Changes Of Microbial Population Structure In Corn Rhizosphere Under Different Nitrogen Application Levels

The long-term application of nitrogen fertilizer can change the soil ecological environment of farmland,change soil nutrient content and may have direct or indirect influence on the community structure and diversity of soil microbes.Different soil types because of their own composition,may also have different effects on soil microbes.To understand the changes of microbial community structure in soil under different nitrogen levels,in this paper,sandy soil,meadow black soil and alluvial soil in corn rhizosphere treated with different nitrogen application levels for a longer period of time were studied.Methods employed for the study were 16S rDNA and ITS Illumina Miseq sequencing methods and Real-Time PCR,modern nucleic acid molecular diagnostic techniques.Structure composition and diversity of bacteria and fungi population of corn rhizosphere microbes,changes in the abundance of the major nutrient cycling function genes and soil ecological environment in three soil types under different nitrogen application levels were analyzed.The objectives of this study were to provide a theoretical basis for rational application of nitrogen fertilizers,nitrogen fertilizer management,and improvement of the agricultural ecological environment.The main results obtained from the study were as follows:?1?The change of soil pH of three soil types under different nitrogen levels showed the same trend,that is the soil pH decreased with the increase of nitrogen application,the long-term application of nitrogen fertilizer can lead to soil acidification.The three rhizosphere soils showed no significant difference in total soil nutrients?TOC,TN,TP and TK,P>0.05?,at different nitrogen levels.However,the difference of soil available nutrient content was significant?P<0.05?.The content of NH₄⁺-N and NO₃^--N under different treatments were significantly different,and the content of NO₃^--N in soil increased with an increase of nitrogen application.The NO₃^--N content of the three soil types was highert when the nitrogen application was 312 kg·ha^-1.?2?The diversity of rhizosphere soil bacterial communities were higher when nitrogen application rate was 168 kg·ha^-1,whiles the bacterial community diversity was lower at 312kg·ha^-1,but there was no significant difference among the treatments?P>0.05?.The relative abundances of bacterial communities in the rhizosphere soil between the five nitrogen levels were significantly different.Among them,Proteobacteria was the main dominant bacteria group,accounting for about 25%-40%.The second was Bacteroidetes,which accounted for 11%-26%.Again,Actinobacteria and Fimicutes,accounting for 10%-37%and 4%-22%.RDA analysis showed that soil pH,water content,TOC,TN,TP and other environmental factors could affect the community composition of rhizosphere bacteria,and soil pH was the main influencing factor.?3?The similarity of dominant fungi in rhizosphere fungi between different treatments.Among them,Ascomycota was the dominant colony of fungi,accounting for about 44%-72%.The second was Basidiomycota,with a relative abundance of 10%-47%.Others were,Zygomycota,Chytridiomycota and Glomeromycota.The results of RDA analysis showed that soil pH,water content,TOC,TN and TP were the main environmental factors affecting the community composition of rhizosphere fungi.?4?Soil types had an important influence on the community composition of rhizosphere microorganisms.The result of the study showed that,regardless of the amount of nitrogen fertilizer,the relative abundance of rhizosphere bacteria and fungal communities in the three soils were significantly different in each classification level.The results of Anosim and NMDS analysis showed that the samples from different soil types were far away from each other,with great differences.This indicates that soil type has certain influence on the community composition of rhizosphere microorganisms.Among the three soil types,the diversity of microbes in the meadow black soil was the highest,and alluvial soil gave the lowest microbial diversity.?5?There was significant difference?P<0.05?in the relative abundance of the nutrient cycling functional genes of the rhizosphere soil under different nitrogen levels.Nitrogen application and soil type were the main influencing factors.The relative abundance of AOA and AOB in sandy soil decreased and increased respectively with the increase of nitrogen application.In the meadow black soil,the relative abundance of AOA,AOB,cbbl and nosZ functional genes were relatively high among the nitrogen levels,whiles the relative abundance of nifH and actinomycetes varied among nitrogen application rates.In alluvial soil,the relative abundance of soil carbon and nitrogen cycle function genes were higher when the amount of nitrogen application was 312 kg·ha^-1.Correlation analysis results showed that,the relative abundance of functional genes of AOB,nifH and actinomycetes was not significantly correlated with the measured soil environmental factors,while the AOA,cbbl and nosZ functional genes were more susceptible to the changes of the soil environment.