| Nitraria is a halophyte with very good tolerance to the salt. The wild Nitraria can growth in the soil with10%salt. But there is a big difference of the salt tolerance between the species of Nitraria. The papers about their salt-tolerant mechanism were few. In order to study the the salt-tolerant mechanism of Nitraria and compare the difference of salt tolerance between different species, the germination indexes of seeds, the growth indexes, physiological and biochemical indexes of the seedlings of Nitraria tangutorum Bobr, Nitraria sibirica Pall and Nitraria sphaerocarpa Maxim were compared, by stress treatment of t0,3%,6%,9%,12%and15%NaCl on the seed and the seedlings. The indexes of seeds included the absolute germination rates, the relative germination rates, germination index, vigor index, the initial germination days, and the tolerance, the half-lethal and the limit concentration of NaCl. The growth indexes included the relative increased plant height, relative leaf area, relative increased stem diameter, relative leaf number, the plant fresh and dry weight, and the root-shoot ratio. The physiological and biochemical indexes included the content of malomdiadehyde, free proline, soluble sugar and the activities of superoxide dismutase and peroxidase in the leaves, and cytomembrane permeability. The anatomical structures of leaf and stern on the different Nitraria species and the change of the same species in normal condition and6%NaCl stress were compared, including the changes of the epidermal cells, the skin cutin layer, the stomatal density, the size of stomatal guard cells, the stoma aperture, the size of mesophyll cell, palisade tissue of the leaves, the changes of the thickness of cork layer and the cell wall outside the cork layer, the vascular tissue, the intramedullary and the intramedullary ray of the stems and the change of ergastic substance in the epidermal cells of the leaf and stern. All the indicators were comprehensively analyzed by subjection function. The results showed that: 1. The seed germination of Nitraria was greatly limited by salt, and there were large differences between the species.The absolute germination rates, the relative germination rates, the germination index and the vigor index were decreased, and the initial germination days were increased in the salt stress. The absolute germination rates, the relative germination rates, the germination index and the vigor index of N. tangutorum were the highest. The absolute germination rates and the relative germination rates of N.sphaerocarpawere lower than N. sibirica in0to1%NaCl, and close to N. sibirica in the concentration lager than1%. The relative germination rates of N. sphaerocarpa were close to N. sibirica in0to0.5%NaCl, and significant higher than N. sibirica in more than0.5%. The vigor index of N.sphaerocarpa were lower than N. sibirica in0to1.5%NaCl, and close to N. sibirica in more than1.5%.The analysis of membership functions in0.5-2.5%NaCl, five kinds of concentration showed that the germination salt tolerance of N. tangutorum were the best, and N. sibirica was better than N.sphaerocarpa in o.5%and2.5%NaCl, and N.sphaerocarpawas better than N. sibirica in1%to2%NaCl. The analysis of comprehensive membership function showed that the salt tolerance sequence were that N. tangutorum was best,next was N. sibirica and-N.sphaerocarpawas worst.The concentration of salt tolerance and the half-lethal concentration of N. tangutorum were the highest, N.sphaerocarpathe second, N. sibirica the lowest. The lethal concentration of N. tangutorum was the highest, N. sibirica the second, N.sphaerocarpathe lowest.2. The seedling growth of Nitraria was greatly limited by the salt stress, and there was large difference between the species.The plant growth of3Nitraria species was inhibited in the salt stress. Among them N. tangutorum was the most sensitive to the NaCl stress. All growth indexes except the dry weight of underground and the root-shoot ratios of N. tangutorum appeared the significant decreased in6%to9%NaCl. The plants on relative increased plant height and stem diameter of N.sphaerocarpa were not sensitive to the salt stress, and other growth indexes showed significant decrease in6%to9%NaCl. The aboveground growth of N. sibirica was significant inhibited by the NaCl, the underground was almost no effected. The growth index of N. sibirica was better than N. tangutorum and N. sphaerocarpa, except the relative increased plant hight and stem diameter was lower than N. sphaerocarpa. The analysis of the growth indexes membership functions in different concentration of NaCl showed that the salt tolerance of N. tangutorum and N. sibirica was better than N.sphaerocarpain3%NaCl, that the salt tolerance of N. sibirica was significant higher than N. tangutorum and N.sphaerocarpa,and the salt tolerance of N. tangutorum and N.sphaerocarpawere close in9%and12%NaCl, and that the salt tolerance of N. sibirica was significant higher than N. tangutorum and N. sphaerocarpa, N.sphaerocarpa was the second, N. tangutorum the worst in15%. The analysis of Nitraria growth indexes comprehensive membership function showed that the salt tolerance of N. sibirica were the best,N.sphaerocarpathe second and N. tangutorum the worst.3. The leaf physiological and biochemical reaction of Nitraria was greatly effected by the salt stress, and there was large difference between the species.The leaf physiological and biochemical reaction of different Nitraria species were greatly influent by NaCl. With the increase of NaCl concentration, the content of proline and soluble sugar of N. tangutorum was increased first and reduces later, the activity of SOD was increased, and the acticity of POD was significantly reduced. The content of MDA, proline and soluble sugar of N.sphaerocarpawere increased first and reduced later, the activity of SOD was increased and the acticity of POD was reduced at first and generally increased then. The content of proline and soluble sugar and the activity of SOD of N. sibirica showed increase trend in the NaCl stress, and the activity of POD was volatile, and showed significant decrease in the high NaCl. The cytomembrane permeability of3species was increased in the salt stress, but there was no difference between the species. The analysis of the leaf physiological and biochemical indexes membership functions in different concentration of NaCl showed that the salt tolerance of N.sphaerocarpawas better in3%to6%NaCl, N. sibirica and N.sphaerocarpa better in6%to12%, and the salt tolerance sequence was N. sibirica> N. sphaerocarpa>N. tangutorum in15%NaCl. The analysis of Nitraria leaf physiological and biochemical index comprehensive membership function showed that the salt tolerance of N. sibirica and N.sphaerocarpawere better than N. tangutorum. The analysis of all the growth indexes and the physiological and biochemical indexes of Nitraria comprehensive membership function showed that the salt tolerance of N. sibirica were the best, N.sphaerocarpa the second and N. tangutorum the worst.4. The anatomical structure of the leaf and stem in3Nitraria speciesFirst, N. sibirica has the thicker epidermal layer cells, stratum corneum and cork layer, the thicker mesophyll tissue and palisade tissue. The stomatal density, the under stomatal room, the size of the stoma and the stoma aperture is the minimum. The number of catheter in the leaf blade and stem is more and pith ray was the most. So the salt tolerance of N. sibirica is the best in3Nitraria species. Second, N.sphaerocarpa has the thicker epidermal layer cells and stratum corneum, the thicker mesophyll tissue and palisade tissue. The thickness of the cork cells and the under stomatal room is in the middle. The total number of catheter in the leaf blade is more. There is more black flavonoid ergastic substance in the epidermal cells and the stem cork layer. The stomatal density and the size of the stoma is the maximum. And the stoma aperture is bigger. The number of catheter in the stem is less, and less pith ray is developed. The salt tolerance of N.sphaerocarpa is in the middle of the three Nitraria species. Third, N. tangutorum had the thiner epidermal layer cells, stratum corneum, mesophyll tissue and palisade tissue, The thinnest cork layer, the biggest under stomatal room, the least number of catheter in the leaf blade. Therefore, the salt tolerance of N. tangutorum was the worst.5. The effect of salt on the anatomical structures of leaf and stern of3Nitraria species.In the salt stress, the average thickness of mesophyll tissue and palisade tissue of N. tangutorum and N. sibirica was significantly increased in the salt stress, but N.sphaerocarpa was reduced. The stoma sinked in in the hole, and the stomatal density decreased. The number of epidermal hair of N. tangutorum and N.sphaerocarpa was increased.There is no effect on the formation of epidermal hair on N. sibirica. The cork layer cells on the stem of N. sibirica was smaller, N. tangutorum was thicker in the salt stress than in the normal condition. The content of black ergastic substance in the cork layer was reduced in the salt stress. There was no obvious change on the basic form of pith tissue and vascular in the middle of the stem of3Nitraria species, and the variable diameters. In the NaCl stress, the pith ray of3kinds of Nitraria appeared different change. But the fiber cells in the xylem were significant reduced. The volum of parenchyma cells in cortex tissue of stem of N. tangutorum and N. sibirica also were increased, and appeared cells breakage.Comprehension the growth indexes, the leaf physiological and biochemical indexes in salt stress and the anatomical structures, the salt tolerance of N. sibirica was the best in the3Nitraria species,N.sphaerocarpathe second and N. tangutorum the worst. |
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