Studies on the Epidermic Browning of Lotus Rhizome

II. The Effects of Soil Reduction and Oxygen Supply from the Leaf on the Browning of Rhizome and Rhizosphere Materials

Abstract

The present investigation is aimed at determining the effects of soil reduction and oxygen supply from leaves to the rhizome system on the browning of the lotus rhizome surface. The results obtained are summarized as follows:
1) When liberal amount of stable manure was applied to the soil to cause the oxidation potential of rhizosphere substances to become lowered thoroughly, the formation and the adherence of dark brown materials to the rhizome surface were considerably reduced as compared to those of controls even when the rhizome of the lotus continued to grow. In addition, the darkness of both the rhizome surface and rhizosphere materials were also reduced after the growth of the rhizome had ceased.
2) The lotus leaves of growing rhizomes supplied its rhizome system with gaseous mixtures of high oxygen concentrations from 22 to 28% in the daytime. A liberal supply of oxygen from leaves to the rhizome system through the aerenchyma seemed to cause the browning of both the rhizome surface and rhizosphere materials.
3) The tissues of lotus rhizomes usually maintained lower oxidation potentials than rhizosphere substances during the growth of rhizomes. However, the oxidation potentials of rhizomes were shifted to a higher range than those of rhizosphere substances when the leaves were artificially removed or naturally died. The darker the color tone of the rhizome surface, the greater the potential alteration caused by defoliation.
4) The browning of the lotus rhizome seems to depend closely on the dynamic equilibrium between oxidizing factors derived from the leaves and reducing factors derived from the rhizosphere substances.