Effects Of NaCl Stress On Photosynthesis And Chlorophyll Fluorescence Characteristics Of Artemisia Argyi Leaves

Soil salinization has become a worldwide problem,and China is one of the countries with serious salinization problem.The total area of salinization soil is about 36 million hectares,accounting for about 5.0%of the available land area in China.Soil salinization can affect plant growth and yield,and salt stress can affect plant absorption of water and fertilizer and photosynthesis,thus affecting plant anabolic substances and their growth and development.Artemisia argyi（Artemisia argyi Lévl.et Van.）is a perennial herb of Artemisia in the asteraceae family.In order to explore the changes of photosynthetic physiology of Artemisia argyi under NaCl stress,this study was based on Qiai and Longcao Artemisia argyi seedlings as experimental materials,with 5 concentrations of NaCl stress treatment of 0,50,100,150,200 mmol/L,with its normal growth of two kinds of Artemisia argyi as the control group,to determine the photosynthetic parameters and physiological and biochemical indicators of artemisia argyi.The results of this study could provide evidence and reference for further understanding the photosynthetic capacity and productivity of Qicao wormwood and Longcao wormwood under salt stress,and for its planting,management and cultivation.The results are as follows:（1）NaCl stress can reduce the photosynthesis of wormwood leaves.When NaCl stress intensified,the transpiration rate（T_r）,net photosynthetic rate（P_n）,stomatal conductance（G_s）and instantaneous carboxylation rate（CUE）showed a gradual decrease,while the water use efficiency（WUE）and intercellular CO₂（C_i）showed an increasing trend.With the increase of NaCl concentration,the stomata of Artemisia sinensis leaves gradually closed,and T_r and G_sshowed a decreasing trend.When NaCl concentration was 0-150 mmol/L,C_i showed a decreasing trend,L_s showed an increasing trend.Stomata factor was the main reason for the decrease of photosynthetic efficiency of Artemisia sinensis.When NaCl concentration was200 mmol/L,C_i increased,L_s decreased,G_s and C_i showed an opposite trend,and non-stomatal factors were the main reason for the decrease of photosynthetic efficiency of Artemisia Argus,which might be caused by the destruction of its photosynthetic system.（2）The chlorophyll fluorescence properties of wormwood leaves were inhibited by NaCl stress.With the intensification of NaCl stress,the initial fluorescence（F_o）of two kinds of Artemisei showed an increasing trend,while the maximum fluorescence（F_m）,actual photochemical efficiency(Φ_PSⅡ),potential photochemical efficiency（F_v/F_o）,maximum photochemical efficiency（F_v/F_m）and photochemical quenching（q P）showed a decreasing trend,and the two kinds of artemisei showed a photoinhibition phenomenon.These results indicated that NaCl stress would accelerate the closure of PSII reaction centers in the two kinds of Artemisium artemisium leaves,resulting in the decrease of F_v/F_m,Φ_PSⅡand electron transport activity.At the same time,the non-photochemical quenching（NPQ）of the two kinds of wormwood increased,indicating that NaCl enhanced the heat dissipation ability of wormwood leaves and alleviated the damage to the photosynthetic system.（3）NaCl stress will cause oxidation and osmotic stress in wormwood.With the increase of NaCl concentration,malondialdehyde（MDA）content in wormwood leaves increases.Wormwood can resist osmotic and oxidative stress by increasing the contents of soluble protein（SP）and soluble sugar（SS）and the activity of antioxidant enzymes.At 0-150 mmol/L,the contents of catalase（CAT）and peroxidase（POD）in two kinds of wormwort increased with the intensities of NaCl stress.When NaCl concentration exceeded 150 mmol/L,the activities of CAT and POD in two kinds of wormwort leaves decreased.At this time,the high concentration of NaCl damaged the antioxidant system of the two kinds of wormwood and broke the balance of their systems.