Radish (Raphanus sativa L. cv. Cherry Bomb II) Growth, Net Carbon Exchange Rate, and Transpiration at Decreased Atmospheric Pressure and / or Oxygen

To simplify engineering requirements for plant growth structures on the Moon or Mars, lower pressures are desirable to reduce mass and decrease atmospheric leakage. In order to establish the effect of reduced pressure and reduced oxygen on carbon assimilation, dark period respiration, transpiration, and plant growth, radishes (Raphanus sativa L. cv. Cherry Bomb II) were grown at 98 (ambient pressure), 66 (2/3 atm), 33 (1/3 atm), and 10 (1/10 atm) kPa total pressures with oxygen partial pressures of 20, 14, 7, and 2 kPa for 21 days. All plants were grown in rockwool using recirculating nutrient film technique hydroponics. Analysis of growth showed no significant difference among the 98, 66, 33, and 10 kPa total pressure environments when the oxygen partial pressure was ≥ 7 kPa, but a significant reduction was observed when the oxygen partial pressure was dropped to 2 kPa, regardless of the total pressure. Net carbon exchange rate (NCER) and transpiration showed a similar pattern, with no significant effect with pressure treatments. Only the reduced oxygen partial pressure treatment of 2 kPa resulted in significant reductions in NCER and transpiration. Results indicate that pressure has little effect on radish productivity as long as oxygen levels are maintained at or above 7 kPa.