Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice : LXXXIV. Effects of the different combinations of day- and night-water-temperatures on the growth of rice seedlings.

摘要

Subjecting two leaf-aged rice seedlings to the conditions of all possible combinations of day-water-temperatures (16°C·21°C·31°C and 36°C) with night-water-temperatures (16°C·21°C·31°C and 36°C) for 26 days, the authors examined temperature effects on the growth of seedlings. (The daytime is taken from 6 a. m. to 6 p. m. and the nighttime from 6 p. m. to 6 a. m.) The results may be summarized as follows. 1) Increased plant height during daytime is greater than that during nighttime when day-water-temperature is higher than night-water-temperature, but it turns reversely when day-water-temperature is lower than night-water-temperature, and it is almost equal to that during night-time when day-water-temperature is equal to night-water-temperature, which suggests that the growth of rice seedlings is mainly influenced by the temperature factor and not by the light factor at all. Furthermore, the optimum combination of day- and night-water-temperature for increasing plant height during daytime is observed to be the combination of day-water-temperature 31°C with night-water-temperature 21°C, while for increasing plant height during nighttime to be the combination of day-water-temperature 21°C with night-water-temperature 31°C. The fact suggests that the optimum combination of day- and night-water-temperature for increasing plant height during daytime is different from that for increasing plant height during nighttime. 2) Response of plant height and root length to the various combinations of day- and night-water-temperatures are in the same pattern as each other. Both plant height and root length increase progressively faster as day-water-temperature as well as night-water-temperature rise up to 31°C, but they increase slowly at 36°C, When the average water-temperature of day and night is identical, the increase of plant height or root length is always slightly greater in the case of day-water-temperature being higher than night-water-temperature than in the case of the reverse. 3) The plant age expressed by leaf number of the main stem respenses differently from the other characters. It is affected only by the average water-temperature of day and night, not being affected by the daily range of water-temperature during day and night, and it advances progressively faster as the average water-temperature rises up to 36°C. 4) The number of tillers increases with the rise of average water-temperature during day and night and with the increase of daily range of water-temperature during day and night. The tillers which branch out from lower nodes fail to develop as the average water-temperature during day and night rises and as the daily range of water-temperature during day and night decreases. 5) The weight of dry-matter increases without exception with the rise of average water-temperature during day and night up to 31°C, but it responses to the water-temperatures differently from the above-mentioned way when the average water-temperature goes up above 31°C. In case of the average water-temperature during day and night being above 31°C, if water-temperature is higher during daytime than during nighttime, the dry-matter is always heavier, but if water-temperature is lower during daytime than during nighttime, the dry-matter is much lighter than that at day-water-temperature 31°C combined with night-water-temperature 31°C. In other words, ill-effects of high night-water-temperatuer on the increase of dry-matter can be clearly recognized in the case of average water-temperature being above 31°C. Furthermore, in case of the average water-temperature of day and night being identical, the dry-matter in the condition of day-water-temperature being lower than night-water-temperature is always much lighter than that in the condition of day-water-temperature being higher than night-water-temperature. [the rest omitted]