhawk’, since it enhances both production and qualitative traits. These results highlight the importance of a proper light intensity to promote plant growth and qualitative traits and to reach high production targets. Hence, preliminary screening of plant performance under different light treatments is recommended to optimise plant response to artificial lighting.
Highlights
Climate changes, as well as the increase in urban populations and the need to fulfil the UN Sustainable Development Goals, pose the need to produce more with less, increasing the resilience of food systems [1,2]
Excess of light in terms of intensity can be harmful to photosystems and induce plants to synthesise different antioxidant compounds and non-photosynthetic pigments to mitigate the excess of light and reactive oxygen species (ROS) scavenging activity, affecting photochemical functions
Compared to BR 130 plants, leaf net photosynthesis and transpiration increased by 34% and 28% under BR 259, and by 122%
Summary
As well as the increase in urban populations and the need to fulfil the UN Sustainable Development Goals, pose the need to produce more with less, increasing the resilience of food systems [1,2]. Controlled Environment Agriculture (CEA) systems like vertical farming (VF) or plant factories with artificial light (PFAL) are proposed as suitable means to produce food in cities [3,4], with several economic and social benefits [5,6]. Crop production in such systems can reach approximately 80–90% higher water and resource use efficiency compared to open field cultivation, thanks to optimal environment. Light is crucial for many processes of plant life, from photosynthesis to circadian rhythm regulation [9]. Finding the right light combination that is able to boost both production time and quality is of crucial importance
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