The Photosynthesis Mechanism Of Potassium Application In Saline-Alkali Land To Regulate Cotton Yield

Soil salinization severely limits land productivity and restricts the sustainable development of agriculture.As a crop with strong salt tolerance,cotton has been widely planted in saline-alkali areas.The presence of high Na+stress in the saline-alkali land leads to a low K+/Na+ratio in the soil,which limits the selective absorption of potassium by the cotton plant,resulting in a lack of potassium in the cotton plant,which seriously affects the increase in cotton yield.The leaf subtending the cotton boll(LSCB)is the main supplier of cotton boll nutrients,and its physiological characteristics directly determine the growth and development of cotton bolls.In order to explore the effect of potassium on the LSCB under the salt stress,field trials were conducted in the saline-alkali field in Dafeng,Jiangsu Province in 2017 and 2018.The experiment adopts the design of split area,the main treatment is the soil salinity content,the auxiliary treatment is the potassium application amount,and the auxiliary treatment is the variety.3 saline with low(EC=1.68～1.78 dS m-1),medium(EC=6.21～6.42 dS m-1),high(EC=10.59～11.08 dS n-1)and 3 potassium application rates(0,150 and 300 kg K2O hm-2)were set,the varieties are CCRI-79(salt-tolerant,birth period about 130 d)and Simian 3(salt-sensitive,birth period about 133 d).The purpose is to study the effects of potassium application in saline-alkali land on the physiological characteristics of LSCB and cotton yield,and to provide theoretical and practical basis for exploring saline-alkali land to increase cotton yield..The main findings are as follows:1.Effects of potassium application on cotton yield under salt stressThe decrease in the total boll number of cotton under salt stress is the main reason for the decrease in cotton yield.Potassium application of 150 and 300 kg hm-2 can alleviate medium salt stress.Under high salt stress,the yield of Simian 3 decreased by 30.1%～46.1%,and the yield of CCRI-79 decreased by 34.4%～65.3%.Seed cotton yield is basically negatively correlated with the Na+ content of cotton plants,and positively correlated with K+content and K+/Na+ratio.The yield of the salt-tolerant variety CCRI-79 is higher than that of the salt-sensitive variety Simian 3.2.Effects of potassium application on cotton plant biomass accumulation characteristics and K+and Na+ content under salt stressWith the increase of salt stress,the Na+content of cotton plants increased,and the maximum accumulation rate(Vm)and average accumulation rate(Vi)of cotton biomass during the rapid accumulation period showed a significant downward trend;with the increase of potassium application,the K+content of cotton plants,K+/Na+ratio increased significantly,Vm and Vt increased significantly;Vm and Vt of medium salt and high salt potassium treatments were significantly lower than that of low-salt potassium treatments.With the increase of salt stress,the proportion of reproductive organ biomass decreased significantly,and with the increase of potassium application,the proportion of reproductive organ biomass increased significantly;the proportion of reproductive organ biomass and its Na+content were basically significantly negatively correlated,while there were significant positive correlation with K+content and K+/Na+ratio.Salt stress increased the Na+content of the LSCB and reduced the accumulation of cotton boll biomass,especially fiber and cottonseed biomass;potassium application increased the K+content of the LSCB,increased the K+/Na+ ratio,and increased the proportion of cotton fiber biomass,Reduced the proportion of cotton seed biomass.The salt-tolerant variety CCRI-79 has a lower Na+content than the salt-sensitive variety Simian 3,with higher K+content and K+/Na+ ratio.CCRI-79 has a higher reproductive organ biomass and proportion.3.Effects of potassium application on photosynthesis of the leaf subtending the cotton boll under salt stressWith the increase of soil salinity,the content of Na+in LSCB increased significantly,the leaf area index,net photosynthetic rate and stomatal conductance decreased significantly,and the chlorophyll decomposition rate accelerated.Potassium application increased the leaf area index,increased K+content,and K+/Na+ Ratio of LSCB,slowing down the Pn and chlorophyll content.Salt stress significantly reduced the soluble sugar content of the LSCB,increased the sucrose and starch content,and reduced the boll weight.Potassium application promoted sucrose transport.The activities of phosphate sucrose synthase(SPS)and sucrose synthase(SuSy)increase with the increase of soil salt content,which was consistent with the change trend of sucrose,and the activity of soluble acid invertase(SAI)was the opposite.Potassium application increased the activity of phosphate sucrose synthase and sucrose synthase.K+/Na+ratio in LSCB of salt-sensitive variety Simian 3 was lower than that of the salt-tolerant variety CCRI-79,which has high chlorophyll content,Pn,and sucrose conversion rate resulting the biomass of CCRI-79 cotton bolls was greater than Simian 3.In summary,potassium application in saline-alkali land is beneficial to increase cotton yield and alleviate the effects of salt stress on the formation and translocation of photosynthetic products of LSCB.Potassium application increased the K+content,chlorophyll content,Pn,sucrose conversion rate,and SPS activity of LSCB,which was beneficial to the transfer of K+and photosynthetic products to cotton bolls,which not only increased the cotton boll biomass,but also reduced the cotton boll shedding rate.Eventually lead to the reduction in production.The salt-tolerant variety CCRI-79 cotton boll had higher K+/Na+ratio,Pn,sucrose conversion rate,boll weight and lower shedding rate,and the final yield was higher than the salt-sensitive variety Simian 3.