Changes in hyperspectral reflectance signatures of lettuce leaves in response to macronutrient deficiencies

The adaptation of specific remote sensing and hyperspectral analysis techniques for the determination of incipient nutrient stress in plants could allow early detection and precision supplementation for remediation, important considerations for minimizing mass of advanced life support systems on space station and long term missions. This experiment was conducted to determine if hyperspectral reflectance could be used to detect nutrient stress in Lactuca sativa L. cv. Black Seeded Simpson. Lettuce seedlings were grown for 90 days in a greenhouse or growth chamber in vermiculite containing modified Hoagland’s nutrient solution with key macronutrient elements removed in order to induce a range of nutrient stresses, including nitrogen, phosphorus, potassium, calcium, and magnesium. Leaf tissue nutrient concentrations were compared with corresponding spectral reflectances taken at the end of 90 days. Spectral reflectances varied with growing location, position on the leaf, and nutrient deficiency treatment. Spectral responses of lettuce leaves under macronutrient deficiency conditions showed an increase in reflectance in the red, near red, and infrared wavelength ranges. The data obtained suggest that spectral reflectance shows the potential as a diagnostic tool in predicting nutrient deficiencies in general. Overlapping of spectral signatures makes the use of wavelengths of narrow bandwidths or individual bands for the discrimination of specific nutrient stresses difficult without further data processing.     

Studies on urine treatment by biological purification using Azolla and UV photocatalytic oxidation

The amount of water consumed in space station operations is very large. In order to reduce the amount of water which must be resupplied from Earth, the space station needs to resolve the problems of water supply. For this reason, the recovery, regeneration and utilization of urine of astronauts are of key importance. Many investigations on this subject have been reported. Our research is based on biological absorption and, purification using UV photocatalytic oxidation techniques to achieve comprehensive treatment for urine. In the treatment apparatus we created, the urine solution is used as part of the nutrient solution for the biological components in our bioregenerative life support system. After being absorbed, the nutrients from the urine were then decomposed, metabolized and purified which creates a favorable condition for the follow-up oxidation treatment by UV photocatalytic oxidation. After these two processes, the treated urine solution reached Chinese national standards for drinking water quality (GB5749-1985).     

Recycling of inorganic nutrients for hydroponic crop production following incineration of inedible biomass.

The goal of resource recovery in a regenerative life support system is maintenance of product quality to sure support of reliable and predictable levels of life support function performance by the crop plant component. Further, these systems must be maintained over extended periods of time, requiring maintenance of nutrient solutions to avoid toxicity and deficiencies. The focus of this study was to determine the suitability of the ash product following incineration of inedible biomass as a source of inorganic nutrients for hydroponic crop production. Inedible wheat biomass was incinerated and ash quality characterized. The incinerator ash was dissolved in adequate nitric acid to establish a consistent nitrogen concentration is all nutrient solution treatments. Four experimental nutrient treatments were included: control, ash only, ash supplemented to match the control treatment, and ash only quality formulated with reagent grade chemicals. When nutrient solutions were formulated using only ash following incineration of inedible biomass, a balance in solution is established representing elemental retention following incineration and nutrient proportions present in the original biomass. The resulting solution is not identical to the control. This imbalance resulted in a suppression of crop growth. When the ash is supplemented with reagent grade chemicals to establish the same balance as in the control--growth is identical to the control. The ash appears to carry no phytotoxic materials. Growth in solution formulated with reagent grade chemicals but matching the quality of the ash only treatment resulted in similar growth to that of the ash only treatment. The ash product resulting from incineration of inedible biomass appears to be a suitable form for recycle of inorganic nutrients to crop production.     

Impaired growth of plants cultivated in a closed system: possible reasons.

Plants in experiments on "man-higher plants" closed ecosystem (CES) have been demonstrated to have inhibited growth and reduced productivity due to three basic factors: prolonged usage of a permanent nutrient solution introduction into the nutrient medium of intra-system gray water, and closure of the system. Gray water was detrimental to plants the longer the nutrient solution was used. However, higher plant growth was mostly affected by the gaseous composition of the CES atmosphere, through accumulation of volatile substances.     

Identification and origin of plant pathogenic microorganisms in recirculating nutrient solutions.

Avoidance of root-infecting microorganisms was originally considered one of the advantages of cultivation of crops in a soilless, recirculating nutrient solution. However, to date, four viral, three bacterial and 21 fungal pathogens have been identified as causal agents of root disease in hydroponically-grown crops. Root-infecting fungi, particularly those which produce a motile stage known as a zoospore, have been the primary pathogens associated with extensive crop losses. Documented sources of these root pathogens in hydroponic systems include peat, surface water such as rivers and streams, and insects. The severity of disease caused by these introduced root pathogens is primarily governed by the genetic susceptibility of each crop and the temperature of the recirculating nutrient solution.     

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.     

Use of biologically reclaimed minerals for continuous hydroponic potato production in a CELSS.

Plant-derived nutrients were successfully recycled in a Controlled Ecological Life Support System (CELSS) using biological methods. The majority of the essential nutrients were recovered by microbiologically treating the plant biomass in an aerobic bioreactor. Liquid effluent containing the nutrients was then returned to the biomass production component via a recirculating hydroponic system. Potato (Solanum tuberosum L.) cv. Norland plants were grown on those nutrients in either a batch production mode (same age plants on a nutrient solution) or a staggered production mode (4 different ages of plants on a nutrient solution). The study continued over a period of 418 days, within NASA Breadboard Project's Biomass Production Chamber at the Kennedy Space Center. During this period, four consecutive batch cycles (104-day harvests) and 13 consecutive staggered cycles (26-day harvests) were completed using reclaimed minerals and compared to plants grown with standard nutrient solutions. All nutrient solutions were continually recirculated during the entire 418 day study. In general, tuber yields with reclaimed minerals were within 10% of control solutions. Contaminants, such as sodium and recalcitrant organics tended to increase over time in solutions containing reclaimed minerals, however tuber composition was comparable to tubers grown in the control solutions.     

New problems to be solved for establishing closed life support system.

New test bed facilities such as Bioplex and CEEF have been constructed to test the new advanced technologies for solving the various problems as follows, (1) how to develop air content stabilization technologies with gas balance between the generation and the absorption by living organisms, (2) how to solve the mismatching between the assimilation rate of autotrophic organisms and the respiration rate of heterotrophic organisms, (3) how to balance the speed of the waste decomposition with the absorption speed of nutrient components in the sequential plant cultivation, (4) how to develop new nutrient adjusting subsystems for each plant species, (5) how to compensate the denitrification during the waste decomposition and anaerobic microbes in the nutrient solution.     

Novel sensor technology for monitoring and control of critical plant nutrient parameters.

A novel dielectric sensor technology has been developed for monitoring and control of plant nutrient delivery systems as part of NASA's Controlled Ecological Life Support System (CELSS) program. A unique measurement phenomenon was discovered in which the electrostatic field is shunted to a third terminal of the sensor, resulting in a much greater sensitivity to changes in the complex dielectric properties of the nutrient solution. Based on this phenomenon, a small, flexible, thin-film shunting dielectric sensor (SDS) was designed to provide low-frequency, non-invasive measurement of both the thickness and nutrient concentration of the layer of solution on a plant growth surface. Test results indicate a sensitivity of +/- 0.05mm in layer thickness while characterization of the ability to measure nutrient concentration continues. The development plan for this sensor is presented and other applications are discussed.     

Integrating biological treatment of crop residue into a hydroponic sweetpotato culture.

Residual biomass from hydroponic culture of sweetpotato [Ipomoea batatas (L.) Lam.] was degraded using natural bacterial soil isolates. Sweetpotato was grown for 120 days in hydroponic culture with a nutrient solution comprised of a ratio of 80% modified half Hoagland solution to 20% filtered effluent from an aerobic starch hydrolysis bioreactor. The phytotoxicity of the effluent was assayed with Waldmann's Green' lettuce (Lactuca sativa L.) and the ratio selected after a 60-day bioassay using sweetpotato plants propagated vegetatively from cuttings. Controlled environment chamber experiments were conducted to investigate the impact of filtrate from biological treatment of crop residue on growth and storage root production with plants grown in a modified half Hoagland solution. Incorporation of bioreactor effluent, reduced storage root yield of 'Georgia Jet' sweetpotato but the decrease was not statistically significant when compared with yield for plants cultured in a modified half Hoagland solution without filtrate. However, yield of 'TU-82-155' sweetpotato was significantly reduced when grown in a modified half Hoagland solution into which filtered effluent had been incorporated. Total biomass was significantly reduced for both sweetpotato cultivars when grown in bioreactor effluent. The leaf area and dry matter accumulation were significantly (P < 0.05) reduced for both cultivars when grown in solution culture containing 20% filtered effluent.     

Direct utilization of human liquid wastes by plants in a closed ecosystem.

Model experiments in phytotrons have shown that urea is able to cover 70% of the demand in nitrogen of the conveyer cultivated wheat. At the same time wheat plants can directly utilize human liquid wastes. In this article by human liquid wastes the authors mean human urine only. In a long-term experiment on "man-higher plants" system with two crewmen, plants covered 63 m2, with wheat planted to--39.6 m2. For 103 days, complete human urine (total amount--210.7 l) was supplied into the nutrient solution for wheat. In a month and a half NaCl supply into the nutrient solution stabilized at 0.9-1.65 g/l. This salination had no marked effect on wheat production. The experiment revealed the realistic feasibility to directly involve liquid wastes into the biological turnover of the life support system. The closure of the system, in terms of water, increased by 15.7% and the supply of nutrients for wheat plants into the system was decreased.     

Significance of rhizosphere microorganisms in reclaiming water in a CELSS.

Plant-microbe interactions, such as those of the rhizosphere, may be ideally suited for recycling water in a Controlled Ecological Life Support System (CELSS). The primary contaminant of waste hygiene water will be surfactants or soaps. We identified changes in the microbial ecology in the rhizosphere of hydroponical1y grown lettuce during exposure to surfactant. Six week old lettuce plants were transferred into a chamber with a recirculating hydroponic system. Microbial density and population composition were determined for the nutrient solution prior to introduction of plants and then again with plants prior to surfactant addition. The surfactant Igepon was added to the recirculating nutrient solution to a final concentration of 1.0 g L-1. Bacteria density and species diversity of the solution were monitored over a 72-h period following introduction of Igepon. Nine distinct bacterial types were identified in the rhisosphere; three species accounted for 87% of the normal rhizosphere population. Microbial cell number increased in the presence of Igepon, however species diversity declined. At the point when Igepon was degraded from solution, diversity was reduced to only two species. Igepon was found to be degraded directly by only one species found in the rhizosphere. Since surfactants are degraded from the waste hygiene water within 24 h, the potential for using rhizosphere bacteria as a waste processor in a CELSS is promising.     

Increased BLSS closure using mineralized human waste in plant cultivation on a neutral substrate

The purpose of this work was to study the full-scale potential use of human mineralized waste (feces and urine) as a source of mineral elements for plant cultivation in a biological life support system (BLSS). Plants that are potential candidates for a photosynthesizing link were grown on a neutral solution containing human mineralized waste. Spring wheat Triticum aestivum L., peas Pisum sativum L. Ambrosia cultivar and leaf lettuce Lactuca sativa L., Vitaminny variety, were used. The plants were grown hydroponically on expanded clay aggregates in a vegetation chamber in constant environmental conditions. During plant growth, a determined amount of human mineralized waste was added daily to the nutrient solution. The nutrient solution remained unchanged throughout the vegetation period. Estimated plant requirements for macro-elements were based on a total biological productivity of 0.04 kg day⁻¹ m⁻². As the plant requirements for potassium exceeded the potassium content of human waste, a water extract of wheat straw containing the required amount of potassium was added to the nutrient solution. The Knop’s solution was used in the control experiments.     

Density and composition of microorganisms during long-term (418 day) growth of potato using biologically reclaimed nutrients from inedible plant biomass.

A study evaluating alternative methods for long term operation of biomass production systems was recently completed at the Kennedy Space Center (KSC). The 418-day study evaluated repeated batch versus mixed-aged production of potato grown on either standard 1/2-strength Hoagland's nutrient solution or solutions including nutrients recycled from inedible plant material. The long term effects of closure and recycling on microbial dynamics were evaluated by monitoring the microbial communities associated with various habitats within the plant growth system (i.e., plant roots, nutrient solution, biofilms within the hydroponic systems, atmosphere, and atmospheric condensate). Plate count methods were used to enumerate and characterize microorganisms. Microscopic staining methods were used to estunate total cell densities. The primary finding was that the density and composition of microbial communities associated with controlled environmental plant growth systems are stable during long term operation. Continuous production resulted in slightly greater stability. Nutrient recycling, despite the addition of soluble organic material from the waste processing system, did not significantly increase microbial density in any of the habitats.     

One-week habitation of two humans in an airtight facility with two goats and 23 crops – Analysis of carbon,oxygen, and water circulation

Human habitation and animal holding experiments in a closed environment, the Closed Ecology Experiment Facilities (CEEF), were carried out. The CEEF were established for collecting experimental data to estimate carbon transfer in the ecosystem around Rokkasho nuclear fuel reprocessing plant. Circulation of O₂ and CO₂, and supply of food from crops cultivated in the CEEF were conducted for the first time in the habitation experiments. Two humans known as eco-nauts inhabited the CEEF, living and working in the Plant Module (PM) and the Animal and Habitation Module (AHM), for a week three times in 2005. On a fresh weight basis, 82% of their food was supplied from 23 crops including rice and soybean, cultivated and harvested in the PM, in the 2nd and 3rd experiments. For the goats, the animals held in the experiments, all of their feed, consisting of rice straw, soybean plant leaves, and peanut shells and peanut plant leaves, was produced in the PM in the 2nd and 3rd experiments. The O₂ produced in the PM by photosynthesis of the crops was separated by the O₂ separator using molecular sheaves, then accumulated, transferred, and supplied to the AHM atmosphere. The CO₂ produced in the AHM by respiration of the humans and animals was separated by the CO₂ separator using solid amine, then accumulated, transferred, and supplied to the PM atmosphere. The amount of O₂ consumed in the AHM was 46–51% of that produced in the PM, and the amount of CO₂ produced in the AHM was 43–56% of that consumed in the PM. The surplus of O₂ and the shortage of CO₂ was a result of the fact that waste of the goats and the crops and part of the human waste were not processed in these habitation experiments. The estimated amount of carbon ingested by the eco-nauts was 64–92% of that in the harvested edible part of the crops. The estimated amount of carbon ingested by the goats was 36–53% of that in the harvested inedible part of the crops. One week was not enough time for determination of gas exchange especially for humans and animals, because fluctuation of their gas exchange was quite high. The amount of transpired water collected as condensate was 818–938 L d⁻¹, and it was recycled as replenishing water compensating transpiration loss of nutrient solution. The amount of waste nutrient solution discharged from the PM was 1421–1644 L d⁻¹. The waste nutrient solutions from rice and other crops were processed through micro filters (MFs) separately. The MF filtrated solutions were processed with reverse osmosis (RO) membrane filter separately and divided into filtrated water and concentrated waste nutrient solution. The concentrated waste nutrient solution from the crops other than rice was processed through an ultra-micro filter (UF) and reused, although that from rice was discharged in 2005. Concentrations of nutritional ions in the UF filtrated solution were determined, the depleted ions were added back, the UF filtrated solution was diluted with the RO membrane filtrated water, and the nutrient solution for the crops other than rice was regenerated. The nutrient solution for rice was newly made each time, using concentrated solution from an external source and the RO membrane filtrated water. Average amounts of water used in the AHM (L d⁻¹) were determined as follows: drinking by humans (filtrated water), 1.5; cooking, etc. (filtrated water other than for drinking), 14.3; drinking by goats, 3.8; showering (hot water), 13.2; showering (cold water), 0.1; washing of hand and face and brushing teeth, 4.1; washing of dishes, dish clothes and towels, 36.4; and washing of animal holding tools, 0.3. The waste water was processed by a RO purification system and recycled for toilet flushing and animal pens washing. A circulation experiment for water was started in 2006 and a circulation experiment for waste materials is planned for 2007. In 2006, a single duration of the air circulation experiments was 2 weeks, although the human habitants were changed after 1 week.     

A biological method of including mineralized human liquid and solid wastes into the mass exchange of bio-technical life support systems

The main obstacle to using mineralized human solid and liquid wastes as a source of mineral elements for plants cultivated in bio-technical life support systems (BLSS) is that they contain NaCl. The purpose of this study is to determine whether mineralized human wastes can be used to prepare the nutrient solution for long-duration conveyor cultivation of uneven-aged wheat and Salicornia europaea L. plant community. Human solid and liquid wastes were mineralized by the method of “wet incineration” developed by Yu. Kudenko. They served as a basis for preparing the solutions that were used for conveyor-type cultivation of wheat community represented by 5 age groups, planted with a time interval of 14 days. Wheat was cultivated hydroponically on expanded clay particles. To reduce salt content of the nutrient solution, every two weeks, after wheat was harvested, 12 L of solution was removed from the wheat irrigation tank and used for Salicornia europaea cultivation in water culture in a conveyor mode. The Salicornia community was represented by 2 age groups, planted with a time interval of 14 days. As some portion of the nutrient solution used for wheat cultivation was regularly removed, sodium concentration in the wheat irrigation solution did not exceed 400 mg/L, and mineral elements contained in the removed portion were used for Salicornia cultivation. The experiment lasted 4 months. The total wheat biomass productivity averaged 30.1 g · m⁻² · day⁻¹, and the harvest index amounted to 36.8%. The average productivity of Salicornia edible biomass on a dry weight basis was 39.3 g · m⁻² · day⁻¹, and its aboveground mass contained at least 20% of NaCl. Thus, the proposed technology of cultivation of wheat and halophyte plant community enables using mineralized human wastes as a basis for preparing nutrient solutions and including NaCl in the mass exchange of the BLSS; moreover, humans are supplied with additional amounts of leafy vegetables.     

Analysis of nitrogen flow in rice cultivation in CEEF.

In order to control the material circulation in the Closed Ecology Experiment Facilities (CEEF), it is necessary to clarify material flow in the Closed Plant Experiment Facility (CPEF) of CEEF. We tried to grow rice plants and measure the nitrogen contents in rice plant and nutrient solution in plant cultivation bed to trace the material balance in CPEF. The measurements were carried out under the condition of 750 ppm (v/v) CO2 at 26/19 degrees C in the plant cultivation room. The measurements showed the absorbed nitrogen amount in plant was less than the outflow nitrogen amount from nutrient solution. This difference between absorbed and outflow quantity reached to 17%.     

Application of ISFETs in closed-loop systems for greenhouses.

In horticulture, growing in artificial substrates such as rockwool is more and more considered to be a sound alternative to growing in soil. This development enables the opportunity to create closed-loop systems which lower the waste of raw materials and reduce pollution of the environment. Applying closed-loop systems needs precise knowledge of the composition of the recirculating nutrient solution. This paper presents basic principles of a measuring system, which can monitor continuously the concentration of nutrients in water. The system is based on ion-selective field effect transistors (ISFETs). By appropriate calibration, a high accuracy is achieved for pH and potassium measurements in the nutrient solution. An accuracy of better than 10% (mMol/l) has been achieved.     

A root moisture sensor for plants in microgravity.

Development of components for bioregenerative life-support systems is a vital step toward long-term space exploration. The culturing of plants in a microgravity environment may be optimized by the use of appropriate sensors and controllers. This paper describes a sensor developed for determining the amount of fluid (nutrient solution) available on the surface of a porous ceramic nutrient delivery substrate to the roots of conventional crop plants. The sensor is based on the change in thermal capacitance and thermal conductance near the surface as the moisture content changes. The sensor could be employed as a data acquisition and control sensor to support the automated monitoring of plants grown in a microgravity environment.     

Dynamics of microorganism populations in recirculating nutrient solutions.

This overview covers the basic microbial ecology of recirculating hydroponic solutions. Examples from NASA and Soviet CELSS tests and the commercial hydroponic industry will be used. The sources of microorganisms in nutrient solutions include air, water, seeds, plant containers and plumbing, biological vectors, and personnel. Microbial fates include growth, death, and emigration. Important microbial habitats within nutrient delivery systems are root surfaces, hardware surfaces (biofilms), and solution suspension. Numbers of bacteria on root surfaces usually exceed those from the other habitats by several orders of magnitude. Gram negative bacteria dominate the microflora with fungal counts usually much lower. Trends typically show a decrease in counts with increasing time unless stressed plants increase root exudates. Important microbial activities include carbon mineralization and nitrogen transformations. Important detrimental interactions include competition with plants, and human and plant pathogenesis.