Effects Of Long-term Potassium Deficiency On Tomato Root Exudates And Rhizosphere Microecology

Years of intensive cultivation resuits in a very serious phenomenon of soil potassium deficiency.Under nutrient stress conditions,active or passive substances secreted from the plant roots can overcome or alleviate nutrient deficiencies.Therefore,the identification of the types and amounts of root exudates in the absence of potassium,as well as the interaction with rhizosphere microorganisms,can be an important theoretical and practical significance used to understand the root-soil-microbe interactions in the rhizosphere ecosystem and the scientific fertilization regulation in the production.In this study,vegetable long-term fertilization experiment is used as a platform,11 treatments is seclected:BN₀（no fertilization control）;BN₁（nitrogen fertilizers）;BK（potassium fertilizers）;BP（phosphate fertilizers）;BNP（nitrogen+phosphate fertilizers）;BNPK（nitrogen+phosphate+potassium fertilizers）;AN₁（organic manure+nitrogen fertilizers）;AK（organic manure+potassium fertilizers）;AP（organic manure+phosphate fertilizers）;ANP（organic manure+nitrogen+phosphate fertilizers）;ANPK（organic manure+nitrogen+phosphate+potassium fertilizers）to analyze the type and quantity of tomato root exudates under long-term potassium deficiency by liquid chromatography.Biolog-ECO microplate method is used to analyze the functional diversity of microbial community in tomato rhizosphere soil.The content of available nutrients in rhizosphere soil is measured,which correlations with root exudates,root growth traits,and rhizosphere microorganisms are studied.Principal component analysis is used to reveal the plant-soil-microbe interactions mediated by root exudates under the regulation of rhizosphere ecosystem,to clarify the response of tomato roots under conditions of potassium deficiency,to provide the theoretical basis for scientific regulation of the rhizosphere ecological processes under adverse conditions.The main results of this study are as follows:1.After 29 years of continuous fertilization,the chemical properties of tomato rhizosphere soil with different fertilization treatments are significantly different.To apply organic fertilizer can obviously increase soil available phosphorus,available potassium,alkaline nitrogen and organic matter.The application of nitrogen fertilizer will increase the content of alkaline nitrogen,but it will reduce the pH of the rhizosphere soil.The degree of acidification can be reduced through the application of organic fertilizer.2.The growth traits of the root system are measured by a root scanner.The treatments differedsignificantly depending on the growth period and fertilization type.The root volume,root surface area,total root length,and roots apical number all increase at first and then decrease with the extension of growth period,but the root mean diameter increase.Applying organic fertilizer can promote root development.The application of N fertilizer will increase the root mean diameter,root length,root surface area and total root apical number;the application of P fertilizer will increase the root mean diameter and root length;the application of K fertilizer will increase the root mean diameter and total root apical number.The correlation analysis shows that the root volume,total root surface area and the available potassium content in the rhizosphere soil are highly significantly positively correlated.3.Tomato plant under the condition of long-term potassium deficiency will secrete a large amount of phenolic acids,organic acids,protons and other substances.In this study,five kinds of phenolic acids（benzoic acid,p-hydroxybenzoic acid,coumaric acid,ferulle acid,cinnamic acid）and four kinds of organic acids（oxalic acid,malic acid,citric acid,succinic acid）are detected by HPLC.The levels of phenolic acids and organic acids secreted from the roots of each treatment differ from each other in the time of emergence,but the amount of secretion is increased with the increase of nutrient deficits.Potassium deficiency can significantly increase the secretion of oxalic acid,succinic acid and cinnamic acid.Potassium deficiency can induce plasma membrane H⁺-ATPase activity and then increase proton secretion.4.Based on Biolog-ECO microplate method,microbial functional diversity is analysised.Thefertilization method of organic fertilizer with nitrogen and phosphorus fertilizer（ANP）shows higher rhizospheric soil microbial functional diversity,which is most conducive to the survival of microorganisms.The combination of organic fertilizers can enhance the ability of microorganisms in tomato rhizosphere soil to use carbon resources and increase the functional diversity of microbial communities.Specific performances are as follow,long-term fertilization changes the ability of soil microorganisms to use carbon sources.The amino acid carbon source becomes the most important carbon source utilization type,while the use of phenolic carbon source is the weakest.Principal component analysis shows that 31 carbons are used.There are 12 kinds of sources that contribute more to PC1,and 8 kinds of sources make a greater contribution to PC2.The Shannon index,Abundance index,and Simpson index of fertilizer application are higher than that of non-fertilizer treatments,but their Mclntosh index decreases.The change of microbial functional diversity is the result of plants adapting themselves to the soil environment through their own regulation,which in turn affects the rhizosphere microecology.This intensive study of plant-soil-microbe interactions will provide a theoretical reference for the scientific regulation of tomato rhizosphere ecological processes.