Microclimate control to increase productivity and nutritional quality of leafy vegetables in a cost-effective manner

Abstract

Food security is one of the key global challenges in this century. In Singapore, our research team has been using novel aeroponic technology to produce fresh vegetables since 1997. Aeroponic systems allow for year-round production of not only tropical, but also sub-tropical and temperate fresh vegetables, by simply cooling the roots suspended in aeroponic systems while the aerial parts grow under tropical ambient environments. It has also been used to investigate the impacts of root-zone CO 2 on vegetables by enriching root-zone CO 2 while their aerial portions were subjected to constant atmospheric CO 2 . To compensate for the lack of available land, Singapore also needs to develop a farming system that can increase productivity per unit land area by many-fold. Over the past 10 years, my research team has established a commercially viable LED integrated vertical aeroponic farming system to grow different leafy vegetables under different LED spectra, intensities, and durations in the tropical greenhouse. The results demonstrate that it is possible to increase shoot production and rate of shoot production of leafy vegetables by increasing light intensity and extending the photoperiod under effective LED lighting. Furthermore, temperate vegetable crops such as lettuce were able to acclimate to high light intensity under supplementary LED lights to natural sunlight in the greenhouse. Supplementary LED lightings promote both leaf initiation and expansion with increased photosynthetic pigments, higher Cyt b 6 f and Rubisco protein contents on a per area basis and thus improve photosynthetic capacity and enhance productivity. Plants sense and respond to changes in their immediate environments (microclimate), manipulating the root zone temperature (RZT) and water supply will impact not only their growth and development but also their nutritional quality. Our on-going research aims to investigate if the nutritional quality of leafy vegetables could be improved under suboptimal RZT and mild water deficit through deficit irrigation. If substantial energy and water savings in urban farming can be achieved without substantial yield penalty but with higher nutritional quality, the amount of water and energy saved can bring substantial benefits to society.

Enhancing Productivity and Improving Nutritional Quality of Subtropical and Temperate Leafy Vegetables in Tropical Greenhouses and Indoor Farming Systems

“…More and more studies have highlighted the importance of LED spectral quality on plants grown indoors [21][22][23][31][32][33][34]. However, the optimal LED spectral combinations vary depending on the plant species [26,30,35,36]. The success of indoor vertical farming illuminated by LEDs also hinges on local energy costs and environmental factors such as temperature, humidity, nutrient availability, and CO 2 levels [35].…”

“…However, the optimal LED spectral combinations vary depending on the plant species [26,30,35,36]. The success of indoor vertical farming illuminated by LEDs also hinges on local energy costs and environmental factors such as temperature, humidity, nutrient availability, and CO 2 levels [35]. Relying solely on energy-intensive indoor vertical farming, which necessitates controlled lighting and environmental conditions, is not sustainable for achieving the "30 by 30" goal, which emphasizes achieving more with fewer resources [35].…”

“…The success of indoor vertical farming illuminated by LEDs also hinges on local energy costs and environmental factors such as temperature, humidity, nutrient availability, and CO 2 levels [35]. Relying solely on energy-intensive indoor vertical farming, which necessitates controlled lighting and environmental conditions, is not sustainable for achieving the "30 by 30" goal, which emphasizes achieving more with fewer resources [35]. Therefore, the final part of this review examines the influence of LED spectral quality, intensity, and duration on various leafy vegetables grown aeroponically in tropical greenhouse environments, aiming to reduce cooling costs.…”

Productivity, photosynthetic light-use efficiency, nitrogen metabolism and nutritional quality of C4 halophyte Portulaca oleracea L. grown indoors under different light intensities and durations

“…For vertical farming, most studies are using different combinations of LED light spectra at low PPFD between 150 to 300 µmol m -2 s -1 ( He et al., 2018 ; Palmer and van Iersel, 2020 ). It has been reported that photosynthetic performance, shoot and root biomass accumulation decreased in low light condition ( Yang et al., 2018 ; He and Qin, 2022 ). For instance, Yang et al.…”

“…Using three different vegetables namely Kai Lan ( Brassica alboglabra ), Nai Bai ( B. chinensis L.) and mizuna ( B. juncea var. japonica) , we ( He and Qin, 2022 ) carried out comparative studies under different LED spectral qualities and quantities. All plants had much higher shoot fresh weight (FW) under a PPFD of 500 µmol m -2 s -1 than under a PPFD of 300 µmol m -2 s -1 regardless of LED combinations.…”