| The continuous increase of nitrous oxide(N2O)concentration in the atmosphere is a global concern,and agricultural soil is a major source of N2O.Based on the flux measurements for decades in situ,N2O emissions have been attributed to N2O emission peaks resulted from natural anthropogenic or perturbations.With the characteristics of the high level of water and fertilizer inputs,high nitrogen(N)application rates and frequent farming practices,vegetable field has become an important factor of frequent and higher N2O emission peaks.Amendment of nitrification inhibitors has a significant impact on N2O emission in vegetable field with long-term nitrogen(N)fertilizer application.N2O emissions is produced by microorganisms in soil.The formation of N2O is mainly by the nitrification and denitrification processes.Therefore,the investigation of N fertilizer and nitrification inhibitors influences on N2O related microbial gene copy numbers and their potential activities in vegetable soil might be helpful to clarify the microbial mechanisms of N fertilizer and nitrification inhibitors on N2O emissions from vegetable soil.Therefore,we used the field experiments in this study,which were divided into the following two sections:(1)A two year field experiment was conducted in a continuously cultivated vegetable cropping system in Nanjing including five experimental treatments(without fertilizer(CK),regular urea(N),urea+dicyandiamide(DCD),urea+nitrapyrin(CP),urea+dimethylpyrazole phosphate(DMPP))and it performed in triplicate was carried out in an intensive vegetable field using the static chamber and gas chromatography method.(2)A field experiment using an isotopocule mapping approach(δ15NSPN2O and δ18ON2O/H2O map)in conjunction with molecular techniques were used to understand the mechanism of nitrification inhibitors(NI,nitrapyrin-SNI and Sorghum bicolor L.-BNI)for N2O mitigation in a Baby bok choy(Brassica chinensis L.)vegetable soil.The results of our study are summeraized as follows:1.In our study,N application significantly increased N2O emissions.N2O emission factors amounted to 1.9%.Compared with the conventional fertilization treatment,the treatment CP,DCD and DMPP significantly decrease of cumulative N2O emissions amounted to 46.1%,41.8%and 21.9%,the N2O emission factors were 0.8%,1.0%and 1.4%,respectively.The effects of application of nitrification inhibitor in reducing N2O emissions,the treatments followed an order of CP>DCD>DMPP.2.During the eight consecutive vegetable crops planting period,N application improved vegetable yield and yield-scaled N2O emissions 44.9%and 282.9%.Compared with the conventional fertilization treatment,the CP treatment significantly increased the vegetable yield by 16.2%,and significantly decreased the yield-scaled N2O emissions by 53.7%.And the DCD treatment significantly increased the vegetable yield by 18.4%,and significantly decreased the yield-scaled N2O emissions by 50.8%.The nitrification inhibitor DMPP has no significant influences on vegetable yield,but significantly decreased the yield-scaled N2O emissions by 28.4%.3.Our results clearly imply that remediation strategies,i.e.,nitrification inhibitors(SNI and BNI),which reduce NO2--N accumulation,have the potential to reduce N2O emissions compared to urea alone.A stronger correlation between soil NO2--N intensity than NO3-intensity with cumulative N2O emissions was found.Compared with the treatment using urea alone,the soil NO2--N and NO3--N intensities were decreased,while the soil Nh4+-N intensity was increased in nitrification inhibitors treatments,suggesting that nitrification inhibitors mitigated the N2O derived from nitrification and/or bacterial denitrification/nitrifier denitrification.This inference was further reinforced by the AOB amoA transcripts being lower in nitrification inhibitors than in the urea treatment.Nevertheless,unexpected increases in non-target nirS,nosZI,and fungal nirK transcripts in the BNI treatment and a decrease in nirK transcripts in SNI treatment were observed.In conclusion,different nitrification inhibitors significantly affect the N2O emissions of vegetable fields and the yield-scaled N2O emissions,which are also reflected in the correlation of functional gene abundace and N2O isotopic. |
