Effects Of Arbuscular Mycorrhizae And Zinc On The Growth And Development Of Citrus Seedlings

Most of China’s citrus production areas are located in rainy areas in the south,where nutrients are easily leached out.The problem of zinc deficiency is very prominent,which can easily lead to zinc deficiency"small leaf disease"in citrus.The citrus production areas represented by Chongqing have an annual precipitation of over 1000mm,and the overall rainfall is abundant.However,there will still be a seasonal drought period from July to August,which also restricts the development of the citrus industry.Arbuscular mycorrhiza fungi（AMF）have a good symbiotic relationship with citrus,which can enhance the absorption of fixed nutrients and water in citrus,and can effectively alleviate the damage of drought stress to citrus.However,there are few reports on the joint role of Arbuscular mycorrhiza and zinc in regulating the growth and development of citrus and the expression of drought resistance genes in citrus itself.In order to explore the optimal level of zinc fertilizer application in citrus,further improve the utilization rate of zinc element,increase the available zinc content in soil,and explore the impact of drought stress on citrus at the molecular level,clarify the potential regulatory effect of AMF under different zinc application concentrations,and improve the methods and methods of zinc application,and apply them to citrus agricultural production,this experiment infected the root system with Claroidoglomus etucatum（C.e）,Four different zinc application levels(0 g.L^-1,1 g.L^-1,2 g.L^-1,3 g.L^-1)were set up and recorded as 0,T1,T2,T3,respectively.The effects of different zinc application levels on the growth of citrus seedlings,mineral element absorption,antioxidant capacity,osmoregulation material content,endogenous kinin synthesis,soil physicochemical properties,and enzyme activity were systematically studied,aswell as the effects of AMF and zinc on the expression of drought stress related genes under short-term drought stress,The main conclusions are as follows:1.Claroideoglomus etunicatum（C.e）can effectively infect the roots of citrus seedlings,and the application of appropriate concentrations of zinc fertilizer(1 g.L^-1、2 g.L^-1)can improve the mycorrhizal infection rate and dependency.Suitable concentrations of zinc fertilizer and AMF inoculation can effectively promote the growth and development of the aboveground and root parts of citrus seedlings,improve the photosynthetic capacity of leaves,and increase the biomass accumulation in the aboveground and underground parts of the seedlings.Applying zinc fertilizer can promote the accumulation of nutrients in citrus plants.Applying zinc can promote nitrogen,potassium,iron,and copper to a certain extent,but the phosphorus content decreases with the increase of zinc concentration.Inoculating AMF will further increase the mineral nutrient content in the leaves and roots of citrus seedlings.2.The application of zinc fertilizer with appropriate concentration increased the MDA content in the leaves and roots of citrus seedlings,stimulated the increase in the activity of antioxidant enzymes（SOD,POD,CAT,APX）,and the accumulation of osmoregulation substances（soluble sugar,soluble protein,and proline）,which was conducive to improving the resistance of citrus seedlings.When the level of zinc application is T3,high concentrations of zinc stress aggravate the oxidative damage of citrus seedlings,thereby hindering their growth and development.Inoculation with AMF alleviated the stress effect of high concentration zinc on citrus seedlings,further improving the antioxidant capacity of citrus seedlings,and being able to better resist the damage of stress to plants.3.Applying zinc fertilizer can affect the accumulation of IAA,GAs,ZR,and ABA in the leaves and roots of citrus seedlings,change the proportional relationship between endogenous hormones,and thereby affect the growth and development of plants.Applying zinc fertilizer can increase the ABA content of citrus seedlings,and appropriate concentrations of zinc fertilizer(1g.L^-1、2g.L^-1)can improve the accumulation of IAA,GAs,and ZR in the plant to a certain extent,thereby promoting plant growth.At high concentration(3 g.L^-1),ABA reached the highest level,while the contents of IAA,GAs,and ZR decreased slightly compared to other treatments,clearly exceeding the optimal concentration range for zinc application,which inhibited plant growth and development.Inoculation with AMF can increase IAA,GAs,and ZR contents in leaves and roots of citrus seedlings,reduce ABA content,and promote plant growth.4.Applying appropriate concentrations of zinc fertilizer(1 g.L^-1、2 g.L^-1)can significantly increase the content of available zinc in soil,but applying high concentrations of zinc fertilizer(3 g.L^-1)has the opposite effect.Applying zinc fertilizer can reduce the content of available nitrogen and phosphorus in soil,and increase the content of available potassium,which has little relationship with zinc concentration.Inoculation with AMF can increase the content of alkali hydrolyzable nitrogen,available phosphorus,and available potassium in soil,and improve the availability of nitrogen,phosphorus,potassium,and zinc in soil.Zinc application can increase the enzyme activity in the rhizosphere soil of citrus seedlings to a certain extent,while high concentration of zinc fertilizer can reduce the enzyme activity in the soil.Inoculating AMF can effectively alleviate this negative effect.Therefore,applying appropriate zinc fertilizer while inoculating AMF can better improve the physical and chemical properties of rhizosphere soil and enhance soil enzyme activity.5.At the later stage of the experimental treatment,the continuous high temperature and dry weather made the citrus seedlings suffer from drought stress.Under short-term drought stress,both AMF inoculation and zinc application increased the relative expression of zinc finger protein genes Cs ZAT10 and Cs CHYR1 related to stress resistance in citrus seedlings to varying degrees,enhancing the adaptability of citrus seedlings to drought environments.