The Physio-ecological Mechanism Of Salt Tolerance Of Medicinal Halophyte Lycium Ruthenicum

In order to explore physio-ecological mechanism of salt tolerance of Lycium ruthencium, osmotic regulation, photosynthesis, leaf ultrastructure of natural saline habitat and seedling growth, organic solute, ion content in simulation condition were studied deeply adopting field test and indoor simulation method. These results could provide theoretical basis for cultivation and resource protection of Lycium ruthencium. The main conclusions showed that:1. With height of Lycium ruthenicum increasing, the degree of leaf succulence was improved, but MDA and proline content decreased. Soluble sugar and soluble protein content of plant that height was below 20 centimeters was the higher than that of plant whose height was between 20 to 40 centimeters. The ratio of K⁺/Na⁺, Ca²⁺/Na⁺, Mg²⁺/Na⁺ and Si⁴⁺/Na⁺ were the highest in plant whose height was 30 to 40 centimeters and lowerest in plant that was height of 10 to 20 centimeters. In conclusion, salt tolerance of individuals in the height of 30 to 40 centimeter was the strongest, while the plant whose height was below 20 centimeter was the poorest.When adjacent plant was Nitraria tangutorum and Tamirix, leaves succulent degree of Lycium ruthenicum was relatively higher, but proline, soluble sugar and soluble protein content lower, the ratio of K⁺/Na⁺, Ca²⁺/Na⁺, Mg²⁺/Na⁺, and Si⁴⁺/Na⁺ higher. But when adjacent plant was Karelinia caspica and Kalidium foliatum, each matter accumulation appeared opposite with above situation. Through comprehensive evaluation of subordinate function value, it was found that its value was the highest when adjacent plant was Nitraria tangutorum, successively Kalidium foliatum, Kalidium foliatum and Karelinia caspica. It showed that salt tolerance of Lycium ruthenicum was highest when adjacent plant was Nitraria tangutorum, and lowest when adjacent plant was Karelinia caspica and Kalidium foliatum.As far as different organs were concerned, Na⁺, K⁺ and Cl^- mainly distributed in overground part of Lycium ruthenicum, Ca²⁺ mainly accumulated in its root, but Mg²⁺ and Si⁴⁺ content were highest respectively in leaf and stem. The ratios of K⁺/Na⁺ and Ca²⁺/Na⁺ in root of Lycium ruthenicum were higher than leaf. And the same time, the change laws of K⁺/Na⁺, Ca²⁺/Na⁺, Mg²⁺/Na⁺, and Si⁴⁺/Na⁺ ratios appeared firstly reducing then adding with root length increasing.2. In Minqin saline area, the order of element content of five desert plants such as Lycium ruthenicum, Kalidium foliatum, Nitraria tangutorum, Karelinia caspica and Phragmites australis was chlorine>calcium>sulfur>potassium>silicon>sodium> phosphorus>magnesium>aluminum. Chlorine, calcium and sulfur element content of salt accumulating and excreting plants was relatively higher, while potassium and silicon element of salt excluding plants was higher than chlorine, calcium and sulfur. Among three salt accumulating plants, the ratios of K/Na, Ca/Na, Mg/Na and Si/Na of Lycium ruthenicum were higher than Kalidium foliatum and Nitraria tangutorum, which showed stronger ability of salt tolerance.Fo and qN of Lycium ruthenicum and Karelinia caspica appeared reverse"V"-type tendency from A.M. 6 o'clock to P.M. 18 o'clock, and their maximum value occurred at noon 13:30. While Fm, Fv/Fm, Fv/Fo andΦ_PSâ…¡ appeared"V"-type tendency, and their minimum value occurred 13:00. In the same habitat, when environment temperature was lower, heat dissipation of Karelinia caspica was lower, its photochemical activity was higher than Lycium ruthenicum. When environment temperature reached the highest, namely close to 39 to 40 centigrade, heat dissipation of Lycium ruthenicum was higher, and its photochemical activity was higher than Karelinia caspica, which showed stronger adapting ability to photoinhibition.3. Slight salt stress could increase relative water content in the leaves of Lycium ruthenicum and Lycium barbarum. But their relative water content declined rapidly with salt concentration increasing. At the same time, relative water content of Lycium ruthenicum was significantly higher than Lycium barbarum in contrast and salt treatment groups. Photosynthetic pigment contents of two plants in salt treatment groups were higher than in contrast, and their contents added with salt concentration increasing. But the ratio of chla and chlb increased in lower salt stress, and then decreased rapidly with stress degree aggravating. Also relative conductivity and MDA content of different organs of two plants increased with salt stress concentration rising, but in medium and high salt stress, MDA content of different organs of Lycium ruthenicum was lower than Lycium barbarum under same salt concentration.In contrast and salt treatment groups, the distribution law of proline and soluble sugar content of two plants was root>stem>leaf. Meanwhile, proline and soluble sugar content of two plants in salt treatment groups added with the increasing of salt stress concentration. Proline content in the leaves of Lycium ruthenicum was higher than Lycium barbarum, but its contents in stem and root of Lycium ruthenicum were significantly lower than Lycium barbarum. There were higher Na⁺ and Cl^- relative content of two seedlings than those of contrast, and its content became gradually higher with salt concentration increasing. Among different organs, accumulation of Na⁺ and Cl^- were the most highest in leaves tissue. On the contrary, K⁺,Ca²⁺,Mg²⁺ and Si⁴⁺ content of seedlings under different salt tolerance reduced or did not vary compared with contrast. At the same time, the K⁺/Na⁺, Ca²⁺/Na⁺, Mg²⁺/Na⁺ and Si⁴⁺/Na⁺ ratios in leaves, stems and roots decreased gradually with salt concentration increasing under NaCl stress. The K⁺/Na⁺, Ca²⁺/Na⁺, Mg²⁺/Na⁺ and Si⁴⁺/Na⁺ ratios in Lycium ruthenicum under salt stress were markedly higher than those in Lycium barbarum, and the descendant degree of these ratios of Lycium ruthenicum were enormously lower than those of Lycium barbarum especially in higher salt concentration.Through comprehensive analysis, it could be found that organic solute and inorganic ions accumulated simultaneously in the organs of Lycium ruthenicum and Lycium barbarum. Differently, organic solute mainly accumulated in roots, but inorganic ions accumulated mainly accumulated in leaves, which showed complementary among different types of osmotic regulation substance. And comparatively speaking, Lycium ruthenicum had stronger ability than Lycium barbarum in salt tolerance. 4. With the extension of stress days, lower salt stress could increase height, root length, fresh dry weight and root/shoot ratio of Lycium ruthenicum. Though higher salt stress suppressed height growth of Lycium ruthenicum, and reduced fresh dry weight of leaves, stems and whole plants, it increased length, fresh dry weight of root and root/shoot ratio. Membrane permeability and MDA content of Lycium ruthenicum increased gradually with stress strength and time increasing, and the accumulation of above two physiological indexes in higher salt stress was larger than lower salt stress with stress time increasing. The accumulation of proline of Lycium ruthenicum firstly increased then decreased during salt stress, but its accumulation at the end of salt stress increased several or even dozens of times compared with stress before, which showed proline was more sensitive to salt stress. Soluble sugar content of Lycium ruthenicum increased in lower salt stress on the whole, but its accumulation was not obvious. Under higher salt stress, soluble sugar content appeared reverse"V"-type tendency with salt stress time increasing, its accumulation at the end of salt stress were bigger compare with stress before. Na⁺ and Cl^- relative content added gradually with salt stress time increasing, and their accumulation in higher salt stress were higher than in lower salt stress. K⁺, Ca²⁺, Mg²⁺ and Si⁴⁺ relative content decreased gradually, and their declining account in higher salt stress were bigger than in lower salt stress. The ratio of K⁺/Na⁺, Ca²⁺/Na⁺, Mg²⁺/Na⁺ and Si⁴⁺/Na⁺ appeared declining tendency with salt stress time increasing.5. Chloroplasts of Lycium ruthenicum became swollen under higher salt environment, even a part of chloroplasts became suborbicular, and starch grains disappeared. Also vacuolated phenomenon was very obvious, the number of like vacuolated structure increased and size largened. These vacuolated structures transferred from edge to thylakoid, which led to thylakoid structure being destroyed. Mitochondria distributed closely around the chloroplast, and its number were a little, the change was not obvious.