低圧環境における植物の生育

Abstract

In order to achieve plant production in a closed ecological life support system (CELSS) in space, environmental control is a key technology because the environment is completely artificial. One advantage of the CELSS in space is that each module's gas composition and total pressure can be regulated at an optimal level. For example, the nitrogen contained in air is not necessary for plant growth, and low oxygen concentration may enhance net photosynthesis by reducing photorespiration. Hypobaric conditions, obtained by reducing nitrogen and oxygen concentrations, could facilitate gas control, reduce construction costs, and simplify maintenance of modules on a lunar base and in plant production systems on Mars. This review summarizes previous papers and evaluates significant effects of total pressure on growth and development of higher plants, especially crops. Previous studies showed that photosynthesis and transpiration of plants were enhanced under low total pressures because gas diffusion rates increase at low total pressures. Spinach and lettuce in vegetative stages can grow normally under 25 to 50 kPa total pressures. Seeds of rice and Arabidopsis thaliana germinated at 25 kPa total pressure. Flowering was normal in Arabidopsis under hypobaric conditions. Seed growth of soybean and Arabidopsis under low total pressures with a low O2 partial pressure was greater than under the atmospheric pressure with the same O2 partial pressure. This indicates that O2 concentrations inside siliques were maintained higher by the higher diffusion rates prevailing under hypobaric conditions. The results indicate that if total and partial pressures are controlled precisely, plants can grow normally in their life cycle from germination to harvest under hypobaric conditions.