An Initial Formation Process of Volcanic Ash Soils with the Development of Bryophyllum Tubiflorum Habitat on Volcanic Ash Freshly Deposited from Mt. Sakurajima

抄録

This study offered an example to investigate the process of introducing living organisms into inorganic parent materials or to establish soil ecosystem. This process was also considered to be the initial stage of soil formation. The well-developed and characteristic habitat of Bryophyllum Tubiflorum as a pioneer plant was observed on the thin volcanic ash layer which deposited within these ten years. The well development of the habitat was needed to be enough and continuous supply of nutrients. Nitrogen is one of the most important elements for plant growth. But original ash contained very small amount of nitrogen source. Therefore, it was suggested that large numbers of micro-organisms inhabited in the ash layer before the appearance of higher plant growth on the layer and the decomposed nitrogen from the organisms were ensured the plant growth, i.e. The essential nutrient for the growth of the plant except N, were provided in original volcanic ash as watersoluble ions. The cationic ions of them were changing to exchangeable forms as the advancing of the vegetative succession accompanying the weathering of volcanic ashes. This finding means that the surfaces of the particles of the ash layer were becoming gradually to be negatively charged ones capable to retain cations though soil formation was yet in very young stage.