Salt Tolerance Analysis Of Different Ulmus Pumila Strains In Coastal Saline-alkali Land

The coastal area of salinized land is vast,soil salinity is high,vegetation is difficult to grow,restricting the local economic development and ecological construction.Using biological measures to improve saline-alkali land is the most lasting and effective way.Breeding and introducing salt-tolerant plants is the key to repair the coastal saline-alkali land.There were not only inter-species but also intra-species differences in the salt tolerance of plants,but also differences in the effect of saline-alkali land improvement.Ulmus pumila is one of the main tree species for afforestation in saline-alkali land in China because of its drought resistance and saline-alkali resistance.Five four-year-old U.pumila strains in natural habitats were selected as experimental materials.Field sampling and indoor testing were used to analyze the effects of different U.pumila strains on soil improvement and the distribution and migration of Na⁺,K⁺,Ca²⁺,Mg²⁺in various organs?roots,stems and leaves?.The differences of osmotic regulators,antioxidant enzymes and microanatomical characteristics of leaves and roots of different U.pumila strains were studied.Applying subordinate function and principal component analysis,the salt tolerance of five U.pumila strains was evaluated comprehensively.The results showed that:?1?U.pumila can improve coastal saline-alkali land and reduce the content of salt ions in soil.After planting U.pumila,the content of Na⁺in soil decreased by 50.4%-66.1%compared with that in control land,and the content of Cl^?was significantly lower than that in control land.The total salt content in soil of different U.pumila strains decreased by 55%-63.1%compared with that in control land,and the decrease range was No.30>112>105>34>5.The effect of No.30 and No.112 on saline-alkali soil improvement was better than that of other U.pumila strains.?2?Under salt stress,U.pumila accumulated Na⁺,K⁺,Ca²⁺,Mg²⁺preferentially in leaves,and maintained high K⁺/Na⁺,Ca²⁺/Na⁺,Mg²⁺/Na⁺ratios in leaves.Different U.pumila strains adapted to salt stress environment by establishing new ion balance.The ion absorption selectivity coefficients of U.pumila are S_Mg,Na<S_Ca,Na<S_K,Na.The absorption selectivity of Ca²⁺and Mg²⁺in U.pumila is lower than that of K⁺.Intraspecific differences among different U.pumila strains resulted in different selective abilities to absorb Na⁺,K⁺,Ca²⁺and Mg²⁺.Roots of No.5 had the strongest absorption ability to Ca²⁺,Mg²⁺,while roots of No.30 had the strongest absorption ability to K⁺.?3?There are significant differences among physiological indexes in leaves of different U.pumila strains.Under salt stress,U.pumila can resist salt damage by accumulating osmotic regulators such as proline,soluble sugar,soluble protein and increasing antioxidant enzyme activity,thus maintaining normal physiological activities and improving its salt tolerance.The contents of proline,soluble sugar,soluble protein and MDA in leaves of No.5 were the highest,while the activities of SOD,POD and CAT in leaves of No.34 with weak salt tolerance were the lowest.The activities of SOD,POD and CAT of No.30 and No.112 with strong salt tolerance were higher.?4?By changing the anatomical structure of leaves and roots,U.pumila alleviates the influence of physiological water shortage on itself in the salt stress environment,ensures its normal growth under the salt stress environment,and improves its adaptability to the salt stress environment.The anatomical structures of leaves and roots of different U.pumila strains were different,and the anatomical indexes of roots and leaves of No.112 were significantly higher than those of other U.pumila strains.?5?The salt tolerance of five U.pumila strains was evaluated by subordinate function method and principal component analysis with 47 indexes including ion content,physiological index and anatomical structure.The order of salt tolerance of five U.pumila strains was No.112>30>5>105>34.The salt tolerance of No.112 is the strongest among the five strains of U.pumila,and it is suitable for the priority selection of U.pumila for ecological restoration of coastal saline-alkali land.