Variation Of PhoD Bacterial Community Structure And Screening Of Plant Growth Promoting Rhizobacteria Resources In The Retreat Area Of Hailuogou Glacier

Phosphorus(P)is an essential nutrient element for plant growth,but it is easily fixed in soil and has low effectiveness,which has became one of the important factors limiting plant growth.Microorganisms can solubilize inorganic P and hydrolyze organic P to orthophosphates through theproduction of phosphatases.When P is scarce,microorganisms up-regulate genes in the phosphate(Pho)regulation that includes genes encoding phosphatases and phosphate transporte rs for mobilizing soil P.The phoD alkaline phosphatase is produced by microorganisms in response to the restriction of phosphorus in the environment,which has been widely found in aquatic and soil environments.Phosphorus-decomposing microorganisms have the biological characteristics of dissolving soil insoluble phosphorus into available phosphorus that plants can absorb and use,which can not only increase the effective phosphorus content in the soil,but also promote the growth of plants.It has become the key research direction in agricultural and forestry production practice.Phosphorus availability is an important factor that affects the primary successional system of Hailuogou glacier,but there are few reports on the diversity of phosphorus cycling microorganisms and strain resources in this area.Therefore,the soil developed after the retreat of Hailuogou glacier was taken as our study object.The composition and diversity of phosphorus-related microbial communities in this area were studied by high-throughput sequencing technology,and further combined with pure cultivation technology to excavate the resources of phosphorus-promoting bacteria.Below are key research findings:(1)Characteristic of soil properties along the chronosequence: The soil development showed the three stages,and soil changed from alkaline to acidic across the succession,and the contents of organic carbon,total nitrogen,and alkaline nitrogen gradually increased.Available phosphorus and available potassium is increasing first and then decreasing with the increased in the successional years.Soil inorganic phosphorus and organic phosphorus are highest in mature soil.(2)Variations of phoD bacterial community composition and diversity: The diversity index of phoD bacterial community gradually increases with soil development,and the apha diversity index is peaked at 129 years.The composition of phoD bacterial community changes with the succession time.At the level of the phylum,Proteobacteria(75.87-92.65%)and Actinomycota(5.74-21.80%)dominanted the entire succession process.At the level of the order,Burkholderiales(29-36%)and Rhizobiales(24-42%)are the most abundant groups in the succession process,followed by Pseudomonadales(11-15%)and Streptomycetales(5-14%).At the genus level,Cupriavidus(19-35%)and Bradyrhizobium(14-38%)are the main groups in the succession process,followed by Pseudomonas(11-15%),Streptomyces(5-14%)and Collimonas(1-10%).In general,there are abundant phosphorus-associated microorganism resources in this area,which provides species resources for excavating phosphorus-decomposing microorganisms.(3)Isolation and screening of high-effect phosphatesoluble bacteria: 430 strains were initially isolated from solid medium,32 strains were capable of decomposing organic phosphorus,26 strains were capable of decomposing inorganic phosphorus,12 of which had both dissolved organic phosphorus and Inorganic phosphorus capacity.Though quantitative determination,three strains PSB-56,PSB-52 and PSB-53 with the strongest organic phosphorus ability were obtained,and available phosphorus contents were 46.49,31.28 and 27.96μg/ml,respectively.Strains PSB-56,PSB-60 and PSB-53 were the strongest inorganic phosphorus ability,and the available phosphorus contents were 264.25,204.24 and 237.40 μg/ml,respectively.(4)PGPR(plant growth promoting rhizobacteria,PGPR)characteristics of phosphatesoluble bacteria: 8 strains have strong nitrogen-fixing ability,5 strains have strong potassiumsoluble ability,and 2 strains have strong cellulose degradation ability,9strains have stronger ability to produce extracellular alkaline phosphatase,5 strains have strong ability to produce IAA(IAA content> 40 μg/ml),and 3 strains have ability to resist multiple pathogens.Among them,strain PSB-37 produced IAA content was 40.22 μg/ml and resistant to 5 kinds of pathogenic bacteria,strain PSB-56 produced IAA content was40.32 μg/ml and resist 4 kinds of pathogenic bacteria.(5)16S r RNA molecular taxonomy identification: The 17 excellent probiotics belonged to 4 genera,6 strains to Arthrobacter sp.,5 strains to Myroides sp.,2 strains to Pseudomonas sp.,3 strains to Bacterium sp.,and 1 strain to Stenotrophomonas sp..The strains PSB-37 and PSB-56 belong to Bacterium and Myroides,respectively.(6)The effect of phosphatesoluble bacteria on the growth of cucumber growth: The application of phosphatesoluble bacteria significantly increased the agronomic characters and biomass of cucumber.The effect of single bacterial treatment on promoting growth of cucumber cucumber was better than mixed bacterial treatment,and the effect of strain PSB-37 on promoting growth of cucumber was the best.