Effect of reduced total air pressure on spinach growth

Abstract

Spinach growth experiments were conducted to study the feasibility of growing plants under hypobaric condition in order to achieve plant production for a controlled ecological life support system (CELSS) in space. An environmental control system, including a reduced-pressure growth chamber, was constructed to grow spinach under low total air pressures. The system controls total and partial pressures, temperature, and relative humidity in the chamber. Spinach (Spinacia oleracea L.), which was grown at atmospheric pressure (101 kPa), was transplanted in the chamber and exposed to various pressure conditions for 10 days. PPFD was maintained at 120μmol m-2s-1, and the light period was set at 14 h/day, pH was set at 6.0, and electric conductivity (EC) was 220 mS/m. Air temperature and relative humidity (RH) were 20°C and 73 to 75%, respectively. Thirty plants of 0.6 g fresh weight each were transplanted to the chamber 15 days after seeding and were exposed to various pressure conditions for 10 days. Relative growth rates at 50 and 75 kPa for the half period (Day 0-Day 5) showed higher values, possibly because the CO2 diffusion rate was higher at the lower total pressures, boundary layer and stomatal resistances became smaller, and as a result, the photosynthetic rate increased. However, at Day 10, there was no significant difference in spinach growth among 50, 75, and 100 kPa treatments with the same CO2 partial pressure condition (100 Pa). Since spinach grew more at 100 Pa of CO2 partial pressure than at 50 Pa, CO2 enrichment is considered to be effective under reduced air pressure conditions. © 1995, The Society of Agricultural Meteorology of Japan. All rights reserved.