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Mars is likely the best candidate for future planetary exploration however the Martian atmosphere is at a pressure of ~0.6 kPa. This extremely low pressure demands that plant growth structures be isolated from the ambient environment. While it is clear that it is desirable to predict the contributions that plants will make to bioregenerative life support systems at reduced atmospheric pressures, research has been limited. This study examines carbon exchange and evapotranspiration in order to establish a baseline that will aid in the development of an atmospheric composition that allows for reduced pressure plant growth without compromising the plant production yields required for human life support.

It is understood that plants and microorganisms will be an intrinsic part of future advanced life support (ALS) systems. The photosynthetic process is uniquely able to provide food and water from transpiration, remove carbon dioxide, and produce oxygen. However, atmospheric management with typical monoculture batch plant growth is made difficult due to fluctuating rates of CO2 assimilation and O2 production during different phases of plant growth and development. Experiments on the effect of continuous production of multiple crops with rotational planting on atmospheric stability within a sealed environment were performed in the Controlled Environment Systems Research Facility ambient pressure controlled environment chambers. Two of the ESA-MELiSSA candidate crops, beet and lettuce, were continuously grown with a ten day staggered planting interval, resulting in a plant canopy with all representative stages of physiological growth within a common atmosphere.

This study investigates the impacts of staged planting on the apparent quantum yield of beet stands. Experiments were conducted with both staged and batch planted beet in full canopy sealed environment chambers under fixed environmental (light, CO2, temperature) conditions. Empirical results indicated a higher average apparent quantum yield than that of the batch planted stand. Observed increases in quantum yield were used to simulate the joint effects of a range of additional daily labour requirements associated with staged scenarios and changes in crop production cost. The implications of these findings on bioregenerative system and physico-chemical system tradeoff are discussed.

In dense plant canopies, shaded leaves represent considerable unused photosynthetic capacity that can be exploited to improve production in closed environments. By coupling Fusion Systems Solar 1000 microwave powered lights to 100 mm diameter glass tubes lined with 3M Optical Lighting Film, energy equivalent to approximately 420 μmol m-2 s-1 PAR was delivered to the inner canopy of a developing soybean (Glycine max L. Merr. cv. Secord) crop. Inner canopy irradiation enhanced plant growth and altered biomass partitioning within the canopy. With inner canopy lighting, edible biomass, carbon dioxide removal and water and oxygen production were increased by 9, 30, 160, and 100 percent respectively. Ethylene production in the closed environment was also increased during several months of canopy development.