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

对土壤微生物的进一步分析和有效利用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。本研究从花生根系的形成、根瘤菌与菌根的协同作用和根际微生物区系的分子生物学分析两方面进行了研究。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能的。此外，花生根瘤菌和菌根双接种试验表明，菌根有助于维持花生根瘤的活性，特别是在盐胁迫下。本研究采用分子生物学方法研究了土壤微生物群落结构和生物量以及作物种类和栽培管理对其影响。即利用PCR-DGGE和FISH技术对水田和旱地水稻根际细菌群落以及轮作油菜根际细菌群落进行了分析。分析结果表明，水田和旱地油菜根际细菌优势种明显不同，优势菌生物量随环境条件的变化而变化。本研究表明，利用分子生物学手段调控根瘤菌和菌根与作物的协同作用，监测根际微生物区系，有助于建立环境负荷小、可持续发展的新型种植制度。

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.