Hypobaric Conditions Affect Gas Exchange, Ethylene Evolution, and GRowth of Lettuce for Advanced Life Support Systems (ALS)

by Chuanjiu He, Fred T. Davies, Jr., and Ronald E. Lacey

There are important engineering and crop production advantages in growing plants under hypobaric (reduced atmospheric pressure) conditions for extraterrestrial base of spaceflight enviroments. Advantages include reduced pay load, greater safety because of lower pressure gradients, and improved plant growth. Elevated levels of the plant hormone, ethylene, can occur in enclosed crop production systems and in spaceflight enviroments, leading to adverse plant growth and sterility. Objectives of this research were to characterize the influence of hypobaria on growth and ethylene evolution of lettuce (Lactuca sativa L. cv. Buttercrunch). GRowth was comparable in lettuce grown under 50 and 101 kPa (ambient) total gas pressures in a series of short-term experiments lasting up to 6 days. However, tip burn occurred under ambient pressure, but no low pressure. Tip burn also increased under high light (600 compared to 300 µmol m-2 s-1) and high pCO2 (600 compared to 100 Pa). Under ambient pressure, there were higher CO2 assimilation rates and considerably greater dark respiration rates (higher night consumption of metabolites) compared to low pressure. This could lead to greater growth (biomass production) of plants grown in low pressure over longer crop production cycles. Ethylene evolution was lower under low than ambient pressure.