The authors have been making a series of researches for the production of tomato fruits with high Brix in the nutrient solution cultivation system with granular rockwool. For the production of tomato fruits with high Brix, the rockwool has to be kept low water condition. In order to control the irrigation under low water condition, the transpiration rate of tomato plants under low water condition has to be analyzed. The experiment was carried out in a glasshouse in Ehime University in 1999.
As the results of the measurement of the pF of three kinds of granular rockwools (granularrockwool (1), granular rockwool (2) and their mixture), it was made clear that the pF increased rapidly at a certain value of water content in the process of the decrease of water content and that the value was particular to each granular rockwool.
In the measurement of the transpiration rate of tomato plants (Lycopersicon esculentum Mill. cv. Hausu-Momotaro), three treatments were tested. The granular rockwool in the treatment 1 had the saturated water content (1740 g·pot^-1), and the water content in the treatment 2 and the treatment 3 were 750 g and 1500 g less than the water content in the treatment 1 respectively. The wight of the rockwool cube and the granular rockwool were 107 g and 120 g respectively. The transpiration rate and water potential of leaf in the treatment 2 were about the same as those in the treatment 1. On the other hand, much lower transpiration rate and water potential were observed in the treatment 3.
The diurnal changes in the transpiration rate in the three kinds of granular rockwools showed that the transpiration rate was affected by the pF which was determined by the water content and the kind of the granular rockwool.

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For the low cost vegetable transportation, the applicability of a low O₂ closed system was examined under ambient temperature. Heads of leaf lettuce grown under the controlled climate of a commercially operated plant factory individually placed in airtight containers filled with normal air or with low O₂ mixed gas (5% 0₂+95% N₂) were stored for 11 d and 13 d at 15°C and for 7 d at 20°C. Populations of mesophilic aerobic bacteria from levels of 10⁷ to 10⁹ CFU/g were detected at the end of storage on lettuce heads in control treatment (normal air). Contrary to this, final populations on lettuce heads in low O² treatment were 10²- to 10⁵-fold less than those in control treatment. As the final populations were less than 1 x 10⁷ CFU/g, leaves of lettuce heads in low O₂ treatment were not spoiled for all storage experiments. Supplementary examinations indicated that low O₂ treatment was not effective to suppress bacterial populations on lettuce heads having large populations as about the level of 10⁵ CFU/g or more at the beginning of storage. Hence, the low O₂ closed system can be applied exclusively to the leaf lettuce grown in plant factory that can normally assure small populations of bacteria. Adding to this bacterial point of view, cumulative quantity of CO₂ showed a reduction in respiration of lettuce head in low O₂ treatment. Moreover, large amount of ascorbic acid was lost in control treatment as compared to that in low O₂ treatment. However, no significant difference was observed in weight loss regardless of treatment.

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This study examined the possibility of reducing the heat injury of spinach incurred by the roots. In the first experiment, spinach plants (Spinacia oleracea L. cv. Okame) were controlled or subjected to salt stress by adding 43mM NaCl to 30°C nutrient solution for 11 days. In the second experiment, plants were grown in three different concentration of salt (control, 43mM, 130mM) or PEG (29gl^-1) treatments each for 2 days at 34°C. In the first experiment, at 30°C solution temperature, root weight of 43mM NaCl treatment was larger than that of control, while at 20°C solution temperature, the weight was almost same between the treatments. In the second experiment, 43 mM NaCl treatment increased shoot and root weights compared to those of control. However, 130mM treatment as well as PEG treatment did not show any positive effect on growth. The results indicate that addition of 43mM NaCl could reduce the heat injury of spinach root under high nutrient solution temperatures.

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Carbon dioxide (CO₂) absorption rates of Phalaenopsis spp. plants were measured under different duration of light/dark periods from 2/22 to 22/2 h/d. Typical photosynthetic pattern of CAM plants was observed when light period was between 6 and 16 h/d. When light period was longer or shorter than the range, CO₂ absorption during the dark period was decreased. The CAM type photosynthetic pattern was most obvious near 10 h/d light period. There was a linear relationship between daily light absorption and daily photosynthetic amount. As the light period became longer, amount of CO₂ absorbed during the light period increased. Therefore, environmental management based on the assumption that Phalaenopsis plants absorb CO₂ mainly at night would not be rational or profitable since large amount of CO₂ is absorbed during the daytime.

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