Physiological and Growth Characteristics of Brassica rapa 'Tokyo Bekana' Grown within the International Space Station Crop Production System

摘要

The National Aeronautics and Space Administration (NASA) as well as many other space research organizations across the globe have advanced the idea of using plants as a method of bioregenerative life support for decades. Currently, the International Space Station (ISS) houses a small vegetable-production system named "Veggie." Veggie is equipped with a light-emitting diode (LED) cap, a reservoir that provides water to the root zone through capillary action, and adjustable bellows that enclose the growing environment allowing for controlled air circulation. However, Veggie draws air from the cabin space and ISS environmental conditions are controlled for human comfort and function as opposed to optimal plant growth conditions. During the first experiment within Veggie aboard the ISS, temperature averaged 22 ºC (+/- 0.25), relative humidity was 43.9% (+/- 3.7), and CO2 fluctuated around 2,800 ppm (+/- 678). Preliminary trials selected Chinese cabbage (Brassica rapa 'Tokyo Bekana') as the most suitable cultivar for production within Veggie based on its horticultural, organoleptic, and nutritional characteristics. Introducing this cultivar into ISS conditions (mimicked in a growth chamber) led to extensive chlorosis, necrosis, and growth inhibition. Attempts to ameliorate this observed stress by changing light spectrum, slow-release fertilizer composition, and growth substrate were unsuccessful suggesting that this issue could be attributed to environmental conditions. Analyzing effects of CO2 at 450, 900 and 1350 ppm on growth, photosynthesis, and stomatal conductance in this cultivar revealed a poor ability to acclimate to this environmental variable. In order to develop an efficient system of plant production aboard the ISS or other potential spacecraft, a more efficient CO2 regulation system must be implemented within the cabin space or within a defined plant production area and species should be screened based on their ability to thrive in such an environment.