Just as the Earth's atmosphere is cleansed by plants with the help of the Sun, so our artificial atmosphere can be renewed... The plants we take with us on our journey can work continuously”. This was written at the beginning of the 20th century by the Russian astronautics pioneer Konstantin Tsiolkovsky. Humanity is preparing for space missions that could last several months or years, where essential resources such as oxygen, water and food will be severely limited and cannot be replenished except by supply missions. The answer is the same as it has been since Neolithic times: agriculture. Growing plants on other worlds not only reduces dependence on resupply missions, but also paves the way for a renewable source of food that can contribute to the long-term sustainability of extraterrestrial environments. Space is a hostile environment for agriculture and presents a number of problems that need to be solved, including the absence of gravity, the need for artificial lighting, the scarcity of water and other vital nutrients, and the limited amount of land available. Gravity plays an important role in plant development, as it tells plants where to grow their leaves and roots. Therefore, in the microgravity conditions typical of space flight, plant development is significantly affected and innovative adaptations are needed to ensure successful cultivation. Radiation also poses a threat, which must be countered by effective radiation protection measures to safeguard plant health. To understand the state of the art in space agriculture, we interviewed Stefania De Pascale, full professor at the Department of Agriculture of the University of Naples Federico II and head of the ESA Laboratory of Crop Research for Space.
Plants play an important role for humanity. What should be the role of plant-based food production in space exploration?
“The role of plants in human life on Earth goes far beyond the simple production of food and will be equally important for human survival in space. The solution proposed by researchers is to create an artificial ecosystem in space called a Bioregenerative Life Support System (BLSS), in which different biological organisms interact, as they do in terrestrial ecosystems. The aim is to create an ecosystem based on interactions between producer organisms (algae, green plants and other photosynthetic organisms), decomposer organisms (bacteria, fungi and detritivores such as worms and insect larvae) and consumer organisms (the human crew), housed in separate compartments, where each uses the waste products of the other as a resource, in an ideal closed cycle.”
What is the Melissa Consortium?
“Since 2013, the Department of Agriculture at the University of Naples Federico II has been an official partner of the Melissa Consortium (Micro-Ecological Life Support System Alternative), the European Space Agency (ESA) programme that has been studying closed-loop life support systems with an ecosystem-based approach since 1987. Since then, we have been actively participating in projects related to the compartment dedicated to plant cultivation for a BLSS as part of this ambitious programme. On 19 November 2019, we inaugurated the Laboratory of Crop Research for Space in our Department, the first laboratory in Europe dedicated to plant cultivation for regenerative life support systems in space, created in collaboration with ESA and the Italian Space Agency.”.
How do plants grown in microgravity differ from those grown on Earth?
“Gravity plays a crucial role in guiding plant growth through what is known as gravitational tropism. In space, in the absence of gravitational stimuli, plants exhibit random growth patterns or respond to different stimuli (for example, roots grow towards water and foliage towards light). Microgravity also indirectly affects plants by altering the availability of resources and the efficiency of the systems used to support their growth, for example through the interaction between gravity and fluid dynamics. In the microgravity environment of the International Space Station (ISS), water does not behave as it does on Earth, i.e. it does not remain at the bottom of a container and cannot be poured, and if it is sprayed, it forms droplets that collide and aggregate, forming increasingly larger drops that remain suspended in the air.
Are there any other problems besides irrigation?
“It is important to provide plants with the necessary nutrients. Controlled nutrient release systems can be incorporated into the substrate to ensure a constant supply of nutrients. Experiments conducted on the ISS and other space missions have demonstrated the feasibility of growing plants, providing valuable scientific information on plant response and for optimising cultivation systems, such as capillary substrates and irrigation and nutrition techniques suitable for microgravity. Leafy vegetables (salads) have shown good adaptability to microgravity conditions and are successfully grown on board the ISS in so-called salad machines. They are very useful for providing fresh ingredients for astronauts“ diets. Cereals, tomatoes, beetroot, radishes and numerous other plants for food purposes are also already being grown in space. One small bite for man, one giant leap for mankind: with these words, NASA commented on the first official tasting in space of romaine lettuce produced in Veggie, one of NASA's facilities installed on board the ISS, and consumed locally in 2015 by astronauts. But that was really just a taste. The Microgreens x Microgravity project for the production of microgreens in space, funded by the Ministry of University and Research and coordinated by the Italian Space Agency (ASI), for which I am the scientific director, aims to define the scientific requirements for a flight apparatus for the production of fresh microgreens to be harvested and consumed on board the ISS. Microgreens are young seedlings of various horticultural, herbaceous or aromatic species, which are harvested just one or two weeks after sowing, when the first true leaves begin to develop. They are small and tender, but contain a high concentration of phytonutrients, vitamins, antioxidants and minerals. This nutritional richness differentiates them from both sprouts and mature vegetables of the same species. The growth apparatus is currently in the industrial design phase, thanks to new funding from the Italian Space Agency (ASI), and this phase is being coordinated by Thales Alenia Space Italia. This apparatus will make it possible to produce enough microgreens on board the ISS to provide astronauts with the recommended daily dose of vitamin C, a powerful antioxidant but unfortunately unstable, and therefore unsuitable for transport on long space journeys.
Which crops are ideal for the space?
“The choice of crops to grow in space is based on several key factors, including high resource regeneration efficiency, high nutritional value, fast growth cycle, ease of cultivation in a controlled environment, and tolerance to environmental stress. However, the choice also depends on the mission scenario. On board orbiting stations such as the ISS, technical limitations depend on the reduced availability of space and energy, as well as crew time. In these environments, crops characterised by a short cycle, small size, tolerance to cultivation in small volumes in microgravity and high productivity, also understood as harvest index, i.e. the ratio between the edible fraction and the total biomass of the plants, are preferred.
What about long-term missions and future space colonies?
To meet the nutritional needs of the crew, crops that provide high-energy foods rich in carbohydrates and proteins (such as soft wheat and durum wheat, rice, potatoes, and soybeans) are preferred, as well as crops for fresh consumption (tomatoes and lettuce). We should not expect plants like those in Frank Oz's Little Shop of Horrors, but the same crops that form the basis of our diet on Earth. The selection of crops for space cultivation will also depend on the ability to effectively manage the life cycle of plants, starting with pollination, in a closed and controlled environment.
Is it possible to make the soil on the Moon or Mars suitable for growing plants?
“This operation is one of the most intriguing challenges for long-term space exploration of the Moon and Mars. The soil of these celestial bodies, known as regolith, presents several problems, including the presence of compounds that are potentially toxic to plants, the absence of organic matter, and the lack of nutrients essential for plant growth. However, there are several approaches being explored to overcome these challenges. To support plant growth, the soil on Mars and the Moon will require substantial amendment, with the addition of organic substances obtained from the treatment of crop residues and mission waste (food waste, faeces, urine), as well as microbial and non-microbial amendments and biostimulants to enable plant growth.
Can research into growing plants in space lead to systems that can also be used on Earth?
“Space agriculture is a rapidly evolving field that promises to revolutionise space exploration and have positive repercussions on Earth. By developing sustainable and resilient cultivation systems in space, we can learn to better manage our planet's resources and ensure food security for future generations, thereby helping to meet the great challenge facing agriculture: feeding an ever-growing population. The knowledge gained and technologies developed for growing plants in space will enable cultivation in extreme terrestrial areas, from the poles to deserts to the heart of modern megacities, gaining more space for plants on Earth. My motto reflects this ideal: More plants in space. More space for plants on Earth.
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