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具有日本特色的利用闲置田的轮作制度和可持续的环境友好型耕作制度的工具。本项目主要开展两项研究：(1)花生根系形成及根瘤菌和菌根的协同作用研究；(2)利用分子生物学方法对花生根际微生物区系进行分析。在前一项研究中，由于花生具有低投入可持续种植的高潜力，因此对其进行了研究。分析了根瘤分布及其固氮能力与根系结构的关系。结果提示通过调控根系形态来控制结瘤的可能性。此外，花生双接种根瘤菌和菌根的试验表明，菌根有助于维持花生根系的根瘤活性，特别是在盐胁迫下。后一项研究采用分子生物学方法研究了土壤微生物的群落结构和生物量，并探讨了作物种类和栽培管理对其的影响。利用PCR-DGGE和FISH技术，对旱地和低地水稻以及轮作系统包括油菜的根际细菌群落进行了分析。分析表明，油菜根际优势菌的种类在低地和高地间存在明显差异，优势菌的生物量随环境条件的变化而变化。研究表明，利用分子生物学方法调控根瘤菌和菌根与作物的协同作用条件，监测根际微生物区系，有助于建立环境负荷小的新型可持续种植体系。

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.