| Alfalfa plays an important role in environment construction and industrial structure adjustment because of its excellent feeding value and ecological function in Loess Plateau.In view of the study on microbiological mechanism of N2O emission of alfalfa in loessial soil is less,so,this study took the alfalfa with different growth years in semi-arid rain-fed agricultural area in Loess Plateau as research object,static chamber-gas chromatographic techniques were used to continuously measure and analyze the N2O fluxes of alfalfa with different growth year?L2003,L2005,L2012?during 2018 to 2019,quantitative PCR and Illumina MiSeq high-throughput sequencing were applied to investigate abundance,community structure,and diversity of ammonia-oxidizing archaea?AOA?and ammonia-oxidizing bacteria?AOB?in loessial soil with continuous alfalfa growing.Through the study of N2O emission dynamic and the abundance,diversity,community structure of AOA and AOB of alfalfa soil with different growth years,to reveal the soil N2O emission of microbial drive mechanism,in order to provide scientific basis and effective theory reference for lucerne land rational utilization on western Loess Plateau and productivity sustainable development on rainfed agricultural area.The research main conclusions are as follows:?1?The Alfalfa soil in the semi-arid rain-fed agricultural area of the Loess Plateau is the N2O emission source,and presents the seasonal variation characteristics of summer and autumn are higher than spring and winter.The N2O emission flux showed an obvious trend of unimodal variation and reached its peak in July,the emission fluxs were 0.1679 mg·m-2·h-1?2018?and 1715 mg·m-2·h-1?2019?,With the extension of alfalfa growth years,the cumulative emissions and the warming potential gradually increased,which was shown as L2003>L2005>L2012.Compare with L2005 and L2012,The cumulative emissions and the warming potential were significantly greater in L2003 than in L2005 and L2012,high 4.47%and 14.14%.?2?The abundance of AOA and AOB in alfalfa soil were 6.14×106-12.68×106copies·g-1 dry soil and 0.27×106-7.7×106copies·g-1 dry soil,and both decreased gradually with the deepening of soil layers.With the increase of alfalfa growth years,the AOA abundance in each soil layer was L2003>L2005>L2012,and the AOB abundance was L2005>L2003>L2012,and were significantly correlated with soil total nitrogen,nitrate nitrogen,organic carbon,microbial biomass carbon,microbial biomass nitrogen and urease activity.?3?The richness and diversity of AOA and AOB in alfalfa soil on Loess Plateau increased with the deepening of soil layer.With the extension of alfalf a growth years,the diversity of AOA in the 0-30 cm soil layer showed L2003>L2005>L2012,and Shannon index by L2012 was significantly higher than th at of L2003?P<0.05?;The richness showed L2012>L2003>L2005,the diversity of AOB showed L2005>L2003>L2012,the richness showed L2003>L2005>L2012.In 30-60 cm soil layer,the diversity of AOA showed L2005>L2003>L2012,the richness showed L2012>L2003>L2005;The diversity of AOB showed L2012>L2005>L203,and the richness showed L2003>L2012>L2005.Correlation an alysis found that the diversity of AOA and AOB were significantly correlated with soil organic carbon,nitrate nitrogen,microbial biomass carbon,microbial biomass nitrogen and urease.Long-term cultivation of alfalfa did not significant ly affect the diversity of AOB.?4?The dominant phylum?>1%?of AOA were Crenarchaeota and unclass ifiednorankArchaea,with relative abundance of 51.50%-96.16%and 3.80%-47.13%,respectively.The dominant genera?>1%?were norankc<sub>environmentals amplesp<sub>Crenarchaeota,unclassifiedk<sub>norankd<sub>Archaea and norankc<sub>en vironmentalsamplesp<sub>Thaumarchaeota,with relative abundance of 51.50%-96.16%,3.80%-47.13%and 0.04%-1.10%.Soil nitrate,organic carbon,microbial b iomass carbon,microbial biomass nitrogen and urease activities were the main factors affecting AOA community genera groups.The relative abundance of alf alfa was not significantly changed after continuous alfalfa growing.The domina nt phylum?>1%?of AOB were Proteobacteria,unclassifiedk<sub>norankd<sub>Bact eria and ammoniaoxidisingbacteriaensemble,with the relative abundance of45.28%-67.73%,20.92%-28.01%and 10.96%-31.58%,respectively.With the inc rease of alfalfa growth years,the relative abundance of Proteobacteria was sig nificantly increased,and the relative abundance of ammoniaoxidisingbacteriaensemble was significantly decreased.The dominant genera were Nitrosospira,unclassifiedk<sub>norankd<sub>Bacteria,norankp<sub>ammoniaoxidisingbacteriaense mble,unclassifiedo<sub>Nitrosomonadales and norankf<sub>environmentalsamples,with the relative abundance of 21.11%-52.01%,17.88%-28.01%,10.96%-31.58%,10.95-23.07%and 2.566-15.96%,which were mainly affected by total nitrogen,organic carbon,microbial biomass carbon,microbial biomass nitrogen and pH.With the extension of alfalfa growth years,the relative abundance of Nitrosos pira increased gradually,and the relative abundance of norankp<sub>ammoniaoxi disingbacteriaensemble decreased gradually.?5?RDA analysis results show that the soil organic carbon?P=0.004?and urease?P=0.005?were the most important factors influencing the AOA community structure,soil nitrite nitrogen?P=0.025?,microbial biomass carbon?P=0.013?and microbial biomass nitrogen?P=0.048?were the secondary factors influencing the AOA community structure,soil ammonium nitrogen?P=0.014?and the microbial biomass carbon?P=0.037?were the main factors influencing the AOB community structure.?6?N2O emission is affected by both environmental and biological factors.Soil temperature,total nitrogen,soil organic carbon,microbial biomass carbon nitrite nitrogen and pH are environmental factors that affected N2O emission,and the norankc<sub>environmentalsamplesp<sub>Crenarchaeota,unclassifiedk<sub>n orankd<sub>Archaea,norankc<sub>environmentalsamplesp<sub>Thaumarchaeota,nora nkp<sub>environmentalsamplesk<sub>norank of AOA community and the unclassif iedk<sub>norankd<sub>Bacteria of AOB community are biological factors that affe cted N2O emission. |
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