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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.

The production of essential commodities (O2, H2 O, and edible biomass) and removal of CO2 by higher plants in bioregenerative life support systems would be seriously limited by the occurrence of disease epidemics. Among several treatment possibilities is ultraviolet (UV) radiation, which is one of the preferred sterilization techniques due to cost considerations and observed effectiveness against pathogens in hydroponic systems. Doses of 20 to 40 mW.s/cm2 as estimated in a laboratory flowthrough apparatus inactivated 99.99% of Pythium aphanidermatum, a common pathogen of hydroponic crops. Inactivation increased logarithmically with UV radiation dose. NCER (Net Carbon Exchange Rate) provides an indirect method to determine the effectiveness of UV in reducing Pythium infection, by measuring any changes in primary plant productivity.

The occurrence of disease epidemics in bioregenerative life support systems would seriously limit the production of essential life support requirements. The capacity of diseased plants in closed environment chambers to scrub CO2 was studied with lettuce plants infected with a common greenhouse pathogen, Pythium.At harvest, infected lettuce showed less edible biomass, decreased leaf area, and reduced photosynthesis averaging 50% on a per chamber basis. These results and others are discussed to show the potential of using existing instrumentation in life support systems to monitor the health of the plant canopy, predicting early onset of disease and refining remediation strategies.

Among the species which are considered suitable candidates for life support programs, legumes would be highly valued because of their high protein content and their capacity to fix N2 under symbiotic conditions. The legume, Pisum sativum, has a short life-cycle (48 days), is easily cultivated, does not required any special seed treatment to germinate, and all parts of its shoot are edible, all of which make peas a possible candidate crop for life support programs. In conventional pea cultivars, the leaf has a compound structure with over 95% of the laminar surface provided by leaflets and stipules. In the semi-leafless pea mutants, where the “afila” mutation is present, all leaflets are replaced by tendril complexes.

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.