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- Author or Editor: C.L. Mackowiak x
As humans explore the solar system, life support will need to be increasingly self-sufficient. Growing higher plants and using recycling technologies can improve self-sufficiency. Sodium is an essential mineral for humans, but not typically for plants. Recycling sodium back to humans through food crops may reduce the need for sodium supplements in the human diet. However, if sodium from waste streams is added to the plant system in greater quantities than it is removed, then plant toxic levels may result. The recommended daily sodium requirement is 3000 mg per person. Based on a 20-m2 growing area per person, 150 mg·m–2 sodium would need to be removed each day. Most crops will not remove enough salt when grown at very low sodium levels; however, when grown in 20 mM sodium, plant uptake may meet the 3000 mg/d human sodium requirement without affecting yields. We grew four different salad crops (lettuce, radish, spinach, and table beet) hydroponically and calculated plant uptake rates and partitioning with 0, 20, 40, or 80 mM sodium supplemented nutrient solutions (corresponding to ≈1.4, 4.0, 8.0, and 13.0 dS·m–1 electrical conductivity). Sodium at 40 and 80 mM reduced edible yields. Sodium replaced tissue potassium in most cases, whereas calcium and magnesium concentrations were much less affected, particularly at 20 mM sodium. This data will be used to model sodium flows within a bioregenerative life support system and determine the feasibility of sodium recycling using food crops.
Leaf stomatal conductance was monitored with a steady-state porometer throughout growth and development of soybean and potato plants grown at 500, 1000, 5000, and 10,000 (potato only) μmol mol-1 carbon dioxide (CO2). All plants were grown hydroponically with a 12-hr photoperiod and 300 μmol m-2 s-1 PPF. As expected, conductance at 1000 was < 500 μmol mol-1 for both species, but conductance at 5000 and 10,000 μmol mol-1 was ≥ that at 500 μmol mol-1. Subsequent short-term (24-hr) tests with potato and wheat plants grown at 1000 μmol mol-1 showed that raising CO2 to approx. 10,000 μmol mol-1 or lowering CO2 to 400 μmol mol-1 increased conductance compared to 1000 μmol mol-1 for potato, while only lowering CO2 to 400 μmol mol-1 increased conductance for wheat. Furthermore, raising the CO2 to 10,000 μmol mol-1 increased dark-period conductance in comparison to 1000 μmol mol-1 for potato, while dark-period conductance for wheat leaves was low regardless of the CO2 concentration. Results suggest that very high CO2 levels (e.g. 5000 to 10,000 μmol mol-1) may substantially increase water use of certain crops.
Lettuce (cv. Waldmann's Green) and radish (cv. Giant White Globe) plants were grown hydroponically with a 18-hr photoperiod and 300 μmol m-2 s-1 PPF. Treatments consisted of 400, 1000, 5000 and 10000 μmol mol carbon dioxide (CO2). Leaf stomatal conductance was monitored with a steady-state porometer across one diurnal period at 21 days and all plants were harvested at 25 days. Conductance at 400 and 10000 was > 1000 μmol mol-1 for lettuce and conductance at 5000 and 10000 was > 1000 and 400 μmol mol-1 CO2 for radish. Carbondioxide treatments having the lowest leaf conductances also resulted in the highest yields, viz. 1,000 μmol mol-1 CO2 for radish and 5000 μmol mol-1 CO2, for lettuce. Dark-period conductance was higher at 5000 and 10000 μmol mol-1 CO2 compared to 400 and 1000 μmol mol-1 CO2. The higher dark-period conductances were 70% of the light-period rates for lettuce and 30% for radish. Water use efficiency (WUE) (g biomass kg water-1) was lowest at 400 μmol mol-1 CO2 for both lettuce and radish and was highest at 1000 μmol mol-1 CO2 for lettuce and 5000 μmol mol-1 CO2 for radish. The results suggest that WUE was improved with moderate CO2 enrichment but declined at very high concentrations, i.e. 10000 μmol mol-1 for lettuce and radish.
Radish (Raphanus sativus cv. Giant White Globe) and lettuce (Lactuca sativa cv. Waldmann's Green) plants were grown for 25 days in growth chambers at 23 °C, ≈300 μmol·m-2·s-1 PPF, and 18/6 photoperiod, and four CO2 concentrations: 400, 1000, 5000, and 10,000 μmol·mol-1. Average total dry mass (g/plant) at the 400, 1000, 5000 and 10,000 μmol·mol-1 treatments were 6.4, 7.2, 5.9, and 5.0 for radish and 4.2, 6.2, 6.6, and 4.0 for lettuce. Each species showed an expected increase in yield as CO2 was elevated from 400 to 1000 μmol·mol-1, but super-elevating the CO2 to 10,000 μmol·mol-1 resulted in suboptimal growth. In addition, many radish leaves showed necrotic lesions at 10,000 μmol·mol-1 by 17 days and at 5000 μmol·mol-1 by 20 days. These results are consistent with preliminary tests in which radish cvs. Cherry Belle, Giant White Globe, and Early Scarlet Globe were grown for 16 days at 400, 1000, 5000, and 10,000 μmol·mol-1. In that study, `Giant White Globe' produced the greatest total dry mass at 1000 (3.0 g/plant) and 5000 μmol·mol-1 (3.0 g/plant), and the least at 10,000 μmol·mol-1 (2.2 g/plant). `Early Scarlet Globe' followed a similar trend, but `Cherry Belle' showed little difference among CO2 treatments. Results suggest that super-elevated CO2 can depress growth of some species, and that sensitivities can vary among genotypes.
Peanut (Arachis hypogaea L.) plants were grown hydroponically, using continuously recirculating nutrient solution. Two culture tray designs were tested; one tray design used only nutrient solution, while the other used a sphagnum-filled pod development compartment just beneath the cover and above the nutrient solution. Both trays were fitted with slotted covers to allow developing gynophores to reach the root zone. Peanut seed yields averaged 350 g·m-2 dry mass, regardless of tray design, suggesting that substrate is not required for hydroponic peanut production.
Requirements for water, nutrient replenishment and acid (for pH control) were monitored for stands of wheat, soybean, potato, and lettuce grown in a recirculating hydroponic culture using a modified 1/2 Hoagland solution with NO3-N. Water use at full canopy cover for all crops ranged from 4 to 5 L m-2 day-1. When averaged over the entire crop cycle, nutrient stock solution (∼0.9 S m-1) use varied from 0.2 L m-2 day-1 (lettuce: to 0.75 L m-2 day-1 (wheat), while acid use varied from 6 mmol m-2 day-1 (lettuce and soybeans) to over 40 mmol m-2 day-1 (wheat). Water-per unit biomass was highest for soybean and lettuce (0.3 to 0.4 L g DW), and least for wheat and potato (0.15 L g DW). Nutrient replenishment per unit biomass was highest for lettuce, 34 mL g-1 DW, with other crops ranging from 21-26 mL g-1 DW. Acid requirements were highest for wheat, 1.2 mmol g-1 DW, and lowest for potato, 0.7 mmol g-1 DW. On a PAR basis, acid needs were highest for wheat, 0.6 mmol mol-1 photons, with all other crops near 0.4 mmol mol-1. Acid data suggest that wheat nutrient uptake favors anions more strongly than the other species, or that more nitrate loss (e.g., denitrification) may occur during wheat growth.
Critical levels of nutrients in leaf tissue are influenced by plant metabolism, environment, and nutrient availability. In this study, we measured the elemental concentrations in fully expanded, upper canopy potato (Solunum tuberosum cv. Norland) leaves throughout growth and development in a controlled environment. Plants were grown hydroponically (NFT) in NASA's Biomass Production Chamber using a complete nutrient solution with the electrical conductivity maintained continuously at 0.12 S m-1. Photoperiod and air and root zone temperatures were changed midseason to promote tuberization, while CO2 levels were maintained at 1000 μmol mol-1 throughout growth. During vegetative growth, leaf nutrient concentrations remained relatively constant, except for a decline in Ca. During tuber enlargement and plant maturation, overall nutrient uptake decreased. Concentrations of the less mobile nutrients such as Ca, Mg, and B increased in the leaf tissue during mature growth, but somewhat surprisingly, highly mobile K also increased. Leaf concentrations of P, Zn, and Cu decreased during maturation.
Wheat, soybean, potato, and lettuce crops were grown in a large (20 m2), closed chamber to test plant production for life support in a Controlled Ecological Life Support System (CELSS). Plant crude protein levels were about 15% in wheat and potato biomass, 20% in soybean biomass, and 27% in lettuce biomass at harvest. Nitrate levels were not assayed, but likely contributed to the protein estimates. Nitric acid (used in hydroponic system pH control) contributed 43% for wheat nitrogen needs, 33% for soybean, 30% for potato, and 27% for lettuce. Lettuce contained the highest percent ash (22%) and wheat the lowest (10%). It was likely that the continuous nutrient supply in the hydroponic systems resulted in high ash values. The percentage of plant macronutrients in the inedible biomass was 7% in lettuce, 50% in soybean and potato, and 80% in wheat. Based on these values, perhaps 50% of the macronutrients needed in a multi-crop system could be removed from the inedible biomass and recycled back into the hydroponic system. Applicable technologies for nutrient recovery would include wet or dry oxidation (ashing), water soaking (leaching), or bioreactor degredation. The mass of reagent-grade salts needed in place of nutrient recycling could equal about 30% of the dry food mass required per person day-1.
Potato (Solanum tuberosum L. cvs. Norland and Denali) plants were grown under high-pressure sodium (HPS), metal halide (MH), and blue-light-enhanced SON-Agro high-pressure sodium (HPS-S) lamps to study the effects of lamp spectral quality on vegetative growth. All plants were initiated from in vitro nodal cultures and grown hydroponically for 35 days at 300 μmol·m–2·s–1 photosynthetic photon flux (PPF) with a 12-hour light/12-hour dark photoperiod and matching 20C/16C thermoperiod. `Denali' main stems and internodes were significantly longer under HPS compared to MH, while under HPS-S, lengths were intermediate relative to those under other lamp types, but not significantly different. `Norland' plants showed no significant differences in stem and internode length among lamp types. Total dry weight of `Denali' plants was unaffected by lamp type, but `Norland' plants grown with HPS had significantly higher dry weight than those under either HPS-S or MH. Spectroradiometer measurements from the various lamps verified the manufacturer's claims of a 30% increase in ultraviolet-blue (350 to 450 nm) output from the HPS-S relative to standard HPS lamps. However, the data from `Denali' suggest that at 300 μmol·m–2·s–1 total PPF, the increased blue from HPS-S lamps is still insufficient to consistently maintain short stem growth typical of blue-rich irradiance environments.
The vegetative growth of potato (Solanum tuberosum L.) cvs. Norland (NL) and Denali (DN) was investigated comparing SONAGRO high-pressure sodium (HPS-S), standard high-pressure sodium (HPS), and metal halide (MH) lamps. Plants were initiated from nodal culture and grown hydroponically in a reach-in growth chamber for 35 d with a 12-hr light/12-hr dark photoperiod and corresponding thermoperiod of 20/16 C. PPF for each treatment was maintained at 300 μmol m-2 s-1 and CO2 levels maintained at l000 μmol mol-1 to promote growth. Results showed that main stem length (SL) and number of internodes (INT) for DN were significantly higher under HPS compared to MH, while HPS-S was not significantly different from the other lamp types. Total dry weight (TDW) of NL plants was significantly higher for HPS than for either HPS-S and MH, however there was no significant difference in SL and INT among lamp types. The data suggest that the 12.6% increase in blue light (400-500 nm) with HPS-S in comparison to conventional HPS lamps may not be sufficient to consistently decrease the stem elongation effects commonly seen with plants grown under HPS.