Effects Of Salt Stress And Its Alleviation By Calcium Chloride In Ligustrum Obtusifolium Sieb.et Zucc. Seedlings

Two methods of snow removal,artificial snow removal and snowmelting agent（chlorine salt）,are often used in highway snow removal in Northeast China.Chlorine salt snowmelting agent has adverse effects on plant growth,physiology and other aspects,thus reducing the effect of highway landscape greening.Ligustrum obtusifolium,with high adaptability,is a commonly used tree species in the isolation zone of highway in the Northeast.IN this paper,Na Cl stress and Ca Cl₂mitigation tests with different concentrations in Ligustrum obtusifolium Seedlings were conducted to provide guide for the planting,maintenance and application of Ligustrum obtusifolium.In highway greening in Northestern China.The main results are as follows:（1）Under Na Cl stress,leaf margin dried and turned yellow,and leaf withered under high concentration.Na Cl at a low concentration promoted the growth of the aboveground part of Ligustrum obtusifolium seedlings,while Na Cl at a high concentration inhibited the growth of the aboveground part of Ligustrum obtusifolium seedlings,which showed that the seedling height growth first increased and then decreased,the biomass and relative water content of leaves overall decreased,and the root-to-shoot ratio overall increased.After the application of Ca Cl₂treatment,the seedling height,relative water content of leaves first increased and then decreased,biomass increased and root-to-shoot ratio decreased.Ca Cl₂had an alleviating effect on the growth and development of Ligustrum obtusifolium seedlings under Na Cl stress.（2）Under Na Cl stress,net photosynthetic rate（Pn）,stomatal conductance（Gs）,transpiration rate（Tr）and chlorophyll content all decreased,while intercellular CO₂concentration（Ci）increased.Na Cl stress inhibited plant photosynthesis.After Ca Cl₂was applied,Pn,Gs and Tr showed a trend of first increasing and then decreasing,and Ci showed a trend of first decreasing and then increasing,indicating that Ca Cl₂could alleviate the photosynthesis of Ligustrum obtusifolium seedlings under Na Cl stress.（3）MDA and Pro decreased first and then increased under Na Cl stress.The activities of SOD and POD decreased first,then increased and then decreased.The content of soluble sugar and soluble protein decreased first and then increased.Overall,the relative conductivity showed an upward trend.Na Cl stress damaged the membrane of leaves and increased the content of protective enzymes and osmotic regulatory substances in vivo,thus reducing salt damage.When Ca Cl₂is applied,the relative conductivity decreases with the increase of Ca Cl₂concentration.MDA content decreased first and then increased.The contents of Pro,POD and SOD rose first and then decreased.The content of soluble sugar soluble protein increases,Ca Cl₂reduced the degree of membrane peroxidation in Ligustrum obtusifolium seedling leaf,and improved the content of protective enzymes and osmotic regulating substances.In general,the effects of Na Cl on Ligustrum obtusifolium seedling growth and physiological indexes were related to Na Cl concentration.Ligustrum obtusifolium can resist the membrane peroxidation induced by salt stress by increasing the content of its own protective enzymes and osmotic regulating substances.The application of Ca Cl₂can alleviate the stress degree of Ligustrum obtusifolium seedlings,but it cannot restore plants to the state of good growth without the stress of adversity.Ca Cl₂alleviated differently at different concentrations,and excessive concentration may form new ion stress on plants.