The elucidation and use of a soil microorganism function for Japan-specific rotation system establishment

进一步分析和有效利用土壤微生物有望成为建立日本特有的利用闲置土地的轮作制度和可持续的环境友好型耕作制度的工具。本课题以花生为研究对象，对花生根系的形成及根瘤菌和菌根的协同作用进行了研究，并对花生根际微生物区系进行了分子生物学分析。结合根系结构分析了根瘤的分布及其固氮能力。结果表明，通过调控根系形态来控制结瘤是可行的。此外，根瘤菌和菌根双重接种花生的试验表明，菌根有助于维持花生根系的根瘤活性，特别是在盐胁迫下。利用PCR-DGGE和FISH技术对低地、高地水稻和轮作（包括油菜）水稻根际细菌群落进行了分析。结果表明，低地和高地油菜根际细菌优势种存在明显差异，根际细菌优势种生物量随环境条件的变化而变化，因此，利用分子生物学方法调控根瘤菌和菌根与作物的协同条件，监测根际微生物区系，有助于建立新的可持续种植模式系统环境负荷小。

Farther analysis and effective use of soil microorganisms are expected as a tool to establish the Japan-specific rotation system with utilizing idle fields and the sustainable environmentally-friendly cultivation system. In the present project, the two studies were conducted : (1) the formation of root system and the synergetic effect of rhizobium and mycorrhiza in peanut, and (2) analysis of microflora in rhizosphere using molecular biological methods.In the former study, peanut was studied because of its high potentiality for low-input sustainable cultivation. The distribution of root nodules and their nitrogen-fixing ability were analyzed associated with the structure of root system. The results suggested the possibility to control the nodulation by manipulating the root system morphology. Moreover, the experiment of the dual inoculation of rhizobium and mycorrhiza to peanut suggested that the mycorrhiza contribute to the maintenance of root nodule activity in the root system of peanut, in particular under salinity stressIn the latter study, molecular biological methods were applied to examine the community structure and biomass of soil microorganisms and to investigate the effects of crop species and cultivation managements on them. Namely, the bacterial communities in the rhizosphere of rice cultivated in lowland and upland fields, and that in rotation system including rape were analyzed using PCR-DGGE and FISH. The analysis showed clear difference in dominant species of rhizosphere bacteria between lowland and upland fields and the change of biomass of dominant bacteria by environmental conditions in the rape rhizosphere.The present studies suggested that the manipulation of the synergetic conditions of rhizobium and mycorrhiza with crop plants and the monitoring of microflora in rhizosphere using molecular biological methods could contribute to establish the new sustainable cropping system with small environment load.