Studies on the Effects of Soil Temperatures on Rice Plant Growth : I. Effects of soil temperatures upon growth regulating substances and the metabolisms of carbohydrates and nitrogen (1)

Abstract

Growth regulating substances, carbohydrates (sugars and starch), and nitrogenous compounds (proteid nitrogen and soluble nitrogen) were chemically analysed at various growth stages of rice plants, in order to show the relationship between soil temperature and those substances. Plants of different growth stages were subjected to various soil temperatures such as 30°C, 25°C, 15°C, 30°·20°C, and 30°·15°C (the last two in the series of temperature means changes from high to low) for 10 days. The results were as follows: 1) The contents of the growth-promoting-substances in roots at 15°C or 20°C were much more than those at 30°C. Their largest amounts were, however, found in the plots of alternating temperature. 2) The amount of growth promoting substances in root decreased as the plant grew. They were almost hardly detectable at the highest tillering stage, but they appeared again when the ear primordia began to differentiate. 3) Growth promoting substances were able to be extracted from leaf sheaths including young panicles in 30°C plot, but in 20°C plot they were scarcely recognizable. 4) Larger amount of proteid nitrogen seemed to be accumulated in 25°C and 20°C plots at each stage of growth than in 30°C and 15°C plots; especially in 30°·20°C plot its accumulation was most vigorous. 5) The metabolism and translocation of carbohydrates such as starch and sugars seemed to be most active at 25°C. Low temperatures such as 20°C and 30°·20°C, on the contrary, disturbed the migration of those substances to ear from culm.