Effects Of Potassium Application On Cotton Seedling And Potassium Transport Capacity Of Fiber Elongation Under Salt Stress

Under the background of land competition between grain and cotton,it is gradually that cotton which as a pioneer crop planted in saline-alkali land concentrated in saline-alkali land.Due to the high salt content and low K⁺/Na⁺ratio in saline-alkali land,it is not conducive to crop production.Potassium application in saline-alkali land can effectively alleviate the sodium-induced potassium deficiency problem,promote the absorption and utilization of potassium,and reduce salt damage.Therefore,the study on the regulation mechanism of potassium application on cotton seedling and the potassium transport capacity of fiber elongation under salt stress and the physiological mechanism of alleviating cotton salt injury can provide a theoretical basis for optimizing cotton planting technology in coastal saline soil.The study mainly consists of two parts:1.CCRI 79（salt-tolerant）and Simian 3（salt sensitive）varieties were used as material,the sand culture method was adopted to set up four Na Cl levels(EC=1.3 d S m^-1,2.4 d S m^-1,4.7 d S m^-1,6.7 d S m^-1,the corresponding Na Cl were 0.1%,0.2%,0.4%,0.6%respectively)and seven K⁺/Na⁺ratio（1:4,1:3,1:2,1:1,2:1,3:1 and 4:1）to study the influence on cotton seed germination and their agronomic characters and physiological characteristics of cotton seedlings under different levels of K⁺/Na⁺ratio.2.The above two cotton varieties were used by setting potted experiment in saline-alkali land.Three soil salts(S1,EC=1.7～1.8d S m^-1;S2,EC=6.4～6.9 d S m^-1;S3,EC=10.6～11.8 d S m^-1)and three K application rates(0,150 and 300 kg K₂O ha^-1)was carried out to investigate the alleviating mechanism of potassium application on cotton yield and fiber length under salt stress.The results are as follows:1.Effects of potassium application on seed germination and seedling quality under salt stress（1）The germination rate of cotton seed was more favorable under 0.2%or less Na Cl treatments without potassium application,and the germination rate was very low under 0.4%Na Cl treatment or more.（2）Compared with other treatments,K⁺/Na⁺ratio of 2:1 under 0.1%Na Cl concentration and K⁺/Na⁺ratio of 1:2 under 0.2%Na Cl concentration had the best agronomic traits（root-shoot biomass,biomass per plant,leaf area per plant,SPAD value）.The content of soluble sugar and soluble protein in cotton seedling was the highest.The activities of SOD,POD and CAT were the highest,while the content of MDA was the lowest.The K⁺content and K⁺/Na⁺ratio in organ of cotton plant were maintained at a high level.The traits of the salt-tolerant variety CCRI 79 were better than that of salt-sensitive variety Simian 3.2.Effects of potassium application on cotton yield and fiber length under salt stress（1）Salt stress significantly reduced boll number and boll weight,thus reducing seed cotton yield which can be increased by applicating potassium under salt stress.With the increase of salt stress degree,the alleviating effect of potassium application weakened.Under S2 salt level,150 and 300 kg K₂O ha^-1 treatments could completely alleviate the yield decline caused by salt stress.The alleviating coefficient by 300 kg K₂O ha^-1treatment of boll number of CCRI 79 and Simian 3 were 89.8%and 65.1%,the alleviating coefficient of boll weight were 76.4%and 75.0%and which of seed cotton yield were 85.1%and 68.9%at S3 salt level.（2）The fiber length during fiber elongation stage and final stage decreased with the increase of salt stress,and the fiber length of lower fruit branch was significantly sensitive by salt.Potassium application increased the fiber length of each fruit branch under salt stress significantly,and the increase rate in lower and middle fruit branches was higher than that in upper fruit branches.With the increase of salt stress,the alleviating effect of potassium application on fiber length decreased significantly.Under S2 salt level,the fiber length remission coefficients of CCRI 79 and Simian 3 were 113.4%and 155.1%and 90.5%and 136.6%respectively under 150 kg K₂O ha^-1 and 300 kg K₂O ha^-1 treatments;Under S3salt level,the fiber length remission coefficients of CCRI 79 treated with 150 kg K₂O ha^-1and 300 kg K₂O ha^-1 were 40.1%and 60.4%respectively,and those of Simian 3 were 33.4%and 49.9%respectively.The fiber length remission coefficients of CCRI 79 treated with150 kg K₂O ha^-1 and 300 kg K₂O ha^-1 were 60.4%and 49.9%respectively.（3）During fiber elongation stage,salt stress reduced the contents of turgor pressure material which content sucrose and K⁺and increased the content of malate,while potassium application had a significant alleviating effect.The increase of potassium application was mainly concentrated before 15 d after anthesis.Compared with without potassium,the increase of tuger content decreased with the increase of the degree of salt stress.The activities of Susy enzyme decreased with the increase of salt stress,while the activities of PEPC,PPase and V-ATPase increased.They can reach the peak value at 15 d after anthesis,meanwhile 300 kg K₂O ha^-1 was more conducive to the increase of enzyme activity and thus to fiber elongation.3.Effects of potassium application on potassium transport capacity in leaf and boll system of cotton under salt stress（1）Salt stress significantly increased Na⁺content,reduced K⁺content and K⁺/Na⁺ratio in leaf and boll system of the two cultivars.However it is opposite after potassium application.The contents of K⁺and Na⁺in various organs showed a decreasing trend from fruit branch to parapatid leaf to boll shell to fiber,while the fiber energy kept a high K⁺/Na⁺ratio.The contents of K⁺and the ratio of K⁺/Na⁺ratio in leaf and boll system of CCRI 79 were higher than those of Simian 3,but the trend of Na⁺content was opposite.（2）There was a significant positive correlation between fiber length and K⁺content and K⁺/Na⁺ratio,and a significant negative correlation between fiber length and Na⁺content.The correlation coefficients between fiber length and K⁺content in fiber and boll shell,and K⁺/Na⁺ratio in boll shell and fruit branch were higher than those of other organs.（3）With the increase of salt stress,the transport capacity of K⁺(S_K+,Na+)from leaf and boll shell to fiber were decreased,while the S_K+,Na+from fruit branch to fiber increased continuously.Under salt stress,potassium application can promote the selective transport capacity of K⁺in all organs,but there is no significant difference between varieties.The S_K+,Na+from leaf to fiber are stronger than that of fruit branch and boll shell.In summary,the appropriate K⁺/Na⁺ratio under salt stress can improve the germination rate of cotton seeds and quality of cotton seedlings.Potassium application alleviated the yield and quality of cotton under salt stress to a certain extent.Potassium application increased the content of turgor substance,increased the activity of enzymes metabolizing turgor substance,decreased the content of Na⁺in leaf and boll system,increased the content of K⁺and K⁺/Na⁺ratio,promoted the transport capacity of K⁺and thus improved the fiber length.Under the condition of this experiment(300 kg N ha^-1),potassium application of 300 kg ha^-1 had a better alleviating effect on cotton yield and quality.The alleviating effect of potassium application on seedling quality,yield and quality of salt tolerant variety CCRI 79 was higher than that of salt sensitive variety Simian 3 under salt stress.