Physiological And Biochemical Responses To Mixed Saline-Alkali Stress Of ’junzao’ Jujube

In recent years,jujube cultivation has become an important industry for farmers to increase their income and wealth in Xinjiang,and soil salinization is a serious obstacle to sustainable development of agricultural in southern Xinjiang.In order to fully exploit the resource advantages of jujube and understand its physiological adaptation characteristics to mixed saline-alkali stress,this study took‘Junzao’at full fruit stage as material to study the mixed salt-alkali stress with different concentrations（Na Cl:Na HCO₃=3:1）on the physiological characteristics of‘Junzao’.By measuring the leaf structure,photosynthetic parameters,fluorescence parameters,antioxidant enzymes,osmotic regulatory substances and other indicators,the salt tolerance evaluation of‘Junzao’under different salt concentrations was analyzed by principal component analysis,and the salt tolerance mechanism of‘Junzao’was understood.The main findings of the study are as follows:（1）The microstructure and ultrastructure of chloroplasts were significantly damaged by high concentrations of mixed saline stress.Under mixed saline stress,the cuticle of the leaf was thickened,the epidermal cells were thinned as a whole,the cells were irregularly arranged and the spongy tissue cells were shortened.In addition,the vesicles were distorted and deformed,and the osmiophilic granules increased and became larger,appearing in heaps.The higher the stress concentration,the more severe the damage.（2）Under mixed saline stress treatment,the relative conductivity and malondialdehyde content of‘Junzao’leaves increased,and the Na⁺and K⁺content of the leaves increased.‘Junzao’plants reduce saline injury mainly through the synergistic effects of soluble sugars,soluble proteins and proline on each other,with soluble proteins playing the main osmoregulatory role in the early stages of stress,and the accumulation of soluble sugars and proline playing the main role in maintaining cellular osmotic pressure in the late stages of stress.Compared to SOD and CAT enzymes,POD enzymes show a more sustained role.（3）High concentrations of mixed salinity stress significantly reduced the chlorophyll content and photosynthetic and fluorescence parameters of‘Junzao’leaves.Mixed salinity stress had a certain inhibitory effect on net photosynthetic rate,stomatal conductance and transpiration rate of‘Junzao’.With increasing salt concentration,stomatal conductance of‘Junzao’leaves showed a decreasing trend,but intercellular CO₂concentration showed an increasing trend,and the decrease of net photosynthetic rate might be non-stomatal limitation.Fo increased significantly under high salt concentration treatments of240mmol·L^-1and 300mmol·L^-1,while Fm,Fv/Fm and Fv/Fo decreased significantly.The decrease in total chlorophyll content was mainly caused by the decrease in chlorophyll b content.（4）The 17 physiological indicators under each concentration of stress were subjected to principal component analysis.The results showed that the overall score of‘Junzao’under high concentration of mixed stress at 300mmol·L^-1was negative,and all salt treatments below 240mmol·L^-1were positive,indicating that 240mmol·L^-1is the critical concentration for‘Junzao’.（5）Mixed saline-alkali stress promoted‘Junzao’fruit colouration,reduced fruit hardness and increased the content of soluble sugars,organic acids,soluble protein and V_Cin fruit.