By Gabriela Toledo-Ortiz and Phoebe Sutton, Lancaster University, Lancaster Environment Centre. Plant Molecular Photobiology Lab.
At present, the UK imports 47% of its fresh vegetables 1. With the unknown impact of Brexit and climate change on markets, the costs associated with these imports could rise, pricing out lower income families from essential dietary nutrients. Urban vertical farming development can revolutionize the production of vegetables in the UK and as such, vertical hydroponics is a fast growing sector already worth $2.23 billion (2018) and expected to rise to $12.77 billion by 2026 2, with innovation currently centred in the Netherlands.
What is Vertical Farming?
Vertical farming is a method of growing plants on top of each other in shelving units or columns. LED (Light-Emitting Diodes) lighting is placed within the stacking as an energy saving method to provide the light required for plant growth. Commonly, these systems are hydroponic, where a growing medium for plant rooting replaces soil, and liquid nutrient solution used as water 3. As a closed loop system, vertical farms can conserve up to 90% water in comparison with soil-based farming methods and supply more produce per square meter than conventional methods.
The various combinations of these technologies are highly versatile, meaning these systems can be placed anywhere there is space – from underground to rooftops – and need – in restaurants, schools, and hospitals within cities. Moreover, they are scalable and can tower several metres high, filling entire warehouses as ‘Plant Factories’ 3. These facilities are already being built in the UK. For example, a smaller system has been constructed in disused sections of the London Underground, and one of the largest Plant Factories in the world is located in Scunthorpe. These and other start-ups are facilitating the production and consumption of local, affordable salad herbs, and present new urban agriculture opportunities within UK industry.
LED-driven Plant Factories.
The benefits of LED-driven ‘Plant Factories’ are numerous. In addition to minimising water use, food can be grown in disused urban spaces, within and surrounding city centres, and distributed directly to the consumer. This reduces food miles, as well as the associated carbon costs, and the freshness of the produce is unparalleled, as it can be harvested the very same day it is consumed. Yield is maximised by growing vertically 4, and by controlling the temperature, humidity, and lighting. However, at present, the LED lighting is generalised across the horticultural industry as “Grow Lights”, and holds great potential for targeted optimization.
Plants and the light spectrum.
Light is food for plants, and as immobile organisms it is vital for them to sense their environment. Plants recognize colors across the visible light spectrum and even further into the UV and Far-Red (FR) spectrums. The distribution of the colors of light and their intensity determines the light quality. Light quality affects a broad range of plant responses including growth, photosynthesis and importantly nutrient production. LEDs deliver specific light colors that can target all these responses. LEDs currently used in horticulture use only Red and Blue light, but UV and FR light also play key roles in plant development and metabolism. While at high doses UV can be damaging, at moderate ranges, it can boost the production of antioxidants 6,7,8. FR light can also affect the production of phytonutrients, tuning down the effects of red-light in most cases. However, plant species respond very differently to light quality, based on their evolutionary adaptions and breeding, and therefore their nutritional content will not be maximised under a generalized light recipe.
Light signals and the production of nutrients in plants.
In the UK, the FAO (2018) 9,10 reports that 10% of children (up to 3 million) and up to 16% of adults with children suffer from food insecurity and food poverty, where individuals experience hunger or the lack a nutritionally adequate diet 11. “Hidden hunger”, defined as micronutrient (vitamins and minerals) malnutrition, can result in adverse health effects including anaemia, debilitation of the immune system, and chronic diseases 12. Hidden hunger is associated with an inability to access a diverse diet, common in ‘Food Deserts’ – areas devoid of production of fresh fruit and vegetables. In the UK, 76% of ‘Food Deserts’ are in urban areas 13; this is especially concerning as, due to urbanization, future population increases will be concentrated in such areas 14 . The combination of industrial urban vertical farming and plant light research (photobiology) presents a unique opportunity to remedy the lack of local food production, while making cheaper, highly nutritious food available. However, at present there is limited information on the influence of specific light inputs for each crop plant in increasing phytonutrient content at harvest. Knowledge gained on the effect of light in the accumulation of micronutrients in plant crops within vertical farms, could play a major role in alleviating urban nutritional deficiencies.
Plant photobiology and plant nutritional quality.
Recent research in model plants and crops has established that the plant light photoreceptors modulate in response to light quality, quantity and timing, multiple plant biochemical pathways essential to humans, such as the production of plant pigments with antioxidant properties and vitamins. Thus, photobiology research presents with the exciting opportunity to experiment on boosting for example vitamin content in the plant products we eat, by delivering specific wavelengths via precise and tunable LED technologies. Fine tuning the light spectrum also presents with the possibility of designing energy saving and sustainable plant factories by controlling light quality, quantity and timing.
Considering that individual plant species react differently to these light quality, establishing the light type responses of crops and addressing the signals coordinated by the plant light photoreceptors is an important area of research for the optimization of plant factories.
In particular, the production of plant antioxidants and vitamins is strongly modulated by light/temperature inputs under the plant photoreceptors and the circadian clock control. As such, increasing our understanding of the role of light in vitamin production can be applied to the commercial sector to optimize the production of healthy and sustainable food. An optimized lighting regime engineered to maximise the nutritional value of different crops can also help to address a hidden hunger of micronutrient deficiencies in modern day society.
Examples of important micronutrients to target include pro-vitamin A, a derivative from carotenoids, whose deficiency is the leading cause of preventable blindness globally and chronic disease including, delayed growth in children, and liver, skin and digestive disorders. Also Vitamin E (tocopherols) is essential for immune and nervous system function as a powerful antioxidant. Humans cannot directly synthesize pro-vitamin A or E, and must ingest these compounds in their diet from plant products, as the main sources. Being the synthesis of both vitamins in plants strongly light driven 15,16,17,18 they are ideal candidates for photobiology research to modulate their accumulation in plants grown in LED driven vertical farms. Salad herbs such as Basil and Coriander are not only highly valued within vertical farming industry, but their preference for Blue and Red light, respectively, make them good experimental models for light quality driven responses. Moreover, as a range of dishes commonly uses these plants as seasoning or salad herbs, they are an affordable and accessible source of nutrients to a wide population, contributing to better nutrition. Combination of research in these herbs and model plants can lead to the dissection of the molecular and physiological mechanisms behind the light modulation of vitamin A and E accumulation in plants towards the design of optimal production in vertical farms.
(1) DEFRA, 2019; (2) Patil and Baul, 2019; Allied Market Research; (3) Resh et al., 1995, Woodbridge Press Publishing Company; (4) Kozai et al., 2020, Academic Press; (5) Touliatos et al., 2016, Food and Energy Security; (6) Agrawal et al., 2009, Advances in Botanical Research; (7) Huché-Thélier et al., 2016, Environmental and Experimental Botany; (8) Fraser et al., 2017, Scientific Reports; (9) FAO, 2018; (10) https://www.rsnonline.org.uk/
(11) www.endhungeruk.org, 2019; (12) Muthayya et al., 2013, PLoS ONE; (13) Corfe, 2018, Social Market Foundation; (14) UN, 2018; (15) Toledo-Ortiz et al., 2010, PNAS; (16) Tanaka et al., 2015, Plant Science; (17) Chenge-Espinosa et al., 2018, The Plant Journal; (18) Kobayashi and DellaPenna, 2008, The Plant Journal; (19) Demotes-Mainard et al., 2015, Environmental and Experimental Botany