Effects of air current speed on gas exchange in plant leaves and plant canopies.

To obtain basic data on adequate air circulation to enhance plant growth in a closed plant culture system in a controlled ecological life support system (CELSS), an investigation was made of the effects of the air current speed ranging from 0.01 to 1.0 m s-1 on photosynthesis and transpiration in sweetpotato leaves and photosynthesis in tomato seedlings canopies. The gas exchange rates in leaves and canopies were determined by using a chamber method with an infrared gas analyzer. The net photosynthetic rate and the transpiration rate increased significantly as the air current speeds increased from 0.01 to 0.2 m s-1. The transpiration rate increased gradually at air current speeds ranging from 0.2 to 1.0 m s-1 while the net photosynthetic rate was almost constant at air current speeds ranging from 0.5 to 1.0 m s-1. The increase in the net photosynthetic and transpiration rates were strongly dependent on decreased boundary-layer resistances against gas diffusion. The net photosynthetic rate of the plant canopy was doubled by an increased air current speed from 0.1 to 1.0 m s-1 above the plant canopy. The results demonstrate the importance of air movement around plants for enhancing the gas exchange in the leaf, especially in plant canopies in the CELSS.     

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.     

Effects of air velocity on photosynthesis of plant canopies under elevated CO2 levels in a plant culture system.

To obtain basic data for adequate air circulation for promoting plant growth in closed plant production modules in bioregenerative life support systems in space, effects of air velocities ranging from 0.1 to 0.8 m s-1 on photosynthesis in tomato seedlings canopies were investigated under atmospheric CO2 concentrations of 0.4 and 0.8 mmol mol-1. The canopy of tomato seedlings on a plug tray (0.4 x 0.4 m2) was set in a wind-tunnel-type chamber (0.6 x 0.4 x 0.3 m3) installed in a semi-closed-type assimilation chamber (0.9 x 0.5 x 0.4 m3). The net photosynthetic rate in the plant canopy was determined with the differences in CO2 concentrations between the inlet and outlet of the assimilation chamber multiplied by the volumetric air exchange rate of the chamber. Photosynthetic photon flux (PPF) on the plant canopy was kept at 0.25 mmol m-2 s-1, air temperature at 23 degrees C and relative humidity at 55%. The leaf area indices (LAIs) of the plant canopies were 0.6-2.5 and plant heights were 0.05-0.2 m. The net photosynthetic rate of the plant canopy increased with increasing air velocities inside plant canopies and saturated at 0.2 m s-1. The net photosynthetic rate at the air velocity of 0.4 m s-1 was 1.3 times that at 0.1 m s-1 under CO2 concentrations of 0.4 and 0.8 mmol mol-1. The net photosynthetic rate under CO2 concentrations of 0.8 mmol mol-1 was 1.2 times that under 0.4 mmol mol-1 at the air velocity ranging from 0.1 to 0.8 m s-1. The results confirmed the importance of controlling air movement for enhancing the canopy photosynthesis under an elevated CO2 level as well as under a normal CO2 level in the closed plant production modules.     

Carbon dioxide interactions with irradiance and temperature in potatoes.

Separate controlled environment studies were conducted to determine the interaction of CO2 with irradiance and interaction of CO2 with temperature on growth of three potato cultivars. In the first study, an elevated CO2 concentration of 1000 micromoles mol-1 and an ambient CO2 of 350 micromoles mol-1 were maintained at the photosynthetic photon fluxes (PPF) of 17 and 34 mol m-2 d-1 with 12 h photoperiod, and at the PPF of 34 and 68 mol m-2 d-1 with 24 h photoperiod (400 and 800 micromoles m-2 s-1 PPF at each photoperiod). Tuber and total dry weights of 90-day old potatoes were significantly increased with CO2 enrichment, but the CO2 stimulation was less with higher PPF and longer photoperiod. Shoot dry weight was affected more by photoperiod than by PPF and CO2 concentrations. The elevated CO2 concentration increased leaf CO2 assimilation rates and decreased stomatal conductance with 12 h photoperiod, but had only a marginal effect with 24 h photoperiod. In the second study, four CO2 concentrations of 500, 1000, 1500 and 2000 micromoles mol-1 were combined with two air temperature regimes of 16 and 20 degrees C under a 12 h photoperiod. At harvest, 35 days after transplanting, tuber and total dry weights of potatoes reached a maximum with 1000 micromoles mol-1 CO2 at 16 degrees C, but continued to increase up to 2000 micromoles mol-1 CO2 at 20 degrees C. Plant growth was greater at 20 degrees C than at 16 degrees C under all CO2 concentrations. At 16 degrees C specific leaf weight increased substantially with increasing CO2 concentrations as compared to 500 micromoles mol-1 CO2, but increased only slightly at 20 degrees C. This suggests a carbohydrate build-up in the leaves at 16 degrees C temperature that reduces plant response to increased CO2 concentrations. The data in the two studies indicate that a PPF of 34 mol m-2 d-1, 20 degrees C temperature, and 1000-2000 micromoles mol-1 CO2 produces optimal tuber yield in potatoes.     

Plant responses to short- and long-term exposures to high carbon dioxide levels in closed environments.

When higher plants are exposed to elevated levels of CO2 for both short- and long-term periods photosynthetic C-gain and photoassimilate export from leaves are generally increased. Water use efficiency is increased on a leaf area basis. During long-term exposures, photosynthesis rates on leaf and whole plants bases are altered in a species specific manner. The most common pattern in C3 plants is an enhanced rate of whole plant photosynthesis in a well irradiated canopy. Nevertheless, in some herbaceous species prolonged exposure to high CO2 results in remobilization of nitrogenous reserves (i.e., leaf protein degradation) and reduced rates of mature leaf photosynthesis when assayed at ambient CO2 and O2 levels. Both short- and long-term exposures to those CO2 levels (i.e., 100 to 2,000 microliter l-1) which modify photosynthesis and export, also modify both endogenous ethylene gas (C2H4) release, and substrate, 1-aminocyclopropane-1-carboxylic acid (ACC), saturated C2H4 release rates from irradiated leaves. Photosynthetically active canopy leaves contribute most of the C2H4 released from the canopy. Prolonged growth at high CO2 results in a persistent increase in the rate of endogenous C2H4 release from leaves which can, only in part, be attributed to the increase of the endogenous pools of C2H4 pathway intermediates (e.g., methionine, M-ACC, and ACC). The capacity for increasing the rate of C2H4 release in response to short-term exposures to varying CO2 levels does not decline after prolonged growth at high CO2. When leaves, whole plants, and model canopies of tomato plants are exposed to exogenous C2H4 a reduction in the rate of photosynthesis can, in each case, be attributed to the classical effects of C2H4 on plant development and morphology. The effect of C2H4 on CO2 gas exchange of plant canopies is shown to be dependent on the canopy leaf area index.     

Instrumentation for plant health and growth in space.

The present-day plant growth facilities ("greenhouses") for space should be equipped with monitors and controllers of ambient parameters within the chamber because spacecraft environmental variations can be unfavorable to plants. Moreover, little is known about the effects of spaceflight on the greenhouse and rooting media. Lack of information about spaceflight effects on plants necessitates supplying space greenhouses with automatic, non-invasive monitors of, e.g., gas exchange rate, water and nutrient ion uptake, plant mass, temperature and water content of leaves. However, introduction of an environmental or plant sensor into the monitoring system may be reasonable only if it is justified by quantitative evaluation of the influence of a measured parameter on productivity, efficacy of illumination, or some other index of greenhouse efficiency. The multivariate adaptive optimization in terrestrial phytotrons appears to be one of the best methods to assess environmental impacts on crops. Two modifications of greenhouses with the three-dimensional adaptive optimization of crop photosynthetic characteristics include: (1) irradiation, air temperature and carbon dioxide using a modified simplex algorithm; and (2) using irradiation, air temperature, and humidity with sensitivity algorithms with varying frequency of test exposures that have been experimentally developed. As a result, during some stages of plant ontogensis, the photosynthetic productivity of wheat, tomatoes, and Chinese cabbage in these systems was found to increase by a factor of 2-3.     

CO2 enrichment influences yields of 'Florunner,' 'Georgia Red' and 'New Mexico' peanut cultivars.

Three peanut cultivars, 'Florunner,' 'Georgia Red,' and 'New Mexico,' were grown in reach-in chambers to determine response to CO2 enrichment. CO2 treatments were ambient (400 micromol mol-1) and 700 micromol mol-1. Growth chamber conditions included 700 micromol m-2 s-1 photosynthetic photon flux (PPF), 28/22C, 7O% RH, and 12/12 h photoperiod. Growth media consisted of a 1:1 mixture (v/v) of vermiculite and sterilized sand. Six 10 L pots of each cultivar were fertilized three times per week with 250 mL of nutrient solution containing additional Ca (10 mM) and NO3 (25 mM) and watered well. Beginning 21 days after planting (DAP) and every three weeks thereafter up to 84 days, the second leaf from the growing axis (main stem) was detached to determine CO2 effect on leaf area, specific leaf area (SLA) and dry weight. Plants were harvested 97 DAP, at which time total leaf area, leaf number, plant and root weights and pod production data were taken. Numbers of pods per plant, pod fresh and dry weights, fibrous root and plant dry weights were higher for all cultivars grown at 700 micromol mol-1 than at ambient CO2. Also, leaf area for all cultivars was larger with CO2 enrichment than at ambient. SLA tended to decline with time regardless of CO2 treatment. Percentage of total sound mature kernels (%TSMK) was similar for both treatments. Plants grown at 700 micromol mol-1 CO2 had slightly more immature pods and seeds at final harvest.     

Performance of a centrifugal phytotron.

It is possible to cultivate plants under an artificial gravity field generated by a centrifugal device in space. In order to determine an optimal magnitude of gravity, there is a need to investigate the relationship between plant and growth and gravity, including not only reduced gravity but also gravity greater than 1G. A prototype centrifugal phytotron was designed and fabricated in order to investigate the relationship between plant growth and increased gravity. This device enables us to cultivate plants over the long term by controlling environmental conditions in the phytotron such as temperature, relative humidity, CO2 concentration and light intensity. The results of our experiment indicate that plant seeds can germinate and grow even under an artificial gravity which changes sinusoidally from 2G to 4G.     

Effects of lighting and air movement on temperatures in reproductive organs of plants in a closed plant growth facility

Temperature increases in plant reproductive organs such as anthers and stigmas could cause fertility impediments and thus produce sterile seeds under artificial lighting conditions without adequately controlled environments in closed plant growth facilities. There is a possibility such a situation could occur in Bioregenerative Life Support Systems under microgravity conditions in space because there will be little natural convective or thermal mixing. This study was conducted to determine the temperature of the plant reproductive organs as affected by illumination and air movement under normal gravitational forces on the earth and to make an estimation of the temperature increase in reproductive organs in closed plant growth facilities under microgravity in space. Thermal images of reproductive organs of rice and strawberry were captured using infrared thermography at air temperatures of 10–11 °C. Compared to the air temperature, temperatures of petals, stigmas and anthers of strawberry increased by 24, 22 and 14 °C, respectively, after 5 min of lighting at an irradiance of 160 W m⁻² from incandescent lamps. Temperatures of reproductive organs and leaves of strawberry were significantly higher than those of rice. The temperatures of petals, stigmas, anthers and leaves of strawberry decreased by 13, 12, 13 and 14 °C, respectively, when the air velocity was increased from 0.1 to 1.0 ms⁻¹. These results show that air movement is necessary to reduce the temperatures of plant reproductive organs in plant growth facilities.     

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.     

Atmosphere behavior in gas-closed mouse-algal systems: An experimental and modelling study

Concepts of biologically-based regenerative life support systems anticipate the use of photosynthetic organisms for air revitalization. However, mismatches in the rates of production and uptake of oxygen or carbon dioxide between the crew and the plants will lead to an accumulation or depletion of these gases beyond tolerable limits. One method for correcting these atmospheric changes is to use physicochemical devices. This would conflict with the constraint of minimal size and weight imposed upon the successful development of a competitive bioregenerative system. An alternate control strategy is based upon reducing the gas exchange mismatch by manipulation of those environmental parameters known to affect plant or algae gas exchange ratios. We have initiated a research program using a dual approach of mathematical modelling and laboratory experimentation aimed at examining the gas exchange characteristics of artificial animal/plant systems closed to the ambient atmosphere. Our goal is to develop control techniques and management strategies for maintaining the atmospheric levels of carbon dioxide and oxygen at physiological levels. A mathematical model simulating the atmospheric behavior in these systems has been developed and an experimental gas-closed system has been constructed. These will be described and preliminary results will be presented.     

Wheat production in controlled environments.

Our goal is to optimize conditions for maximum yield and quality of wheat to be used in a controlled-environment, life-support system (CELSS) in a Lunar or Martian base or perhaps in a space craft. With yields of 23 to 57 g m-2 d-1 of edible biomass, a minimum size for a CELSS would be between 12 and 30 m2 per person, utilizing about 600 W m-2 of electrical energy for artificial light. Temperature, irradiance, photoperiod, carbon-dioxide levels, humidity, and wind velocity are controlled in state-of-the-art growth chambers. Nutrient solutions (adjusted for wheat) are supplied to the roots via a recirculating system that controls pH by adding HNO3 and controlling the NO3/NH4 ratio in solution. A rock-wool plant support allows direct seeding and densities up to 10,000 plants per meter2. Densities up to 2000 plants m-2 appear to increase seed yield. Biomass production increases almost linearly with increasing irradiance from 400 to 1700 micromoles m-2 s-1 of photosynthetic photon flux (PPF), but the efficiency of light utilization decreases over this range. Photoperiod and temperature both have a profound influence on floral initiation, spikelet formation, stem elongation, and fertilization. High temperatures (25 to 27 degrees C) and long days shorten the life cycle and promote rapid growth, but cooler temperatures (20 degrees C) and shorter days greatly increase seed number per head and thus yield (g m-2). The life cycle is lengthened in these conditions but yield per day (g m-2 d-1) is still increased. We have evaluated about 600 cultivars from around the world and have developed several breeding lines for our controlled conditions. Some of our ultra-dwarf lines (30 to 50 cm tall) look especially promising with high yields and high harvest indices (percent edible biomass).     

Potato growth in a porous tube water and nutrient delivery system.

Potato (Solanum tuberosum L.) cv. 'Norland', vegetative growth and tuber productivity grown in the porous water and nutrient delivery system (PTNDS) developed by the Wisconsin Center for Space Automation and Robotics were compared with the vegetative growth and tuber productivity of plants grown in a peat:vermiculite potting mixture (PT/VR). The plants were grown at 12, 16, and 24-h light periods, 18 degrees C constant temperature, 70% relative humidity, and 300 micromol m-2 s-1 photosynthetic photon flux. Canopy height of plants grown in the PT/VR system was taller than that of plants grown in the PTNDS system. Canopy height differences were greatest when the plants were grown under a 24-h photoperiod. Leaf and stem dry masses were similar for plants grown in the two systems under the 12-h photoperiod. Under the 24-h photoperiod, leaf and stem dry masses of plants grown in the PT/VR system were more than 3 times those of plants grown in the PTNDS system. Tuber dry masses were similar for plants grown in the two systems under the 12-h photoperiod. Under the 24 h-photoperiod, tuber dry weights of plants grown in the PT/VR system were more than twice those of plants grown in the PTNDS system. A slightly higher harvest index (ratio of tuber weight to leaf plus stem weight) was noted for the plants grown in the PTNDS than for the plants grown in the PT/VR system. Plants grown in the PTNDS system at the 24-h photoperiod matured earlier than plants grown at this photoperiod in the PT/VR system. Vegetative growth and tuber productivity of plants grown under the 16-h photoperiod generally were intermediate to those noted for plants grown under the 12 and 24-h photoperiods. These results indicate that potato plants grown in a PTNDS system may require less plant growing volume, mature in a shorter time, and likely produce more tubers per unit area compared with plants grown in the PT/VR system. These plant characteristics are a distinct advantage for a plant growing unit of a CELSS.     

The Spacelab-Mir-1 "Greenhouse-2" experiment.

The Spacelab-Mir-1 (SLM-1) mission is the first docking of the Space Shuttle Atlantis (STS-71) with the Orbital Station Mir in June 1995. The SLM-1 "Greenhouse-2" experiment will utilize the Russian-Bulgarian-developed plant growth unit (Svet). "Greenhouse-2" will include two plantings (1) designed to test the capability of Svet to grow a crop of Superdwarf wheat from seed to seed, and (2) to provide green plant material for post-flight analysis. Protocols, procedures, and equipment for the experiment have been developed by the US-Russian science team. "Greenhouse-2" will also provide the first orbital test of a new Svet Instrumentation System (SIS) developed by Utah State University to provide near real time data on plant environmental parameters and gas-exchange rates. SIS supplements the Svet control and monitoring system with additional sensors for substrate moisture, air temperature, IR leaf temperature, light, oxygen, pressure, humidity, and carbon-dioxide. SIS provides the capability to monitor canopy transpiration and net assimilation of the plants growing in each vegetation unit (root zone) by enclosing the canopy in separate, retractable, ventilated leaf chambers. Six times during the seed-to-seed experiment, plant samples will be collected, leaf area measured, and plant parts fixed and/or dried for ground analysis. A second planting initiated 30 days before the arrival of a U.S. Shuttle [originally planned to be STS-71] is designed to provide green material at the vegetative development stage for ground analysis. [As this paper is being edited, the experiment has been delayed until after the arrival of STS-71.]     

Effects of several environmental factors on sweetpotato growth.

Effects of relative humidity, light intensity and photoperiod on growth of 'Ga Jet' and 'TI-155' sweetpotato cultivars, using the nutrient film technique (NFT), have been reported. In this study, the effect of ambient temperature regimes (constant 28 degrees C and diurnal 28:22 degrees C day:night) and different CO2 levels (ambient, 400, 1000 and 10000 microliters/L--400, 1000 and 10000 ppm) on growth of one or both of these cultivars in NFT are reported. For a 24-h photoperiod, no storage roots were produced for either cultivar in NFT when sweetpotato plants were grown at a constant temperature of 28 degrees C. For the same photoperiod, when a 28:22 degrees C diurnal temperature variation was used, there were still no storage roots for 'TI-155' but the cv. 'Ga Jet' produced 537 g/plant of storage roots. For both a 12-h and 24-h photoperiod, 'Ga Jet' storage root fresh and dry weight tended to be higher with a 28:22 degrees C diurnal temperature variation than with a constant 28 degrees C temperature regime. Preliminary results with both 'Ga Jet' and 'TI 155' cultivars indicate a distinctive diurnal stomatal response for sweetpotato grown in NFT under an ambient CO2 level. The stomatal conductance values observed for 'Ga Jet' at elevated CO2 levels indicated that the difference between the light- and dark-period conductance rates persisted at 400, 1000, and 10000 microliters/L.     

Quantifying energy and mass transfer in crop canopies: sensors for measurement of temperature and air velocity.

Here we report on the in situ performance of inexpensive, miniature sensors that have increased our ability to measure mass and energy fluxes from plant canopies in controlled environments: 1. Surface temperature. Canopy temperature measurements indicate changes in stomatal aperture and thus latent and sensible heat fluxes. Infrared transducers from two manufacturers (Exergen Corporation, Newton, MA; and Everest Interscience, Tucson, AZ, USA) have recently become available. Transducer accuracy matched that of a more expensive hand-held infrared thermometer. 2. Air velocity varies above and within plant canopies and is an important component in mass and energy transfer models. We tested commercially-available needle, heat-transfer anemometers (1 x 50 mm cylinder) that consist of a fine-wire thermocouple and a heater inside a hypodermic needle. The needle is heated and wind speed determined from the temperature rise above ambient. These sensors are particularly useful in measuring the low wind speeds found within plant canopies. 3. Accurate measurements of air temperature adjacent to plant leaves facilitates transport phenomena modeling. We quantified the effect of radiation and air velocity on temperature rise in thermocouples from 10 to 500 micrometers. At high radiation loads and low wind speeds, temperature errors were as large as 7 degrees C above air temperature.     

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.     

Evaluation and modification of commercial infra-red transducers for leaf temperature measurement.

Accurate measurement of the leaf to air temperature gradient is crucial for the determination of stomatal conductance and other plant responses in both single leaves and in plant canopies. This gradient is often less than 1 degree C, which means that leaf temperature must be known to within about +/- 0.1 degree C. This is a challenging task, but new, miniature infra-red transducers from Exergen Corporation (Newton, MA) and Everest Interscience (Tucson, AZ) can be modified and calibrated to achieve this accuracy. The sensors must be modified to add thermal mass and the Exergen sensor requires a measurement of sensor body temperature. Significant error is caused by the discharge of a capacitor in the standard Exergen sensor, but we tested it without the capacitor. The sensors respond rapidly to changes in target temperature, but require 2 to 10 minutes to respond to changes in sensor body temperature, which is often the largest source of error. A new, sensitive method for measuring field of view indicates substantial peripheral vision for both sensors and a wider field of view than specified by the manufacturers. Here we describe sensor output as a function of target and sensor body temperatures, and provide a generic (sensor independent) equation that can be used to achieve +/- 0.2 C accuracy with Exergen sensors. The equation was developed and verified using two black body calibrators.     

Current and potential productivity of wheat for a Controlled Environment Life Support System.

The productivity of higher plants is determined by the incident photosynthetic photon flux (PPF) and the efficiency of the following four physiological processes: absorption of PPF by photosynthetic tissue, carbon fixation (photosynthesis), carbon use (respiration), and carbon partitioning (harvest index). These constituent processes are analyzed to determine theoretical and potentially achievable productivity. The effects of optimal environmental and cultural factors on each of these four factors is also analyzed. Results indicate that an increase in the percentage of absorbed photons is responsible for most of the improvement in wheat yields in an optimal controlled environment. Several trials confirm that there is an almost linear increase in wheat yields with increasing PPF. An integrated PPF of 150 mol m-2 d-1 (2.5 times summer sunlight) has produced 60 g m-2 d-1 of grain. Apparently, yield would continue to increase with even higher PPF's. Energy efficiency increased with PPF to about 600 micromoles m-2 s-1, then slowly decreased. We are now seeking to improve efficiency at intermediate PPF levels (1000 micromoles m-2 s-1) before further exploring potential productivity. At intermediate and equal integrated daily PPF levels, photoperiod had little effect on yield per day or energy efficiency. Decreasing temperature from 23 degrees to 17 degrees increased yield per day by 20% but increased the life cycle from 62 to 89 days. We hope to achieve both high productivity and energy efficiency.     

The effect of gravity on plant germination.

An axis clinostat was constructed to create micro and negative gravity also a rotated flat disk was constructed with different rotation rates to give increased gravity, by centrifugal force up to 48 g. Rice seeds were grown on agar in tubes at the constant air temperature of 20 degrees C under an average light condition of 110 micromol/m2/sec(PPF). Humidity was not controlled but was maintained above 90%. Since the tube containers were not large enough for long cultivation, shoot and root growth were observed every 12 hours until the sixth day from seeding. The lengths of shoots and roots for each individual plant were measured on the last day. The stem lengths were increased by microgravity but the root lengths were not. Under the negative gravity, negative orthogeotropism and under microgravity, diageotropism was observed. No significant effect of increased gravity was observed on shoot and root growth.