Hypobaria, hypoxia, and light affect gas exchange and the CO2 compensation and saturation points of lettuce (Lactuca sativa)
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There are important engineering and crop production advantages in growing plants under hypobaric (reduced atmospheric pressure) conditions for extraterrestrial base or spaceflight environments. The objectives of this research were to determine the influence of hypobaria and reduced partial pressure of oxygen (pO2) (hypoxia) under low and high light irradiance on carbon dioxide (CO2) assimilation (CA), dark-period respiration (DPR), and the CO2 compensation and CO2 saturation points of lettuce (Lactuca sativa L. Buttercrunch). Plants were grown under variable total gas pressures [25 and 101kPa (ambient)] at 6, 12, or 21kPa pO2 (approximately the partial pressure in air at normal pressure). Light irradiance at canopy level of the low-pressure plant growth system (LPPG) was at 240 (low) or 600 (high) molm2s1. While hypobaria (25kPa) had no effect on CA or the CO2 compensation point, it reduced the DPR and the CO2 saturation point, and increased the CA/DPR ratio. Hypoxia (6kPa pO2) and low light reduced CA, DPR, and the CA/DPR ratio. Hypoxia decreased the CO2 compensation point regardless of total pressure. Hypoxia also decreased the the CO2 saturation point of ambient-pressure plants, but had no effect on hypobaric plants. While low light reduced the CO2 saturation point, it increased the CO2 compensation point, compared with high-light plants. The results show that hypobaric conditions of 25kPa do not adversely affect gas exchange compared with ambient-pressure plants, and may be advantageous during hypoxic stress.
