Arbuscular Mycorrhizal Fungi Amorpha Nitrogen-fixing Ability

Nearly 80% of all land plant form a symbiotic relationship with arbuscular mycorrhizal fungi as arbuscular mycorrhiza. This structure performed as vesicular while spores outside of the root. The large amount of mycelium increase the contact area between the root and soil, so as to improve the nutrient absorption of plant to accelerate the plant growth. The AM fungi could infect the legume plant Amorpha fruticosa L. to form the arbuscular mycorrhiza structure, so do the rhizobia to form the nodule. These three could form the AM fungi- Amorpha fruticosa L.-rhizobia tripartite symbiosis.The contribution of nitrogen fixation of AM fungi to Amorpha fruticosa L. was studied. This study tested the activity of nitrogenase in the rhizospheric soil, activity of urease in the rhizospheric soil, activity of leaf nitrate reductase, nitrogen concentration in frond and soil, biomass of Amorpha fruticosa L., the time-space variation of infection of AMF and rhizobia.The result suggested that the the activity of nitrogenase in the rhizospheric soil of inoculation AM and dipl-inoculation (AM fungi and rhizobia) is lower than inoculation rhizobia. It suggested that urease and leaf nitrate reductase of dipl-inoculation (AM fungi and Rhizobia) is higher than non-inoculation and the control in certain period. The nitrogen fixing capacity of Amorpha fruticosa L. is enhanced suggested by the determination of nitrogen concentration in Amorpha fruticosa L. and the soil. It is also showed in the result that dipl-inoculation (AM fungi and Rhizobia) could enhance the growth of Amorpha fruticosa L. especially in the aspects of height of seedling, root length and fresh weight of the host compared to the control. It is proved through the observation of optical microscope and scanning electron microscopy that the infection of AM fungi to Amorpha fruticosa L. is earlier than that of Rhizobia, and part of AM fungi tissue is found inside the root where the nodule forms.This study will improve the theory of biological nitrogen fixation with arbuscular mycorrhizal fungi. The results can be used for improving the biological nitrogen fixation ability of legume plant. It is really helpful to increase the production of crop and cutting down the amount of chemical fertilizer.