Influence Of Field Managements On N₂O Emissions And The Abundance Of N-cycling Related Functional Genes In Vegetable Field

Recently,China's vegetable planting acreage increased year by year.Typically,vegetable fields undergo intensive management involving multiple cropping,high nitrogen(N)application rates,and frequent farming practices.The cropping pattern with excessive N fertilizer use has resulted in serious environmental problems,such as N loss and soil acidification.In addition,the excessive use of N fertilizer is considered a dominant source of nitrous oxide(N2O)emissions from agricultural soils.Thus it is necessary to carry out research in studying the influence of field managements on N2O emissions and the abundance of N-cycling related microbes in vegetable ecosystem.The primary objective of this study was to gain an insight into the effect of different field managements which decrease N2O emissions in vegetable field and the N2O emission reduction mechanism.Therefore,we used the indoor incubation experiments and field experiments in this study,which is divided into the following three sections:(1)To evaluate the effects of biochar on N2O emissions and microbial mechanism,the indoor experiment was carried out in an intensive vegetable field applied biochar using real-time quantitative PCR technology.(2)To evaluate the effects of organic fertilization on N2O emissions and microbial mechanism,the indoor experiment was carried out and the conversionin of nitrogen,the abundance of microbial and N2O emissions were observed dynamically in an intensive vegetable field applied biochar using real-time quantitative PCR technology.(3)To evaluate the effects of nitrification inhibitor on the abundance of N-cycling related functional genes,N2O emissions,vegetable yields and yield-scaled N2O emissions,a 1-yr field experiment was carried out in an intensive vegetable field using real-time quantitative PCR technology,the static chamber and gas chromatography method.The main findings are as follows:1.The laboratory experiments results of combined application of biochar and nitrogen fertilizer showed biochar application significantly increased the content of soil organic carbor and total organic nitrogen by 40.4%and 8.9%,respectively.Meanwhile biochar simulated amoA-AOB and nosZ gene copy numbers.Biochar application had no significated effects on N2O emissions which because of the low background value of N2O emissions.Nitrogen application significantly increased N2O emissions by 6.7 times compared with CK treatments,following with higher content of inorganic nitrogen and nirS,nirK,nosZ gene copy numbers.Under the coditon of conventional nitrogen application,the addition of biochar significantly increased the content of SOC,cation exchange capacity,the abundance of amoA,nirK,nirS and nosZ gene copy numbers.Biochar addition reduced N2O emissions by 33.3%,which ducing the nosZ genes promoting complete denitrification and accerated reverting N2O to nitrogen(N2).A significant interaction was observed between biochar and nitrogen ferilization,which suggested that application of biochar and N fertilizer increased the risk of N2O emissions of vegetable land.2.The laboratory experiments results of combined application of organic fertilizer and biochar showed compared with the CK treatment,the treatments receiving N fertilization(N,N+B,N+M and N+B+M)greatly inhibited the copies of ammonia oxidizing bacteria(amoA-AOB)and ammonia oxidizing archaea(amoA-AO A),stimulated the copies of nirS,nirK and nosZ functional genes and increased N2O cumulative emissions throughout the incubation period.Although it greatly increased nirK and nirS genes by 58.8%and 7.1%,respectively,and had no significant effects on the abundance of amoA-AOA,amoA-AOB and nosZ functional genes.Whereas the N+M treatment had no significant influence on N2O emissions as compared with the N treatment.Compared with the N treatment,the N+B treatment significantly increased soil pH by 11.1%,and simulated the copies of amoA-AOB,amoA-AOA,nirS,nirK and nosZ genes by 105.8%,57.3%,22.0%,176.2%and 229.2%,respectively,thus decreased cumulative N2O emissions by 58.1%.The N+B+M treatment greatly stimulated amoA-AOB,nirK,nirS and nosZ gene copies by 30.7%,68.7%,6.5%and 99.2%,respectively,had no significant effects on amoA-AO A gene numbers and finally decreased cumulative N2O emissions by 14.4%as compared with the N treatment.The results show that organic manure addition had no significant effects on N2O emission.The combined application of organic manure and biochar significantly decreased N2O emissions which mainly attributed to biochar.3.The field experiments results of combined application of nitrification inhibitor and biochar showed the applicaton of nitrification inhibitor(N+D treatments)significantly increased soil pH on average by 18.1%(p<0.05),had no significant effects on the abundance of amoA-AOB,nirS,nirK and nosZ genes,however significantly decreased amoA-AOA by 16.5 times compared with CK treatments.The application of nitrification inhibitor significantly reduced seasonal N2O emissions during the cold period and had no effects on annual N2O emissions.Biochar addition(N+B treatments)greatly increased soil organic carbon(SOC)by 28.3%and total nitrogen(TN)by 9.2%compared with CK treatments.Biochar addition significantly increased amoA-AOA,amoA-AOB and nirS,nirK,nosZ gene copy numbers by 34.3%,4.8%,38.7%,29.3%and 17.8%,respectively.The application of biochar significantly reduced seasonal N2O emissions during the cold period and had no effects on annual N2O emissions.Compared with the N+B and N+D treatments,the N+B+D treatments had no significant effects on annual N2O emissions.The results showed that the application of nitrification inhibitor significantly reduced seasonal N2O emissions during the cold period and had no significant effect on the annual N2O emissions.The addition of nitrification inhibitor(DCD)significantly inhibited the nitrification activity by amoA-AOA,accompanied by dereasing the abundance of amoA-AOA.gene.Therefore,this study indicated that biochar application effectively increased soil carbon pool and improved soil physical and chemical properties.The application of biochar significantly increased the abundance of amoA-AOA?amoA-AOB and nirK?nirS and nosZ genes.The application of biochar increases the risk of N2O emissions of vegetable soil mainly due to accelerate N2O translating to N2.The addition of organic manure had little effects on N2O emission although it increased the gene abundance of nirS and nirK genes,but had no significant effects on amoA-AOA,amoA-AOB,nosZ genes.The application of nitrification inhibitor effective improved soil acidification and inhibitted the abundance of amoA-AOA gene,and had no significant effects on amoA-AOB,nirS,nirK and nosZ gene copy numbers.Although they had no significant influences on the annual N2O emissions,biochar and nitrification inhibitor significantly reduced yield-scaled N2O emissions.However,under the conditions of conventional fertilization,the combination of biochar and DCD is not superior to single application in the intensified vegetable field.