Isolation And Identification Of Salt-tolerant Potassium-resolving Bacteria And Study On Plant Growth Promotion Mechanism

Potassium(K)is extremely important for crop production and growth.In agricultural production,K fertilizer is mainly used to meet the needs of crops for K elements.However,excessive or long-term use of chemical fertilizers can cause environmental pollution,reduce soil quality and salinization.The content of K element in the soil is relatively abundant,and there is a large amount,but most of it is fixed by some metal ions,etc.,and is not used by plants.Potassium(K)-solubilizng bacteria(KSB)is a microorganism that can dissolve compound K compounds.They can release the fixed K element in the soil for absorption and utilization by plants.The KSB preparation has the characteristics of low cost in the production process,sustainable,simple process and low pollution,so it can alleviate or reduce the environmental pollution and cost problems caused by the excessive use of K fertilizer.It can be widely used in agricultural production.Broad market prospects.Soil salinization is currently a common challenge facing global agriculture.The production of salinized agricultural areas must first ensure the normal growth of crops.The use of KSB strains is one of the ways to solve the problem,but how to improve KSB strains in salinized soil The ability to survive and grow in KSB and maximize its efficiency in solving K is one of the main problems that need to be solved in the application of KSB.In this study,13 strains of salt-tolerant bacteria with the ability to resolve insoluble K(K feldspar)were screened on beef extract peptone medium containing Na Cl(10 g/L)and modified Aleksandrov medium.In the shaker test of the K-resolving(insoluble state)ability,the K-resolving efficiency of 13 strains ranged from 2.19% to 13.87%,of which 8 strains had the K-resolving efficiency greater than 10%;Enterobacter ludwig(Enterobacter Ludwigil strain XN-K13 has the highest K solution efficiency,reaching 13.87%,followed by Burkholderia cepacia strain NG-K8,which has a K solution efficiency of12.46%,and both XN-K13 and NG-K8 are acceptable Secrete siderophore,produce Indcie acetic acid(IAA),dissolve inorganic phosphorus(P),synthesizeδ-aminolevulinic acid(ALA)and have nitrogen fixation(N)effect.XN-K13 and NG-K8 still have strong K dissolution efficiency and growth-promoting properties at a concentration of 20 g/L Na Cl.The K dissolution mechanism is mainly through the generation of acids to dissolve the cations of insoluble K minerals.Afterwards,the growth-promoting effects of the two strains were studied in depth.Resistance spectrum research shows that XN-K13 and NG-K8 have strong tolerance to salt-alkali,heavy metals and drought.XN-K13 can withstand at least 100 g/L Na Cl,p H 9.5,1 m M Al,2.25 m M Pd,2.0 m M Cd,0.75 m M Co,1.75 m M Cu,50% PEG-6000;NG-K8 can withstand at least 100 g /L Na Cl,p H9.5,0.75 m M Al,2.75 m M Pd,1.75 m M Cd,4.0 m M Co,2.25 m M Cu,60%PEG-6000.It can significantly promote the seed germination rate,fibrous root number,embryo length,radicle length,hypocotyl length,seedling dry weight and root dry weight of corn under the stress of 5.84 g/L Na Cl,1 m M Cd and20% PEG-6000.Potted growth promotion results showed that under the conditions of soluble K and insoluble K,compared with the control without inoculation or using exogenous substances,the exogenous application of XN-K13,NG-K8 strain and silicon(Si)alone can be significantly Promote the growth of maize.The results showed that the dry weight of the above-ground part,the dry weight of the underground part,the content of K,the content of Si,the content of P,and the activity of CAT of corn plants when the XN-K13 strain was applied alone under soluble K conditions compared with the control,POD activity,SOD activity,plant hormone IAA content and total chlorophyll content increased by61.11%,38.66%,37.94%,6.09%,29.82%,69.71%,60.86%,30.32%,26.45%and 20.52%,respectively;in insoluble Under the condition of K,the increase was 91.23%,106.49%,160.99%,27.84%,146.84%,217.07%,154.99%,13.20%,28.97% and 54.80% respectively.Compared with the control,the dry weight of the above-ground part,the dry weight of the underground part,K element content,Si element content,P element content,CAT activity,POD activity,SOD activity,plant hormone IAA content and total chlorophyll content increased by 9.32%,7.48%,14.42%,12.13%,88.44%,51.40%,19.19%,46.25%,61.20% and 8.54% respectively;under the condition of insoluble K,respectively Increased by 26.08%,41.00%,60.11%,240.93%,144.50%,41.87%,151.50%,8.35%,54.66% and 34.52%.However,the growth-promoting effect of Si in combination with XN-K13 and NG-K8 was more significant.The results showed that the combination of XN-K13 strain and 300 mg/kg Si under soluble K conditions showed that compared with the control,corn plants had The dry weight of the above-ground part,the dry weight of the underground part,K element content,Si element content,P element content,CAT activity,POD activity,SOD activity,plant hormone IAA content and total chlorophyll content increased by 130.35%,56.21%,and 46.22%,respectively,12 times,227.83%,137.84%,337.05%,127.15%,175.53% and 52.75%;under the condition of insoluble K increased by 98.67%,113.90%,207.78%,250.37%,334.06%,322.22%,290.62%,respectively,117.89%,77.03% and 62.57%.The green fluorescent protein labeling results showed that XN-K13 and NG-K8 initially colonized the root tip of maize,and then entered the root meristem or entered the surface parenchyma from the junction of the main root and lateral root In the gap,a few bacterial cells are still located in the epidermis,root hairs and surface cells.5 d after the inoculation treatment,the bacterial cells develop to the endothelial layer and can reach the xylem.The XN-K13 and NG-K8 strains in this study show potential production and medical value,and at the same time provide physiological and histocellular location for further in-depth study of the growth-promoting mechanism of K-lytic bacteria.