Screening And Characterization Of Soil Phosphorus-regulating Microorganisms

Phosphorus is an essential nutrient element for plant growth,and it is mainly involved in physiological and biochemical processes such as lipid metabolism,cell membrane and nucleic acid biosynthesis.Because of its high chemical affinity for soil minerals and organic matter,it is easy to be fixed into an insoluble state.The phosphorus content in the soil that can be directly utilized by plants is low.In agriculture,phosphorus fertilizers are used to meet the needs of crop growth.However,due to long-term excessive application,a large amount of phosphorus accumulates in the soil,which increases the risk of phosphorus leaching.Easily leads to eutrophication of water bodies and causes serious environmental problems.Microorganisms play an important role in the soil phosphorus cycle.Phosphorus solubilizing bacteria(PSB)can convert the difficult-to-use phosphorus in the soil into a form that can be absorbed and utilized by plants,thus improving the utilization efficiency of phosphorus.Phosphorus-accumulating bacteria(PAB)refer to microorganisms that can absorb excessive phosphorus and store phosphorus.PAB are used more in the biological phosphorus removal process of sewage,but less in soil.In order to understand the application potential of PSB and PAB in controlling soil phosphorus leaching,this study isolated and screened highly active PSB and PAB from the soil.Column leaching test were performed to study their effects on phosphorus in soil leaching solution.PSB and PAB were applied to corn roots to study their effects on the growth of corn plants and phosphorus in soil leaching solution.High-throughput amplicon sequencing was used to study the effects of PSB and PAB on the rhizosphere microbiota of corn.This study provided a scientific basis for using microbial technology to improve the utilization efficiency of phosphorus in the soil,reduce soil phosphorus leaching,and control nonpoint source pollution.The main findings are as follows:(1)Strains with phosphorus solubilization and phosphorus accumulation activities were isolated and screened from the soil.According to the quantitative determination,the PSB strain JP233(Pseudomonas sp.)with strong phosphorus solubilizing ability were screened.And the PAB strain Fp64(Arthrobacter sp.)with good phosphorus removal ability was selected for follow-up research.The non-targeted metabonomic analysis of PSB strain JP233 found that 2-keto-D-gluconic acid was the main phosphate solubilizing factor produced by this strain.Through HPLC detection,it was found that the highest concentration of 2-keto-D-gluconic acid in the fermentation broth of JP233 could reach19.01 mg/m L.(2)Through the soil column leaching test,the total phosphorus(TP)and molybdate reaction phosphorus(MRP)content of the soil leaching solution applied with JP233 and Fp64 were determined.It was found that the TP(2.16 ± 0.22 mg)and MRP(0.363 ± 0.027mg)of the cumulative leaching loss for treatment JP233 are both the highest,indicating that the application of PSB strain JP233 has a tendency to promote soil phosphorus leaching,but the statistical analysis showed that the differences with CK(1.93 ± 0.13 mg,0.345 ± 0.028 mg)was not significant.The application of Fp64 did not change TP and MRP content(1.95 ± 0.08 mg,0.354 ± 0.02 mg)much in the soil leaching solution.(3)Inoculation of PSB strain JP233 and PAB strain Fp64 could promote the growth of corn compared with the control without inoculants.PSB strain JP233 increased the dry weight of corn roots and shoots by 12.4% and 55.7%,respectively.PAB strain Fp64 increased the dry weight of corn roots and shoots by 57.6% and 93.8%,respectively.Moreover,the application of strain JP233 and Fp64 could significantly reduce the phosphorus content in the soil leaching solution.The cumulative loss of TP and MRP in soil leaching solution for CK were 4.29 ± 1.09 mg and 2.38 ± 0.99 mg,while the values for JP233 were 2.49 ± 0.53 mg,0.75 ± 0.40 mg,and for Fp64 were 1.96 ± 1.49 mg,0.71± 0.82 mg,respectively.The results showed that the application of strain JP233 and Fp64 to corn significantly reduced the soil phosphorus leaching loss from the soils.(4)High-throughput sequencing of 16 S r DNA and ITS amplicons was performed to study the corn rhizosphere microbiota.The analysis showed that the inoculation of strain JP233 and Fp64 both changed the population structure of corn rhizosphere microbiota and enhanced the relative abundance of beneficial microorganisms such as Bacillus spp.and Trichoderma spp.,and reduced the relative abundance of pathogenic fungi such as Fusarium spp.These results indicate that inoculation of strain JP233 and Fp64 improved the health of corn rhizosphere microbiota.Through the above research,we found that inoculating the phosphorus solubilizing bacteria JP233 and phosphorus accumulating bacteria Fp64 alone in the soil did not significantly change the leaching of soil phosphorus.Inoculation of the above-mentioned strains to plant roots could significantly promote the growth of plant roots and aboveground parts,promote the absorption and utilization of soil phosphorus by plants,and significantly reduce soil phosphorus leaching.Moreover,the inoculation of strain JP233 and Fp64 could improve plant rhizosphere microbial population structure,which is beneficial to protect plant health.