Analysis of root growth characteristics based on a pipe-model theory and distribution of root nodules in soybean (Glycine max Merr.).

摘要

Based on the pipe-model theory, the root growth characteristics and root nodule distribution in soyabeans grown in pots were analyzed using cv. Fukuyutaka and two mutants derived from cv. Enrei (super-nodulating (En6500) and non-nodulating). Plantswere grown under various nitrogen levels, soil hardness, shading levels and bacterial densities. The ratio of the amount of thin roots which did not conform to the pipe model to that of thick roots which conformed to the model was nearly the same regardless of cultivation conditions. The formation of nodules began in minute radicles of 0.2-0.3 mm diameter, and about 95% of root nodules were distributed in thin roots of 1 mm diameter or less. A high correlation was observed between the amount of roots and the number of root nodules in every root-diameter class. Large root nodules (larger than 3 mm in diameter) tended to be distributed over all root-diameter classes equally. It is suggested that the distribution of root nodules with high nitrogen-fixingability is closely related to the amount of the vascular bundles in each root diameter class.