| Based on the extensive available literature at home and abroad, this dissertation summarized the research advance on the saline-alkali soil comprehensive management, salt-resistance or salt tolerance and their salt-resistant or salt-tolerant mechanism. In this pot experiments treated with NaCl and the field experiments in the saline-alkali soils, with a common stock of Mulberry - Shishengsang(实生桑)(Morus alba),which adapted to the Yellow River valley and northwestern areas , as experimental materials, seedling emergences of seeds, the survival rate of seedlings, photosynthesis and chlorophyll fluorescence and other indicators were measured, and the physiological and biochemical process of mulberry seedlings in salt stress environment were systematically analyzed, moreover, their salt-resistant mechanism was researched . Main conclusions are as follows:(1) For Mulberry - Shishengsang(实生桑)(Morus alba)at different stages, it showed salt tolerance of 1 year-old seedlings was higher than that of its seeds. NaCl semi-lethal concentration for 1 year-old mulberry seedlings was 0.3% (g / g. DW) or so. Its seeds showed extremely sensitive to salt, and its Seedling emergences was 9.67 % under 0.1% NaCl concentration treatment , while 0 % under 0.2% NaCl concentration, so it is difficult to use and promote them in the saline-alkali soil Comprehensive Management by sowing.(2) Salinity significantly inhibited the growth and development of mulberry seedlings. During the experiments, Salinity significantly inhibited the growth of mulberry leaves, elongation of renewal branches and elongation and formation of lateral roots, and the sensitivity to salt of different organs performed lateral root> renewal branch> leaf. Under NaCl concentration of 0.5 to 0.7%, lateral root augment declined 81.33-92.35%, while that of renewal branches and leaves declined 70.94-84.62% and 56.18-75.97%, respectively. In addition, the root-shoot ratio of mulberry seedlings significantly decreased under salt stress, it showed that the plants suffered extremely seriously, and more than 80% of plants withered, when the root -shoot ratio would be below 0.071 to 0.067.(3) The net photosynthetic rate (Pn) of mulberry seedlings under 0.1% NaCl concentration was above that of control, but it was contrary when under 0.3%, 0.5% and 0.7% NaCl concentration treatments, moreover, net photosynthetic rate gradually decreased with NaCl concentration increasing. It denoted the main factor inhibiting Pn is non-stomatal control. In addition, salinity had significant effects on stomatal conductance(Gs), intercellular CO2 concentrations(Ci),and transpiration rate(Tr), water use efficiency (WUE)and stomatal limiting value (Ls) , and in which Gs, Tr, WUE and Ls dropped, but Ci rose with NaCl concentration increasing. To some extent, enhancing PAR or CO2 concentration may enhancing Pn .Salinity had significant impact on the chlorophyll fluorescence of mulberry seedling leaves. During the experiments, it showed a declining trend for Fo, but the differences of it between various treatments were not obvious with NaCl concentration increasing. Fv / Fm, Fv / Fo, Fm andΦPSⅡdeclined, but NPQ is first increased and then decreased. with NaCl concentration increasing .there may exist many accesses to photosynthesis inhibition of mulberry seedlings for salt stress, one was by hampering photosynthetic electron transfer, reducing the photochemical efficiency and energy conversion efficiency to curb the plant photosynthesis, the other, by destructing the membrane system structure and function, lowering photosynthetic synthase activity and triggering the photosynthesis Reaction Center abnormal. In the end, Na + and Cl - ions played a major role in to curb photosynthesis of mulberry seedlings, and the effect of Cl– ion on inhibiting photo- synthesis was greater than that of Na + ion.(4)The damages of salinity to mulberry (Morus alba) seedlings may attribute to ion toxicity, nutritional imbalance or deficiency, osmotic stress effects and destructible membrane structure and function, which were testified by the negative effects of salinity on mulberry morphology and ecophysiology, such as Na+ and Cl- ion mass cumulation in plants, a decline of Ca2+,K+,Mg2+ ion concentration in mulberry organs, a drop of K+/ Na+, Ca2+/ Na+and Mg2+/ Na+ ratio, a decrease of water moisture, fading mulberry leaves as well as an increase of MDA content and memberane permeability.(5) Adaptability mechanisms of mulberry seedling to salt stress can be included as below: ion compartmentalization, ion homeostasis regeneration, osmotic regulation and antioxidant protection systems self-defense, which could be suggested by the proofs such as①Na + compartmentalization at the organ level had impacts on the salt tolerance of mulberry seedlings, and for 1-year-old mulberry seedlings, its threshold may be between from 0.3% to 0.5%.②In the early-stage of experiments, salinity had a positive impact on Ca2+,K+ and Mg2+ ions uptake and distribution of mulberry seedlings, and K+/ Na+,Ca2+/ Na+,Mg2+/ Na+ ratio can be control to maintain life.③Na+ and Cl- in mulberry seedlings, which occupied 32.53%～66.96% in osmotic potential when treated with 0.5-0.7% NaCl concentrations, may take a major position in the osmotic regulation. For organic substances, proline was an important osmolyte under salt stress condition, and it may act as a mediator of osmotic adjustment. In addition, there may be other organic material to balance the osmotic potential between the cytoplasm and the vacuole.④antioxidant enzymes activity such as SOD, POD and CAT to perform at first increasing and then decreasing may be suggested that antioxidant enzyme system activities, to a certain extent, can reduce or mitigate salt damage to mulberry seedlings under salt stress.(6) After applied to saline-alkali soils, mulberry trees can improve the soil physicochemical properties, enhance soil nutrition contents, decrease salt concentratations, enhance enmyzes activities and multiple soil microbes.
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