【Objective】Effects of uptake and translocation of NO₃^- in arbuscular mycorrhizal symbiosis and formation of arginine(Arg) in extraradical mycelium(ERM) and mycorrhizal root when ERM was exposed to NO₃^-or NH₄⁺, affecting growth of their host plants were studied. 【Method】In this study a dual split culture system was established with Ri T- DNA transformed carrot root and Glomus intraradices(Rhizophagus intraradices) and the ¹⁵N/¹³C isotope tracing technique was used to explore pathways of the uptake and transport of NO₃^-, and determine how much arginine accumulated in ERM and mycorrhizal root after NO₃^- or NH₄⁺ was absorbed and translocated in the fungal compartment, and a field experiment was conducted too to address how uptake and translocatiton of NO₃^-or NH₄⁺ affect growth of the host plants. 【Result】Results show that AM hypha preferred to uptake NH₄⁺ over NO₃^- when they both were available in the soil. When AM extraradical hypha were exposed to NH₄¹⁵ NO₃^- for 1 week, though the free amino acids, include Arg, in the extraradical mycelium (ERM) were not labelled by¹⁵N, those in the mycorrhizal tissues were, indicating that ¹⁵ NO₃^- in the fungal compartment were transported directly via mycelium into mycorrhizal tissues rather than any new translocation mode; on the contrary, when extraradical hypha were cultured with ¹⁵NH4 NO₃^-, only Arg was ¹⁵N-labelled therein, while the form of nitrogen composed of other amino acids in the ERM was ¹⁴NO₃^- translocated mainly from the hypha compartment and hence not labelled. While exposed to ¹³C₆-Glucose for 6 weeks, the ERM was found to have no¹³C-labelled Arg or protein, which indicates that ERM is unable to utilize glucose. When exposed to ¹³C_1,2-acatate, the ERM was found to have Arg and protein¹³C labelled up to 8.5%2.3% and 7.6%0.7%, respectively; when exposed to ¹³C_1,2-acatate plus ¹⁵NO₃^-, the ERM increased the concentration of free Arg with increasing N input, up to 54.2%19.3% and ¹³C labelled Arg and protein up to 57.4%4.8% and 50.3%2.8%, respectively, which indicates that increased C and N inputs in the hypha compartment may promote formation of Arg. In the field experiment, in the field low in P level, addition of KNO₃ increased significantly weight of the AM-inoculated sweet corm plants by 12.28%, as compared to the control, but addition of NH₄SO₄ did not have such an effect and instead decreased biomass of the plants by 8.19%, and addition of urea did by 13.02%; however amendment of organic manure to urea application mitigated the adverse effect.【Conclusion】There are two different modes of AM fungi absorbing and transporting ammonium and nitrate. AM fungi absorb and transport ammonium nitrogen (NH₄⁺ and urea), via GS-GOGAT in ERM, and most of the absorbed nitrogen is integrated into Arg molecules, and the synthesized arginine is intactly transported to the intraradical mycelium by ERM. Meanwhile, NO₃^-in the AM fungi symbiosis, as revealed by the isotope tracing technique, is adsorbed by ERM and transported via ERM to intraradical mycelium. Application of NO₃ may promote growth of the AM fungi-hosted sweet corn, while application of NH₄⁺ may affect the crop reversely.