The Mechanism Of Utilization Inorganic Nitrogen By Arbuscular Mycorrhiza

Arbuscular mycorrhizal fungus (AMF) can form symbiosis with more than 80% plant species in land. It is well known that mycorrhizal symbiosis can improve the nutrient status of host plants and help survive in stress environment and which improve the competibility then contribute the fitness of host plants in ecosystem.Nitrogen (N) is one of the most essential mineral elements and the major limited nutrient for plants. More and more research showed that mycorrhiza inoculation can contribute to nitrogen nutrition status of host plant. To explore the mechanism of uptake, utilization inorganic nitrogen by AMF, experiments were carried out in experiment lab conditions which may help to elucidate the role of AMF in nitrogen cycle in ecosystem and obtain the main results as followed.(1) To investigated the effect of different nitrogen and phosphorus (P) supplied level on development of arbuscular mycorrhizal fungi, a pot experiment was conducted with cucumber (Cucumis sativus) and tomato (Lycopersicon esculentum) as the host plants and the semi-hydroponic system was composed with perlite and nutrient solution with different N, P concentration based on LAN solution. The resultes showed that here was no significant difference of the biomass between mycorrhizal and non-mycorrhizal cucumber as well as tomato in the same N/P treatment level. AM development, however, was significantly affected by N or P level. In general, the more N supplied the more AM structures were formed. But the AM structures of P supplied treatments were varied by N level: in the low N level treatment (0.3 mmol·L^-1) , the number of AM structures form was significantly decreased by P level enhanced. However, in the high N level treatment (3 mmol·L^-1) , the number of AM structures form was significantly increased, and was little affected by P supplied levels. The results could be presumed that the form of AM structure was indirectly modulated by supplied N, and may be derived from the interaction between nitrogen and phosphorus.(2) Compartmented rhizoboxes incorporating an air-gap was used to investigate the direct uptake nitrogen by AMF hyphae. The results showed that inoculation with both Glomus intraradices and Glomus mosseae decreased nitrate concentration in hyphal compartment with 68% and 42% compare with non-mycorrhizal treatment., correspondingly Glomus intraradices had higher hyphae density than that of Glomus mosseae.(3) In the other semi-hydroponics experiment, with the different N supplied, two key enzyme activities for N assimilation were detected. The results showed that: Nitrate reductase activity on maize leave was enhanced by Glomus intraradices inoculation when NH₄⁺:NO₃^-＝3:1 supplied, which was also enhanced by Glomus mosseae when NH₄⁺:NO₃^-＝1:3 supplied. The activity of glutamine synthetase of maize leave was not affected significantly by AMF, but all the three AMF inoculation enhanced glutamine synthetase activity of roots at NH₄⁺:NO₃^-=3:1, ratio of ammonium assimilated in roots increased also. Mycorrhizal inoculation had the more significant impact upon promoting plant growth when more ammonium supplied and increasing activity of root glutamine synthetase, it is assumed that AMF play an more important role in ammonium utilization of host plants.