| The nitrogen cycle is closely related to agriculture and environment.Crop yields increase via human-made N-fertilizer,but meanwhile the loss of nitrogen which lead to the imbalance of nitrogen cycle has led to global environmental problems.The rhizosphere provides critical interface supporting the exchange of resources between plants and their associated soil environment.Previous researches revealed that inoculation with diazotrophic strains could promote plant growth via biological nitrogen fixation,albeit instability and low efficiencies of crop inoculation were always related to environmental factors.And the ecological impacts as inoculum might have on the indigenous microrganisms have not been well investigated.In this study,Pseudomonas stutzeri A1501 and maize are suitable model for the research towards colonization of bacteria and contribution of diazotrophs to plant N via biological nitrogen fixation.And the objective of the present study also is to evaluate effects of water condition and diazotrophic Pseudomonas stutzeri A1501 inoculation on maize plant growth and community and activity of functional microorganisms involved in N cycle.Our work will provide theoretical base for increasing nitrogen fixation efficiency and reducing fertilizer usage in agriculture,by definiting the interaction between the associative diazotroph P.stutzeri A1501 and plant host.The major results show as followed:1,Using microscopy and plate counting method,significant higher amount of P.stutzeri A1501 was re-isolated from maize roots both in hydroponic and soil culture in the inoculation treatment than the no-inoculated control,indicating the colonization of P.stutzeri A1501 in maize rhizosphere.2,In the sterile soil microcosm planted with maize,the plant growth was significantly affected by water condition and diazotrophic P.stutzeri A1501 strains inoculation.Inoculation of maize with P.stutzeri A1501 caused a significant increase in shoot weight(32.5%)compared to the non-inoculated control in well-watered treatment.The same was the case under water stress although the rise(22.7% improved versus control of no A15 inoculation)was not statistically significant.In the natural soil microcosm planted with maize,the plant growth was also significantly affected by water condition,while the effect of P.stutzeri A1501 inoculation was not statistically significant.By using 15 N diluted method,average %Ndfa measured in maize stems was approximately 31.6% under well-watered conditions as compared to 20.1% under water stress.Therefore our study indicated the nitrogen of maize growth could be partially provided by diazotrophic P.stutzeri A1501 strains inoculation.3,By using pyrosequencing and qPCR,the effects of P.stutzeri A1501 inoculation and water condition on the structure of indigenous community and the population dynamics,and transcript activities of N-fixers and ammonia-oxidizing bacteria(AOB)and archaea(AOA)were examined.It revealed that water conditions affected populations and transcriptional activities,but not the compositions of diazotrophs and ammonia oxidizers in the rhizosphere.Besides,inoculation with P.stutzeri A1501 caused significant disturbances to the population and transcriptional activity of diazotrophs,AOB,AOA,and the composition of the diazotroph ic community in the rhizosphere.We also found significant differences between diazotroph and ammonia oxidizer distributions and activities in different soil compartments indicating niche differentiation.Diazotrophs favored the rhizosphere environment while AOB and AOA were predominant in the surface soil,and all likely influenced by soil properties such as organic C and N concentrations.Our study demonstrated a significant promotion of plant growth and clear disturbances on the rhizospheric microbiota caused by inoculation with N-fixing bacterium P.stutzeri A1501 although this consequence varied to a smaller extent between inoculation treatments than between the two soil compartments. |
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