Physiological Effects Of Exogenous Ealcium On Elaeagnus Angustifolia Under Saline-Alkali Stress

Elaeagnus angustifolia L.is a pioneer tree species in saline-alkali land greening,which has both ornamental and economic value.Calcium is an essential mineral element for plant growth,and plays an important role in the process of plant perception,transmission,response and adaptation to stress.In this paper,E.angustifolia is used as the research object,three concentration levels(50,100,200mmol·L^-1)of saline alkali stress（Na Cl:Na HCO₃=3:1）and three concentration levels(0,5,10,20mmol·L^-1)of exogenous calcium（Ca Cl₂）were set.The relative growth of plant,photosynthesis parameters,ion and osmoregulation substance content,enzyme activity of E.angustifolia were measured,to explore the effects of exogenous calcium on salt tolerance and physiological characteristics of E.angustifolia under saline alkali stress,so as to provide theoretical reference for landscaping,introduction and planting and variety breeding of E.angustifolia in saline alkali land.The study concluded that:（1）Under saline alkali stress,the relative growth of stem height and ground diameter;leaf growth of E.angustifolia were inhibited,the biomass accumulation decreased,the root to shoot ratio increased,and the water content of plant decreased.Supplementing exogenous calcium can significantly alleviate the salt damage of E.angustifolia,which is manifested in two aspects:first,promoting the leaf growth of E.angustifolia under saline-alkali stress,increasing leaf area and leaf number;second,reducing the effect of saline-alkali stress on the biomass distribution pattern of E.angustifolia,and the root and shoot of E.angustifolia is lower than that of the CK group.（2）Through the evaluation of the salt tolerance of exogenous calcium on E.angustifolia,it was found that the salt tolerance of E.angustifolia treated with 50 or 100mmol·L^-1 salt concentration supplemented with 5mmol·L^-1 exogenous calcium was the strongest;The salt tolerance of E.angustifolia treated with 200mmol·L^-1 salt concentration was the strongest when10mmol·L^-1 exogenous calcium was supplementet.（3）Under saline alkali stress,the chlorophyll content of E.angustifolia leaves decreased,the value of chlorophyll a:chlorophyll b increased,the stomatal conductance,transpiration and net photosynthetic rate of E.angustifolia leaves decreased,and the light reaction activity of leaves decreased.The chlorophyll content and net photosynthetic rate of E.angustifolia increased,and the photoreaction activity of E.angustifolia increased when treated with appropriate amount of exogenous calcium(5 or 10mmol·L^-1).（4）With the increase of saline-alkali stress,the contents of Na⁺and Cl^-in roots and crowns of E.angustifolia increased,the osmoregulation substances（SS and Pro）in leaves gradually increased,and the activities of SOD,POD,APX and CAT increased,while the contents of MDA and H₂O₂ increased.With proper application of exogenous calcium,the contents of Na+and Cl-in roots and aboveground parts of E.angustifolia decreased,the contents of osmotic regulators（SS and Pro）,MDA and H₂O₂ in E.angustifolia leaves decreased compared with the control group,and the activities of antioxidant enzymes in E.angustifolia leaves increased in different degrees.Based on the above results,the supplement of an appropriate amount of exogenous calcium(5 or 10mmol·L^-1)can alleviate the ion and osmotic stress of E.angustifolia under saline alkali stress,improve the photosynthetic physiological activity and antioxidant enzyme activity of E.angustifolia leaves,regulate the biomass distribution and promote the growth of E.angustifolia leaves and finally enhance the salt tolerance of E.angustifolia.The effect of exogenous calcium with high concentration(≥20mmol·L^-1)on salt damage of E.angustifolia is reduced,and will even aggravate the degree of salt damage of E.angustifolia.