Investigation On Physiological Response And Tolerance Characteristics Of Different Varieties Of Willow Seedlings To Salt Stress

Soil salinization is one of the most important environmental problems in the world.The salt ions in soil mainly inhibit the growth and development of plants through osmotic stress and ion toxicity,resulting in the decrease of their productivity.In the current,the phytoremediation is one of the most economic and efficient land amelioration measures and the screen of salt-tolerant plant is a key for the vegetation restoration.Three willow seedlings—Salix matsudana’Wuxu1’,Salix matsudana’Shidi1’and Salix matsudana‘J172’—are selected as materials to compare their morphological adaptation,physiological response and salt tolerance mechanism under the stress of gradient NaCl and analyze the differences and regular characteristics of their salt tolerance.Besides,combined with five methods of salt tolerance evaluation,the salt tolerance of the three willow seedlings under different salt concentrations was ranked.Based on these,it can be concluded as follows:1.The biomass of the three willow cultivars under NaCl gradient stress decreased gradually with the increase of salt stress,and all showed negative growth under the highest concentration of NaCl.The aboveground/underground values also showed a general downward trend,and most of the photosynthetic parameters were gradually decreased under the influence of increasing salt concentration.However,the photosynthetic rate of’Shidi1’was basically unchanged,and the biological growth was also the maximum of the three varieties.The stomatal factor not was the limiting factor of photosynthesis.The photosynthetic pigments of‘Shidi1’and’Wuxu1’were opposite to those of’J172’.2.The cell damage marker—relative conductivity and MDA—increased with the increase of NaCl stress to varying degrees.The changes of H₂O₂ in the three cultivars were different.Gradient NaCl stress triggered the response of antioxidant enzyme system.SOD,CAT,POD,APX and GR antioxidant enzymes cooperated to remove reactive oxygen species.However,under high salt concentration,the activities of all the measured enzymes decreased to different degrees,except for CAT in the root.Compared with’Shidi’、’J172’,’Wuxu1’had the most active enzyme defense system.3.The roots and leaves of the three willow cultivars regulated osmotic pressure through accumulation of soluble protein and soluble sugar to reduce osmotic potential of plant somatic cells,thus improving the water-holding capacity and water absorption capacity of cells;while,free proline only acts as an osmotic regulator of’Shidi1’in the root,implying’Shidi1’was different in modulation mechamism from the other two varieties.4.The capacity of’Wuxu1’of accumulation and restriction of Na⁺transport to the aboveground was not as good as that of’J172’and’Shidi1’,but it could balance Na⁺by increasing K⁺uptake in the root,and reduce the damage caused by salt stress by enhancing the absorption of Ca,Mg,Fe and Zn.The good salt tolerance of’Shidi1’was related to the restriction of Na⁺transfer to the aboveground and the balance of Na⁺salt damage by the increase of K⁺content in leaf roots.The above ground storage capacity of’J172’was higher by isolating Na⁺in vacuoles and stems,and the accumulation of Mg²⁺and Ca²⁺in roots was one of the mechanisms of salt tolerance.5.Combined correlation analysis,entropy weight,principal component,clustering four analysis methods with regression equation,considering the accessibility of data at the same time,the stomatal conductance,soluble protein,free proline and relative electric conductivity of leaf can be chosen as willow seedling salt resistance main appraisal indicators.At the same time,element content of Ca,Fe,Zn in blade can be used as a supplement for the important reference index of salt resistance.6.Based on 26 salt tolerance indexes of willow leaves,five objective analysis methods,namely membership function method,equal weight grey correlation analysis,entropy weight grey correlation analysis,principal component analysis,and principal component-grey correlation analysis,were used to analyze the three willow seedlings at different NaCl concentrations.According to the five evaluation methods,’Wuxu1’has the best salt tolerance,followed by’Shidi1’、’J172’.However,in terms of the conventional evaluation criteria of salt tolerance,such as the net photosynthetic rate of biological growth and the restricted absorption of Na⁺,’Shidi1’present the better performance in resisting salt stress.But,in terms of the storage capacity of Na⁺in the aboveground,the’J172’variety has the most advantage.Considering the practical application value in salt-tolerant willow tree species selection,‘Shidi1’and’Wuxu1’as excellent germplasm resource can be applied to a high concentration of salt in the practice of land use,and’J172’is more suitable for low salt concentration of green vegetation and soil improvement.Three willow varieties are available for salt tolerance breeding and salt resistance mechanism research to provide material support.The Principal component-grey correlation analysis used for an evaluation method of salt tolerance of plants is scientific and pratical,and can be used as one of the alternative methods for comprehensive evaluation of salt tolerance of willow seedlings...