The Effects of Salt Stress on Chlorophyll Fluorescence of Cotton Seedling Leaves

【Objective】 To study the effects of salt stress on chlorophyll fluorescence characteristics of cotton seedling leaves, and it provides reference for salt stress to inhibit the physiological process of cotton seedlings. 【Method】 Using “Xinluzhong 37” as the experimental material in the artificial climate chamber, the changes of chlorophyll fluorescence parameters in cotton leaves were analyzed with four salt concentrations of 50, 100, 150 mmol/L and 200 mmol/L and Hoagland nutrient solution as the control treatment (CK). 【Result】 Results showed that the relative chlorophyll content (SPAD), maximum quantum efficiency (Fv/Fm), actual quantum efficiency (Y(II)) and photochemical quenching (qP) of cotton leaves in the treatment of 50 mmol/L were close to or lower than those values in CK, The maximum fluorescence (Fm) was slightly higher than that of CK, but the SPAD Fv/FmY(II) and other parameters were significantly decreased under 100~200 mmol/L salt treatment, and (Y(II)) showed a decreasing trend under 200 mmol/L salt treatment. However, the excess light energy ((1-qP)/NPQ) and non-photochemical quenching parameter NPQ of 100~200 mmol/L high salt treatment were significantly increased by 21.5%, 25.7%, 43.3% and 6.4%, 20.8% and 23.8%, respectively, compared with the control treatment. However, there was no significant difference between 50 mmol/L low salt concentration treatment and the control treatment. 【Conclusion】 Cotton can avoid the damage of light reaction system through its own regulation mechanism in the low salt concentration of 50~100 mmol/L. When the salt concentration reaches 150 mmol/L, the light emission and electron transfer of cotton leaves are blocked, resulting in the significant decrease of light energy utilization efficiency of cotton leaves, and finally limiting the plant growth.