Abstract: A pot culture with unsterilized soil as growth substrate showed that AM fungi had significant effects on the growth of Astragalus membranaceus (Fabaceae) under different N application levels. Inoculation with AM fungi promoted the AM infection of A. membranaceus roots, but high N application level suppressed the infection. Inoculating AM fungi increased the growth rate, soluble protein and sugar contents, and SOD, POD and CAT activities of A. membranaceus. Under 50 and 100 mg·kg-1 of N application, new bands of POD isozyme occurred in inoculated plants, and the contents of flavonoid, N, and P in A. membranaceus also had definite increase. The best inoculation effect was observed under the N application level of 50〖KG-*2〗-〖KG-*7〗100 mg N·kg-1 soil.

Key words: AM fungi, N application level, nutritional component, physiological character, Astragalus membranaceu, nitrification inhibitor, dicyandiamide (DCD), inhibition mechanism, inhibition effect, nitrogen fertilizer efficiency.