| Zinc is an important and essential micronutrient for the citrus growth and developmnt, it is also one of the commonly lacking mineral nutrients in production. Trifoliate orange seedling is used as rootstock in major citrus producing areas of China. The largest navel orange variety cultivated in our country is’Newhall’. However, in recent years, due to zinc deficiency or magnesium deficiency, distinct symptom of chlorisis was presented on leaves of citrus in citrus producing areas. Arbuscular mycorrhizas (AM) are mutualistic symbioses that form between arbuscular mycorrhizal fungi and the roots of host plants, and can enhance the mineral nutrients uptake by host from the soil. Trifoliate orange (Poncirus trifoliata Raf.), ’Ponkan’and’Newhall’grafted on trifoliate orange were taken as experimental materials, using pot culture by root confinement technique experiment and pot experiment, effects of AM fungi on the mycorrhizal colonization, growth, several mineral element contents, photosynthesis, and physicochemical properties of rhizosphere soil under zinc deficiency stress. The main results were as follows:1. A pot culture by root confinement technique experiment was conducted to study the effects of arbuscular mycorrhizal (AM) fungus, Glomus versiformes (G. v) and G. iniraradices (G. i) inoculation on growth, activities of antioxidant enzymes and related enzymes in rhizosphere soil, osmotic regulation matters contents, contents of zinc (Zn), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), as well as copper (Cu) in different parts of trifoliate orange seedlings, and glomalin content and value of pH in rhizosphere soil under zinc deficiency. The results showed that the two AM fungi inoculation increased the seeding plant height, tap root length, root volume, leaf area and dry weight per plant, inoculated by G. i were significantly higher than that of G. v inoculation, the order of mycorrhizal dependency was G. i>G. v. Contents of leaf chlorophyll, soluble protein, proline, soluble sugar, root viability, leaf and root superoxide, peroxidase, and catalase activities were higher in plants inoculated by G. i than those of G. v inoculation, but leaf conductivity and malondialdehyde contents were significantly lower than the Non-AM control and G. v inoculation. Activities of acid phosphatase, catalase, invertase and urease in rhizosphere soil (0-2 cm& 2-4 cm) of mycorrhizal plants were significantly higher than those in control (exception of invertase in rhizosphere soil of2-4 cm), and four kinds of enzyme activities in rhizosphere of 0-2 cm were higher than the rhizosphere soil of 2-4 cm, while the four kinds of enzyme activities in rhizosphere soil (0-2 cm) of plants inoculated by G. i were higher than other treatments. The pH of rhizosphere soil (0-2 cm & 2-4 cm) about mycorrhizal plants reduce significantly. EEG and TG contents in rhizosphere soil (0-2 cm) of mycorrhizal plants were less than the value of rhizosphere soil (2-4 cm), as well as inoculated by G. i contents were significantly higher than that of G. v inoculation treatment in EEG and TG contents. Zn, P, K, Cu available form and Zn, P total form contents in shoots and roots of G.i inoculation were significantly higher than those of Non-AM control and G. v inoculation treatments. The K, Cu available form contents of two AM fungi inoculation were both significant higher than the control too. Mg available form and total form contents of G. i inoculation were significantly higher than those of control in shoots and roots, but G. i inoculation treatment had less influence to Ca content of seeding plant In summary, G. i inoculation promote the growth of the trifoliate orange seedling, and improve the antioxidant enzymes activities and osmotic regulation matters contents in mycorrhizal seedling, as well as activities of related enzymes and glomalin contents in rhizosphere soil, reduces the value of rhizosphere soil pH, thus promote Zn, P, K, Mg and Cu uptake by triofoliate orange seedling under zinc deficiency stress.2. A pot experiment was conducted to study the effects of inoculation with G. intraradices (G. i) on growth, activities of antioxidant enzymes, contents of Zn, P, K, N, Mg, Ca, as well as Cu in different parts about two types of citrus, related enzymes of rhizosphere soil, and osmotic regulation matters contents under zinc deficiency. The results showed that the AM fungi inoculation increased plant height, tap root length, root viability and dry weight per plant about two types of citrus, the order of mycorrhizal dependency was ’Newhall’>’Ponkan’. AM fungi inoculation treatment increased significantly the dry weight in all parts of two types citrus plant, the dry weight of root was the highest. Content of Zn (exception of Zn content in stem of scion of’Newhall’), P, N, K, Mg, Ca and Cu increased significantly in all parts of two types citrus inoculated by AM fungi. Mineral element contents in’Newhall’were significantly higher than that of’Ponkan’. Inoculation with G. i significantly improved acid phosphatase, neutral phosphatase, alkaline phosphatase, total phosphatase, CAT, sucrase and urease activity in rhizosphere soils of’Ponkan’and ’Newhall’, and the activity of acid phosphatase was the highest. Rhizosphere soil enzyme activity in’Newhall’were significantly higher than those of’Ponkan’. Under zinc deficiency, content of H2O2 and MDA in two types of citrus reduce significantly inoculation with G. i. Inoculation with G. i significantly improved SOD, POD, CAT and DHAR in roots of two types of citrus, and APX, GR in roots of’Newhall’. There was no significant effect about APX and GR in roots of’Ponkan’. Enzyme activity in’Newhall’ significantly higher than those of’Ponkan’, while, the content of MDA and H2O2 were relatively low in’Newhall’. Inoculation with G.i significantly improved content of ASC, DHA (except for’Ponkan’), TASC, soluble protein, starch, soluble sugar,’Newhall’ were significantly higher than thoes of’Ponkan’and reduce significantly content of proline in two types of citrus. So, AM fungi promote Zn uptake and other mineral elements in two types of citrus under zinc deficiency through improve related enzymes of rhizosphere soil, antioxidation ability and osmotic adjustment function, effect of’Newhall’ was especially obvious.3.The effects of chloroplast pigment content, photosynthetic characteristics and chlorophyll fluorescence parameters inoculation with G. intraradices (G. i) in’Ponkan’and ’Newhall’ under zinc deficiency. The results show that the AM fungi inoculation significantly improved content of chloroplast pigment (chlorophyll a, chlorophyll b, chlorophyll (a+b) and carotenoid), chlorophyll a/b and leaf area in two types of citrus. Inoculation with G. i significantly improved leaf net photosynthetic rate, stomatal conductance, transpiration rate and intercellular CO2 concentration in’Ponkan’and ’Newhall’ under zinc deficiency. Under zinc deficiency, initial fluorescence reduce significantly, and significantly improved the maximum fluorescence values, PS II potential activity and the maximal photochemical efficiency of PS Ⅱ inoculation with G. i in two types of citrus. Chlorophyll content and photosynthesis in’Newhall’ were significantly higher than those of’Ponkan’, while, initial fluorescence in’Ponkan’was significantly higher than that of’Newhall’. Leaf net photosynthetic rate were not diversity in two types of citrus. In summary, AM fungi enhanced plant photosynthesis, effect of’Newhall’was especially obvious, through improve chloroplast pigment, chlorophyll a/b and leaf area in two types of citrus under zinc deficiency. |
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