| Saline soil is widely distribute in China And has become one of the main limiting factors that restrict the development of agroforestry.As a suitable tree species in the north of China,improving the ability of Ulmus pumila to resist salt stess will improve the growth of U.pumila on saline soil.Generous studies have shown that exogenous application of salicylic acid could enhance the ability of many plants to resist salt stress,therefor it was important for developing saline soil forestry by adding salicylic acid to improve salt tolerance of U.pumila.The annual U.pumila tissue culture seedling “Bai wa NO.1” was chose as experimental material in this research.The effect of 0,0.5,1.0,2.0 mmol·L-1 SA by foliar spraying on the height,biomass,water physiology,photosynthetic carbon assimilation capacity,osmotic adjustment,membrane lipid peroxidation,ionic uptake and migration of the leaves and roots of U.pumila seedlings were studied under 0,50,100,150 mmol·L-1 Na Cl in order to reveal the physiological mechanism of salicylic acid on salt tolerance of U.pumila.The results showed that:1.Exogenous spraying SA improved relative water content(RWC)under salt stress,which could improve the water status of U.pumila.Meanwhile,SA accelerated U.pumila seedling growth,and increased plant height,biomass,root to shoot ratio.Moreover,the photosynthetic pigment(Chla,Chlb,Chl a+b)content of U.pumila,the photosynthetic gas exchange parameters(net photosynthetic rate,stomatal conductance,transpiration rate and intercellular CO2 concentration),and the capacity of photosynthetic carbon assimilation of U.pumila were augmented by using exogenous SA,and alleviated plant height and biomass reduction caused by salt stress,and the salt tolerance ability was improved.2.The exogenous spraying SA could reduce the content of H2O2 and MDA and electrolyte leakage significantly in the leaves of U.pumila under salt stress,which indicate that exogenous SA could reduce the accumulation of peroxide under salt stress,thus alleviating the damage of membrane lipid peroxidation to cell structure caused by oxidative stress and maintaining the integrity of cell membrane structure.Exogenous SA could regulate the osmotic potential and relieve the damage caused by salt stress through increasing the content of proline and soluble sugar of U.pumila.Moreover,the optimal concentration was 1.0 mmol·L-1 SA.3.The uptake of K+,Ca2+ and Mg2+ in leaves and roots of U.pumila effectively increased by using exogenous SA under salt stress,while the absorption of Na+,Na+/K+,Na+/ Ca2+ and Na+/ Mg2+ ratio were reduced.It was indicated that SA can relieve ion poisoning by controlling the ionic uptake and migration.The optimal concentration of improving ion content in leaves was 1.0 mmol·L-1 SA,and the optimal concentration of improving ion content in roots was 2.0 mmol·L-1 SA.In summary,exogenous SA could improve moisture physiology status of U.pumila seedlings under salt stress.The photosynthetic pigment content and the photosynthetic gas exchange parameters were increased,but the level of membrane lipid peroxidation was reduced by using exogenous SA,and the ability of osmotic regulation was increased,the ionic balance was adjusted effectively,which promoted the growth and improved salt tolerance of Ulmus pumila. |
