Effects Of Photosynthetic Characteristics Of Cotton To Salinity Stress Determined By FvCB Model

Cotton is an important economic crop and a pioneer crop in saline-alkali land.While cotton growth and yield formation are often limited by water and salt stress.Therefore,it is of great significance to investigate effects of salinity stress on photosynthetic and biochemical process of cotton to reveal the salt tolerance mechanism and ensure the high and stable yield.The pot experiments were conducted in a climate-controlled chamber and under rainproof shed,and designed with 5 leves of salt stress.In this study,the effects of salt stress on photosynthetic characteristics of cotton were systematically investigated with the FvCB model,the response of Na⁺/K⁺ratio and nitrogen content in cotton leaves to salt gradient was analyzed,the effects of salt stress on photosynthetic parameters such as carboxylation rate,electron transfer rate and mesophyll conductance were discussed,and the quantitative relationships between photosynthetic parameters,nitrogen content,Na⁺/K⁺ratio in cotton leaves were established.The main conclusions are as follows:?1?Under salt stress,cotton leaves protected PSII activity to maintain normal growth by increasing the dissipation of excess light energy.The non-photochemical quenching parameters?qN,NPQ?of cotton leaves in the climate-controlled chamber increased with the increase of salt concentration and the NPQ value significantly increased in the treatment of150 and 200 mmol·L^-1 salt concentration.The photochemical quenching parameters?qP?in cotton leaves was reduced by salt stressand the significant decrease of qP was measured in the treatment of 100-200 mmol·L^-11 salt concentration.Salt stress significantly limited the maximum photosynthetic efficiency?F_v/F_m?of photosystem II in cotton leaves.The 150 and200 mmol·L^-1 salt concentration significantly decreased the actual photosynthetic efficiency?Y?II??,while increased the excess light energy parameter?1-qP?/NPQ.However,the response of chlorophyll fluorescence parameters to salt stress in pot-planted cotton was not significant,which may be due to role of the soil characteristics and microclimate environment in alleviating the inhibition of salt stress.?2?Salt stress limited the photosynthetic rate,but the limiting factors of salt stress were different in different environments.The results obtained from the climate-controlled chamber showed that the maximum salt tolerance threshold of cotton ranged between 100 and150 mmol·L^-1.When the salt concentration was low,the photosynthetic characteristics of cotton leaves were limited by stomata.As increasing salt concentration,the photosynthetic characteristics of cotton leaves were gradually limited both by stomata and mesophyll,and finally by stomata,mesophyll and carboxylation.The experiments of rainproof shelter showed that the net photosynthetic rate and stomatal conductance of cotton grown in sand decreased with the increase of salt concentration,and the photosynthesis of cotton under the salt concentration of 8 g·L^-11 was restricted by stomata;The response of photosynthetic parameters to salt stress of cotton grown in loam was not significant,because limitation of sality stress on cotton was different in different soil textures.?3?The contents of nitrogen,K⁺and Na⁺in cotton leaves were significantly affected by salt stress and correlated with photosynthetic parameters of leaves.The nitrogen content of cotton leaves grown in sand soil under rainproof shelter and the in climate-controlled chamber decreased gradually with the increase of salt concentration,while the leaf nitrogen content of cotton grown in loamy soil under rainproof shelter changed as a curve with single peak in response to salinity stress.Compared with CK,salt stress significantly reduced K⁺content and increased Na⁺content in cotton leaves grown in climate-controlled chamber.The content of K⁺and Na⁺in pot-planted cotton leaves in loamy soil increased firstly and then decreased with the increase of salt concentration,and the contents of Na⁺and K⁺changed at 4 g·L^-1 and6 g·L^-1 respectively;the content of K⁺of cotton leaves in the pots with sand soil had no significant change in response to salt stress,while the content of Na⁺significantly increased.Under the condition of salinity stress,there was a quadratic relationship between leaf nitrogen content,ion content and photosynthetic parameters?maximum electron transfer rate,maximum carboxylation rate and mesophyll conductance?.Multiple regression analysis indicated that there was a significant linear correlation between the net photosynthetic rate and the nitrogen content of cotton grown in sand soil under the rainproof shed and the climate-controlled chamber,but the fitting parameters of K⁺/Na⁺factor were not significant.There was also a linear correlation between the net photosynthetic rate and the nitrogen content of cotton leaves grow in loamy soil under rainproof shelter,but the fitting parameters were not significant.