| Salt and alkali is one of the key stress factors inhibiting survival rate, growth, fruit yield and quality of Ziziphus jujuba Mill. The information on salt tolerance and control technology of jujube were very little in world wide. The availability of silicon in soils for plants is usually low though it is the second abundant element in soils. Some people reported that silicon could alleviated ion toxicity of plants, including Na~+ and Cl-. Nevertheless, the relation between silicon and salt tolerance of plants is still not understood well. The differences of salt tolerance among four super jujube cultivars were investigated in this dissertation. The main objects of the this study were focused on the relation between silicon and salt tolerance of Z.jujuba cv.jinsixiaozao, a very famous jujube variety in China, and its mechanism. X-ray electron probe microanalysis, ultra-structure observation and analysis, chlorophyll fluorescence technology and other scientific methods were used to release the secretary. Salt and silicon source was sodium chloride and silicate potassium, respectively. The test material were 2-year old grafting seedlings. The main results of the dissertation were presented as follows: 1) Salt injure grade and speed of 4 jujube varieties, such as inhibition of growth, reduction of biomass, declining of leaf physical status, became more and more heavier with the increase of soil salt content. However, salt tolerances of 4 jujube varieties were significantly different. According to synthetic evaluation, salt tolerance of Z.jujuba cv. jinsixiazao was the strongest in the 4, second and third was Z.jujuba cv. lizao and Z.jujuba cv.Dongzao, respectively.The weakest tolerance to salt stress was Z.jujuba cv.daguazao. 2) The experimental results also showed that salt ions had distinctively toxic effects on jinsi jujube plants grown on soils containing 0.3﹪(w/w, dw) or 0.5﹪NaCl for more than 6 months while added silicon ameliorated the toxicity of salt on jinsi jujube. The differences of growth and physiological status between the plants added and no added silicon (0.4 ‰Si, w/w, dw)under the two salt stresses were significant. Silicon increased the relative water content of leaf blade and decreased the plasma membrane permeability. The photo-system II activity of potential chemistry (Fv/Fo), maximum efficiency of photo-chemistry (Fv/Fm), net photosynthetic rate (Pn) and the water use efficiency were all promoted by added silicon. The leading stem length, a key growth index of Z.jujuba under salt stress, was much larger by added silicon. Silicon improved the growth and physiology of Z.jujuba under salt stress. 3) The analysis results of ion micro-distribution status on the across sections of root tip and leaf blade of Z. jujuba cv jinsixiaozao clearly showed that added silicon enhanced the relative content of K+ in almost all cells of the root tip and leaf blade under salt stress while the relative weight of Na+ and Cl-in palisade tissue of leaf blade was decreased significantly . Therefore, the ion balance in the plants and the ion homeostasis in photosynthetic cells were better maintained. 4) The experimental results showed that 0.3﹪NaCl stress for 30 d lightly wounded while significantly wounded the ultra-structure of leaf blade stressed for 165 compared with that of salt stress. Same was 0.5﹪NaCl stress for 30 d and 165 d, respectively. However, added Si alleviated injure of leaf blade ultra-structure under 0.3﹪and 0.5﹪NaCl whether it was for 30 d or 165 d. The main effects of silicon on this respect were keeping with the stability and integrity of ultra-structure of membrane system under salt stress, suppressing aging of chloroplast and des-integrity of the lamellae. Silicon also increased the production of osmiophilic granule, starch grain, and other vesicles. Therefore, silicon is benefit to maintain the photosynthetic efficiency and osmotic regulation capacity of Z.jujuba.cv.jinsixiaozao under salt stress. 5) The effect of silicon on fatty acid content and composition of root and leaf membrane lipid of the fruit tree under salt stress were significantly different. In root of the plant, the content of saturated fatty acid decreased by exogenous silicon compared with no silicon addition under salt stress. Both the content of unsaturated fatty acid and the index of unsaturated fatty acid of root membrane were all promoted due to addition of silicon under salt stress. The effects of silicon on fatty acid content and composition of leaf membrane lipid were adverse to those of root under salt stress, which implied that the physiological function of silicon in alleviating the injure of salt stress to Z. jujuba cv. jinsixiaozao was closely correlated with the physiological function and growth characteristics of the tree,s organs. |
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