The purpose of this study is to investigate the relation which related studies have not made clear between the soil water qualities, the ground level and the distribution of Bruguiera gymnorrhiza and Rhizophora stylosa in the south-east coast of Iriomote Island in Okinawa Prefecture. The investigations were carried out on the distribution of B. gymnorrhiza and R. stylosa, the ground level and the soil water quality at the fringe that was chosen as the main object in this study to replace the riverine which related studies have focused on. As a result, a strong relation was observed between the distribution and the ground level. The ground level of the seaward edge of the range of R. stylosa stand showed 102±2cm, that of the border between R. stylosa stand and B. gymnorrhiza stand showed 133±1 cm and that of the landward edge of the range of B. gymnorrhiza stand showed 167±0 cm (0 cm is set to be the same as the datum line in Ishigaki Is. in 1990) . A strong relation was observed between the distribution and the soil water qualities, too. The soil water salinity from the depth of 60 cm of the seaward edge of the range of R. stylosa stand showed 31.5±1.6‰; that of the border between R. stylosa stand and B. gymnorrhiza stand showed 25.7±0.9‰; that of the landward edge of the range of B. gymnorrhiza stand showed 19.3±2.2‰. The soil water qualities were influenced by the fresh ground water from the landward side. Small stands of R. stylosa were found surrounded by the vegetation of B. gymnorrhiza. Judging from the ground level, B. gymnorrhiza must grow in those areas, but the soil water quality in those areas were suitable for R. stylosa. This suggests that the relation between the distribution and the soil water qualities is stronger than the other.

View full abstract

A simple water-culture for leafy vegetable using controlled-release fertilizer and rockwool was tested in this study. The recommended application is N. 0.5g pot^-1 (plant^-1) with 70 day and 100 day types. The concentration of nitrate, phosphorus and potassium from the controlled-release fertilizers was sufficient for plant growth and each varied within the range of the standard culture solution (Enshi-shoho) . The fertilizers would be able to be used for water-culture methods which store nutrient solutions and they would be adequate for the double-cropping of leafy vegetables such as lettuce growing for about 40 days. However, it seems that the concentration of ammonium from the fertilizers was excessive and the concentrations of Ca and Mg would be insufficient for plant growth, though they never induced excess or deficiency symptoms.

View full abstract

Potted fig (Ficus carica L. cv. Masui Dauphine) cuttings were grown in a controlled greenhouse at 20/15 or 30/25°C (day/night) and subjected to 0 or 50 mM NaCl for 12 weeks. The NaCl application was started at the time shoot growth started every year, and the plant growth was observed for 3 years. Their growth habit was replicated approximately every 32 weeks as a cycle, and the temperature and NaCl application did not affect their growth cycle. The growth of plants at 30/25°C fluctuated annually, and the number of flower buds and fruits was less than that at 20/15°C. On the other hand, the growth of plants at 20/15°C was stable and the number of fruits was always bigger than that at 30/25°C. Vegetative growth was suppressed by NaCl application at both temperature plots, but their flower bud formation was accelerated in the first and second year. These results suggest the possibility that application of NaCl at a lower level than 50 mM suppresses strong tree vigor and improves fruit sugar content.

View full abstract

A chill unit model for ‘Nijisseiki’ pear was developed for prediction of leaf bud rest completion under Koyama and Saji conditions. The model assigns full effect for chilling accumulation for temperatures below 8°C until its value reaches 1200, and then it cuts the lower temperature below -4.0°C off for chilling accumulation. The model is more suitable in predicting rest completion of ‘Nijisseiki’ pear than previously reported models. By using the model, it is suggested that chilling requirement of leaf bud of ‘Nijisseiki’ pear should be 1400 chill unit.

View full abstract

Phototropic sensitivity in hypocotyls of dark-grown, 4-d-old radish seedlings (Raphanus sativus L. cv. Miyashige) was investigated with reference to the influence of pre-exposure treatment. The magnitude of the second positive phototropic curvature in response to continuous unilateral irradiation was increased when the seedlings were pre-exposed with white light from above. This effect of the pre-exposure on the phototropic sensitivity increased with duration of the treatment and reached a plateau 3 h after the onset of the treatment. The pre-exposure treatment on the hypocotyls was only efficient to enhance the phototropic sensitivity, but the treatments on the apex and cotyledons have no effect. These results suggest that the site of perception of the pre-exposure light to enhance the phototropic sensitivity could be located within the phototropically responding organ, hypocotyl itself.

View full abstract

Carbon dioxide concentration profiles in a test tube-type tissue culture vessel containing a plantlet cultured on sugar free medium were measured during the photoperiod. The CO₂ concentration at 70 mm below the lid was higher than that at 5 mm below the lid, and it decreased linearly with increasing the distance from the lid. When the photosysnthetic photon flux density (PPFD) was set at 20, 50, 80 or 140μmol m^-2 s^-1, the CO₂ concentration at 70 mm below the lid was 263, 150, 96 or 91μmol mol^-1, respectively, under a CO₂ concentration of 360μmol mol^-1 outside the vessel and an air temperature of 25°C inside the vessel. The CO₂ concentration difference inside the vessel between at 5 and 70 mm below the lid was 70, 137, 179 or 185μmol mol^-1, respectively, under the four levels of PPFD. When the CO₂ concentration outside the vessel was maintained 130, 340, 870, 1 890 or 2 570μmol mol^-1, the CO₂ concentration at 70 mm below the lid was 91, 104, 171, 363 or 770μmol mol^-1, respectively, under a PPFD of 110μmol m^-2 s^-1 and an air temperature of 25°C inside the vessel. The CO₂ concentration difference between at 5 and 70 mm below the lid was 27, 147, 477, 1 002 and 1216μmol mol^-1, respectively, under the five levels of CO₂ concentration outside the vessel. These results show that the CO₂ diffusion resistance inside the vessel is high and thus the net photosynthetic rate of the plantlet is restricted by low CO₂ concentration near the plantlet.

View full abstract

Mangrove trees grow under reductive soil conditions which is normally injurious to root growth. This study focused on discussing the mechanism of mangrove trees in adapting to soil conditions. In the forests of Rhizophora stylosa and Bruguiera gymnorrhiza which are developed along the coast and clearly distributed zonally, iron, manganese, sulfur, boron and tannins contained in the soil environment and leaves were analyzed. H₂S damage is alleviated by the fact that FeS₂ is formed by Fe²⁺ reacting with H₂S formed by the sulfate reduction. The quantity of FeS₂ was limited by the concentration of Fe²⁺ and SO₄-S in the soil water. However the concentration of Fe²⁺ was kept under except in landward sites. Thus we will assume that Fe²⁺ has eluted by the reductive effect of tannins. Otherwise the Fe²⁺ would be insufficient for forming FeS₂. The tannins have eluted with rather high concentrations to soil water from the roots at seaward sites, then Fe²⁺ and Mn²⁺ have eluted due to the tannins. At the seaward edge of R. stylosa the concentrations of Fe and Mn in leaves were high. Mn, especially, accumulated in high concentrations. The reason is that the reductive effect of tannins accumulated in high concentrations in leaves like Mn kept a balance with the oxidation effect of Mn. In addition, at the seaward edge of R. stylosa the concentrations of B in leaves were also high. The reason is that B is related to the formation of catechin that is one of the principal ingredients of the tannins. Thus we will assume that the tannins, Mn and B play important roles in adaptation under the reductive soil conditions. In addition, a change in the concentrations in leaves between R. stlosa and B. gymnorrhiza may limit the distribution.

View full abstract

There is a simulator for analyzing the plant-environment system in the National Institute for Environmental Studies. This simulator is a wind tunnel with air conditioner, solar simulator and control unit of soil environment. Profile of air temperature and humidity are controlled automatically in the simulator but that of wind velocity was not. Wind tunnels in other research fields have also been in a similar situation. We have therefore developed an automatic control system of wind velocity profiles in the simulator, and then examined the performance of the system and its application.

View full abstract

Characterizing mass and energy balance at a plug sheet consisting of plug seedlings and soil mix is essential for optimum control of soil-mix moisture in plug seedling production. Time courses of rates of net photosynthesis, evapotranspiration and sensible and latent heat transfers of a tomato plug sheet under artificial light and the volumetric percent water content of soil mix were estimated micrometeorologically using the measured data on CO₂ concentrations, dewpoint temperatures at two heights above the plug sheet and weight of the plug sheet measured with an electronic balance. The first watering was done at the start of measurements and the second watering 16 hours after the first watering. After the first watering, the volumetric percent water content of soil mix decreased with time. Sensible heat transfer rate increased, and evapotranspiration and latent heat transfer rates decreased with decreasing volumetric percent water content when it was lower than about 20%. Net photosynthetic rate decreased with decreasing volumetric percent water content when it was lower than about 12%. One to three hours after the second watering, all the rates returned to the levels at the start of measurement. The present method is useful for on-line monitoring of micrometeorological and water-stress status of the plug sheet and for automatic watering based upon the status.

View full abstract

Water (or moisture) content of soil-mix in a plug tray with limited-volume can easily be changed by evapotranspiration from a plug sheet and watering. Thus, timing and the amount of watering are the most important skills in plug seedling production. An automatic watering system for controlling water content of soil-mix in a plug tray was developed. A tomato plug sheet consisting of plug seedlings, soil mix in a greenhouse was watered by the watering system. The weight of the plug sheet was measured continuously with an electronic balance. When the weight of the plug-sheet decreased to a lower-limit setpoint by evapotranspiration, a solenoid switch of the watering system with overhead mist spray nozzles was turned on, and the plug sheet was watered. When the weight of the plug-sheet increased to a higher-limit setpoint by watering, the solenoid switch of the watering system was turned off. Watering was conducted only during the daytime. In this way, the weight of the plug sheet was controlled accurately in a range between the lower- and higher-limit setpoints during the culture period.

View full abstract