Community Structure Characteristics And Ecological Effects Of Phosphorus Solubilizing Bacteria In Rhizosphere Of Suaeda Salsa In Coastal Wetland

Suaeda salsa is an important dominant vegetation group in coastal wetlands.During the process of ecological restoration of saline-alkali soil,there is a mutual interaction among plants,soil and microorganisms,in which soil microorganisms are capable of responding quickly to changes in the external soil environment.In the context of global scarce phosphorus resources,phosphate-solubilizing bacteria（PSB）can convert insoluble phosphorus in soil into available phosphorus that can be absorbed by plants,thus stimulating plant root growth and promoting the accumulation of biomass.The use of plant growth-promoting bacteria in the rhizosphere to improve plant stress resistance is an ecologically friendly method for dealing with salt stress.Therefore,this study focuses on different habitat Suaeda salsa in the Yellow River Delta,and investigates the relationship between plant traits,soil physicochemical properties,and rhizosphere phosphate-solubilizing bacterial communities of different habitat Suaeda salsa plants through laboratory experiments and high-throughput sequencing technology.In addition,efficient and salt-tolerant phosphate-solubilizing bacteria are isolated and screened,and their strain characteristics,optimal indoor conditions,and the promotion effect of mixed application of phosphate-solubilizing bacterial agents on Suaeda salsa growth are explored,in order to provide theoretical basis for the adaptation mechanism of salt-tolerant plants,microorganisms,and soil habitats in response to environmental changes under salt stress.The main research results are as follows:（1）Three types of saline habitats exhibit different plant phenotypes in Suaeda salsa.During the fruiting stage,the EC and p H values of the soil samples in the intertidal zone were higher than those of the transition and inland zones,while the AP content in the soil samples of the inland zone was significantly higher than that in the soil samples of the intertidal and transition zones.During the fruiting stage,the total phosphorus content in the leaf organs of Suaeda salsa was significantly higher than that in the root and stem organs,and the total phosphorus content of the plant increased from the beginning to the end of the reproductive phase while the total phosphorus content of the root and stem organs decreased with time.During the entire fruiting stage,the total phosphorus content in the leaf organs of the Suaeda salsa in the three habitats was significantly higher than that in the root and stem organs,and the total phosphorus content in the plant increased at the end fruiting period compared to the entire fruiting period.The total phosphorus content in the root and stem organs of Suaeda salsa decreased with increasing time.（2）During the entire fruiting period,the abundance and diversity of rhizosphere phosphate-solubilizing bacterial communities gradually decrease from the inland zone to the intertidal zone.The relative abundance of Actinobacteria and Streptomyces is the highest at the phylum level of rhizosphere phosphate-solubilizing bacteria in Suaeda salsa,and there are significant differences among groups.At the genus level,the dominant genera are Mesorhizobium,Nitratireductor,Skermanella,Aurantimonas and Sulfitobacter.NMDS analysis reveals significant differences in rhizosphere phosphate-solubilizing bacterial communities of Suaeda salsa among different habitats.The structural equation model shows that soil TN,EC,AP,and AK are the dominant factors that affect the community of phosphate-solubilizing bacteria and plant traits.（3）A total of 21 efficient and salt-tolerant phosphate-solubilizing bacteria were co-isolated from the rhizosphere soil of Suaeda salsa,Quantitative determination showed that all strains had the ability to solubilize inorganic phosphorus and that 17strains produce indole acetic acid（IAA）,while 5 strains could fix nitrogen.（4）The optimal cultivation conditions for the phosphate-solubilizing bacterium PSBDYJP20210001 are as follows:carbon source was glucose,nitrogen source was（NH₄）₂SO₄,salt concentration was 1%,carbon-nitrogen ratio was 200:1,p H was 5,and temperature was 25°C.The optimal culture conditions for the composite bacterial agent of phosphate-solubilizing bacteria PSBDYJP20210001 and PSBDYJP20210002are:carbon source was glucose,nitrogen source was（NH₄）₂SO₄,salt concentration was1%,carbon-nitrogen ratio was 200:1,p H was 6,and temperature was 30°C.（5）Indoor germination rate and growth promotion experiments showed that the germination rate,plant height,and root length of all treatment groups were significantly higher than those of the control group.The germination rate of the group treated with composite bacterial agent was higher than that of the group treated with single bacterial agent,and the germination rate of the composite bacterial agent 1:2treatment group was significantly higher than that of the other treatment groups.Especially,the effect of the composite bacterial agent inoculated with the 1:2 treatment was more significant.Field growth promotion results showed that the plant height of all different ratio composite bacterial agent treatment groups was significantly higher than that of the control group,and the plant height and root length of the composite bacterial agent 5:3:2 treatment group were higher than those of other treatment groups and significantly higher than those of the control group and the 1:1:1 treatment group.