Effects Of Combined Application Of Organic Fertilizers And Nitrogen Fertilizers On The Diversity Of Nitrate Dissimilation And Reduction To Ammonium In Greenhouse Vegetable Fields

In recent years,the dissimilatory reduction of nitrate to ammonium（DNRA）has become a major research hotspot in the soil nitrogen cycle.It has been widely studied in oceans,lakes,wetlands,and sludge,but it has been widely studied in facility soil ecology.The DNRA process in the system is rarely reported.The dissimilative reduction process of nitrate in soil is mainly divided into two ways:denitrification and dissimilative reduction of nitrate to ammonium（DNRA）.This thesis is based on the long-term fertilization experiment of Shenyang Agricultural University,under the condition of combined application of organic fertilizer and nitrogen fertilizer,that is,no fertilizer treatment N₀,single nitrogen fertilizer treatment N₁,single application of double nitrogen fertilizer treatment N₂,single application of organic fertilizer Fertilizer treatment MN₀,organic fertilizer combined with nitrogen fertilizer treatment MN₁,and organic fertilizer combined with double nitrogen fertilizer treatment MN₂.Using molecular biology methods,high-throughput sequencing of DNRA functional genes in facility soils was performed,and DNRA bacterial community composition,bacterial diversity,and correlation with other physical and chemical factors and biological characteristics were analyzed.It aims to clarify the relationship between DNRA flora and soil fertility,and at the same time provide a research basis for the rational use of fertilizers and the emission reduction of N₂O gas.The main research results of this paper are as follows:1.In terms of basic physical and chemical factors of soil,long-term organic fertilizer combined with nitrogen fertilizer can alleviate soil acidification,reduce soil bulk density,improve soil water retention capacity,and improve soil porosity.At the same time,the nutrient content and microbial biomass content of the soil are increased.On the whole,the effect of doubling nitrogen fertilizer with organic fertilizer is the best;long-term single application of nitrogen fertilizer increases the content of ammonium nitrogen and nitrate nitrogen in the soil,and increases the degree of soil acidification.2.In terms of soil carbon and nitrogen cycle related enzyme activities,long-term organic fertilizer combined with nitrogen fertilizer can significantly increase the activity of hydrolytic enzymes in the soil;long-term single application of nitrogen fertilizer and excessive single application of nitrogen fertilizer can significantly increase soil nitrate reduction Enzyme,nitrite reductase and hydroxylamine reductase activities,combined with organic fertilizer treatments,the results are opposite;the order of soil comprehensive hydrolase activity is:MN₂>MN₀>MN₁>N₁>N₀>N₂.3.In terms of DNRA and denitrification gene abundance,N₂ and MN₂ inhibited the copy number of nirS,nirK,nosZⅠ,and nrfA genes in the soil to a certain extent.On the whole,MN₁ treatment contained the largest number of gene copies,followed by It is MN₀.4.Through high-throughput sequencing analysis,a total of 5 phyla were defined in all experimental treatments,namely Proteobacteria,Verrucomicrobia,Nitrospirae,and Actinobacteria and other bacteria that exist but are not classified（Others）.Among them,Verrucomicrobia and Nitrospira phylum are the dominant flora in all treatments.A total of 12 genera were defined in all treatments,among which the most abundant is unclassified＿d＿＿Bacteria,followed by Anaeromyxobacter,Nitrospira,Lacunisphaer,Archangium,Myxococcus,etc.On the whole,Myxobacteria and unclassified bacteria are the dominant flora in DNRA of facility soil.5.Correlation analysis studies show that there is a close correlation between soil physical and chemical properties and enzyme activities.In all treatments,the four hydrolase activities are significantly related to the measured physical and chemical indicators;nitrate reductase is significantly related to total nitrogen and bulk density Related;Nitrite reductase is significantly related to total organic carbon,organic matter,and microbial biomass carbon and nitrogen;Hydroxylamine reductase is significantly related to total organic carbon,nitrate nitrogen,bulk density,organic matter,total nitrogen,and microbial biomass carbon and nitrogen.6.The environmental factors that affect the diversity of DNRA flora include organic matter,nitrate nitrogen,water content,bulk density,p H,carbon-nitrogen ratio,etc.Among them,the DNRA flora has a significant positive correlation with the carbon-nitrogen ratio;DNRA flora and The activities of urease,catalase,cellulase,nitrite reductase and hydroxylamine reductase are most closely related.According to the genus of bacteria,the genus Sorangium is most closely related to the activities of enzymes related to the carbon and nitrogen cycle,and there is a significant positive correlation with the activities of various enzymes.