Screening Of Plant Growth-promoting Rhizobacteria And Investigation Of Their Promoting Effects In Alpine Meadow In The Northwester Sichuan

In recent years,under the combined influence of various human and natural factors,the degradation of alpine meadows in northwestern Sichuan has been increasing,which has brought far-reaching impacts on the regional ecological environment and animal husbandry development.The application of microbial bacterial fertilizer may be an important way to restore the degraded meadow in the future,and the microbial fertilizer using plant rhizobacteria as an inoculant has the characteristics of safety,circulation and non-pollution,and is provided for the preparation of microbial bacterial fertilizer in alpine meadow soil.The rhizobacteria resources of alpine meadow in northwestern Sichuan are abundant,but research and development are obviously insufficient.Therefore,this paper studies the diversity of rhizosphere growth-promoting bacteria of dominant plants in alpine meadow in northwestern Sichuan,and simultaneously screens and isolates the strains to obtain high-efficiency strains and evaluate the growth promotion of plant rhizosphere growth-promoting bacteria.The effect is to clarify the composition of the rhizosphere probiotics flora in the alpine meadow soil,to explore the development of microbial bacterial fertilizer to provide high-quality bacterial sources,and to provide a new way for the restoration and management of the alpine meadow ecosystem.（1）In this study,high-throughput sequencing technology was used to analyze and sequence the 16Sr DNA gene V4 of the dominant plants rhizosphere soil bacteria in Kobresia setchwanensis,Gueldenstaedtia diversifolia Maxim,Aster alpinus,Elymus nutans and Astragalus mongholicus.The results showed that the bacterial community and richness of rhizosphere soil of Kobresia setchwanensis are the tallest.The proteobacteria,acidobacteria,sphingomonas,and phagobacteria were in a higher abundance position in the horizontal and genus level bacterial population structure;functional prediction analysis showed that the coding cell membrane of the rhizosphere of Kobresia setchwanensis in genes functional for transport,functional genes encoding translation,replication and repair are higher than other samples.The rhizosphere of Gueldenstaedtia diversifolia Maxim encodes functional genes for xenobiotics biodegradation and metabolism,glycan biosynthesis and metabolism,and encodes signal transduction and lipid of qualitative metabolism are higher than other samples.（2）44 strains of bacterial strains were isolated from the rhizosphere of dominant plants in alpine meadow soil.Count the distribution of bacterial strains in different parts of the plant rhizosphere,and it was found that the distribution of the surface of the root system was significantly more than that in the root and the surface soil.25 strains capable of dissolving inorganic phosphorus and 24 strains capable of dissolving organic phosphorus were screened.As a result,it was found that the amount of phosphorus dissolved by the inorganic phosphorus strains was between 8.91μg·m L^-1 and90.27μg·m L^-1.The strain RPNY4 isolated from the rhizosphere of Gueldenstaedtia diversifolia Maxim was the hightest amount of phosphorus-dissolving and the strain RPKS3 isolated from Kobresia setchwanensis with the smallest amount of phosphorus-dissolving.The amount of phosphorus dissolved by the organic phosphorus strains was between 10.58μg·m L^-1and 75.13μg·m L^-1.Among them,the strain RPKY3 isolated from Gueldenstaedtia diversifolia Maxim had the largest amount of dissolved phosphorus.（3）20 strains with nitrogen-fixing ability were selected from 44 rhizobacteria strains.Quantitative determination of the nitrogenase activity of these nitrogen-fixing strains was between 5.23 nmol（C₂H₄）h^-1·m L^-1-64.87 nmol（C₂H₄）h^-1·m L^-1,of which the strain RPKZ4 isolated from Aster alpine was the most active,the strain RPKS5 isolated from Kobresia setchwanensis has the smallest nitrogenase activity;among the nitrogen-fixing strains,the number of strains with nitrogenase activity below20 nmol（C2H4）h^-1·m L^-1（5 strains）is the largest,accounting for 25.00%of the strains;strains with nitrogenase activity more than 50 nmol（C2H4）h^-1·m L^-1 are RSNZ3,RPKZ4,HPKY3 and HPKY4,respectively.（4）21 strains with potassium-resolving ability were selected from 44 rhizobacteria strains.As a result,it was found that these strains can stably dissolve potassium and the amount of potassium-dissolving varies widely（P<0.05）.The potassium-resolving amount was between 9.23μg·m L^-1 and 73.21μg·m L^-1.Among them,the strain RSNY4isolated from the rhizosphere of Gueldenstaedtia diversifolia was the largest,and the one with the smallest potassium release is the strain RSKS4 isolated from Kobesia sichuanensi;the number of strains with potassium-resolving amount above 40μg·m L^-1was the largest（9 strains）,accounting for 42.86%of the total strains.（5）Through comprehensive evaluation of the strain morphology and physiological and biochemical characteristics,12 rhizobacteria strains with excellent growth promoting properties were screened from 44 bacterial strains,and their species were identified by 16Sr DNA gene sequence analysis.12 strains of excellent bacteria were used to design different bacterial liquid fertilizer formulas,and the results of pot experiments inoculated with different bacterial liquid formulas showed that the 12PGPRs screened had excellent growth-promoting characteristics,they can significantly promote plant growth compared with sterile liquid treatment,increasing their seedling height,stem and leaf length,and aboveground biomass.The results of the study will provide basic data for the development of rhizosphere growth-promoting bacterial strain resources of alpine meadow plants in northwestern Sichuan,and provide a theoretical basis for the future development of microbial fertilizers.