Study On Soil Salinization Characteristics And Salt Tolerance Of Main Cotton Varieties During Seedling Stage In Xiaohaizi Irrigation Area Of Xinjiang

Object:Aiming at the practical problems such as the wide distribution and large area of salinized soil,unclear salinization characteristics,and unclear salt tolerance of main cotton varieties（Tahe No.2,Xinluzhong No.56,Xinluzhong No.87）in Xiaohaizi Irrigation District,Xinjiang.In this study,through field sampling analysis,the type and degree of soil salinization were identified,and the current situation of soil salinization in Xiaohaizi Irrigation District was clarified.The response of growth physiological indexes of main cotton varieties to salt was studied by control experiments.Moreover,based on the characteristics of soil salinization and salt tolerance of cotton varieties,the best cotton varieties were recommended according to local conditions;This study provides a scientific basis for the selection of cotton varieties in Xiaohaizi Irrigation District and data support for water and salt management in cotton fields.Methods:This study was completed through field sampling analysis,seed germination test,salt tolerance threshold test and pot experiment.Soil salinization field sampling analysis was conducted in 2021.A total of 324 cultivated soil samples were collected from Xiaohaizi Irrigation District,and the total and partial salt contents were measured.The characteristics of cultivated soil salinization were determined by Kriging interpolation method.The variety germination test and pot experiment were conducted in 2022.The germination test used undisturbed soil leaching salt solution,set 12 salt gradients,and observed the germination rate of three main cotton varieties（Tahe No.2,Xinluzhong No.56,Xinluzhong No.87）on the3rd and 7th days respectively.The salt tolerance threshold test was conducted at eight different soil salt content levels,each treatment was repeated 3 times,and the dry matter mass was measured at the 55th day.The pot experiment set up four soil salinity levels:non saline soil(1 g·kg^-1),low salt(3 g·kg^-1),medium salt(4.5 g·kg^-1),and high salt(6 g·kg^-1).Cultivation,plant height,stem diameter,photosynthesis,and enzyme activity at the 75th day were measured.Result:（1）the distribution of salt in the Xiaohaizi Irrigation District generally followed a pattern of low in the southwest and high in the northeast,with 51st and 53rd groups being the most severely affected by soil salinization.Most areas of the 51st and 44th regiments,as well as some areas of the 50th and 53rd regiments,were dominated by chloride sulfated soil.At the junction of the 44th,50th,and 51st regiments,sulfated soil was distributed,while the majority of the 49th regiment was chloride saline soil.（2）Under different concentrations of salt solution stress treatment,the relative germination potential and germination rate of three cotton varieties showed a significant decreasing trend with the increase of salt solution concentration,while the relative salt damage rate significantly increased with the increase of salt solution concentration.Three varieties of cotton promoted the accumulation of aboveground dry matter mass at low salt levels,but exhibit significant inhibitory effects when the salt content exceeds 3 g·kg^-1.（3）The SPAD values of different cotton varieties significantly decreased with the increase of soil salt content,and decreased by 14%compared to CK treatment.The leaves of net photosynthetic rate（Pn）,stomatal conductance（Gs）,intercellular carbon dioxide concentration（Ci）,and transpiration rate（Tr）of various cotton varieties significantly decreased with the increase of soil salt content（4）Under salt stress treatment,the overall trend of changes in plant height and stem diameter of various cotton varieties was relatively consistent,and significantly decreases with the increased of soil salinity.The maximum reduction in plant height was observed in variety Z56,which decreased by 33%compared to CK treatment.The same reduction in stem thickness was observed in both Z56 and Z87varieties,both of which were 28%.（5）The MDA content,osmotic regulating substances content,and antioxidant enzyme activity of cotton leaves significantly increased with the increase of soil salt content.The cotton variety Z56 showed the greatest increase in leaves MDA content,POD activity,Pro content,and SS content,reaching 114%,165%,99%,and 123%,respectively.The varieties with the highest increase in leaves SOD and CAT activity were Z87 and TH2,which increased by 68%and 169%respectively compared to CK treatment.（6）The salt tolerance thresholds of TH2,Z56 and Z87 were calculated using regression equations to be 7.14 g·kg^-1(1.49 ds·m^-1),6.62 g·kg^-1(1.36 ds·m^-1),and 6.54 g·kg^-1(1.34 ds·m^-1),respectively.The results of ranking salt tolerance of three cotton varieties using the membership function method showed that TH2 had the strongest salt tolerance among the three varieties,followed by Z56,and Z87 had the worst salt tolerance.Conclusion:The relative germination potential and relative germination rate of various cotton varieties showed a significant decreasing trend with the increase of salt solution concentration,while the relative salt damage rate significantly increased.Under stress treatment with different concentrations of salt in soil,all three varieties of cotton showed a promotion of dry matter accumulation at low salt levels,while being significantly inhibited at high salt levels.Under salt stress,plant height,stem diameter,root morphological parameters,leaves SPAD value and photosynthetic gas exchange parameter value of cotton varieties were significantly reduced.The MDA content,osmotic regulating substances content,and antioxidant enzyme activity of cotton leaves showed a significant increase trend with the increase of soil salt content.Based on the above results,the salt tolerance of cotton varieties is TH2,Z56,and Z87 in sequence.