Effects Of Salt-alkali Stress On The Growth And Physiological Characteristics Of Ulmus Pumila Seedlings

Soil salinization has become the most serious ecological and environmental problem in the world.The chloride,sulfate and salt content in saline-alkali soil will have a certain impact on the survival of plants,and become the most direct limiting factor for plant growth and vegetation restoration in saline-alkaline soil distribution areas.the elements of.Facing the characteristics of plant salt-tolerant research and cultivating salt-tolerant plants is the main link of biological improvement of saline soil.Ulmus pumila is an important native tree species in northern my country.It grows fast,has good quality,and has strong resistance to saline-alkali.It can be used for saline-alkali land improvement and afforestation.This thesis analyzes the changes in the growth and physiological indexes of Ulmus pumila seedlings caused by NaCl,Na HCO₃ and mixed salt stress,and understands the relationship between Ulmus pumila seedling growth and soil salt under saline-alkali stress,and aims to explore the salt-tolerant ability of Ulmus pumila and its It provides certain theoretical basis for practical application in saline-alkali environment.In this study,three different salts were used to stress the seedlings of Ulmus pumila,neutral salt NaCl,alkaline salt Na HCO₃,mixed salt（molar ratio NaCl:Na HCO₃=1:1）,Take distilled water as the control group（CK）,and use 5 salt concentration levels respectively,NaCl is（20,50,100,150,200 mmol/l）,Na HCO₃ and mixed salt are（10,30,50,70,100mmol）/l),4 different stress durations（7d,14d,21d,28d）to determine the main growth indicators,physiological indicators and photosynthesis of Ulmus pumila seedlings in the growth stage under salt stress conditions Changes in important indicators such as characteristic parameters.The results and conclusions are as follows:1.Under different salt-alkali stresses,the plant height increment and ground diameter increment of Ulmus pumila seedlings decreased,and the growth and development were significantly inhibited;the biomass accumulation decreased;the root-to-shoot ratio was greater than that of the control group（CK）.2.Under different salt-alkali stresses,Ulmus pumila seedlings gradually increased with the degree of salt stress,malondialdehyde（MAD）and relative conductivity;soluble protein content（SP）and soluble sugar（SS）content both increased first In the three salt stress treatment groups,under the same salt stress concentration and different treatment time or the same treatment time and different stress concentration,the SP content in each treatment group was greater than CK.3.Under different salt-alkali stresses,superoxide dismutase（SOD）,peroxidase（POD）and catalase（CAT）all showed a trend of first increasing and then decreasing with the increase of salt concentration.Chlorophyll（CHL）content,net photosynthetic rate（Pn）,transpiration rate（Tr）,and stomatal conductance（Gs）showed a linear downward trend with the increase of salt concentration.The intercellular CO₂（Ci）concentration of Ulmus pumila seedlings showed a gradually increasing dynamic change.4.Under the stress of NaCl,Na HCO₃ and mixed salt,with the deepening of the stress,the metabolic level of Ulmus pumila seedlings decreased,the activity of antioxidant enzymes decreased,and the damage of the membrane system caused the damage of Ulmus pumila seedlings to increase.The analysis results of the difference of NaCl,Na HCO₃ and mixed salt showed that the damage degree of three different salt stresses to Ulmus pumila seedlings was in order of Na HCO₃stress>mixed salt stress>NaCl stress.