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In a potted greenhouse experiment,Citrus tangerine Hort.ex Tanaka was inoculated with arbuscular mycorrhizal (AM) fungus,Glomus versiforme (Karsten)Berch,or non-AM fungus as control.Arbuscular mycorrhizal and non-AM seedlings were grown tmder well-watered or water-stressed conditions after 97 days of acclimation.The reactive oxygen metabolism of C.tangerine leaves was studied in order to elucidate whether AM symbiosis affects enzymatic and non-enzymatic antioxidants.The results showed that water stress caused a decrement of 33% for the colonization of G.versiforme on C.tangerine roots.Under well-watered and water-stressed conditions,G.versiforme inoculation increased the leaf phosphorus (P) content by 45% and 27%,and decreased the leaf malondialdehyde and hydrogen peroxide contents by 25% and 21%,and 16% and 16%,respectively,compared with the control.Inoculation with G.versiforme enhanced the activities of leaf superoxide dismutase,peroxidase,catalase and ascorbate peroxidase,and increased the contents of leaf soluble protein,ascorbate and total ascorbate notably,regardless of soil moisture conditions.Under water-stressed conditions,G.versiforme inoculation decreased the leaf superoxide anion radical (O2-) content by 31%.It is concluded that drought resistance of C.tangerine leaves is enhanced due to the improvement of reactive oxygen metabolism after G.versiforme inoculation.