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R.M. Wheeler, C.L. Mackowiak, J.C. Sager, B. Vieux, and W.M. Knott

Lettuce (Lactuca sativa cv. Waldmann's Green) plants were grown in a large, tightly sealed chamber for NASA's Controlled Ecological Life Support Systems (CELSS) program. Plants were started by direct seeding and grown in 64 0.25-m2 trays (six plants per tray) using nutrient film technique. Environmental conditions included: 23°C, 75% relative humidity, 1000 ubar (ppm) CO2, a 16/8 photoperiod, and 300 umol m-2 s-1 PPF from metal halide lamps. Although the chamber was typically opened once each day for cultural activities, atmospheric ethylene levels (measured with GC/PID) increased from near 15 ppb at 23 days after planting (DAP) to 47 ppb at 28 DAP. At harvest (28 DAP), heads averaged 129 g FW or 6.8 g DW per plant, and roots averaged 0.6 g DW per plant. Some tipburn injury was apparent on most of the plants at harvest. By 28 DAP, stand photosynthesis rates for the entire chamber (approx. 20 m2) reached 17.4 umol CO2 m-2 s-1, while dark-period respiration rates reached 5.5 umol CO2 m-2 s-1. Results suggest that good yields can be obtained from lettuce grown in a tightly sealed environment.

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R.M. Wheeler, K.A. Corey, J.C. Sager, C. L. Mackowiak, and W.M. Knott

Soybean plants [Glycine max (L.) Merr. cv. McCall] were grown from seed to harvest (90 days) in NASA's Biomass Production Chamber. The chamber provides approximately 20 m2 of growing area with an atmospheric volume of 113 m3. Photosynthesis and respiration rates of the stand were tracked by monitoring CO2 increase during the 12-h dark period and the subsequent drawdown to controlled set point (1000 ppm) when the lamps were turned on each day. Stand photosynthesis [under 875 μmol m-2 s-1 photosynthetic photon flux (PPF)] peaked at 35 μmol m-2 s-1 at 30 to 35 days after planting (DAP) and averaged 22 μmol m-2 s-1 throughout the life cycle. Dark period respiration peaked near 8 μmol m-2 s-1 at 30 to 35 DAP and averaged nearly 5 μmol m-2 s-1 throughout the life cycle. Prior to full canopy closure near 30 DAP, the light compensation point (LCP) for stand photosynthesis was lass than 100 μmol m-2 s-1 PPF; by 54 DAP the LCP had increasad to 175 μmol m-2 s-1. Stand transpiration rates peaked at 8.2 L m-2 day-1 at 40 to 45 DAP and averaged 4.3 L m-2 day-1 throughout growth.

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R.M. Wheeler, K.A. Corey, B.A. Vieux, S.W. Mosakowski, J.C. Sager, and W.M Knott

Ethylene concentrations were monitored using gas chromatography (GC/PID) throughout growth and development of wheat, soybean, and lettuce stands grown hydroponically inside a large, closed growth chamber (20 m2 area, 113 m3 vol.). For wheat (cv. Yecora Rojo), ethylene concentration increased from < 10 ppb to about 120 ppb at about 28 days after planting (pre-anthesis) and then declined sharply over the next 4 weeks to a plateau of about 10 ppb during canopy maturation and senescence. A similar pattern of evolution was measured for soybean stands (cv. McCall), with peak concentrations of 40 to 70 ppb occurring near 50 days after planting. Unlike wheat, a slight increase in ethylene was noted in the latter stages of soybean stand senescence. For lettuce stands (cv. Waldmann's Green), ethylene increased slowly to 10 to 15 ppb by 24 days after planting, and then rose sharply to 40 ppb by 28 days, when plants were harvested. Data will be used to define ranges for phytotoxicity studies and to project atmospheric contaminant control needs for tightly closed plant growth systems.

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R.M. Wheeler, C.L. Mackowiak, J.C. Sager, N.C. Yorio, W.M. Knott, and W.L. Berry

Two studies were conducted in which `Waldmann's Green' lettuce (Lactuca sativa L.) was grown hydroponically from seed to harvest in a large (20-m2), atmospherically closed growth chamber for the National Aeronautics and Space Administration's controlled ecological life support system (CELSS) program. The first study used metal-halide (MH) lamps [280 μmol·m-2·s-1 photosynthetic photon flux (PPF)], whereas the second used high-pressure sodium (HPS) lamps (293 μmol·m-2·s-1). Both studies used a 16-hour photoperiod, a constant air temperature (22 to 23C), and 1000 μmol·mol-1 CO2 during the light period. In each study, canopy photosynthesis and evapotranspiration (ET) rates were highly correlated to canopy cover, with absolute rates peaking at harvest (28 days after planting) at 17 μmol CO2/m2 per sec and 4 liters·m-2·day-1, respectively. When normalized for actual canopy cover, photosynthesis and ET rates per unit canopy area decreased with age (between 15 and 28 days after planting). Canopy cover increased earlier during the study with HPS lamps, and final shoot yields averaged 183 g fresh mass (FM)/plant and 8.8 g dry mass (DM)/plant. Shoot yields in the first study with MH lamps averaged 129 g FM/plant and 6.8 g DM/plant. Analysis of leaf tissue showed that ash levels from both studies averaged 22% and K levels ranged from 15% to 17% of tissue DM. Results suggest that lettuce should be easily adaptable to a CELSS with moderate lighting and that plant spacing or transplant schemes are needed to maximize canopy light interception and sustain efficient CO2 removal and water production.