Effects Of Nitrogen Application Rate On Winter Wheat Soil Microbial Community Structure And Soil Physicochemical Properties

Nitrogen fertilizer is essential for wheat growth and yield.However,excessive application of nitrogen fertilizer will cause excess soil nutrients in wheat fields and pollution to groundwater,and the physicochemical properties of soil will also change with the amount of nitrogen applied.This is mainly due to changes in the soil ecosystem,which have an impact on the soil microbial community and soil physicochemical properties,therefore,through the study of soil microbial community and physicochemical properties,the soil nutrient status can be understood from multiple angles and levels.Therefore,the experiment set up 5 nitrogen gradient 0(N0,control),90(N6),180(N12),240(N16),300(N20)kg N·hm-2,combined with high-throughput sequencing,the effects of different nitrogen application rates on soil microbial communities and physicochemical properties were studied.In order to provided a basis for scientific fertilization and sustainable soil ecosystem in this area.(1)The p H and total carbon in the soil under different nitrogen application rates were not significantly different.Soil bulk density decreased with the increase of nitrogen application.The soil moisture content,total soil porosity,and soil aeration porosity showed an upward trend with the increase of nitrogen application rate.The soil three-phase ratios showed that the solid phase ratio gradually decreased with the increase of nitrogen application rate,and the liquid phase and gas phase ratio gradually increased.When the nitrogen application rate exceeded N12 treatment,the three-phase ratios did not change significantly.(2)The proportion of water stable aggregates in the 1-5mm particle sizes under N12 treatment is higher than that in other treatments,while the proportion of water stable aggregate in the 0.25-1mm particle size under N16 was lower than that of other treatments.The average weight diameter(MWD)and average geometric diameter(GMD)tend to increase first and then decrease with the increase of nitrogen application,the MWD and GMD under N12 were higher than other treatments.The stability rate is the largest and the destruction rate is the smallest under N0 treatment,while N20 treatment is the opposite.(3)Soil phosphatase and urease activities increased first and then decreased during the whole growth stage,and reached the maximum during the anthesis stage,while soil invertase activity showed a decreasing trend and reached its maximum during the winter stage.With the exception of the urease activity in anthesis stage and the invertase activity during harvest stage,higher soil enzyme activities were found under N12 treatment in other stage.(4)The amount of nitrogen applied had a significant effect on the soil microbial diversity index,the Chao1 and ACE indexes of bacteria,ammonia oxidizing bacteria(AOA),nif H and nir K bacteria under N12 treatment were significantly higher than those of other treatments.Except for nir K bacteria,the Shannon index under N12 treatment was significantly higher than other treatments;the Simpson index of AOA under N12 treatment was significantly higher than that under high nitrogen treatment.(5)Proteobacteria were found in the dominant groups of bacteria,nif H and nir K bacterial communities in phylum and class levels treated with different nitrogen application.It was found that the relative abundance of Acidobacteria and Chloroflexi at the phylum level of bacteria was significantly higher in the N0 treatment than in other treatments.N12 treatment significantly increased the relative abundance of Proteobacteria,Bacteroidetes,Nitrospirae and Rokubacteria.N16 treatment significantly increased the relative abundance of Actinobacteria;It was found at the AOA phylum level that N20 treatment significantly increased the relative abundance of Thaumarchaeota;N0 significant difference was found in the levels of nif H and nir K bacteria.(6)Cluster analysis found that AOA,nif H,and nir K bacteria were all distributed in a single cluster under N12 treatment.In the cluster analysis of bacteria,although N12 treatment was not in a separate cluster,N12 was farther away from N0 and N6.Redundant analysis showed that soil aerated porosity and GMD significantly affected the bacterial community structure,GMD,MWD,and stability rate significantly affected the AOA community structure,and GMD significantly affected the nir K anti-nitrification bacteria community structure,p H,and total Carbon significantly affected the community structure of nif H nitrogen-fixing bacteria(phylum level).Correlation analysis showed that bacterial diversity was significantly positively correlated with yield,AOA diversity was significantly negatively correlated with p H,and nir K bacterial diversity was significantly positively correlated with total carbon.(7)The spike,1000-grain weight and yield of nitrogen treatment were significantly higher than those without nitrogen treatment,and there was no significant difference in grains per spike and yield between N12,N16 and N20 treatments.The 1000-grain weight increased first and then decreased with the increase of nitrogen application rates.Grain per spike was negatively correlated with p H and soil bulk density and positively correlated with GWC and soil porosity.There was no significant correlation between wheat yield and soil physicochemical properties and microbial diversity.Based on the results of this study,it is shown that when the amount of nitrogen is 180 kg N hm-2,the yield and soil fertility can be improved,the soil microbial community structure can be effectively improved,and the foundation for maintaining the balance of the ecosystem can be laid.