For Space exploration, the realization of long-term manned missions requires the possibility to grow plants in extra-terrestrial environments. Indeed, life support in Space will be based on the in situ regeneration of resources (e.g. air, water and food) needed by the crew that can be achieved in plant-based closed artificial ecosystems. At the same time the cultivation of edible plants can be useful to integrate astronauts’ diet with fresh food directly produced onboard of Space platforms.
In this context the production of microgreens is gaining popularity as easy ‘vegetal systems’ that can be grown in a few days, in small volume, providing high nutritional values.
However, one of the main constraints for the in-orbit production of fresh food of vegetable origin is the establishment of scientific requirements for a flight apparatus dedicated to the production of such species.
In this study we used a multidisciplinary approach to understand the effects of the environmental factors on morpho-functional and biochemical aspects of different species of microgreens.
To do so, we set-up various growth chamber experiments to test different type of substrate, nutritional solutions, light intensities and VPDs (vapour pressure deficits) on Brassica oleracea var. sabauda cv. Vertus and Raphanus raphanistrum subsp. sativus cv. Saxa microgreens. In additional experiments, we evaluated the effect of different light qualities (red, blue and optimum spectrum) on the biometric, qualitative and anatomical parameters of Petroselinum crispum.
More specifically, once obtained the optimum light spectrum, we tested two type of substrates (cellulose sponge and coconut fiber) and two nutritional solutions (quarter strength throughout the cycle vs. half strength for the first half of the cycle followed by osmotic water during the second half). Then, using the quarter strength nutrient solution throughout the cycle and the coconut fiber substrate, we tested two different light intensities of an optimum light spectrum (300 µmol photons m-2s-1 vs. 150 µmol photons m-2s-1) and two different VPD levels (low VPD of 0.3 KPa and high VPD of 1.2 kPa).
To understand the best combination of environmental factors on microgreens growth in small controlled artificial systems, we compared the biomass production, morphological traits, visual quality parameters (through the leaf colorimetry coordinates) and biochemical traits including chlorophylls, anthocyanins, ascorbic acids, and soluble sugars content. Microgreens were then collected and subjected to the preparation for microscopy analyses to detect possible environmental factor-induced modifications to the anatomical structure.
The overall analysis showed that the microgreens-response is strictly influenced by environmental factors. Results suggested that the possible occurrence of positive outcomes (increments in antioxidant and biomass production) in microgreens can be severely influenced by environmental conditions: such a phenomenon should be taken into account in the design of plant-based modules for crop production in Space.The outcomes of this study will also be helpful to optimize microgreens production in controlled environment agriculture systems on Earth.