Studies on Water Management in the Ill-drained Paddy Field : IV The effect of surface drainage to the morphology and structure of rice roots.

摘要

In the previous meetings we reported that the root system of rice plant as well as the growth, yield and chemical composition of the top were influenced by surface-draining in the in-drained paddy field. Considering that the increase of Top/Root ratio by surface-draining treatment was due to the increase of the roots function, we began the morphological and anatomical investigations on the rice roots, with referrence to water management, as a preliminary step of physiological investigations. We cultured rice plants in the paddy field in 1956, and young plants in Wagner's-pots in 1957. We divided the growth stage into two parts-the earlier stage and the latter stage, combining draining treatment with them respectively, and obtained four plots-the irrigation-irrigation plot, irrigation-drainage plot (irrigated in the earlier stage, but, drained in the latter stage), drainage-irrigation plot, and drainage-drainage plot. We divided rice roots into four classes-A·B·C·D-chiefly by their colour, and found that the ratio of lightly colored roots (A·B) were increased, but the ratio of heavily colored roots (C·D) were decreased by surface-drainage. For the anatomical study, we made permanent preparations by the paraffin method, and classified lignificating grades by the intensity of safranin staining. The remaining rates of epidermal cells, exodermal cells, parenchymatous cells of the cortex tended to decrease, but the thickness of cell wall, and lignification degrees of sclerenchyma and endodermis in the cortex, metaxylem and fundamental thick-walled parenchyma in the stele tended to increase, in proportion to the intensity of the outside colour, and with the lapse of time. As to the influence of the water management, the remaining rates of epidermal cells, exodermal cells, and parenchymatous cells of cortex, the thickness of cell walls, and lignification grades of sclerenchyma, endodermis in the cortex, metaxylem and fundamental thick-walled parenchyma in the stele, tended to increase by surface-draining treatment.