Microbial Regulation Of Soil Phosphorus Availability In Saline-Alkali Farmland Of The Yellow River Delta

As a major backup soil resource,saline land can be exploited to its full potential to alleviate the increasingly serious human-land conflict.The nutrient imbalance of nitrogen and phosphorus triggered by long-term high salt and alkalinity is one of the main challenges for saline land improvement and utilization.For phosphorus in saline soils,it faces the double pressure of low effectiveness and susceptibility to loss by salt washing.Microbial improvement has received much attention due to its green economy,especially phosphorus-dissolving bacteria and phosphorus-polymerizing bacteria as phosphorus cycle-related microorganisms are expected to pry up the phosphorus cycle of saline soils,and play an important role in increasing the effective phosphorus content,promoting crop growth and reducing phosphorus loss due to salt washing.Currently,the source of phosphate-solubilizing bacteria is common soil,and its colonization and function under saline-alkali conditions are often limited.Phosphorus-accumulating bacteria are widely used in wastewater treatment,such as activated sludge,but their application in regulating soil phosphorus activity in agriculture is rarely reported.Based on the above background,this thesis intends to screen saline-tolerant strains with efficient solubilization of inorganic phosphorus and mineralization of organic phosphorus from saline agricultural fields in the Yellow River Delta,combined with a highly efficient strain of phosphorus-polymerizing bacteria Pseudoalteromonas sp.CF8-6 already in the laboratory,and study the interaction effect of phosphorus-polymerizing and phosphorus-dissolving bacterial agents and their sequential addition on soil phosphorus loss,morphological transformation and effectiveness.The effect of the interaction between the phosphorus-polyphosphate and phosphorus-dissolving bacteria and their sequential addition on soil phosphorus loss,morphological transformation and effectiveness were investigated.Meanwhile,batch and pot experiments were conducted using assimilated sludge and pre-screened phosphate solubilizing bacteria in our laboratory to investigate whether phosphate solubilizing bacteria can promote phosphorus release from activated sludge and provide ideas for resource utilization of sludge.The main research contents and conclusions are as follows:(1)Six salt-tolerant strains were screened from the saline-alkali farmland of the Yellow River delta,the strain S2-5 with the strongest ability of dissolving inorganic phosphorus reached 273.37 mg/L in 5 days in PVK medium.The phosphorus-solubilizing ability of the mixture was tested under different phosphorus,carbon and nitrogen sources.In PVK Medium,the effect of phosphate-solubilization of composite bacteria was better than that of single bacteria,and the highest phosphorus-solubilization rate was 333.99 mg/L.S2-5+ S2-13 was selected as the test strain to carry out the follow-up soil culture experiment.It was found that the content of available phosphorus in soil was increased by 72.14%by inoculating the compound strain,the soil pH decreased by 0.34.(2)The effect of phosphorus solubilizing bacteria secretion on the release of organic phosphorus enrichment by polyphosphorus bacteria was investigated by interactive experiments and NMR detection,and the role of microbial agents in reducing phosphorus loss and improving phosphorus availability was investigated by inoculating polyphosphorus bacteria and phosphorus solubilizing bacteria in batches.The experimental results showed that the secretion of S2-5 and S2-13 of Phosphorolytic bacteria could promote the decomposition and release of microbial organic phosphorus enriched by the polyphosphorus bacteria CF8-6;the inoculation of CF8-6 significantly reduced the loss of soluble phosphorus by 22.6%and the loss of particulate phosphorus by 17.3%during the drenching process.Inoculation of phosphorus-dissolving bacteria after drenching significantly enhanced the phosphorus effectiveness,the abundance of culturable phosphorus-dissolving bacteria and the activity of soil alkaline phosphatase,especially the combined treatment of phosphorus-polyphosphate and phosphorus-dissolving bacteria had the most significant effect on the enhancement of effective phosphorus in soil.The results of the pot experiment showed that the combined treatment of the fungicides increased the above-ground biomass of wheat by 13.1%and the phosphorus content by 11.3%.In addition,soil microbial community analysis showed a reduction in bacterial community abundance and diversity in the soil after the bactericide treatment,with the dominant microbial species in Bacteroides,Blastomonas and Acidobacter largely unaffected by the introduction of exogenous bacteria,The dominant species of Patesci bacteria and Actinobacillus were inhibited by PAB inoculation.The abundance of the Bacillus was increased in the two experimental groups inoculated with Bacillus S2-5.(3)It was demonstrated by interaction experiments that the phosphorus understanding bacteria could promote the release of phosphorus from activated sludge.The pot experiment demonstrated that the application of activated sludge significantly increased the nutrient contents of soil organic matter,N,P,and K.as well as the plant height,biomass,and phosphorus content of potted plants,while the combined treatment of inoculated phosphorus-dissolving bacteria and activated sludge produced significant synergistic effects,with plant height increased by 7.51%and 6.96%,and plant phosphorus content increased by 33.86%and 66.74%.The phosphorus-relieving bacteria treatment increased the relative content of some organic acids,while the sludge treatment also significantly increased the content of protein and nucleic acid metabolites in the soil.In summary,this study screened out saline-tolerant complex bacterial groups with efficient phosphorus solubilization ability,explored the effect of synergistic action of polyphosphorus bacteria and phosphorus solubilizing bacteria on soil phosphorus,and developed a microbial means to regulate soil phosphorus based on polyphosphorus bacteria and phosphorus solubilizing bacteria.The effect of dephosphorylating bacteria on phosphorus release from sludge was also verified,which provided ideas for sludge resource utilization and saline land improvement based on microbial means.