Study On Physiological Adaptation Of Three Fraxinus Chinensis Clones Under Salt And Drought Stress

As the main afforestation tree species in coastal saline-alkali land in my country,Fraxinus velutina has strong salt tolerance and drought tolerance.To study the physiological and biochemical reactions of F.velutina under salt and drought stress,to clarify the salt-tolerance mechanism of F.velutina The physiological adaptability of the three clones of F.velutina to salt and drought stress was compared by pot experiment.In this experiment,three F.velutina clones（Lula 2,Yanla 2,Lurong 3）were used as the research objects,and the salt stress gradient was set as 1‰（T1）,3‰（T2）,5‰（T3）,7‰（T4）;drought stress gradient is mild stress（B）55%-60%,moderate stress（C）40%-45% and severe stress（D）30%-35%,analyzed the changes of growth index,photosynthetic index,physiological index and root index under salt and drought stress,and discussed the effect of salt and drought stress on the growth of F.velutina.Using the membership function method,the stress resistance of three F.velutina clones to salt and drought stress was compared.The main findings are as follows:In terms of growth performance,under severe drought,Lula 2 and Yanla 2 began to die under the salt stress of T3（5‰ salt）,and Lurong 3 was under T2D（3‰ salt,severe drought）treatment at this time.The mortality rate reaches 30%.The mortality of Lurong 3 under the same stress was higher than that of Lula 2 and Yanla 2;under5‰ and 7‰ heavy salt stress,the three white wax clones under partial drought treatment The mortality rate reached 100%,indicating that the severe salt-drought double stress inhibited the growth of F.velutina,and the inhibition degree was higher than that of single salt stress or drought stress.With the increase of salt concentration and the aggravation of drought,except for T1B（1‰ salt,mild drought）,T1C（1‰salt,moderate drought）,T2B（3‰ salt,mild drought）treatments,the seedling height,ground diameter and biomass were all inhibited,and the degree of inhibition became more obvious with the extension of time.The root-shoot ratio increased with the increase of the stress degree,and increasing the input to the root system may be one of the important countermeasures for F.velutina Analysis of variance showed that there were significant differences in seedling height growth,ground diameter growth and biomass among the three F.velutina clones.Judging from the performance of the overall seedling height and growth,Yanla 2 > Lula 2 > Lurong 3.Judging from the performance of ground diameter growth and biomass,Lula 2 > Yanla 2 > Lurong 3.The chlorophyll of the three F.velutina mild water stress could alleviate the inhibition of salt stress on F.velutina;under severe salt stress,drought treatment aggravated the inhibition of chlorophyll synthesis of the three F.velutina clones.The main factor of photosynthetic limitation under mild salt-drought stress was non-stomatal limitation of the three F.velutina clones,and the main factor of photosynthetic limitation under severe salt-drought stress was stomatal limitation.The photosynthetic rates of the three F.velutina clones were significantly different.The chlorophyll content and photosynthetic rate were in the order of Lula 2> Yanla 2>Lurong 3.Under salt stress,drought stress and double stress,the membrane permeability and MDA content of the three F.velutina Under mild stress,the activities of SOD and POD of F.velutina showed an upward trend,which strengthened the scavenging ability of protective enzymes to reactive oxygen species and prevented further damage to cell membranes by free radicals.With the increase of the stress level,the enzyme activities of the three F.velutina.With the increase of salt and drought stress and the prolongation of time,the contents of proline,soluble sugar and soluble protein in the three F.velutina clones continued to increase.The content of osmotic adjustment substances under the dual stress of salt and drought was higher than that under the single stress,reflecting the cross adaptability.The decreasing trend of soluble sugar content under severe dual stress may be due to the reduction of photosynthetic rate and the reduction of dry matter content produced in the body,resulting in the reduction of soluble sugar.Na+showed an upward trend with the increase of salt concentration,and K+/Na+ showed a downward trend with the increase of salt concentration.Salt stress had a significant effect on Na+ and K+/Na+,while drought stress and salt-drought cross stress had no significant effect on Na+ and K+/Na+.Fuzzy membership function analysis method was used to comprehensively evaluate the salt and drought resistance of 3 F.velutina clones on 12 indicators such as growth,physiology and biochemistry is Lula 2>Yanla 2>Lurong 3.To sum up,the three F.velutina clones had similar adaptation modes under salt and drought stress,but there were differences in their adaptability.The growth of F.velutina seedlings was inhibited by both salt stress and drought stress.Under the dual stress of mild salt and drought,F.velutina seedlings showed cross-adaptability.Appropriate water stress could improve the salt-tolerance of F.velutina.