Research On The Physiological-Ecological Mechanism Of Salt Tolerance In Ulmus Pumila

The pot experiment in salt stress simulation method was used to research physiological responses under salt stress of 2-year Ulmus pumila seedlings and their salt tolerance differences and physiological adoption mechanism in different habitats. Finally, the theory basis was provided for tree selection, cultivation and species introduction in coast saline-alkali soil forestation. The results revealed that the membrane permeability, Na content and Na/K in leaves of U. pumila which the seeds are taken from medium-salinity and mild-salinity habitats, were lower than that of samples in non-saline habitats with increasing of salt concentration. However, leaf proline content, soluble sugar and K content had a higher growth rate than that in non-saline habitats. In addition, the decreasing rate of leaf starch content, net photosynthetic rate(Pn),transpiration rate(Tr), intercellular CO2 concentration(Ci ) and stomatic conductance (gs) were lower than that in the non-saline habitats. The order of salt-resistance (high-low) of U. pumila was: medium-saline habitat (0.776%) > mild-saline habitat (0.737%) > non-saline habitat (0.695%). U. pumila from salinity habitat may have stronger saline environment adaptability than that in non-salinity habitat. Comparing with non-salt soil habitat, various physiological indices of U. pumila in moderate and low salt soil habitat showed stronger adaptability to salt soil environment.By controlling salt content in soil, the effects of salt stress on seed germination, emergence and seedling growth and photosynthetic performance were studied. With the insights of impact mechanism salinization soil on U. pumila seed germination, emergence and seedling growth, the relationship between U. pumila germination & seedling growth status and salt concentration in soil were discussed in the paper. Consequently, it showed that adaptability mechanism had great meaning during U. pumila seed germination, emergence and seedling growth stage. The results showed that: with increasing concentration of salt stress, not only the germination rate and germination index decreased, but also the time of seedling germination delayed significantly with the increasing intensity of salt-stress. The rate of emergence, planting percent and survival rate of Seedling decreased with the increase of salt concentration and salt stress inhibits the growth of seedling height and root length of U. pumila. Because of the salt tolerance is weak in Seedling stage, a large number of seedling died under salt stress. With the increase in salt stress, Yields or flux ratios (φPo,Ψo andφEo), Phenomenological energy fluxes(ABS/CSM,TRO/CSM and ETO/CSM),Density of reaction centers (RC/CSO and RC/CSM),Performance indexes( PIABS and PICSM)and Driving force per unit area basis (DFCSM)decreased, Absorption flux per CS(ABS/CSO),quantum yield for energy dissipation (φDo) and dissipated energy flux per CS ( DIO/ CSM ) increased.By controlling salt content in soil, the growth, physiological property, nutrient balance, impedance parameter and photosynthesis of 1-year U. pumila were studied. discuss U. pumila adaptability mechanism in salting habitat was discussed and the theory basis for salt tolerant seedling breeding was provided in the paper.1. Under salt stress condition, U. pumila leaf salt damage index increased and its survival percentage and growth rate decreased. As a result, U. pumila growth will be restrained. With the growth of salt stress concentration and extension of stress time, cell membrane permeability, relative conductivity and internal per-oxidation product MDA content increased. However, U. pumila leaf SOD, POD, CAT, free proline content and soluble sugar content increased to the maximum and then decreased.2. Under salt stress, mineral nutrition balance of plant leaves is damaged. With the growth of salt concentration in soil and extension of stress time, Na accumulates in leaves continuously. As a result, N, K, Ca and Ma content decreases in the leaf. Fe and Zn content increases. However, Fe and Zn content increases to the maximum and then decreases. In addition, ratio of all elements to Na is reduced in U. pumila leaf. Accumulation of Na has influence to main nutrition ion absorption and distribution and utilization during physiological metabolism. U. pumila cannot perform its normal physiological function. Meanwhile, U. pumila adjusts itself continuously to adopt the salt habitat.3. If salt concentration is lower than 0.3 %, it has little difference in radian and span in U. pumila leaf electrical impedance map. If the salt concentration is higher than 0.4%, radian and span presents a reduction trend. In different salt concentrations, U. pumila leaf electrical impedance parameter electric resistance r, electric resistance r1, exocellular resistance, internal resistance and relaxation time shows a reduction trend generally. However, relaxation time distribution coefficient increases to the maximum and then decreases. Under salt stress conditions, U. pumila leaf exocellular resistance, internal resistance and relaxation time has positive correlation with content of N, K, Ca, Mg and Mn and negative correlation with Na content. These parameters have no significant relationship with P, Fe and Zn content in U. pumila leaf.4. With the salt stress influence, Fm,φPo andψo decreases, QA electron delivery capability is also reduced, which can results inφEo reduction and significant growth of φDo and FO With extension of salt stress time,φPo,ψo andφEo decrease andφDo in leaf increases. With addition of salt stress time and concentration, chlorophyll content, net photosynthetic rate (Pn), transpiration rate (Tr) and stomatic conductance (gs) decreases gradually. Intercellular CO2 concentration (Ci) increases to the maximum and then decreases. Salt stress pushes reduction of RC/CSO, RC/CSM, TRO/CSM, ETO/CSM, PIABS, PICSM and DFCSM in U.pumila leaf. However, it can enhance DIO/CSM. In addition, salt stress results in PSⅡreaction center degradation or inactivation and decreased light energy collection volume. It also breaks electron delivery in U. pumila leaf electron delivery chain receptor side, defers chlorophyll composition and reduces leaf PSII activity. As a result, it activates corresponding defense mechanism in leaf.