Effects Of AMF On Soil Properties And Cotton Seedling Physiology Under Saline Alkali Stress

Objective:Soil salinization is one of the main abiotic stress factors limiting cotton yield and reducing cotton quality.Because the cotton seedling stage is not strong in salt and alkali resistance,it is necessary to enhance the salt and alkali resistance of cotton seedling stage and improve the saline-alkali soil environment,so as to improve the yield and quality of cotton.In this thesis,arbuscular mycorrhizal fungus（AMF）was used as a biological method to study the improvement of salt tolerance and soil environment in the root zone of cotton.Methods:In this study,three different AMF were inoculated into cotton under saline-alkali stress by pot experiment:Cystocystis mosaicus（Gm）,Rhizocystis（Gi）,and Saccharomyces penicillatus（Ge）.Using sterile substrate（Gx）as the control,the infection rate of three AMFs on cotton,root morphology of cotton flowers,root physiology and other indicators were analyzed,and the effects of different AMFs on cotton saline-alkali tolerance were compared,To screen the dominant strains symbiotic with cotton under saline-alkali stress.On the basis of this experiment,the dominant AMF was inoculated at the root of cotton with different concentrations of mixed saline-alkali stress,and the mixed saline-alkali concentration was set at 0,25,50,100,150 and 200 mmol/L,taking the non-inoculation treatment as the control.Through the analysis of cotton morphology,cotton physiology,and the physical and chemical properties of rhizosphere soil,the mechanism of AMF improving the salt and alkali tolerance of cotton seedlings was revealed,which provided a basis for improving the salt and alkali tolerance of cotton and the utilization of saline and alkaline land in Xinjiang.Results:（1）Compared with the treatment without inoculation of AMF,the inoculation of AMF increased the content of osmotic regulating substances,antioxidant enzyme activity and nutrient content of roots.Under saline-alkali stress,inoculation with AMF could reduce soil salt content.Under saline-alkali stress,the infection rate and mycorrhizal dependence of cotton roots inoculated with Gm were significantly higher than those of Ge and Gi treatments.Inoculation with Gm can significantly increase root activity,root water content,osmotic regulating substances,antioxidant enzyme activity and soil nutrients under saline-alkali stress,and significantly reduce soil salt content.Inoculation with Gi can significantly improve root activity,root water content,osmotic regulating substances,POD activity,CAT activity and soil nutrients.The soil conductivity was significantly reduced.Inoculation with Ge could significantly increase the root osmoregulation substances,antioxidant enzyme activities and soil nutrients under saline-alkali stress,and significantly reduce the soil salt content.According to the analysis of membership function,Gm has the best comprehensive performance on the salt and alkali tolerance of cotton seedlings.（2）Inoculation with AMF significantly reduced the soil p H under 100,150 and 200 mmol/L saline-alkali stress concentrations.With the increase of saline-alkali stress concentration,the effect of inoculation of AMF on the reduction of soil conductivity is more significant.Inoculating AMF significantly increased the content of K⁺,Ca²⁺,Mg²⁺and other cations,and decreased the content of Na⁺,Cl^-,HCO₃^-plasma.When the concentration of saline-alkali stress was 50 mmol/L and 100 mmol/L,inoculation of AMF significantly increased the content of soil alkali-hydrolyzable nitrogen.With the increase of saline-alkali stress concentration,the content of soil available phosphorus,available potassium,organic matter,soil sucrase activity and soil urease activity showed a downward trend under inoculated and uninoculated conditions,while the catalase activity showed an overall upward trend.Through comprehensive index analysis,it can be concluded that AMF has the greatest effect on improving soil quality when the concentration of saline-alkali stress is 200 mmol/L.（3）The infection rate of cotton roots gradually decreased with the increase of saline-alkali stress concentration,and the mycorrhizal dependence increased with the increase of saline-alkali concentration.Inoculation with AMF significantly reduced the electrolyte permeability and malondialdehyde content of cotton roots under saline-alkali stress,and significantly increased the content of root osmoregulation substances.With the increase of saline-alkali stress concentration,the activities of SOD,POD and CAT in the roots of cotton seedlings without inoculation increased at first and then decreased.Saline-alkali stress increased the activities of antioxidant enzymes in cotton roots,and inoculation with AMF significantly increased the activities of SOD,POD and CAT in cotton seedling roots.The comprehensive index analysis showed that AMF had the best effect on alleviating cotton saline-alkali stress injury when the concentration of saline-alkali stress was 200 mmol/L.（4）Inoculation of AMF can significantly promote the growth and development of cotton.Under various saline-alkali stress treatments,inoculation of AMF can significantly improve the morphology of cotton seedlings and the content of C,N and P in cotton seedlings.Under saline-alkali stress,inoculation of AMF could significantly reduce the Na⁺content of different organs of cotton seedlings,as well as Na⁺/K⁺,Na⁺/Ca²⁺,Na⁺/Mg²⁺,and significantly increase the K⁺,Ca²⁺,and Mg²⁺content of different organs of cotton seedlings.The inoculation of AMF reduced the Na⁺content of cotton roots by 32.7%-46.7%.The comprehensive index analysis showed that AMF had the best effect on promoting leaf nutrient accumulation in cotton under saline-alkali stress concentration of 100mmol/L,and had the best effect on nutrient accumulation in stems and roots under saline-alkali stress concentration of 150mmol/L.Conclusion:Inoculating AMF can significantly promote the growth and development of cotton.Inoculating three kinds of AMF can alleviate the damage of saline-alkali stress on cotton seedlings,and Gm has the best effect on alleviating the stress.Compared with the treatment without inoculation,the inoculation of AMF significantly reduced the content of soil Na⁺,Cl^-,HCO₃^-,and increased the content of soil nutrients,K⁺,Ca²⁺,Mg²⁺and soil enzyme activity.With the increase of saline-alkali stress concentration,the AMF infection rate of cotton roots decreased and the mycorrhizal dependence increased.Inoculating AMF can reduce the membrane lipid peroxidation of cotton roots,increase the activities of osmoregulation substances and antioxidant enzymes in cotton roots,and thus eliminate reactive oxygen free radicals to reduce cell permeability.With the increase of saline-alkali stress concentration,the nutrient content of cotton roots,stems and leaves decreased.Inoculating AMF can effectively alleviate the damage of Na⁺on cotton and the inhibition of Na⁺on K⁺,Ca²⁺and Mg²⁺.Through comprehensive index analysis,it can be concluded that the effect of AMF inoculation on soil quality improvement and alleviating the saline-alkali stress injury of cotton roots is the best under S200 treatment,the effect on promoting leaf nutrient accumulation is the best under S100 treatment,and the effect on stem and root nutrient accumulation is the best under S150 treatment.