Alleviative Effects And Its Mechanism Of Exogenous Arbuscular Mycorrhizal Fungi (AMF) On Watermelon Seedlings Under Salinity-Alkalinity Stress

Soil salinization has become one of the soil environmental disasters of great concern in China and even in the world.China's saline and alkaline land area is about 1 million hm²,which is widely distributed in northern China and coastal areas.Salinity-alkalinity is the main abiotic stress that restricts plant growth and reduces crop yield.With the continuous deterioration of the global climate environment,this figure is likely to continue to increase,making salinity become another major environmental problem restricting agricultural production.Watermelon rich in nutrition,is an important economic horticultural crop.However,with the continuous expansion of the greenhouse area,soil secondary salinization is continuously aggravating,which seriously affects the yield and quality of the facility watermelons.It has become an urgent problem to be solved to restrict the development of the vegetable.Arbuscular Mycorrhiza?AM?can symbiotic with plants in nature.Its essence is the reciprocal symbiosis established between Arbuscular Mycorrhizal Fungus?AMF?in soil and host plants.After AMF infects plant root system,it can participate in plant physiological and biochemical metabolism,improve plant nutrition and enhance plant stress resistance.In this study,the watermelon variety"fuyunlai"was used as the material and the method of substrate soil cultivation was adopted,and 4 treatments were set in the experiment:?1?CK?control,no AMF?;?2?S?saline-alkali stress?;?3?M?inoculated with AMF?;?4?MS?inoculated with AMF+saline-alkali stress?.The concentration of salinity-alkalinity mixture was 60 mmol·L^-1,and the formula was as follows:NaCl,Na₂SO₄,NaHCO₃ and Na₂CO₃ salts were mixed at 1:9:9:1,pH was 8.63,and EC was 0.45 ms/cm.To study the effect of salinity-alkalinity stress under the condition of inoculation Moses balloon mold?G.mosseae?on the growth of watermelon seedlings,water and nutrient absorption,chlorophyll content,photosynthetic characteristics,xanthophyll cycle,D1 protein turnover,root system secretions,root zone environment and watermelon yield and quality,etc.To investigate the effect of AMF inoculation on watermelon plants under salinity-alkalinity stress and the mechanism of increasing yield and quality.The main results are as follows:1.AMF inoculation can improve the salt tolerance of watermelon seedlings,including G.mosseae had the best effect.Compared with non inoculated watermelon seedlings inoculated with AMF watermelon induced by salt and alkali resistance increased mainly in mycorrhizal watermelon significantly reduced the salt injury index,increase the amount of dry matter of plants,and promote plant growth;watermelon can significantly improve the plant height and leaf area,ensure the normal physiological metabolism;to the accumulation of soluble sugar and soluble protein,improve osmotic adjustment ability;can increase the chlorophyll content and polyphenol content,promote photosynthetic efficiency and plant resistance;can activate SOD,CAT and POD activity,remove ROS and alleviate membrane peroxidation.2.Salinity-alkalinity stress significantly inhibited the growth of watermelon seedlings inoculated with AMF,can stem the flow of Watermelon Leaves and plant water use efficiency,improve the absorption of water.Inoculation of AMF through the promotion of mineral elements in the watermelon plant root absorption,improve seedling growth of underground part to alleviate the harm of plants inoculated with AMF.Stimulation of photosynthetic products transferred to root carbohydrates,the formation of carbon in roots.AMF inoculation stimulated brassinosteroids and zeatin riboside in plant root generation;at the same time promoting saline conditions,synthesis of plant leaves and decreased the content of gibberellin,auxin and abscisic acid in leaves,by adjusting the hormone levels in plants to improve plant resistance,alkali stress.3.With AMF O₂^-and H₂O₂ content on salinity-alkalinity stress of watermelon leaves increased,higher levels of ROS increased lipid peroxidation,MDA content increased,the electrolyte leakage rate increased significantly.Salinity-alkalinity stress also induced SOD,CAT,APX,GR,MDHAR and antioxidant enzyme activity,ASA DHA,GSSG,GSH and antioxidant content,and soluble sugar,soluble protein,proline and other major osmolyte accumulation.Watermelon seedlings inoculated with AMF increased the activity of antioxidant enzymes,antioxidant contents and accumulation of osmotic adjustment substances,thereby reducing the level of ROS,reduce the damage of peroxidation of membrane fat.Therefore,the comprehensive effect of AMF eventually enhanced salinity-alkalinity stress tolerance of watermelon seedling plants.4.Under salinity-alkalinity stress condition,the inoculation of AMF increased watermelon seedling dry matter content,chlorophyll content,photosynthetic rate,violaxanthin and total lutein,and zeaxanthin content circulating library.Improved thylakoid membrane lipid peroxidation resistance,stable chloroplast and thylakoid membrane structure,alleviate the salinity stress on watermelon seedling growth inhibitory effect.Under salinity-alkalinity stress,inoculation of AMF,enhanced the photochemical quenching coefficient of watermelon,improved the violaxanthin,zeaxanthin and lutein library,reduce the rate of epoxidation,induced the synthesis of watermelon leaf to A and Z,accelerate the xanthophyll cycle,enhance the surplus energy dissipation,effectively improve the D1protein content,prevent the D1 protein degradation,thus accelerate the D1 protein turnover,protect the stability of the watermelon leaf PS?reaction center structure,alleviate the photoinhibition of salinity stress on watermelon.5.AMF is easy to establish mutual symbiotic relationship benefit and watermelon seedling roots was not affected by short-term salinity-alkalinity stress and reduce the infection rate.Under salinity-alkalinity stress,AMF inoculation can increase watermelon seedling root length,root surface area,total volume,branch number and root proportion,improve the root vigor and bleeding intensity in order to promote the root root,the maximum absorption of nutrients and water,improve the enzyme system of rhizosphere soil by rich soil microorganisms,increase the free amino acid content in root exudates,and ultimately enhance the resistance of plants to salt alkali stress of watermelon seedlings.6.Salinity-alkalinity stress reduces the single fruit weight and total yield of watermelon fruit,improve the brightness,increase the fruit of watermelon is red color saturation,color saturation and fruit shape index,reduced color angle and fruit firmness,improve the commodity of watermelon fruit;under salinity-alkalinity stress,inoculation with AMF increased soluble solids,VC,soluble sugar,and soluble protein,reduce nitrate content,improve the quality of the watermelons;under salinity-alkalinity stress,inoculation with AMF can improve the SOD,POD,APX,lycopene,total flavonoids and total phenolics,enhance the antioxidant capacity of watermelon fruit,fruit flesh color is more bright;changed the special aroma components,reduce watermelon bitterness,improve watermelon flavor taste.