Screening,identification Of Indole-3-acetic Acid(IAA) Producing Bacteria And The Application Of Biochar As Carrier Material For The Bacteria

The amount of fertilizer applied for agricultural production has been increasing over years.The excessive amounts of fertilizers applied can result water eutrophication and other detrimental environmental impacts.Microbial fertilisers could be used to reduce the amount of chemical fertilizer and increase crop yield,while at the same time,reducing environmental pollution.Indole-3-acetic acid(IAA)as an important plant hormone,could promote plant growth.The utilization of IAA-producing bacteria as a microbial fertilizer may play an important role in agricultural production.Biochar is a soil conditioner,and it has direct or indirect impacts on soil microbes.Using biochar as a carrier for IAA-producing bacteria can improve the activity of IAA-producing bacteria in the soil.The main purpose of this study was to screen high efficient IAA-producing bacteria,and test the promoting effect on plant growth.Research on the effects of biochar on soil microbial diversity,can provide theoretical basis for its environmentally friendly function.IAA-producing bacteria were inoculated onto biochar,and the changes of the biochar-IAA producing bacteria complex in the synthesis of IAA in the soil were studied.The results of the study were as follows:(1)We screened a toal of 95 bacterial strains in the rice rhizosphere,and 30 bacterial strains produced pink reaction by the Salkowski reagents.And the color of six bacterial strains were the most significant.We further confirmed the production of IAA by high performance liquid chromatography(HPLC).The concentration of IAA produced by A5,A48 and A60 were all about 4 mg/L.A rice seed germination and seedling growth experiment showed that the promotion effects of A48 and A60 were the most significant.By comparing the 16S rRNA gene sequences in the NCBI databases,the six IAA producing bacteria strains were found to belong to four genus:Bacillus,Agrobacterium,Pseudomonas and Aeromonas.(2)We applied 16S rRNA gene sequencing with an internal standard gene to quantitatively investigate biochar-mediated changes in microbial composition and abundance in the rhizosphere and bulk soils.The results indicated that the biochar amendment significantly altered the soil microbial abundance and community.The bacteria in the rhizosphere soil showed more evident responses to biochar addition than in the bulk soil.The biochar treatment increased the absolute abundances of Actinobacteria and Planctomycetes in the rhizosphere.But there were no changes in the bulk soil.A linear discriminant analysis(LDA)effect size(LefSe)differential analysis showed the number of responding bacteria species in the rhizosphere were more than that in the bulk soil.Our research demonstrated that different soil physicochemical properties(e.g.,water content and available K)and biogenic resources(e.g.,root biomass)had distinct influences on the microbial community.(3)We studied the effect of pine biochar as a bacterial carrier on IAA synthesis in the soil.Results showed that IAA-producing bacteria could be inoculated to the surface and interspace of the pine biochar.After 28 days of cultivation,the concentration of IAA in the biochar-A60 treatment was higher than others,which indicted that bacteria with biochar promoted the IAA synthesis by the IAA-producing bacteria over a short period of time.After 7 days,the concentration of IAA gradually decreased to 0 mg/kg.These results showed that innoculated bacteria to biochar cannot maintain its activity in the long-term in our experiment.