Abstract
A crop root system morphology can be determined by the development of different component roots, such as nodal root axes and their concomitant lateral roots of two different types ; long, large in diameter, and branching (L type), and short, small in diameter, and non-branching (S type). In this respect, we attempted to examine the cultivar difference in root system morphology among rice cultivars and to evaluate phenotypic plasticity in the root system morphology when grown under different nitrogen (N) application regimes. Four rice cultivars that are known to differ in adaptability for heavy manuring (AHM) and ecotype (indica and japonica) were grown for 14 days under three N levels. Cultivar difference in root system morphology existed among the four cultivars. The differences were recognized in the ratio of lateral roots to the entire root system length, and more remarkably in the ratio of S type to L type lateral root number. The difference in the former parameter could be well related to that in the ecotype, while the latter to the AHM of the cultivar. As to the phenotypic plasticity, the three component roots differed in production response, while they were fairly similar in elongation response. The root system morphology of a cultivar with low AHM was considerably phenotypically plastic, while that of the other cultivars were relatively stable to the changes of N conditions in soil.
