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M.E. Musgrave, A. Kuang, L.K. Tuominen, L.H. Levine, and R.C. Morrow

Although plants are envisioned to play a central role in life support systems for future long-duration space travel, plant growth in space has been problematic due to horticultural problems of nutrient delivery and gas resupply posed by the weightless environment. Iterative improvement in hardware designed for growth of plants on orbital platforms now provides confidence that plants can perform well in microgravity, enabling investigation of their nutritional characteristics. Plants of B. rapa (cv. Astroplants) were grown in the Biomass Production System on the International Space Station. Flowers were hand-pollinated and seeds were produced prior to harvest at 39 days after planting. The material was frozen or fixed while on orbit and subsequently analyzed in our laboratories. Gross measures of growth, leaf chlorophyll, starch and soluble carbohydrates confirmed comparable performance by the plants in spaceflight and ground control treatments. Analysis of glucosinolate production in the plant stems indicated that 3-butenylglucosinolate concentration was on average 75% greater in flight samples than in ground control samples. Similarly, the biochemical make-up of immature seeds produced during spaceflight and fixed or frozen while in orbit was significantly different from the ground controls. The immature seeds from the spaceflight treatment had higher concentrations of chlorophyll, starch, and soluble carbohydrates than the ground controls. Seed protein was significantly lower in the spaceflight material. Microscopy of immature seeds fixed in flight showed embryos to be at a range of developmental stages, while the ground control embryos had all reached the premature stage of development. Storage reserve deposition was more advanced in the ground control seeds. The spaceflight environment thus influences B. rapa metabolite production in ways that may affect flavor and nutritional quality of potential space produce.

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D. Marshall Porterfield, Mary E. Musgrave, and Thomas W. Dreschel

A ground-based comparison of plant nutrient delivery systems that have been developed for microgravity application was conducted for dwarf wheat (Triticum aestivum L. `Yecora Rojo') and rapid-cycling brassica (Brassica rapa L. CrGC#1-33) plants. These experiments offer insight into nutrient and oxygen delivery concerns for greenhouse crop production systems. The experiments were completed over a 12-day period to simulate a typical space shuttle-based spaceflight experiment. The plant materials, grown either using the porous-tube nutrient delivery system, the phenolic foam support system, or a solidified agar nutrient medium, were compared by plant-growth analysis, root zone morphological measurements, elemental composition analysis, and alcohol dehydrogenase enzyme activity assay. The results of these analyses indicate that the porous tube plant nutrient delivery and the phenolic foam systems maintain plant growth at a higher level than the solidified agar gel medium system. Root zone oxygenation problems associated with the agar system were manifested through biochemical and morphological responses. The porous tube nutrient delivery system outperformed the other two systems on the basis of plant growth analysis parameters and physiological indicators of root zone aeration. This information is applicable to the current crop production techniques used in greenhouse-controlled environments.

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Chuanjiu He, Fred T. Davies, and Ronald Lacey

There are advantages in growing plants under hypobaric (reduced atmospheric pressure) conditions in biomass production for extraterrestrial base or space-flight environments. Elevated levels of the plant hormone ethylene occur in enclosed crop production systems and in space-flight environments—leading to adverse plant growth and sterility. Objectives of this research were to characterize the influence of hypobaria on growth and ethylene evolution of lettuce (Lactuca sativa L. cv. Buttercrunch). Growth was comparable in lettuce grown under low (25 kPa) and ambient (101 kPa) total gas pressures. However, tip burn occurred under ambient, but not low pressure—in part because of adverse ethylene levels. Under ambient pressure, there were higher CO2 assimilation rates and dark respiration rates (higher night consumption of metabolites) compared to low pressure. This could lead to greater growth (biomass production) of low pressure plants during longer crop production cycles.

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Chuanjiu He, Fred T. Davies, Ronald E. Lacey, and Sheetal Rao

There are engineering and payload advantages in growing plants under hypobaric (reduced atmospheric pressure) conditions in biomass production for extraterrestrial base or spaceflight environments. Objectives of this research were to characterize the influence of hypobaria on growth, gas exchange, and ethylene evolution of lettuce (Lactuca sativa L. cv. Buttercrunch). Elevated levels of the plant hormone, ethylene, occur in enclosed crop production systems and in space-flight environments—leading to adverse plant growth and sterility. Lettuce plants were grown under variable total gas pressures [25 (low) or 101 kPa (ambient)]. During short growth periods of up to 10 days, growth was comparable between low and ambient pressure plants. Regardless of total pressure, plant growth was reduced at 6 kPa pO2 compared to 12 and 21 kPa pO2. At 6 kPa pO2 there was greater growth reduction and stress with ambient (101 kPa) than low (25kPa) pressure plants. Plants at 25/12 kPa pO2 had comparable CO2 assimilation and a 25% lower dark-period respiration than 101/21 kPa pO2 (ambient) plants. Greater efficiency of CO2 assimilation/dark-period respiration occurred with low pressure plants at 6 kPa pO2. Low pressure plants had a reduced CO2 saturation point (100 Pa CO2) compared with ambient (150 Pa CO2). Low pO2 lowered CO2 compensation points for both 25 and 101 kPa plants, i.e., likely due to reduced O2 competing with CO2 for Rubisco. Ethylene was 70% less under low than ambient pressure. High ethylene decreased CO2 assimilation rate of 101/12 kPa O2 plants. The higher dark-period respiration rates (higher night consumption of metabolites) of ambient pressure plants could lead to greater growth (biomass production) of low pressure plants during longer crop production cycles.

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Chuanjiu He, Fred Davies*, Ronald Lacey, and Que Ngo

Elevated levels of ethylene occur in enclosed crop production systems and in space-flight environments—leading to adverse plant growth and sterility. There are engineering advantages in growing plants at hypobaric (reduced atmospheric pressure) conditions in biomass production for extraterrestrial base or spaceflight environments. Objectives of this research were to characterize the influence of hypobaria on gas exchange and ethylene evolution of lettuce (Lactuca sativa L. cv. Buttercrunch). Lettuce was grown under variable total gas pressures [50 and 101 kPa (ambient)]. The six chambered, modular low plant growth (LPPG) system has a Rosemount industrial process gas chromatograph (GC) for determining gas concentrations of oxygen (O2), carbon dioxide (CO2) and nitrogen (N). With the LPPG system, changes in CO2 can be tracked during the light and dark periods on a whole canopy basis, and transpirate collected as a measurement of transpiration. During short growth periods of up to seven days, growth was comparable between low and ambient pressure. However, there was a tendency for leaf tip burn under ambient pressure, in part because of higher ethylene levels. Tip burn increased under high light (600 vs. 300 μmol·m-1·s-1) and high CO2 (600 vs. 100 Pa). The CO2 assimilation rate and dark respiration tended to be higher under ambient conditions. High humidity (100%) reduced CO2 assimilation rate compared to 70% RH. Ethylene was increased by high light (600 vs. 300 μmol·m-1·s-1) and high CO2 (600 vs. 100 Pa). Ethylene was higher under ambient than low pressure. Enhanced plant growth under low pressure may be attributed to reduced ethylene production and decreased dark respiration (lower night consumption of metabolites).

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Matthew Sisko, Jeffrey Richards, Sharon Edney, Neil Yorio, Gary Stutte, and Raymond Wheeler

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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Gary W. Stutte and Greg Goins

In preparation for a spaceflight experiment to measure photosynthesis of wheat (PESTO), four solid media were evaluated for use in the rooting modules of the Biomass Production System (BPS), a new plant growth unit for microgravity. The media were commercial peat-vermiculite (PV) mixture, zeolite developed at Johnson Space (Z/JSC), commercial zeolite developed by Boulder Innovative Technologies (Z/BIT), and arcillite (AR) with slow-release fertilizer. Wheat (cv. USU Super Dwarf) was grown in the media at 1500 μmol/mol CO2, 350 μmol·m-2·s-1 PAR, 23 °C, and 75% relative humidity for 18 to 21 days. Water was delivered to the media through porous tubes imbedded in the media, and NDS pressures of -0.1 to -0.5 kPa were maintained with either a static or recirculating standpipe. Plant height, leaf area, and fresh mass were determined for each experiment. Results indicated that the AR and Z/BIT media resulted in larger and more uniform plants than Z/JSC or PV at the same NDS pressure. Additional experiments were conducted with AR to evaluate interactions between particle size and NDS pressure. At ≈14 days after planting, there was a loss of NDS prime in AR >2.0 mm when the NDS pressure was less than -0.3kPa. This resulted in drying of the media and poor plant growth. There was excess water in the media, which resulted in reduced plant size, in AR <1.0 mm at NDS pressures more than -0.3 kPa.

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G.W. Stutte, I. Eraso, and E.C. Stryjewski

The RASTA (Radish Assimilation in Spaceflight Testbed Atmospheres) space flight experiment is being designed to evaluate effects of spacecraft environment on carbon partitioning in radish. Carbon dioxide concentration and air temperature effects on radish partitioning are being evaluated to optimize conditions on orbit. Determining effects of these stresses on growth will allow environmental stress effects to be isolated from microgravity effects during the mission. Three cultivars, Cherriette, Cherry Belle, and Early Scarlett Globe, have been grown at 23 °C at 400, 1500 and 10,000 ppm CO2 to determine effects of super-elevated CO2 on growth. Total biomass production was greatest at 1500 ppm CO2, with a decline at 10,000 ppm CO2. Harvest index of all cultivars was also highest at 1500 ppm. `Cherry Belle' and `Early Scarlet Globe' were grown at ambient CO2 under temperatures ranging from 18 to 30 °C. Total biomass production was greatest at 22 °C, with significant declines in total dry mass and harvest index with increasing temperatures. Temperatures less than 22 °C resulted in decrease in total biomass, but partitioning to storage roots was enhanced. (Supported by NASA NCC10-0034)

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Gregory D. Goins, Neil C. Yorio, and Raymond M. Wheeler

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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John D. Lea-Cox, G.W. Stutte, W.L. Berry, and R.M. Wheeler

Maintaining pH to optimize nutrient availability in unbuffered nutrient solutions is important for closed spaceflight hydroponic systems and in agriculture. Total nutrient uptake is reflected by electrical conductivity (EC) measurements, while pH reflects the net imbalance of cation and anion absorption. The pH of nitrate-only (0 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document}: 100 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document}) nutrient solutions normally increases, whereas with equimolar (50 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document}: 50 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document}), solutions, pH decreases. However, when solution pH was controlled to 5.8 by a mixed N sources (25 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document}: 75 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document}), plant yields of semi-dwarf wheat (Triticum aestivum cv. `Yecora Rojo') were equal to the control (0 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document}: 100 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document}) system. When nutrient uptake was monitored at 15-min intervals, it was found that \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} were taken up simultaneously. Uptake of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} was more rapid than \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document}. The change in pH and EC was primarily a function of the absorption of three ions, namely \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document}, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document}, and K+. A significant amount of the K+ uptake was highly correlated (P < 0.001) to the presence of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} in solution. When the daily N requirement was supplied as a 25 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document}: 75 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} mixture, comparatively little change in solution pH occurred, with reduced K+ uptake by the plants. Thus, by knowing the daily crop N requirement from the relative growth rate, the pH fluctuations within hydroponic nutrient solutions can be reduced with daily additions of a balanced nutrient solution with a 25 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document}: 75 \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} mixture of N.