Effect of CO2 and O2 on development and fructification of wheat in closed systems.

The cultivation of wheat (Triticum aestivum L.) was performed in controlled environment chambers with the continuous monitoring of photosynthesis, dark respiration, transpiration and main nutrient uptakes. A protocol in twin chambers was developed to compare the specific effects of low O2 and high CO2. Each parameter is able to influence photosynthesis but different effects are obtained In the development, fructification and seed production, because of the different effects of each parameter on the ratio of reductive to oxidative cycle of carbon. The first main conclusion is that low level of O2, at the same rate of biomass production, strongly acts on the rate of ear appearance and on seed production. Ear appearance was delayed and seed production reduced with a low O2 treatment (approximately 4%). The O2 effect was not mainly due to the repression of the oxidative cycle. The high CO2 treatment (700 to 900 microl l-1) delayed ear appearance by 4 days but did not reduce seed production. High CO2 treatment also reduced transpiration by 20%. Two hypothesis were proposed to explain the similarities and the difference in the O2 and CO2 effects on the growth of wheat.     

Application of crop gas exchange and transpiration data obtained with CEEF to global change problem.

In order to predict carbon sequestration of vegetation with the future rise in atmospheric CO2 concentration, [CO2] and temperature, long term effects of high [CO2] and high temperature on responses of both photosynthesis and transpiration of plants as a whole community to environmental parameters need to be elucidated. Especially in the last decade, many studies on photosynthetic acclimation to elevated [CO2] at gene, cell, tissue or leaf level for only vegetative growth phase (i.e. before formation of reproductive organs) have been conducted all over the world. However, CO2 acclimation studies at population or community level for a whole growing season are thus far very rare. Data obtained from repeatable experiments at population or community level for a whole growing season are necessary for modeling carbon sequestration of a plant community. On the other hand, in order to stabilize material circulation in the artificial ecological system of Closed Ecology Experiment Facilities (CEEF), it is necessary to predict material exchange rates in the biological systems. In particular, the material exchange rate in higher plant systems is highly variable during growth periods and there is a strong dependence on environmental conditions. For this reason, dependencies of both CO2 exchange rate and transpiration rate of three rice populations grown from seed under differing conditions of [CO2] and day/night air temperature (350 microL CO2 L-1, 24/17 degrees C (population A); 700 microL CO2 L-1, 24/17 degrees C (population B) and 700 microL CO2 L-1, 26/19 degrees C (population C)) upon PPFD, leaf temperature and [CO2] were investigated every two weeks during whole growing season. Growth of leaf lamina, leaf sheath, panicle and root was also compared. From this experiment, it was elucidated that acclimation of instantaneous photosynthetic response of rice population to [CO2] occurs in vegetative phase through changes in ratio of leaf area to whole plant dry weight, LAR. But, in reproductive growth phase (i.e. after initiation of panicle formation), the difference between photosynthetic response to [CO2] of population A and that of population B decreased. Although LAR of population C was almost always less than that of population A, there was no difference between the photosynthetic response to [CO2] of population A at 24 degrees C and that of population C at 26 degrees C for its whole growth period. These results are useful to make a model to predict carbon sequestration of rice community, which is an important type of vegetation especially in Asia in future global environmental change.     

Crop yield and light/energy efficiency in a closed ecological system: Laboratory Biosphere experiments with wheat and sweet potato.

Two crop growth experiments in the soil-based closed ecological facility, Laboratory Biosphere, were conducted from 2003 to 2004 with candidate space life support crops. Apogee wheat (Utah State University variety) was grown, planted at two densities, 400 and 800 seeds m-2. The lighting regime for the wheat crop was 16 h of light-8 h dark at a total light intensity of around 840 micromoles m-2 s-1 and 48.4 mol m-2 d-1 over 84 days. Average biomass was 1395 g m-2, 16.0 g m-2 d-1 and average seed production was 689 g m-2 and 7.9 g m-2 d-1. The less densely planted side was more productive than the denser planting, with 1634 g m-2 and 18.8 g m-2 d-1 of biomass vs. 1156 g m-2 and 13.3 g m-2 d-1; and a seed harvest of 812.3 g m-2 and 9.3 g m-2 d-1 vs. 566.5 g m-2 and 6.5 g m-2 d-1. Harvest index was 0.49 for the wheat crop. The experiment with sweet potato used TU-82-155 a compact variety developed at Tuskegee University. Light during the sweet potato experiment, on a 18 h on/6 h dark cycle, totaled 5568 total moles of light per square meter in 126 days for the sweet potatoes, or an average of 44.2 mol m-2 d-1. Temperature regime was 28 +/- 3 degrees C day/22 +/- 4 degrees C night. Sweet potato tuber yield was 39.7 kg wet weight, or an average of 7.4 kg m-2, and 7.7 kg dry weight of tubers since dry weight was about 18.6% wet weight. Average per day production was 58.7 g m-2 d-1 wet weight and 11.3 g m-2 d-1. For the wheat, average light efficiency was 0.34 g biomass per mole, and 0.17 g seed per mole. The best area of wheat had an efficiency of light utilization of 0.51 g biomass per mole and 0.22 g seed per mole. For the sweet potato crop, light efficiency per tuber wet weight was 1.33 g mol-1 and 0.34 g dry weight of tuber per mole of light. The best area of tuber production had 1.77 g mol-1 wet weight and 0.34 g mol-1 of light dry weight. The Laboratory Biosphere experiment's light efficiency was somewhat higher than the USU field results but somewhat below greenhouse trials at comparable light levels, and the best portion of the crop at 0.22 g mol-1 was in-between those values. Sweet potato production was overall close to 50% higher than trials using hydroponic methods with TU-82-155 at NASA JSC. Compared to projected yields for the Mars on Earth life support system, these wheat yields were about 15% higher, and the sweet potato yields averaged over 80% higher.     

Anaerobic degradation of inedible crop residues produced in a Controlled Ecological Life Support System.

An anaerobic reactor seeded with organisms from an anaerobic lagoon was used to study the degradation of inedible crop residues from potato and wheat crops grown in a closed environment. Conversion of this biomass into other products was also evaluated. Degradation of wheat volatile solids was about 25% where that of potato was about 50%. The main product of the anaerobic fermentation of both crops was acetic acid with smaller quantities of propionate and butyrate produced. Nitrate, known to be high in concentration in inedible potato and wheat biomass grown hydroponically, was converted to ammonia in the anaerobic reactor. Both volatile fatty acid and ammonia production may have implications in a crop production system.     

Evaluation of an anaerobic digestion system for processing CELSS crop residues for resource recovery.

Three bioreactors, connected in series, were used to process CELSS potato residues for recovery of resources. The first stage was an anaerobic digestor (8 L working volume; cow rumen contents inoculum; fed-batch; 8 day retention time; feed rate 25 gdw day-1) that converted 33% of feed (dry weight loss) to CO2 and "volatile fatty acids" (vfa, 83:8:8 mmolar ratio acetic:propionic:butyric). High nitrate-N in the potato residue feed was absent in the anaerobic effluent, with a high portion converted to NH4(+)-N and the remainder unaccounted and probably lost to denitrification and NH4+ volatilization. Liquid anaerobic effluent was fed to an aerobic, yeast biomass production vessel (2 L volume; Candida ingens inoculum; batch [pellicle] growth; 2 day retention time) where the VFAs and some NH4(+)-N were converted into yeast biomass. Yeast yields accounted for up to 8% of potato residue fed into the anaerobic bioreactor. The third bioreactor (0.5 L liquid working volume; commercial nitrifier inoculum; packed-bed biofilm; continuous yeast effluent feed; recirculating; constant volume; 23 day hydraulic retention time) was used to convert successfully the remaining NH4(+)-N into nitrate-N (preferred form of N for CELSS crop production) and to remove the remaining degradable soluble organic carbon. Effluents from the last two stages were used for partial replenishment of minerals for hydroponic potato production.     

Effects of temperature, CO2/O2 concentrations and light intensity on cellular multiplication of microalgae, Euglena gracilis.

Microalgae culture is likely to play an important role in aquatic food production modules in bioregenerative systems for producing feeds for fish, converting CO2 to O2 and remedying water quality as well as aquatic higher plants. In the present study, the effects of culture conditions on the cellular multiplication of microalgae, Euglena gracilis, was investigated as a fundamental study to determine the optimum culture conditions for microalgae production in aquatic food production modules including both microalgae culture and fish culture systems. E. gracilis was cultured under conditions with five levels of temperatures (25-33 degrees C), three levels of CO2 concentrations (2-6%), five levels of O2 concentrations (10-30%), and six levels of photosynthetic photon flux (20-200 micromoles m-2 s-1). The number of Euglena cells in a certain volume of solution was monitored with a microscope under each environmental condition. The multiplication rate of the cells was highest at temperatures of 27-31 degrees C, CO2 concentration of 4%, O2 concentration of 20% and photosynthetic photon flux of about 100 micromoles m-2 s-1. The results demonstrate that E. gracilis could efficiently produce biomass and convert CO2 to O2 under relatively low light intensities in aquatic food production modules.     

Incineration of biomass and utilization of product gas as a CO2 source for crop production in closed systems: gas quality and phytotoxicity.

This study addressed the recycle of carbon from inedible biomass to CO2 for utilization in crop production. Earlier work identified incineration as an attractive approach to resource recovery from solid wastes because the products are well segregated. Given the effective separation of carbon into the gaseous product stream from the incinerator in the form of CO2 we captured the gaseous stream produced during incineration of wheat inedible biomass and utilized it as the CO2 source for crop production. Injection rate was based on maintenance of CO2 concentration in the growing environment. The crop grown in the closed system was lettuce. Carbon was primarily in the form of CO2 in the incinerator product gas with less than 8% of carbon compounds appearing as CO. Nitrogen oxides and organic compounds such as toluene, xylene, and benzene were present in the product gas at lower concentrations (< 4 micromol mol-1); sulfur containing compounds were below the detection limits. Direct utilization of the gaseous product of the incinerator as the CO2 source was toxic to lettuce grown in a closed chamber. Net photosynthetic rates of the crop was suppressed more than 50% and visual injury symptoms were visible within 3 days of the introduction of the incinerator gas. Even the removal of the incinerator gas alter two days of crop exposure and replacement with pure CO2 did not eliminate the toxic effects. Both organic and inorganic components of the incinerator gas are candidates for the toxin.     

Carbon balance in bioregenerative life support systems: some effects of system closure, waste management, and crop harvest index.

In Advanced Life Support (ALS) systems with bioregenerative components, plant photosynthesis would be used to produce O2 and food, while removing CO2. Much of the plant biomass would be inedible and hence must be considered in waste management. This waste could be oxidized (e.g., incinerated or aerobically digested) to resupply CO2 to the plants, but this would not be needed unless the system were highly closed with regard to food. For example, in a partially closed system where some of the food is grown and some is imported, CO2 from oxidized waste when combined with crew and microbial respiration could exceed the CO2 removal capability of the plants. Moreover, it would consume some O2 produced from photosynthesis that could have been used by the crew. For partially closed systems it would be more appropriate to store or find other uses for the inedible biomass and excess carbon, such as generating soils or growing woody plants (e.g., dwarf fruit trees). Regardless of system closure, high harvest crops (i.e., crops with a high edible to total biomass ratio) would increase food production per unit area and O2 yields for systems where waste biomass is oxidized to recycle CO2. Such interlinking effects between the plants and waste treatment strategies point out the importance of oxidizing only that amount of waste needed to optimize system performance.     

Ethylene production by plants in a closed environment.

Ethylene production by 20-m2 stands of wheat, soybean, lettuce and potato was monitored throughout growth and development in NASA's Controlled Ecological Life Support System (CELSS) Biomass Production Chamber. Chamber ethylene concentrations rose during periods of rapid growth for all four species, reaching 120 parts per billion (ppb) for wheat, 60 ppb for soybean, and 40 to 50 ppb for lettuce and potato. Following this, ethylene concentrations declined during seed fill and maturation (wheat and soybean), or remained relatively constant (potato). Lettuce plants were harvested during rapid growth and peak ethylene production. The highest ethylene production rates (unadjusted for chamber leakage) ranged from 0.04 to 0.06 ml m-2 day-1 during rapid growth of lettuce and wheat stands, or approximately 0.8 to 1.1 nl g-1 fresh weight h-1. Results suggest that ethylene production by plants is a normal event coupled to periods of rapid metabolic activity, and that ethylene removal or control measures should be considered for growing crops in a tightly closed CELSS.     

The CELSS Test Facility project: an example of a CELSS flight experiment system.

The CELSS Test Facility (CTF) is a device for measuring crop plant productivity in the micro-gravity environment of Space Station Freedom. It will allow us to address questions of crop productivity in space, versus that on the ground. The crop productivity factors that will be measured are rates of: 1) biomass production, 2) food production, 3) O2 and CO2 exchange, and 4) water transpiration. In addition, other productivity factors of specific crops will be determined, such as : 1) the ratio of edible to inedible biomass (harvest index), 2) leaf area exposed to and collecting light (leaf area index), 3) ratio of root mass to total biomass, and 4) photosynthetic efficiency (ratio of moles of CO2 fixed (or O2 produced), per mole of photons of specific energies used). Plant and crop morphology, at several levels, ranging from the community to the sub-cellular, will also be evaluated.     

Growth of soybean and potato at high CO2 partial pressures.

Soybean and potato plants were grown in controlled environments at carbon dioxide (CO2) partial pressures ranging from 0.05 to 1.00 kPa. The highest yields of edible biomass occurred at 0.10 kPa for both species, with higher CO2 levels being supraoptimal, but not injurious to the plants. Stomatal conductance rates of upper canopy leaves were lowest at 0.10 kPa CO2, while conductance rates at 0.50 and 1.00 kPa were significantly greater than 0.10 kPa. Total water use by the plants was greatest at the highest CO2 pressures (i.e. 0.50 and 1.00 kPa); consequently, water use efficiencies (biomass produced/water used) were low at the highest CO2 pressures. Based on previous CO2 studies in the literature, the increased conductance and water use at the highest CO2 pressures were surprising and pose interesting challenges for managing plants in a CELSS, where CO2 pressures may exceed optimal levels.     

Effects of CO2 concentration and light intensity on photosynthesis of a rootless submerged plant, Ceratophyllum demersum L., used for aquatic food production in bioregenerative life support systems.

In addition to green microalgae, aquatic higher plants are likely to play an important role in aquatic food production modules in bioregenerative systems for producing feed for fish, converting CO2 to O2 and remedying water quality. In the present study, the effects of culture conditions on the net photosynthetic rate of a rootless submerged plant, Ceratophyllum demersum L., was investigated to determine the optimum culture conditions for maximal function of plants in food production modules including both aquatic plant culture and fish culture systems. The net photosynthetic rate in plants was determined by the increase in dissolved O2 concentrations in a closed vessel containing a plantlet and water. The water in the vessel was aerated sufficiently with a gas containing a known concentration of CO2 gas mixed with N2 gas before closing the vessel. The CO2 concentrations in the aerating gas ranged from 0.3 to 10 mmol mol-1. Photosynthetic photon flux density (PPFD) in the vessel ranged from 0 (dark) to 1.0 mmol m-2 s-1, which was controlled with a metal halide lamp. Temperature was kept at 28 degrees C. The net photosynthetic rate increased with increasing PPFD levels and was saturated at 0.2 and 0.5 mmol m-2 s-1 PPFD under CO2 levels of 1.0 and 3.0 mmol mol-1, respectively. The net photosynthetic rate increased with increasing CO2 levels from 0.3 to 3.0 mmol mol-1 showing the maximum value, 75 nmol O2 gDW-1 s-1, at 2-3 mmol mol-1 CO2 and gradually decreased with increasing CO2 levels from 3.0 to 10 mmol mol-1. The results demonstrate that C. demersum could be an efficient CO2 to O2 converter under a 2.0 mmol mol-1 CO2 level and relatively low PPFD levels in aquatic food production modules.     

Volatile organic compounds detected in the atmosphere of NASA's Biomass Production Chamber.

Atmospheres of enclosed environments in which 20 m2 stands of wheat, potato, and lettuce were grown were characterized and quantified by gas chromatography-mass spectrometry. A large number (in excess of 90) of volatile organic compounds (VOCs) were identified in the chambers. Twenty eight VOC's were assumed to be of biogenic origin for these were not found in the chamber atmosphere when air samples were analyzed in the absence of plants. Some of the compounds found were unique to a single crop. For example, only 35% of the biogenic compounds detected in the wheat atmosphere were unique to wheat, while 36% were unique to potato and 26% were unique to lettuce. The number of compounds detected in the wheat (20 compounds) atmosphere was greater than that of potato (11) and lettuce (15) and concentration levels of biogenic and non-biogenic VOC's were similar.     

Atmospheric dynamics in the "Laboratory Biosphere" with wheat and sweet potato crops.

Laboratory Biosphere is a 40-m3 closed life system equipped with 12,000 W of high pressure sodium lamps over planting beds with 5.37 m2 of soil. Atmospheric composition changes due to photosynthetic fixation of carbon dioxide and corresponding production of oxygen or the reverse, respiration, are observed in short timeframes, e.g., hourly. To focus on inherent characteristics of the crop as distinct from its area or the volume of the chamber, we report fixation and respiration rates in mmol h-1 m-2 of planted area. An 85-day crop of USU Apogee wheat under a 16-h lighted/8-h dark regime peaked in fixation rate at about 100 mmol h-1 m-2 approximately 24 days after planting. Light intensity was about 840 micromoles m-2 s-1. Dark respiration peaked at about 31 mmol h-1 m-2 at the same time. Thereafter, both fixation and respiration declined toward zero as harvest time approached. A residual soil respiration rate of about 1.9 mmol h-1 m-2 was observed in the dark closed chamber for 100 days after the harvest. A 126-day crop of Tuskegee TU-82-155 sweet potato behaved quite differently. Under a 680 micromoles m-2 s-1, 18-h lighted/6-h dark regime, fixation during lighted hours rose to a plateau ranging from about 27 to 48 mmol h-1 m-2 after 42 days and dark respiration settled into a range of 12-23 mmol h-1 m-2. These rates continued unabated until the harvest at 126 days, suggesting that tuber biomass production might have continued at about the same rate for some time beyond the harvest time that was exercised in this experiment. In both experiments CO2 levels were allowed to range widely from a few hundred to about 3000 ppm, which permitted observation of fixation rates both at varying CO2 concentrations and at each number of days after planting. This enables plotting the fixation rate as a function of both variables. Understanding the atmospheric dynamics of individual crops will be essential for design and atmospheric management of more complex CELSS which integrate the simultaneous growth of several crops as in a sustainable remote life support system.     

Specific effects of irradiance and CO2 concentration doublings on productivity and mineral content in lettuce.

Experiments in growth chambers with controlled atmosphere were performed to compare the effects on the productivity of two treatments stimulating photosynthesis: the doubling of CO2 concentration, the doubling of irradiance; the combining of both was also tested. A large effect of light was noticed: (i) the accumulation of carbon was, contrarily to CO2 effect, amplified within time, and led to the most important dry matter production. (ii) the specific leaf weight was about two-fold increased. (iii) the nitrate content was 2-3 fold less. A significant positive effect of CO2 was detected on the fresh biomass production and the iron content of lettuce. A synergy was observed on dry matter production by the interaction of the two factors.     

Comparison of aerobically-treated and untreated crop residue as a source of recycled nutrients in a recirculating hydroponic system.

This study compared the growth of potato plants on nutrients recycled from inedible potato biomass. Plants were grown for 105 days in recirculating, thin-film hydroponic systems containing four separate nutrient solution treatments: (1) modified half-strength Hoagland's (control), 2) liquid effluent from a bioreactor containing inedible potato biomass, 3) filtered (0.2 micrometer) effluent, and 4) the water soluble fraction of inedible potato biomass (leachate). Approximately 50% of the total nutrient requirement in treatments 2-4 were provided (recycled) from the potato biomass. Leachate had an inhibitory effect on leaf conductance, photosynthetic rate, and growth (50% reduction in plant height and 60% reduction in tuber yield). Plants grown on bioreactor effluent (filtered or unfiltered) were similar to the control plants. These results indicated that rapidly degraded, water soluble organic material contained in the inedible biomass, i.e., material in leachate, brought about phytotoxicity in the hydroponic culture of potato. Recalcitrant, water soluble organic material accumulated in all nutrient recycling treatments (650% increase after 105 days), but no increase in rhizosphere microbial numbers was observed.     

Biological and physiochemical methods for utilization of plant wastes and human exometabolites for increasing internal cycling and closure of life support systems.

Wheat was cultivated on soil-like substrate (SLS) produced by the action of worms and microflora from the inedible biomass of wheat. After the growth of the wheat crop, the inedible biomass was restored in SLS and exposed to decomposition ("biological" combustion) and its mineral compounds were assimilated by plants. Grain was returned to the SLS in the amount equivalent to human solid waste produced by consumption of the grain. Human wastes (urine and feces) after physicochemical processing turned into mineralized form (mineralized urine and mineralized feces) and entered the plants' nutrient solution amounts equal to average daily production. Periodically (once every 60-70 days) the nutrient solution was partly (up to 50%) desalinated by electrodialysis. Due to this NaCl concentration in the nutrient solution was sustained at a fixed level of about 0.26%. The salt concentrate obtained could be used in the human nutrition through NaCl extraction and the residuary elements were returned through the mineralized human liquid wastes into matter turnover. The control wheat cultivation was carried out on peat with use of the Knop nutrient solution. Serial cultivation of several wheat vegetations within 280 days was conducted during the experiment. Grain output varied and yield/harvest depended, in large part, upon the amount of inedible biomass returned to SLS and the speed of its decomposition. After achieving a stationary regime, (when the quantity of wheat inedible biomass utilized during vegetation in SLS is equal to the quantity of biomass introduced into SLS before vegetation) grain harvest in comparison with the control was at most 30% less, and in some cases was comparable to the control harvest values. The investigations carried out on the wheat example demonstrated in principle the possibility of long-term functioning of the LSS photosynthesizing link based on optimizations of biological and physicochemical methods of utilization of the human and plants wastes. The possibilities for the use of these technologies for the creation integrated biological-physicochemical LSS with high closure degree of internal matter turnover are discussed in this paper.     

Theoretical and practical considerations for staggered production of crops in a BLSS.

A functional Bioregenerative Life Support System (BLSS) will generate oxygen, remove excess carbon dioxide, purify water, and produce food on a continuous basis for long periods of operation. In order to minimize fluctuations in gas exchange, water purification, and yield that are inherent in batch systems, staggered planting and harvesting of the crop is desirable. A 418-d test of staggered production of potato cv. Norland (26-d harvest cycles) using nutrients recovered from inedible biomass was recently completed at Kennedy Space Center. The results indicate that staggered production can be sustained without detrimental effects on life support functions in a CELSS. System yields of H2O, O2 and food were higher in staggered than batch plantings. Plants growing in staggered production or batch production on "aged" solution initiated tubers earlier, and were shorter than plants grown on "fresh" solution. This morphological response required an increase in planting density to maintain full canopy coverage. Plants grown in staggered production used available light more efficiently than the batch planting due to increased sidelighting.     

Proximate nutritional composition of CELSS crops grown at different CO2 partial pressures.

Two CELSS candidate crops, soybean (Glycine max) and potato (Solanum tuberosum), were grown hydroponically in controlled environments maintained at carbon dioxide (CO2) partial pressures ranging from 0.05 to 1.00 kPa (500 to 10,000 ppm at 101 kPa atmospheric pressure). Plants were harvested at maturity (90 days for soybean and 105 days for potato) and all tissues analyzed for proximate nutritional composition (i.e. protein, fat, carbohydrate, crude fiber, and ash content). Soybean seed ash and crude fiber were higher and carbohydrate was lower than values reported for field-grown seed. Potato tubers showed little difference from field-grown tubers. With the exception of increased crude fiber of soybean seed with increased CO2, no trends were apparent with regard to CO2 effects on proximate composition of soybean seed and potato tubers. Crude fiber of soybean stems and leaves increased with increased CO2, as did soybean leaf protein (total nitrogen). Potato leaf and stem (combined) protein levels also increased with increased CO2, while leaf and stem carbohydrates decreased. Values for leaf and stem protein and ash were higher than values generally reported for field-grown plants for both species. Results suggest that CO2 partial pressure should have little influence on proximate composition of potato tubers or soybean seed, but that high ash and protein levels might be expected from leaves and stems of crops grown in controlled environments of a CELSS.