As space exploration advances beyond lower Earth orbit, re-supply of life support consumables from Earth becomes less feasible. In order to fulfil these aspirations a higher plant-based bioregenerative life support system capable of sustaining a crew with adequate amounts of food, water, and clean air will be required. Mars is likely the best candidate for manned space missions due to its proximity and potentially available resources. Due to the large atmospheric pressure differentials between the Earth and Mars, a reduced pressure plant growth facility has been proposed. Essential for the proper functioning of a Martian based, bioregenerative life support system is a complete understanding of plant water status and related physiology under reduced pressure conditions. Instrumentation used for assessment of plant physiological responses is generally employed at ambient pressures and therefore pressure effects are not considered. This investigation was initiated to examine the in situ stem psychrometer under reduced pressure conditions and derived a correction factor for any resultant pressure effects. Characterization of the pressure influences will allow for the accurate assessment of plant water potential under reduced pressure conditions. Water status was evaluated in terms of transpiration and total plant water potential. An increase in transpiration and a decrease in plant water potentials was associated with decreased atmospheric pressures.
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