Screening Of Efficient Phosphate-Solubilizing Bacteria And Their Growth-Promoting Effects In Interaction With Arbuscular Mycorrhizal Fungi

Robinia pseudoacacia is one of the most widely distributed tree species for soil and water conservation on the Loess Plateau.The lack of soluble phosphorus in the Loess Plateau soil is one of the main factors limiting the growth and development of R.pseudoacacia.Using rhizosphere microorganisms as biofertilizers is beneficial for forestation,ecological preservation,and sustainable forestry production.Phosphours-solubilizing microorganisms and arbuscular mycorrhiza fungi(AMF)are plant rhizosphere microorganisms that widely exist in nature.Applying phosphate solubilizing bacteria as biological fertilizers in soil can fully utilize the potential phosphorus in the soil,converting insoluble phosphorus into plant absorbable forms,and applying AMF can also promote plant nutrient absorption.The study on the effect of phosphate-solubilizing microorganisms and AMF on R.pseudoacacia can provide a theoretical basis for its application in forestry.Therefore,this study isolated,screened,and identified phosphorus-solubilizing microorganisms from the rhizosphere of artificial R.pseudoacacia forests in the southern part of the Loess Plateau.The phosphorus solubilization characteristics of phosphate-solubilizing microorganisms also be explored.In order to clarify the effects of inoculation with phosphate-solubilizing microorganisms on plant growth,as well as the effects of mixed inoculation with phosphate-solubilizing microorganisms and AMF on plant growth,the biomass,phosphorus content,soil available phosphorus content,and phosphatase activity of Robinia pseudoacacia were measured through pot experiments under different inoculation conditions.In addition,we screened out the R.pseudoacacia phosphorus transporter gene that may be induced by AMF from the R.pseudoacacia transcriptome.and analyzed the expression of genes by real-time fluorescence quantitative PCR,then conducted full-length cloning and bioinformatics analysis of some protein genes.To explore the growing-promoting effect of phosphorus-solubilizing microorganisms and their interaction with AMF on R.pseudoacacia.The main research results are as follows:1.Screening of phosphate-solubilizing microorganisms from the rhizosphere of R.pseudoacacia.Five strains of phosphorus-solubilizing fungi(PSF)and eight strains of phosphorussolubilizing bacteria(PSB)were isolated by concentration gradient dilution and plate screening.After verifying their phosphorus solubilization ability,one fungus and two bacteria were ultimately screened.The morphological and molecular biological identification showed that PSF3 belongs to Aspergillus sp.,PSB2 belongs to Pseudomonas sp.,and PSB7 belongs to Inquirinus sp.This study is the first to isolate Inquirinus sp.with high phosphorussolubilization ability from the rhizosphere of Robinia pseudoacacia2.Phosphorus-solubilizing characteristics of PSB and its growth-promoting effect on R.pseudoacacia.The phosphorus-solubilizing characteristics of PSB were explored by changing the nutrient category in the culture medium and measuring the soluble phosphorus content.The results showed that both strains were most efficient at dephosphorylating glucose and ammonium nitrogen as carbon and nitrogen sources.However,PSB2 was more suitable for growth under acidic conditions(p H was 4-6)and PSB7 was more suitable for growth under neutral conditions(p H was 7).The pot experiment showed that compared with inoculation of PSB2,PSB7 had a better effect on the growth of R.pseudoacacia.3.The growth-promoting effect of interaction between PSB and AMF on R.pseudoacacia.The pot experiment with two factors showed that inoculation with PSB7 significantly increased the arbuscular abundance in mycorrhizal parts of root fragments in R.pseudoacacia.Single inoculation with PSB or AMF significantly increased the biomass of plant,and mixed use of AMF and PSB7 significantly increased the phosphorus content of plant roots.The realtime fluorescence quantitative PCR results showed that inoculation with PSB7 significantly increased the expression of RpPHT1-7,and inoculation with AMF significantly increased the expression of RpPHT1-5 and RpPHT1-11.This indicates that inoculation with PSB and AMF may enhance plant’s phosphorus acquisition and improve plant nutritional status by increasing the expression of RpPHT in R.pseudoacacia.4.Cloning and functional prediction of phosphate transporter gene of R.pseudoacacia.Four phosphate transporter genes of the R.pseudoacacia PHT1 family were obtained through full-length cloning: RpPHT1-4,RpPHT1-5,RpPHT1-7,and RpPHT1-8.All four R.pseudoacacia phosphorus transporters are characterized by PHT1 family proteins,and show high protein homology to legume model plants,indicating that the PHT1 family has evolved conservatively among legumes.