Effects Of Wood Vinegar And Humic Acid On Alleviating NaCl Damage To Cotton Seedlings

Salt stress drastically affects the plant growth and development in many crops including cotton,and wood vinegar and humic acid can improve the resistance of plants.It is of great significance to understand the mechanism of salt stress in cotton and to explore the corresponding mitigation measures for the sustainable development of cotton industry.The emergence,seedling establishment,growth,physiological and biochemical responses of cotton under NaCl stress（0,100,150,200,250 mmol/L）were investigated using HM3097 as planting material.Under 200 mmol/L NaCl salt stress,efficacy of wood vinegar（diluted 800,400,200,50 times）and humic acid（0.2,0.6,1.0,1.8 g/L）to alleviate salt stress in cotton was evaluated and mechanism behind the stimulation of stress mitigation was explored,which provided conceivable technical reference for saline-alkali cotton planting.The main results are as follows:1.Salt stress inhibited cotton emergence,seedling growth,and physiological processes.These inhibitory effects increased with the increasing concentration of salt and the duration of stress.With the increase of NaCl concentration,the seedling emergence rate decreased by more than 50%under 200 mmol/L NaCl stress,while the seedling height,stem diameter,leaf area,biomass,root surface area and root volume were gradually decreased.During early phase of salt stress,low concentration of NaCl resulted in longer roots formation,thus the mean root diameter decreased initially and then increased with the increasing NaCl concentration.The root/shoot ratio varied with increasing NaCl concentration,For first 5 days it showed a decreasing trend and after a slightly increased again declined from 10-15 days and eventually remained constant from20-25 days.The elevated salt stress also degraded leaf chlorophyll and carotenoid content,negatively affected Pn,Gs and Tr,while Ci decreased primarily and then increased.The NaCl-induced stress stimulated the production of H₂O₂,O₂^-,MDA and increased relative electric conductivity,Na⁺content and Na⁺/K⁺ratio in cotton leaf,enhanced the activity of SOD,POD,CAT and accumulated high concentration of soluble protein,soluble sugar,proline content in response to NaCl stress,However,the activity of SOD,CAT,and soluble protein and soluble sugar content reduced after reaching the maximum value at150 mmol/L NaCl stress.2.Wood vinegar and humic acid can effectively alleviate NaCl stress in cotton seedlings.Cotton seeds subjected to wood vinegar（200 times dilutions,W3）and humic acid（0.6 g/L,H2）priming,increased the emergence rate of seedlings by 72%and 69%,respectively under 200 mmol/L NaCl stress.The application of wood vinegar and humic acid has significantly increased the seedling height,stem diameter,leaf area,biomass,root/shoot ratio,root surface area,root volume and total root length,photosynthetic pigment content,enhancing Pn,Gs and Tr,SOD,POD and CAT activity,soluble protein,soluble sugar,proline and K⁺content.In addition,these treatments also reduced the accumulation of O₂^-and H₂O₂,MDA,Na⁺and finally minimized the relative electric conductivity in cotton leaves.In conclusion,salt stress inhibits seedling emergence and subsequent growth by disturbing the ion homeostasis of cotton seedlings and causes membrane lipid peroxidation,thus impairing photosynthesis.Soaking seed with wood vinegar and humic acid can improve the antioxidant enzyme activity and osmotic adjustment substance content,maintain the cell ion homeostasis and improve the photosynthetic capacity of of cotton seedlings,and finally alleviating the salt stress injury of cotton seedlings.