Study On Physiological Mechanism Underlying The Resistance To Zinc Excess Stresds Of Trifoliate Orange Improved By Arbuscular Mycorrhiza

Arbuscular mycorrhizal (AM) played important roles in the plant growth, stress physiology, mineral nutrition, etc.Trifoliate orange(Poncirus trifoliata Raf.)seedlings were taken as experimental materials, using pot experiment and hydroponics methods, AM fungi species subjected to Zn contamination were selected first, effects of AM fungi on the mycorrhizal colonization, growth, and several mineral element contents as well as some physiological indices in leaves and roots of trifoliate orange seedlings under different zinc contamination were investigated, and the variation characteristics of H⁺,Ca²⁺ and NO₃^- ion flux in the roots of trifoliate orange seedings inoculated with AM fungus were studied with non-invasive micro-test technique.The main results were as follows:1. A pot experiment was conducted to study the effects of inoculation with AM fungi Glomus versiforme (G. v), G. mosseae (G. m), G. intraradices (G. i), G. aggregatum (G. a), and G. etunicatum (G. e) on the mycorrhizal colonization, growth, and zinc and phosphorus contents as well as some physiological indices in leaves and roots of trifoliate orange seedlings under zinc contamination. In zinc contaminated soil, inoculation with G. i, G. e, or G. m increased the seedlings biomass significantly. The mycorrhizal colonization and mycorrhizal dependency were the highest with G. i inoculation, followed by G. e, and G. v inoculation. Inoculation with AM fungi significantly decreased the shoot zinc content, and promoted the zinc accumulation in roots (except for G. a). The shoot/ root ratio of zinc translocation coefficient was the lowest in treatment G. i, second lowest in treatment G. e,and the highest in treatment G. v. AM fungi inoculation increased the phosphorus content in roots significantly, and G. i inoculation also significantly increased the phosphorus content in shoots. AM fungi inoculation increased the iron content in shoots significantly, the zinc accumulation significantly in roots (except for G. a); copper in roots by G. e inoculation, potassium in shoots by G. m, G. e, G. a inoculation, magnesium,potassium in roots by G. e, G. a and calcium in shoots and roots by G. e, G. a. Inoculation with G. i or G. e significantly decreased the MDA contents in leaves and increased the CAT activity and proline content in roots, but had little effects on the POD activity in roots, compared with the control. Our study showed that G. i inoculation was most beneficial to the tolerance of trifoliate orange against zinc contamination,followed by G. e, and G. v inoculation.2. A pot experiment was conducted to study the effects of inoculation with G. intraradices (G.i) on the mycorrhizal colonization, growth, and several mineral element contents as well as some physiological indices in leaves and roots of trifoliate orange seedlings under different zinc contaminations (0,300 and 600 mg·kg^-1Zn,showed as Zn0,Zn300 and Zn600,respectively). With the increase of zinc contamination, the mycorrhizal colonization rate showed decreasing trend, under the zinc contamination treatments, the seedlings biomass and proline content in roots were significantly increased, MDA contents in roots were significantly decreased with AM inoculation. With the increase of zinc contamination, zinc content in leaves and roots presented increasing trend, zinc content in AM fungus inoculated roots was significantly higher than in non-AM roots . copper content in AM shoots and roots, phosphorus, potassium, magnesium in AM shoots under Zn0 treatment, copper in AM roots under Zn600 and phosphorus contents in AM roots under Zn300 were all significantly higher than those in corresponding non-AM plants, but AM inoculation had no significant effects on calcium content.3. A sand culture experiment was conducted to study the effects of inoculation with G. intraradices (G.i) on the mycorrhizal colonization, growth, and several mineral element contents as well as some physiological indices in leaves and roots of trifoliate orange seedlings under different zinc concentrations (0,5,500μmol·L-1 Zn, showed as Zn0,Zn5 and Zn500, respectively). Compare with Zn0 treatment, the mycorrhizal colonization rate of the Zn5 and Zn500 treatments showed reducing trend, under the zinc contamination treatments, G.i inoculation had no significant effects on the seedlings biomass, inoculation with G.i significantly increased chlorophyll, proline content in roots and decreased relative conductance in roots, but had little effects on POD and CAT activities. Under Zn500 treatment, trifoliate orange seedlings inoculated G.i maintained higher zinc content in shoots, lower zinc content in roots compared to control; under Zn0 and Zn5 treatment, G.i inoculation had no significant effects on zinc content. Trifoliate orange seedlings inoculated G.i had higher copper content in shoots under Zn0 treatment, calcium content in shoots under Zn5 treatment, copper content and calcium content in roots under Zn500 treatment, phosphorus, potassium, magnesium in roots under Zn5 treatment, potassium in roots under Zn500 as compared to the corresponding non-AM plant;.4. The experiment was conducted to study the effects of inoculation with G. intraradices (G.i) on the mycorrhizal colonization, growth, of trifoliate orange seedlings and the fluxes of H⁺,Ca²⁺,NO₃^- in AM and non-AM roots.Inoculation with G.i significantly increased the mycorrhizal colonization and the seedlings biomass,the fungal infection rate was 68.7%. Ca²⁺ efflux at 0μm and 600μm distance from root tip, H⁺ influx at 600μm, NO₃^-influx at 2400μm distance from root tip of trifoliate orange seedlings inoculated with G.i were all significantly higher than those of non-AM plants.