Effect Of Nitrogen Application On Composition Characters Of Soil Microbial Communities

Continuous unreasonable use of N fertilizers could destroy the physical structure of soil and reduce the microbial activity and richness,resulte in soil fertility reduction.Soil microbe is the core of soil biological fertility and plays an important role in the strategic system of the sustainable agricultural development.In this study,according to three types of soils?black,alluvial and sandy soils?from a 6-year fertilizer field experiment,microbial community structure,the carbon substrates metabolic activities and microbial ammonia oxidation processes were investigated by using phospholipid fatty acid analysis?PLFA?,biolog-eco Plate,Illumina Mi Seq platform,real-time quantitative polymerase chain reaction?q PCR?and terminal restriction fragment length polymorphism?T-RFLP?.We discussed the effect of nitrogen application levels on soil microbiological characteristics and the relationship of soil microbiological environment under different soil types.These studies are very important for rational fertilization,soil nutrient balance management soil nutrient transformations andagricultural sustainable development.The main results are as follows:1. Application of different N fertilizers significantly effect the activity of soil microbial biomass and enzyme in three types of soils.The results showed that application of N fertilizers at rates of 168 kg/ha led to significantly higher microbial biomass carbon?SMB-C?in both black and alluvial soils compared with the no fertilization treatment,application of N fertilizers at rate of312 kg/ha significantly increased SMB-C and SMB-N for the sandy soils.The activities of?-glucosidase and urease were the highest in the black soils,and those were higher in the alluvial soils than that in the sandy soils.Nitrogen fertilization significantly increased the activities of urease in all soils at all rates?besides 312Kg/ha in the sandy soils?,the activities of peroxidase in the sandy soils,the activities of 4-MUB-?-D-glucoside in the alluvial soils.Overall,nitrogen fertilization generally maintained or reduced these enzyme activities in the sandy soils?besides 270 Kg/ha in the sandy soils?.2.Application of different N fertilizers lead to the differences of soils microbial communities characteristics and the carbon substrates metabolic activities in three types of soils.Results indicated that N fertilization significantly decreased microbial biomass,bacteria,fumgi,ratios of Gm+to Gm-and actinomycetes in both black and sandy soils regardless of application rate.Nitrogen fertilization also led to significant changes in soil microbial community composition.However,the change differences were gradually dismissed with increase in N application rate.Application of N fertilizers at rates of 312 kg/ha significantly decreased the carbon substrates metabolic activities of soil microbes in three types of soils.3.Application of different N fertilizers change the soil bacterial communities characteristics in three types of soils.Among the total 16S sequences,3190808 qualities?94.5%-98.4%?were classified as belonging to Bacteria.The main phyla across all samples were proteobacteria,actinobacteria,acidobacteria,accounting for 75%and 87%of the total sequences,respectively.The abundance of acidobacteria and alphaproteobacteria were higher in the black than the alluvial and sandy soils,the abundance of gemmatimonadetes was higher in the alluvial soils than that in the black soils,which was also higher than that in the sandy soils.We found the effects of different N application rates on microbial communitiesin three types of soils.Compared with N fertilizers at rates of 168 kg/ha,nitrogen fertilization at rates of 312 kg/ha significantly increased relative abundances of proteobacteria,actinobacteria,gemmatimonadete and chloroflexi,while relative abundances of acidobacteria,bacteroidete and thaumarchaeota were significantly decreased in three types of soils under nitrogen fertilization.Principal component analysis?PCA?showed that the bacterial community of the no fertilization treatment and application of N fertilizers at rates of168 kg/ha was markedly different fromapplication of N fertilizers at rates of 312kg/ha.Redundancy analysis?RDA?results suggested that N fertilization influenced soil microbial communities mainly through its effect on soil p H?available N?TN and SOC.4.Application of different N fertilizers change the nitrification potential?PNA?and ammonia oxidizing bacterial communities characteristics in three types of soils.PNA were significantly influenced in the black and alluvial soils,while PNA were significantly decreased in the sandy soil sunder nitrogen fertilization.Relative abundances of ammonia-oxidizing archaea?AOA?were higher than relative abundances of ammonia-oxidizing bacteria?AOB?in three types of soils.We also observed that relative abundances of AOA and AOB decreased significantly with increase in N application rate in the sandy soils,and had no significant effect in the alluvial soils,while relative abundances of AOB increased significantly with increase in N application rate in the black soils.By T-RFLP analysis,we found that microbial community of AOA was more easily influenced by nitrogen fertilization than AOB.Especially in the sandy soils,nitrogen fertilization significantly decreased the microbial diversity of AOA.There was a correlation?p<0.05?between p H?TN?NH₄⁺-N?NO₃^--N?PNA and microbial community of AOA.