Studies On The Transportation And Distribution Of Zinc In Apple Trees And The Effect Of Zinc Deficiency On Its Physiological Characteristics

Zinc nutrition has been an important factor of the limitation of yield and quality in apple trees. The physiological diseases such as rosette leaves and short branch internode occurred as a result of zinc deficiency in apple trees, however, there was no good effect by supplying zinc in a normal way. In order to master the dynamic changes of absorption and transportation of zinc, the relation of zinc to other elements, and the effect of zinc on growth and metabolism function of apple tree under zinc deficiency, zinc-deficient apple trees (Red Fuji) and Malus hupehensis Rehd seedlings were as experimental materials to investigate the questions, the main results are as follows:1. The differences in vertical distribution of soil available zinc and the low content of available zinc in the soil, where had many roots, were the main factors of zinc deficiency of the filed apple trees. The organic matter, exchangeable potassium and calcium were positively correlated with the availability of zinc in soil; The availability of zinc and the concentration of zinc in the root decreased due to high pH; The balance of zinc and other microelements influenced zinc absorption of apple trees as well.2. The annual regularity of distribution and transportation, and the source-sink dynamic relation of zinc nutrition were changed due to zinc deficiency leading to the formation of rosette leaves. In the normal apple tree, the content of total zinc in the root was steady annually, while zinc concentration was gradually reduced from root to shoot, however, the activity of available zinc in every organ at different stage was high, and the ability of zinc transportation was enhanced at late annual growth stage. The stored zinc was mainly accumulated in the shoot in order to meet the need of bud physiological and morphological differentiation at late growth and dormancy stage respectively. In the diseased apple tree, growing and backboned root maintained the high zinc concentration, however, the concentration and availability of zinc in the shoot were low relatively. The stored zinc mainly accumulated in the root at late growth stage as the zinc source of the tree in the next year, whereas the zinc was deficient when needed by bud physiological and morphological differentiation at dormancy stage. Comparing with the normal tree, there was little difference of distribution proportion of the total zinc in diseased tree xylem and phloem. The low availability of zinc led to the decrease of the transport ability of shoot, so the supplying zinc ability of shoot in diseased tree was lower than in the normal tree. There was no significant difference in the normal and abnormal leaves at the early stage. It is the low content of available zinc that induced the rosette leaves at bud physiological and morphological differentiation stage.3. Zinc stress severely inhibited the growth of Malus hupehensis Rehd seedlings and changed the zinc distribution proportion in organs and relation of zinc to other elements. Under zinc deficiency, the limited zinc distributed to the shoot mostly. At high zinc concentration treatment, the root of Malus hupehensis Rehd accumulated zinc in order to reduce the toxicity in the shoot. Adding the same concentration EDTA could mitigate the zinc toxicity, nevertheless adding EDTA under low zinc concentration would aggravate zinc deficiency. Zinc concentration was positively correlated with copper, and zinc deficiency reduced the copper concentration in Malus hupehensis Rehd, but P, Ca, Mg concentration increased in the shoot and decreased in the root due to zinc deficiency.4. Zinc-Iron interactions had effects on the distribution of different organs and relation of zinc to other mineral elements. Under zinc-deficiency condition, P, Ca, Mg concentration in Malus hupehensis Rehd decreased in the root and increased in the shoot significantly. High zinc concentration improved root to uptake and accumulate iron, whereas it inhibited iron transportation and distribution to the shoot. High iron concentration not only inhibited the root to uptake and accumulate zinc, but also suppressed zinc transportation and distribution to the shoot, which played a role in reducing zinc toxicity. Zinc and iron inhibited each other in leaves. Zinc and iron obviously inhibited manganese absorption and transportation, and iron concentration was negatively correlated with the manganese. The manganese concentration was reduced gradually from root, leaf to stem (root>leaf>stem), so the transportation obstacle of manganese was in root and stem.5.Symptoms of diseased trees were shortening of branch internode and increase of shoot-productive rate in the field. On the condition of zinc deficiency, the number of the chloroplast, starch grain, and mitochondrion decreased, while the number of the osmiophilic granule and the volume of the starch grain increased. Moreover, the membrane structure of leaf cell and mitochondrion, and the chloroplast layer of the mesophyll cell were damaged due to zinc deficiency, as a result, zinc transport ability and restorability of supplying zinc decreased. Zinc deficiency strongly reduced the number of vessel and sieve in nervure, during this time, the sieve in nervure was filled with some matter as well. Zinc deficiency also led to growth suppression of the branches and roots, the incrassation of phloem, the increase of the ratio of branch xylem to phloem, and the decrease of the number of vessel and the diameter of sieve pore.6.Zinc deficiency resulted in the damage of photosynthetic apparatus and the decrease of the water use efficiency and the efficiency of CO2, and light energy in the leaf. In zinc-deficient leaves, it is evident that zinc deficiency resulted in the decrease of excited energy capture, and the increase of heat dissipation and the PSI distribution proportion of excess light energy. In addition, the O2- generation rate increased due to the speedy Mehler reaction, then SOD made O2- translate into H2O2, and by the way of H2O-H2O circle, the excess energy was used up in order to protect the photosynthetic apparatus from the excess excited energy damage. At the same time, zinc deficiency could cause the activity of SOD to decrease, which might accelerate the Haber-Weiss reaction, and increase the yield of 1O2 and .OH, so it enhanced the degree of membrane lipid peroxidation and produced plenty of peroxide such as MDA and so on.7. There was close relation between the way of supplying zinc and zinc nutrition efficiency of zinc-deficient apple tree. The storage of zinc in the branch was greatly increased by foliar application of 15% ZnSO4·7H2O solution before abscission. It had advantage of keeping zinc-content balance among leaf, branch and root as well as among P, K and Zn. It increased the transportation and useful form of zinc, meet the need of growth in apple trees and alleviated the symptom of zinc-deficient. The content of zinc in the root was improved by zinc application in soil in autumn, however, zinc transportation was relatively slow. Leaf spray application of ZnSO4·7H2O improved the content of zinc in the branch at the early stage of three weeks before germination, however, the alleviating effect of the symptom of zinc- deficient was not good . It had little effect on zinc-transportation by spraying the solution of ZnSO4·7H2O on the leaves after three weeks of blooming.