Effects Of Pseudomonas Fluorescens On Root-Zone Soil Environment,Growth And Phosphorus Absorption Of Peach

The soil environment in the root zone is crucial to the growth of peach trees,and the use of plant growth-promoting rhizobacteria to improve the soil microbial environment and regulate plant growth and development has become one of the important scientific strategies for sustainable agricultural development today.Pseudomonas fluorescens is an important plant growth-promoting rhizobacteria that has growth-promoting effects on a variety of plants.Peach is an important horticultural crop in China,however,the growth-promoting effect of P.fluorescens on peach tree has not been reported.In this experiment,the growth-promoting characteristics of three strains of P.fluorescens（PF87,PF70,PF32）were firstly identified by solid culture and liquid fermentation tests,and then 2-year-old grafted seedlings of peach[Prunus persica（L.）Batsch]were used as the test material,with water treatment as the control and single or mixed P.fluorescens suspensions（PF87,P732,PF70,PFMIX,respectively）as the treatment to investigate the effects of P.fluorescens on the soil environment and growth of peach trees in the root zone.Based on the above experimental results,we selected PF70 as the test material and investigated the effect and mechanism of P.fluorescens on phosphorus uptake by peach seedlings under low(0.2μmol·L^-1)and moderate(200μmol·L^-1)phosphorus conditions.The study was conducted to provide theoretical references for the inter-root application of P.fluorescens in peach trees.The main findings were as follows.1.All P.fluorescens had the probiotic properties of indoleacetic acid（IAA）production,solubilization of inorganic and organic phosphorus,solubilization of insoluble potassium,siderophores production and biofilm formation,among which PF32 had the strongest ability of solubilizing inorganic phosphorus with 115.71μg·m L^-1and PF70 had the highest IAA production with 7.52μg·m L^-1.All three strains of P.fluorescens could produce a large amount of organic acids during phospholysis,and the highest content of lactic acid and malic acid.2.P.fluorescens treatment could reduce soil p H and increase soil available phosphorus,alkaline nitrogen,available potassium and effective iron content in the root zone of peach grafted seedlings,among which PF87 significantly reduced soil p H by 2.27%,PF32 and PF87 significantly increased soil effective iron content by 7.79%and 6.54%.P.fluorescens treatment significantly increased soil enzyme activity in the root zone of peach grafted seedlings,and overall PF87 had the most significant effect,significantly increasing soil urease,sucrase,catalase and alkaline phosphatase by 7.89%,37.66%,39.62%and 34.16%,respectively.3.P.fluorescens treatment also significantly changed the structure and diversity of soil bacterial and fungal communities,where PF70 increased both the Shannon and Chao 1indices of soil bacteria and fungi;at the level of bacterial phylum,they increased the relative abundance of soil Proteobacteria,Acidobacteriota and Actinobacteriota,and decreased the relative abundance of Bacteroidota and Firmicutes,and at the genus level,they increased the relative abundance of Sphingomonas,at the species level,they significantly increased the relative abundance of Nitrospira sp.and Acidobacteria bacterium WY11 compared to CK;from the fungal community,PF87 and PF70 significantly changed the relative abundance of Ascomycota,Mortierellomycota and Basidiomycota,which in turn changed the species and relative abundance of each dominant genus,and the relative abundance of Penicillium oxalicum was significantly higher than that of CK by 334.10%and 90.91%respectively.4.P.fluorescens treatment significantly increased the root vigor and growth of peach trees and improved the root system conformation,among which PF70 had the most significant effect,which significantly increased the root vigor,root surface area,volume,tips and dry weight of grafted peach tree by 28.05%,65.08%,35.82%,87.10%and 31.40%,respectively.P.fluorescens significantly increased photosynthesis and chlorophyll content of peach trees,where PF70 significantly increased net photosynthetic rate and total chlorophyll content by 25.30%and 38.62%.P.fluorescens significantly increased the total nitrogen,phosphorus and potassium contents of grafted peach seedlings,and significantly increased the total iron content in the above-ground of peach5.At different Pi levels,P.fluorescens PF70 altered the root conformation and plant phosphorus content of live seedlings of hairy peach.Under low phosphorus conditions,PF70increased the root surface area and root tips by 8.72%and 43.49%,respectively,and increased the total phosphorus content and phosphorus accumulation of the plants,which significantly increased the Pi uptake capacity by 12.73%compared with the control,without significantly changing the distribution of Pi in the plants.6.It was found by fluorescence quantitative PCR that PF70 could regulate the transcript levels of phosphorus transporter Pp PHT1-9 and Pp PHT2-1 in peach seedlings.The transcript levels of Pp PHT1-9 and Pp PHT2-1 were low in the early stage of PF70 treatment,and the highest transcript levels were found at 7 or 15 days after treatment,and under low phosphorus conditions,PF70 had the most significant up-regulation effect on Pp PHT1-9 and Pp PHT2-1in the late stage of treatment,which promoted the uptake of Pi in peach seedlings.