Effect And Mechanism Research On Further Improving The Plant Growth Promotion By Functional Bacteria (SQR9) In Bio-organic Fertilizer Using Galactose

Plant Growth Promoting Rhizobacteria（PGPR）refers to a kind of beneficial microorganisms that colonize the rhizosphere of plants and can effectively promote plant growth.Adding PGPR into organic fertilizers can make bio-organic fertilizers.The application of bio-organic fertilizers can increase crop yield and quality,inhibit soil-borne diseases,and improve plants’resistance to drought,lack of nutrients,heavy metal pollution.How the functional microorganisms in biological fertilizers function in the soil is the prerequisite for biological fertilizers to function.Microorganisms need to consume energy to perform their functions.Decomposing carbon sources is the main source of energy for microorganisms.In this study,a pot experiment was used to screen the carbon source that can further enhance the growth-promoting effect of the bio-organic fertilizer containing Bacillus amyloliquefaciens SQR9.Further studies were carried out under pure culture and co-culture conditions using the screened carbon source to reveal its promotion effect on the plant growth promotion effect caused by bio-organic fertilizer of Bacillus amyloliquefaciens SQR9.The results obtained were as follows:1.The cucumber pot experiment was carried out to screen best carbon source for bio-organic fertilizer from 10 carbon sources（glucose,Arabinose,sorbitol,galactose,mannose,cellobiose,sucrose,maltose,ribose,lactose）favored by strain SQR9.For each carbon source,four treatments were set up,1)organic fertilizer,2)organic fertilizer plus carbon source,3)organic fertilizer plus SQR9 and 4)organic fertilizer plus SQR9 and carbon source.The results showed that the addition of functional bacteria SQR9 and galactose could promote the growth of cucumbers.Among them,the SQR9 plus galactose treatment had the highest plant height,chlorophyll content and fresh weight of cucumber compared with other treatment.These ten carbon sources were further test for their promotion effect on IAA production of the strain SQR9 using Landy medium.The addition of carbon source can promote the ability of strain SQR9 to produce IAA.Under pure culture conditions,the optimal addition amount of galactose is 1.0%.2.Columbian Arabidopsis（Col-0）and IAA-insensitive mutant Arabidopsis（pin4-3）were grown on sucrose free MS medium with galactose gradient（0,0.1%,0.3%,0.7%and1%）and strain SQR9 inoculation gradient(0,10⁶,and 10⁸ cfu m L^-1)for 16 days.The growth status was observed and the root characteristics were determined.The results showed that compared with the treatment without SQR9 strain,as the concentration of SQR9 strain increased,Arabidopsis roots grew vigorously.Among them,the optimal addition amount of galactose was 1.0%and the optimal inoculation amount of strain SQR9 was 10⁸ cfu m L^-1,that all the root system indexes of treatment reached the maximum value.There is no significant difference between the IAA-insensitive mutant Arabidopsis treated with strain SQR9 plus galactose and the control,which indicates that the addition of galactose can promote the IAA production of strain SQR9 is one of the mechanisms that the addition of galactose can promote plant growth-promoting effect of bio-organic fertilizer containing Bacillus amyloliquefaciens SQR9.3.In order to further explore the optimal addition amount of galactose,a gradient of galactose was set up in cucumber pot experiment.The results showed that the optimal addition amount of galactose was 0.5%-1.0%when the biological properties of cucumber reached the maximum compared with other control.In order to explore the IAA productivity of SQR9 strain in the environment,we set up different inoculation concentrations of strain SQR9s with soil to Landy medium containing different concentrations of galactose,and the IAA productivity of different treatments were determined.The results showed that the increase of galactose can promote the IAA production of SQR9 strain in Landy plus soil medium.We further screened 15 strains from the soil.According to their IAA productivity results in Landy’s medium,the 15 strains were artificially classified into three grades:high-yield,medium-yield,and low-yield.Strain SQR9 was co-cultured with the three grades of microbial mixture,the IAA production capacity of different treatments was measured.The IAA production capacity of the strain in the microbial mixture environment is lower compared to pure culture condition.In summary,the addition of galactose can increase the IAA production of strain SQR9under pure culture condition and the microbial mixture under co-culture condition which can further promote the plant growth.Thus the addition of galactose enhances the IAA prodution of strain SQR9 is the main mechanism that galactose addition can improve plant growth-promoting effect of bio-organic fertilizer containing Bacillus amyloliquefaciens SQR9.