Effects Of Potassium On Cotton Fiber Development Under Salt Stress

Soil salinity limits the development of saline soil agriculture in China severely.Saline-alkali land has high salt content and too low potassium-to-sodium ratio,which seriously affects the normal nutrient absorption and metabolic function of the root system,leading to a significant reduction in crop yield and quality.As a pioneer crop,cotton has strong salt and alkali tolerance for development and utilization.Proper potassium nutrition is a guarantee of high yield and quality of cotton which has strong dependence on potassium.Applying potassium on saline land can effectively alleviate sodium-induced potassium deficiency,promote the absorption and utilization of potassium and reduce salt damage in cotton.Therefore,the research on potassium regulating cotton fiber development,affecting yield and quality and clarifying the physiological mechanism of potassium relieving salt damage of cotton under salt stress can contribute to the development of cotton planting in saline land in China.This experiment was performed at the original rice and wheat seed field(120°46′E,33°20′N)in Dafeng,Yancheng,Jiangsu.Cotton cultivar tested were Simian 3(salt-sensitive)and CCRI-79(salt-tolerant).Three potassium(K2O)supply treatments(0,150,300 kg hm-2)under three soil salinity levels(Low salinity,EC=1.68～1.78 dS m-1;Medium salinity,EC=6.21-6.42 dS m-1;High salinity,EC=10.59～11.08 dS m-1)which consist of three soils with similar texture and nutrients were applied to explore the physiological mechanism of potassium regulating fiber development under salt stress,the main results for this study are as follows:1.Effects of potassium on cotton yield and fiber quality under salt stress(1)The salt stress significantly reduced the boll number and boll weight of cotton,eventually reducing yield,and the yield decline increased with the deepening of the salt stress.The reduction of yield under salt stress was completely alleviated by applying potassium to middle salt.K300 treatment had a better mitigation effect on cotton yield under high salinity,with a maximum of 59.1%～65.3%of CCRI-79.(2)Cotton fiber quality deteriorates due to salt stress,while potassium improves fiber quality.With the deepening of salt stress,the mitigation effect of potassium on fiber length and strength decreased significantly,especially at K300 treatment.The maximum degree of relief of fiber length and strength under high salinity was 51.1%～60.0%and 29.8%～40.6%of CCRI-79 respectively.High salt stress is still the main factor restricting fiber yield and quality improvement.The effect of potassium on the yield and quality of salt-tolerant cultivar CCRI-79 is better than that of salt-sensitive cultivar Simian 3.2.Effects of potassium on cotton fiber elongation development under salt stress(1)Salt stress decreased the maximum velocity of fiber elongation(Vmax)which had a significant positive correlation of fiber length.Potassium application promoted the increase of Vmax,improved fiber length and alleviated salt stress by increasing Vmax.The increase of Vmax of potassium on CCRI-79 was greater than that of Simian 3 under salt stress.(2)As main fiber osmotic substance,soluble sugar and K+content decreased,while malate increased by salt stress.Potassium increased the content of osmotic substances under salt stress,and the increase of K+content of fiber was much higher than that of soluble sugar and malate.Potassium application can increase the activities of PEPC,V-ATPase,PPase,and PM H+-ATPase,increase the cell turgor and promote the fiber elongation development by increasing the content of osmotic substance K+in the fiber under salt stress.(3)There was positively correlation between the fiber length and Vmax,so as the ratio of potassium-sodium.3.Effects of potassium on thickening development of cotton fiber under salt stress(1)Salt stress significantly reduced the strength of cotton fiber.The effect under medium and high salt on fiber strength was alleviated by potassium,but there was no significant difference between 150 and 300 kg·K2O·hm-2.The alleviation coefficient of potassium on fiber strength under high salt stress was up to 29.8%～40.6%.The effect of potassium on the fiber strength of CCRI-79 was better than that of Simian 3.(2)Salt stress reduced the accumulation of cellulose during the thickening stage,fiber sucrose was reduced while the content of callose was increased;The maximum accumulation rate of cellulose,the activity of sucrose phosphate synthase and β-1,3-glucanase at 28 DP A were increased by potassium application,which increased the content of sucrose and callose.With the aggravation of salt stress,the alleviating effect of potassium gradually weakened.The maximum accumulation rate of cellulose and the increase of β-1,3-glucanase activity in CCRI-79 were higher than those in Simian 3.In conclusion,soil salt stress will cause a decline in cotton yield and quality,and potassium application under salt stress will improve yield and quality to a certain extent.K300 has a better relief effect on yield and quality.The effect of potassium application on the yield and quality of CCRI-79 under salt stress was higher than that of Simian 3.