TiO 2 photocatalytic decomposition and detoxification of phytotoxic compounds released by the roots of asparagus ( Asparagus officinalis L.) were investigated from the viewpoint of conservation-oriented cultivation. The phytotoxically active fraction was extracted either from dried asparagus roots or from the recycled nutrient solution of an asparagus hydroponic cultivation system. We found that the phytotoxic activity gradually decreased in the fraction with TiO 2 powder under irradiation with ultraviolet (UV) light at an intensity of 1.0 mW/cm (2). The growth of asparagus plants under actual cultivation conditions was also investigated by comparing asparagus grown in a hydroponic system where recycled waste nutrient solution was photocatalytically treated with solar light and a system with untreated recycled waste nutrient solution. The results showed, as measured by growth indices such as stem length and stem thickness, that asparagus growth in the photocatalytically treated system was superior to the untreated one. Furthermore, the yield of asparagus spears was 1.6-fold greater in the photocatalytically treated system, demonstrating the detoxification effect on the phytotoxic compounds and also the killing effect on pathogenic microorganisms.
The effectiveness of photocatalytic treatment under solar light irradiation of waste nutrient solution emitted from a soil-less cultivation system of tomatoes planted in rice hull substrate was investigated from the viewpoint of conservationoriented agriculture. As a model experiment, the phytotoxically active extract from rice hulls was treated with a TiO 2 -coated porous alumina filter irradiated with ultraviolet light at an intensity of 2.0 mW/cm 2 , and the phytotoxic activities before and after irradiation were evaluated from the germination rate of lettuce seeds. The germination rate was 0 % before irradiation, demonstrating the strong inhibitory effect of the rice hull extract, but recovered to 100 % after 4 days of irradiation. The growth of tomatoes planted in rice hull substrate under actual cultivation conditions was also observed in six repeated experiments over a 3-year period by comparing tomatoes grown in a closed soil-less cultivation system with photocatalytically treated waste nutrient solution under solar light (photocatalytically treated system), with tomatoes grown in a closed system with untreated waste nutrient solution (untreated system). The results showed that tomato growth in the photocatalytically treated system was significantly higher than that in the untreated system in six experiments over 3 years, and yields in the photocatalytically treated system were comparable to those in a currently used open cultivation system using rockwool substrate. These results suggest that incorporating photocatalytic treatment of waste nutrient solution under solar light irradiation will allow conservationoriented closed soil-less cultivation systems to be realized.
IntroductionThe signaling and function of a vitamin is regulated by its concentration. A physiological response can also be induced by multiple hormones in synergistic or antagonistic actions, referred to as signaling crosstalk 1,2) . Vitamins are essential and functional compounds that cannot be synthesized by the human body. Vitamins are classified as either lipophilic or water-soluble. Lipophilic vitamins readily accumulate in the body whereas water-soluble vitamins are rapidly flushed from the system. Vitamins are ingested constantly in various foods and vitamin research is important in plant physiology, nutrition science, and the medical field 3−9) .Persimmon (Diospyros kaki) is a deciduous tree belonging to the family Ebenaceae and is cultivated in many countries. The delicious fruit contains nutrients and phyto
Tomato (Solanum lycopersicum L.) intumescence severely affects tomato plants and thereby crop yields. In this study, we investigated the differences in intumescence between varieties. We assessed the shoot:root (S/R) ratio and incidence of intumescence in seedlings of 12 tomato varieties subjected to sudden increases in ambient humidity and soil moisture. The S/R ratio and severity of intumescence injury were positively correlated. Next, three tomato varieties with different S/R ratios and intumescence incidence were assessed. Changes in xylem pressure potential of seedlings occurred in response to a changing water environment in a controlled environment chamber, i.e., from a dry condition (50% relative humidity, no irrigation) to a wet condition (90% relative humidity, sub-irrigation). The xylem pressure potential decreased under dry conditions in relation to the S/R ratio and intumescence incidence but increased rapidly after exposure to wet conditions. Tomato varieties with large S/R ratios showed large changes in their water potential in response to changes in the surrounding water environment, and it is thought that cells are more likely to rupture when water potential increases after a transition from dry to wet conditions.
From the viewpoint of conservation-oriented agriculture, this study investigated a closed cultivation system using a combination of rice hull substrate and TiO 2 photocatalytic treatment of the waste nutrient solution. First, an extract of rice hulls in distilled water was treated with a TiO 2-coated porous alumina filter under ultraviolet light irradiation. Then, rose (Rosa hybrida) rooted cuttings were soaked in the treated extract, untreated extract, or pure nutrient solution. The total weight of the shoot and leaves soaked in the photocatalytically treated extract was heavier than that in the untreated extract, and was similar to that in the pure nutrient solution. Next, rose growth was compared in three practical cultivation systems two closed systems using rice hull substrate with photocatalytically treated or untreated waste nutrient solution (photocatalytically treated and untreated systems), and an open system using rockwool substrate (current system). The growth and yield in the photocatalytically treated system were significantly greater than those in the untreated system and were comparable to those in the current system. These results show that the TiO 2 photocatalytic treatment of the waste nutrient solution is effective in closed soilless cultivation using rice hull substrate.
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