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  • Author or Editor: Neil Yorio x
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Various electric lamp sources have been proposed for growing plants in controlled environments. Although it is desirable for any light source to provide as much photosynthetically active radiation (PAR) as possible, light spectral quality is critical in regard to plant development and morphology. Light-emitting diodes (LEDs) and microwave lamps are promising light sources that have appealing features for applications in controlled environments. Light-emitting diodes can illuminate a narrow spectrum of light, which corresponds with absorption regions of chlorophyll. The sulfur-microwave lamp uses microwave energy to excite sulfur and argon, which produces a bright, continuous broad-spectrum white light. Compared to conventional broad-spectrum sources, the microwave lamp has higher electrical efficiency, and produces limited ultraviolet and infrared radiation. Experiments were conducted with spinach to test the feasibility of using LEDs and microwave lamps for spinach production in controlled environments. Growth and development comparisons were made during 28-day growth cycles with spinach grown under LED (at various red wavelengths), microwave, cool-white fluorescent, or high-pressure sodium lamps. Plant harvests were conducted at 14, 21, and 28 days after planting. At each harvest under all broad-spectrum light sources, spinach leaf growth and photosynthetic responses were similar. Major differences were observed in terms of specific leaf area and weight between spinach plants grown under 700 and 725 nm LEDs as compared to plants grown under shorter red wavelengths.

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The National Aeronautics and Space Administration (NASA) has been conducting controlled environment research with potatoes (Solanum tuberosum L.) in recirculating nutrient film technique (NFT)-hydroponic systems as a human life support component during long-duration spaceflight. Standard nutrient solution management approaches include constant pH regulation with nitric acid (HNO3) and daily adjustment of electrical conductivity (EC) equivalent to half-strength modified Hoagland's solution, where nitrate (NO3-) is the sole nitrogen (N) source. Although tuber yields have been excellent with such an approach, N use efficiency indices are expected to be low relative to tuber biomass production. Furthermore, the high amount of N used in NFT-hydroponics, typically results in high inedible biomass, which conflicts with the need to minimize system mass, volume, and expenditure of resources for long-duration missions. More effective strategies of N fertilization need to be developed to more closely match N supply with demand of the crop. Hence, the primary objective of this study was to identify the optimal N management regime and plant N requirement to achieve high yields and to avoid inefficient use of N and excess inedible biomass production. In separate 84-day cropping experiments, three N management protocols were tested. Treatments which decreased NO3 --N supply indirectly through lowering nutrient solution EC (Expt. I), or disabling pH control, and/or supplying NH4 +-N (Expt. III) did not significantly benefit tuber yield, but did influence N use efficiency indices. When supplied with an external 7.5 mm NO-3 --N for the first 42 days after planting (DAP), lowered to 1.0 mm NO3 -N during the final 42 days (Expt. II), plants were able to achieve yields on par with plants which received constant 7.5 mm NO3 --N (control). By abruptly decreasing N supply at tuber initiation in Expt. II, less N was taken up and accumulated by plants compared to those which received high constant N (control). However, proportionately more plant accumulated N was used (N use efficiency) to produce tuber biomass when N supply was abruptly lowered at tuber initiation in Expt. II. Hence, a hydroponic nutrient solution N management system may be modified to elicit greater plant N-use while maintaining overall high tuber yield as opposed to achieving high tuber yields through excess N supply and shoot growth.

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The effect of photoperiod (PP) on net carbon assimilation rate (Anet) and starch accumulation in newly mature canopy leaves of `Norland' potato (Solanum tuberosum L.) was determined under high (412 ∝mol·m-2·s-1) and low (263 ∝mol·m-2·s-1) photosynthetic photon flux (PPF) conditions. The Anet decreased from 13.9 to 11.6 and 9.3 μmol·m-2·s-1, and leaf starch increased from 70 to 129 and 118 mg·g-1 drymass (DM) as photoperiod (PP) was increased from 12/12 to 18/6, and 24/0, respectively. Longer PP had a greater effect with high PPF conditions than with low PPF treatments, with high PPF showing greater decline in Anet. Photoperiod did not affect either the CO2 compensation point (50 μmol·mol-1) or CO2 saturation point (1100-1200 μmol·mol-1) for Anet. These results show an apparent limit to the amount of starch that can be stored (≈15% DM) in potato leaves. An apparent feedback mechanism exists for regulating Anet under high PPF, high CO2, and long PP, but there was no correlation between Anet and starch concentration in individual leaves. This suggests that maximum Anet cannot be sustained with elevated CO2 conditions under long PP (≥12 hours) and high PPF conditions. If a physiological limit exists for the fixation and transport of carbon, then increasing photoperiod and light intensity under high CO2 conditions is not the most appropriate means to maximize the yield of potatoes.

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Radish (Raphanus sativus L. cv. Cherriette), lettuce (Lactuca sativa L. cv. Waldmann's Green), and spinach (Spinacea oleracea L. cv. Nordic IV) plants were grown under 660-nm red light-emitting diodes (LEDs) and were compared at equal photosynthetic photon flux (PPF) with either plants grown under cool-white fluorescent lamps (CWF) or red LEDs supplemented with 10% (30 μmol·m-2·s-1) blue light (400-500 nm) from blue fluorescent (BF) lamps. At 21 days after planting (DAP), leaf photosynthetic rates and stomatal conductance were greater for plants grown under CWF light than for those grown under red LEDs, with or without supplemental blue light. At harvest (21 DAP), total dry-weight accumulation was significantly lower for all species tested when grown under red LEDs alone than when grown under CWF light or red LEDs + 10% BF light. Moreover, total dry weight for radish and spinach was significantly lower under red LEDs + 10% BF than under CWF light, suggesting that addition of blue light to the red LEDs was still insufficient for achieving maximal growth for these crops.

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Of the many environmental variables, light intensity (PPF) has primary effect on photosynthesis and significantly influences crop yield. With the eventual use of a crop production system on the International Space Station (ISS), Mars transit vehicle, or in a lunar/Martian habitat, there exists certain engineering constraints that will likely affect the lighting intensity available to plants. Tomato and pepper are candidate crops being considered by NASA that were selected based on their applicability to such mission scenarios. To study the effects of lighting intensity, tomato (Lycopersicon esculentum L. cv. Red Robin) and pepper (Capsicum annuum L. cv. Hanging Basket) plants were grown under cool-white fluorescent (CWF) lamps with light intensities of 8.6, 17.2, or 26 mol·m-2 ·d-1, with a constant air temperature of 25 °C, 65% relative humidity, and CO2 supplementation of 1200 μmol·mol-1 in order to duplicate conditions plants might be subjected to in an open environment of a space cabin. Following 105 days of growth, edible and total mass for both tomato and pepper increased with increasing light levels. Fruit development and time to ripening was also affected by light treatments. The effects of lighting when combined with other environmental factors typical of spaceflight systems will help define crop production for future missions that incorporate plant-based life support technologies.

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Environmental factors such as light intensity (PPF) and/or air temperature may be limiting engineering constraints in near or long-term space missions. This will potentially affect NASA's ability to provide either dietary augmentation to the crew or maintain a large-scale bioregenerative life support system. Crops being considered by NASA to provide supplemental food for crew consumption during such missions consist primarily of minimally processed “salad” species. Lettuce (Lactuca sativa L. cv. Flandria), radish (Raphanus sativus L. cv. Cherry Bomb II), and green onion (Allium fistulosum L. cv. Kinka) are being evaluated under a range of PPF and temperature environments likely to be encountered in space systems. Plants were grown for 35 days under cool-white fluorescent (CWF) lamps with light intensities of 8.6, 17.2, or 26 μmol·m-2·d-1, at air temperatures of 25 and 28 °C, and 50% relative humidity, and 1200 μmol·mol-1 CO2. Regardless of temperature, all three species showed an increase in edible mass with increasing light levels. When grown at 28 °C, edible mass of radish was significantly reduced at all lighting intensities compared to 25 °C, indicating a lower optimal temperature for radish. Understanding the interactions of these environmental factors on crop performance is a critical element to defining future missions that incorporate plant-based life support technologies.

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Development of a crop production system that can be used on the International Space Station, long duration transit missions, and a lunar/Mars habitat, is a part of NASA's Advanced Life Support (ALS) research efforts. Selected crops require the capability to be grown under environmental conditions that might be encountered in the open cabin of a space vehicle. It is also likely that the crops will be grown in a mixed-cropping system to increase the production efficiency and variety for the crew's dietary supplementation. Three candidate ALS salad crops, radish (Raphanus sativus L. cv. Cherry Bomb II), lettuce (Lactuca sativa L. cv. Flandria) and bunching onion (Allium fistulosum L. cv. Kinka) were grown hydroponically as either monoculture (control) or mixed-crop within a walk-in growth chamber with baseline environments maintained at 50% relative humidity, 300 μmol·m-2·s-1 PPF and a 16-hour light/8-hour dark photoperiod under cool-white fluorescent lamps. Environmental treatments in separate tests were performed with either 400, 1200, or 4000 μmol·mol-1 CO2 combined with temperature treatments of 25 °C or 28 °C. Weekly time-course harvests were taken over 28 days of growth. Results showed that none of the species experienced negative effects when grown together under mixed-crop conditions compared to monoculture growth conditions.

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The effects of using mixed cropping strategies for reducing overall mass and increasing system efficiency was examined as part of NASA's mission to study minimally-processed or “salad” crops as dietary supplements on long-duration space missions. To test interspecific compatibility, radish (Raphanus sativus L. cv. Cherry Bomb II), lettuce (Lactuca sativa L. cv. Flandria), and bunching onion (Allium fistulosum L. cv. Kinka) were grown hydroponically as either monoculture (control) or mixed-crop within a walk-in growth chamber maintained at 25 °C, 50% relative humidity, 300 μmol·m-2·s-1 PPF, and a 16-h light/8-h dark photoperiod under cool-white fluorescent lamps. Weekly time-course harvests were taken over 28 days of growth. Results showed that none of the species showed any negative growth effects when grown together under mixed-crop compared to monoculture growth conditions. However, radish showed significant increases in edible mass when grown under mixed-crop compared to monoculture conditions. The observed increases in growth are likely attributable to increased light interception due to a decreased guard row effect as well as a faster canopy development for radish.

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The development of a crop production system that can be used on the International Space Station, long-duration transit missions, and lunar or Mars habitats, has been a part of NASA's Advanced Life Support (ALS) research efforts. Crops that can be grown under environmental conditions that might be encountered in the open cabin of a space vehicle would be an advantageous choice. The production efficiency of the system would be enhanced by growing these crops in a mixed-crop arrangement. This would also increase the variety of fresh foods available for the crew's dietary supplementation. Three candidate ALS salad crops, radish (Raphanus sativus L. cv. Cherry Bomb II), lettuce (Lactuca sativa L. cv. Flandria), and bunching onion (Allium fistulosum L. cv. Kinka) were grown hydroponically as either monoculture (control) or mixed-crop within a walk-in growth chamber with baseline environments maintained at 22 °C, 50% RH, 17.2 mol·m-2·d-1 light intensity and a 16-h light/8-h dark photoperiod under cool-white fluorescent lamps. Tests were carried out at three different CO2 concentrations: 400, 1200, and 4000 μmol·mol-1. Weekly time-course harvests were taken over 28 days of growth, and fresh mass, dry mass, and harvest index were determined. Results showed that none of the species experienced negative effects when grown together under mixed-crop conditions compared to monoculture growth conditions under the range of environmental conditions tested.

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