| Pseudomonas putida Rs-198（P.putida Rs-198）was isolated from the rhizosphere of cotton in saline soil in Xinjiang in the early stage of this laboratory which can dissolve phosphorus,fix nitrogen and produce indole acetic acid（IAA）.In this paper,the IAA synthesis pathway of Rs-198 was explored by externally adding IAA intermediate products to the culture medium.The pot experiment verified the ability of P.putida Rs-198 microbial inoculants（Rs-198 inoculum）to replace chemical fertilizers.Field experiments explore the effects of Rs-198 inoculum on soil improvement and microbial diversity.The main research results are as follows.IAA content in the culture medium which coatain 50 mg·L-1,100 mg·L-1,150 mg·L-1,and 200 mg·L-1was 2.47 times,4.02 times,4.88 times and 5.07 times than NA medium at 24 h.The cell concentration of Rs-198 which was cultured in medium contain 150 mg·L-1 and 200 mg·L-1 tryptophan decreased by 14.80%and 17.45%compared with NA medium.The growth trend of Rs-198 which was cultured in medium contained 50 mg·L-1 tryptophan was basically unchanged compared with that in NA medium.The content of IAA reached the maximum at 96 h,which was 55.52 mg·L-1.And it was 3.58 times than the IAA content in NA.In addition,Rs-198 could use tryptophan,indole pyruvic acid（IPyA）,and tryptophan（TAM）to synthesize IAA,indole lactic acid or tryptanol.It proved that P.putida Rs-198 contains multiple routes to synthesize IAA.Rs-198 inoculum and chemical fertilizer combined potted experiment results show that the application of Rs-198 inoculum greatly promoted the seedling formation of pepper,which was 36.64%-44.00%higher than CK.In terms of biomass,the combined treatment of Rs-198 inoculum and chemical fertilizer compared with CK treatment increased the fresh weight,dry weight,root length and plant height of pepper by 46.44%-77.89%,33.88%-71.07%,7.00%-10.87%and 24.26%-41.83%,respectively.The order of soluble protein content from high to low was:T4>T3>T2>T1>CK.POD activity from high to low was:CK>T1>T2>T4>T3.These results indicated that Rs-198 inoculum treatment with chemical fertilizers increased the water-holding capacity of pepper leaves,effectively alleviated damage to plants by active oxygen during plant growth,and promoted the plant’s absorption of nutrients and water from the rhizosphere.Among them,T3 treatment had the best effect,indicating that Rs-198 inoculum replaced 25%of chemical fertilizers and effectively promoted the growth of pepper.The results of field experiments showed that the use of Rs-198 inoculum could promote the fresh weight,length and width of grapes,which were 13.59%-17.24%,5.53%-6.16%and 3.64%-4.36%higher than CK,respectively.The AP content,alkaline phosphatase activity,and invertase activity of the soil treated by Rs-198 inoculum were increased by 12.6%-55.3%,26.1%-27.15%,and 18.67%-48.33%,respectively,compared with CK.Compared with CK soil,the use of Rs-198 inoculum promoted the diversity of species in the rhizosphere soil of grapes.The relative abundances of Halonas,Delftia,Brevibacterium,Acinetobacter,Pseudomonas,Aquicella,Flavobacterium,Niastella,Arenimonas,Pontibacter,Reyranella,Mesorhizobium,Phaselicystis,and Acidibacter increased significantly compared with CK soil.The relative abundances of Nitrospira,Aeromicrobium,and Polycyclovorans decreased significantly compared with CK soil.Analysis of COG function prediction results showed that Rs-198inoculant stimulated microbial metabolism in the rhizosphere.Therefore,Rs-198 was a strain capable of synthesizing IAA through various routes,and the microbial inoculum prepared by it could replace 25%of chemical fertilizers.Microbial agents promoted plant growth,increased soil species diversity,stimulated microbial metabolism,which provided a theoretical basis for the popularization and use of microbial agents. |
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