In a plant production facility designed for human life support in vacuum space, lowering total air pressures within the facilities is expected to have the engineering advantage of reducing the construction cost. In this study, low total pressure treatments were applied to spinach over the entire production period from seeding to harvest. An environment control system was constructed to grow plants under low total pressure for long durations. Spinach seeds were directly sowed on a hydroponic plant bed placed in a reduced-pressure growth chamber. The total and O₂ partial pressures within the growth chamber were set at 101 and 21 kPa, 25 and 21 kPa, and 25 and 10 kPa, respectively. The CO₂ partial pressure was constant at 40 Pa. At 21 kPa of O₂ partial pressure, there were no significant differences in fresh and dry weights, leaf area, and shoot length of spinach at harvest between 101 and 25 kPa of total air pressure. At 10 kPa of O₂ partial pressure and 25 kPa of total pressure, the dry weight was not affected, but the leaf area and shoot length at harvest were smaller than those at 21 kPa of O₂. According to these results, it was evident that the entire cultivation of spinach from seeding to harvest could be carried out at one-fourth atmospheric pressure when the O₂ and CO₂ partial pressures are at atmospheric levels.

View full abstract

The Effect of irradiation on free amino acids contents in tea plants (Camellia sinensis O. kuntze) cultivated by hydroponics was studied. During the period of shoot development, the tea plants were covered with shading sheets to exclude 25-80% of the sunlight for 11 days. After the treatment with 80% shading, free amino acids contents in new shoots (leaves and stems) were increased significantly, while those of the 25 and 60% shaded shoots were not changed. The main free amino acids that greatly increased in new shoot were theanine, arginine and glutamine, and the effect of shading on free amino acids was larger in leaves than that in stems. Caffeine content was also plentiful with 80% shading. The effects of night temperature on shoot growth and free amino acids contents in new shoots were investigated at different night temperatures of 26, 21 and 15°C with a constant day temperature of 26°C under a PPFD of 200 μmol m^-2 s^-1 (day length 13 h) in an artificial light growth cabinet. In this experiment, night temperature was found to have effects on shoot growth and free amino acids contents in new shoots. At day/night temperatures of 26/15°C, the elongation of new shoots and contents of free amino acids in shoots were superior to those at the other temperatures. The main free amino acids that greatly increased at lower night temperature were theanine and glutamine.

View full abstract

In maintaining environments for plant growth effectively and properly, it is necessary to perceive and to evaluate optical radiant conditions not only in indoor areas but also under natural radiation. This is true especially under natural radiation, where optical radiant conditions change frequently as time passes. So it is desirable to be able to measure optical radiant conditions quickly, accurately and easily. In this paper, we report on an application of a spectroradiometer to measure the optical radiant conditions for plant growth. In this system, a fiber optic probe was used to improve the freedom and workability for measurements. A spectral dispersion system and a linear image sensor, which is inexpensive and easy to obtain because of recent developments in solid state technology, was utilized instead of a mechanical wavelength scanning system. The spectral dispersion system and a linear image sensor together are called multi-channel spectroradiometer. High speed measurement can be insured by its use under natural radiation. In designing this measurement system, two points were improved to reduce errors. One cosine-corrected the angular responsibility of the spectroradiometer for the measurement of spectral irradiance under natural radiation. The fiber probe of the spectro-radiometer is cosine-corrected by a shielding tube with a diffuser head. The other point is to provide an automatic wavelength scale calibration system using a 7 line spectrum. The combination and error reduction methods of these instruments contributed to the application of a high-speed and high-accuracy multi-channel spectroradiometer to measure the optical radiant conditions for plant growth.

View full abstract

Seedlings of cherimoya (Annona cherimola Mill.), sugar apple (A. squamosa L.) and soursop (A. muricata L.) were grown at 100, 45, 25, and 5% of full sunlight level to determine the influence of irradiance level on their growth and photosynthesis. For all species the shoot length and dry weight of wholeplant were decreased at 25% sunlight, but there was little difference in them between at 45 and 100% sunlight. Total leaf area tended to increase at 45% sunlight in sugar apple and soursop and to decrease at 25% sunlight in cherimoya and soursop. Leaf area ratio increased with decreasing light intensity in every species, and the degree of increase was the least in cherimoya. With decreasing light intensity, leaves became thinner and the specific leaf weight decreased for all species. Chlorophyll content and photosynthetic rate more decreased at 25% than those at 100 and 45% sunlight in sugar apple and soursop. There were little differences both in the chlorophyll content and photosynthesis among these light intensities in cherimoya. This indicates that cherimoya has higher adaptability to low irradiance than other two species. Under weak light condition the stomatal conductance increased for all species. At 5% sunlight, the plant dry weight was less than about 90% of that of control and photosynthetic rate almost decreased to the light compensation point.

View full abstract

When electric potential on plant surface is to be measured, a potentiometer with high input impedance is required, because electric potential is very little. A chopper amplifier for a potentiometer with a new DC-AC converter using metal oxide semiconductor field effect transistor (MOSFET) was developed by the authors. The dynamic characteristic of the MOSFETs can be controlled by applying voltage to the substrates, so the MOSFETs are tried on the new amplifier as DC-AC converter. The four electrode type p-MOSFET is used for this chopper amplifier which has the electrode of the sauce, the gate, the drain and the substrate. In this chopper amplifier, the back of two MOSFETs are put together. The substrates of them were connected by each other, and are given square wave voltage. Then the input signal voltage is chopped into square wave and amplified differentially. The trial DC amplifier had very high impedance, more than 3.5 × 10¹⁰ Ω and 57 pF in parallel. The electric potential on a living plant surface is desired to be measured with no contact and no infiltrating for the sake of its reproducibility. Therefore conductive sponges were used as electrodes of this potentiometer, because they were made of carbon for a little polarization potential and they adhered easily to plants. Although the output impedance of the standard power source was very high, the input-output characteristic of this potentiometer had a good correlation for input voltage between -1.0 V and + 1.0 V. Surface electric potential voltages of some vegetables and fruits were measured by this potentiometer, and both electric potential voltages changed with time and their preservation ways were examined. From the results, the followings were obtained ;
1. A high impedance potentiometer was designed and constructed for measuring surface potential voltage of living plant tissue.
2. Electrical potential measurement was obtained noninvasively by using the sponge electrode.
3. Correlation between freshness and electric potential voltage on a living plant surface was recognized by the measurements.
4. Preservation in the refrigerator was effective not only for external appearance but for biological and physiological phenomena as well.

View full abstract

The effects of temperature and photoperiod on adult diapause in Chrysolina aurichalcea were investigated by rearing at various temperatures and photoperiods for Matsumoto and Yakushima populations. That all adults entered diapause under all experimental conditions, suggested that the diapause was obligatory for these populations. The diapause termination revealed a short-day response. The speed of termination increased with the decrease of photoperiod below the critical photoperiod. The critical photoperiods of diapause termination in Matsumoto population were 14 h at 15°C and 12 h at 25°C, and that in Yakushima population, 12.75 h at 15°C. The critical photoperiod was estimated to decrease about 1 h with the increase of 5°C of rearing temperature and about 8 min with the increase of 1°N latitude of native habitat. The response controlled the initiation of oviposition in autumn. The diapause was considered as functioning not only to survive at low mortality in the severe summer season but also to control the oviposition period so as to maximize the number of egg survivors when the sprout emergence of the host plant, Artemisia princeps occurs in early spring. The difference of their oviposition strategy between Matsumoto (cold winter : host plant leaves not available in winter) and Yakushima (warm winter : available in winter) were discussed in reference to the difference of the host plant phenology.

View full abstract

Dissolved O₂ concentration in hydroponics was controlled at 0.01, 0.10 and 0.20 mM, and the growth of cucumber plant was analyzed in the respective dissolved O₂ concentrations at a root temperature of 25°C, an air temperature of 25°C, a relative humidity of 70% and a PPFD of 300 μmol m^-2 s^-1 (a photoperiod of 12 h) . Growth of leaves and roots was inhibited at lower dissolved O₂ concentrations, while the nodal development was not affected. At the lowest dissolved O₂ concentration of 0.01 mM, remarkable inhibition of leaf expansion was found with the decreased leaf water content. These facts suggest that leaf expansion was inhibited through leaf turgor loss caused by the depressed water uptake of roots in O₂-deficient nutrient solution.

View full abstract

Sunflower seedlings (Helianthus annuus L. cv. Russian Mammoth) were grown under two different lamps of a 4-band fluorescent lamp with a red/far-red photon flux ratio (R/FR) of 1.10 and a 3-band fluorescent lamp with a R/FR of 12.5. Photosynthetic photon flux density (PPFD) was kept at 160μmol m^-2 s^-1 in both treatments. The stomatal density and stomatal aperture were measured with a microscope after 6 days of treatment. After 7 days of treatment, the stomatal conductance was measured with a porometer. Then the transpiration rate and photosynthetic rate were also measured under a metalhalide lamp, when PPFD was kept at 300 μmol m^-2 s^-1. Compared with the 3-band fluorescent lamp, the plants grown under the 4-band fluorescent lamp increased in top fresh weight, top dry weight and shoot length for the sunflower. The stomatal density and stomatal aperture increased for plants grown under the 4-band fluorescent lamp. The stomatal conductance, transpiration rate and photosynthetic rate of the plants grown under the 4-band fluorescent lamp were greater than under the 3-band. In this study, we found that FR radiation affected the features of the stomata, and as a result, increased the transpiration rate and photosynthetic rate.

View full abstract

Soft wood cuttings each with 3-4 leaves of Photinia glabra and Euonymus japonicus Thunb. were planted into the soil in mist treatment and no-mist treatment. Air temperature and relative humidity were kept at the same level in the two treatments. Rooting of cuttings was repressed in mist treatment. Dry weight of roots and leaves of cuttings was smaller in mist treatment than in no-mist treatment. There was no relationship between rooting and dry weight of current shoots. Differences in the percentage of dry matter between the two treatments were not significant.

View full abstract

Forced flowering of Chinese tree peony cultivars was tested in comparison with Japanese cultivars. All the Chinese cultivars flowered in late December as early as one of the earliest flowering Japanese cultivars. One of the most popular Japanese cultivars flowered late in January. Flower harvest rate was over 80% in all the cultivars except one Chinese cultivar in which flower buds blasted during forcing. Some Chinese cultivars produced crown or bomb type flowers which were rarely found in Japanese cultivars. All the Chinese cultivars had short stems, suggesting that they were suitable for pot flowers rather than cut flowers.

View full abstract