摘要紫花苜蓿因其优良的饲用价值和生态功能，在黄土高原环境建设和产业结构调整中发挥着重要作用。针对目前黄绵土区苜蓿草地N2O释放的微生物机理研究较少的现状，本研究以黄土高原半干旱雨养农业区不同年龄紫花首蓿人工草地为研究对象，于2018-2019年采用静态箱-气相色谱法测定了不同种植年限(L2003、L2005、2012)苜蓿物候期N2O释放通量，同时借助基于MiSeq平台的高通量分子生物学测序技术测定了土壤氨氧化古菌(AOA)和氨氧化细菌(AOB)群落结构和丰度。通过研究不同种植年限紫花首蓿土壤NO排放动态和土壤中氨氧化微生物群落结构、丰度及其多样性及群落，解析黄土高原苜蓿草地系统土壤N2O排放的微生物驱动机制，为西部黄土高原首蓿草地的合理利用和雨养农业系统生产力可持续发展提供理论参考。主要研究结论如下：(1)黄土高原半干旱雨养农业区苜蓿土壤为NO排放源，并呈现出夏秋高春冬低的季节性变化规律：N2O排放通量呈现出明显的单峰变化趋势，并于二茬再生期(7月)达到排放峰值，排放通量分别为0.1679mgm2h(2018)和0.1715mgm2h(2019):随首蓿种植年限的延长，累积排放量及增温潜势增加。(2)半干旱黄绵土区苜蓿土壤AOA和AOB的丰度分别为6.14×1012.68×10 copies.g千土和0.27×10-~7.7×10 copies'g干土，表现为AOA丰度显著高于AOB:随首蓿种植年限延长AOA群落丰度增加显著，但AOB丰度表现为先增加后降低：长期种植苜蓿显著降低土壤AOA群落多样性并提高其丰富度，但对AOB群落多样性和丰富度无明显影响。(3)半干旱黄绵土区首蓿土壤AOA群落优势门(>1%)为泉古菌门(Crenarchaeota)和unclassified norank_Archaea,相对丰度分别为51.50%-96.16%和3.80%47.13%；优势属(>1%)为norank_c_environmental samples p_Thaumarchaeota,相对丰度为51.50%-96.16%、3.80%-47.13%和0.04%-1.10%(4)半干旱黄绵土区苜蓿土壤AOB群落优势门为变形菌门、unclassified k norank d Bacteria ammonia_oxidising bacteria ensemble,对丰度分别为45.28%-67.73%、20.92%-28.01%和10.96%-31.58%，长期种植苜蓿后显著增加变形菌门的相对丰度，并降低ammonia oxidising bacteria ensemble的相对丰度；优势属为亚硝化螺菌属、unclassified k norank d_Bacteria、norank_pammonia_oxidising_bacteria_ensemble unclassified_o Nitrosomonadalesnorank f environmental samples,其丰度分别为21.11%-52.01%、17.83%-28.01%、10.96%-31.58%、10.95%-23.07%和2.56%-15.96%，随苜蓿种植年限的延长而增加，亚硝化螺菌属相对丰度显著增加，norank_p_ammonia_oxidising bacteria ensembl相对丰度显著降低。(5)RDA分析结果表明，土壤有机碳(P-0.004)、硝态氮(P-0.025)、微生物量碳(P-0.013)、微生物量氮(P-0.048)和脲酶(P-0.005)是影响AOA群落结构的主要因素：土壤NH4-N(P0.014)和微生物量碳(P-0.037)是影响AOB群落结构的主要因素。(6)N2O排放通量同时受到环境因素和生物因素的共同影响，其中土壤温度、SOC、TN、NO3-N、MBC和pH是影响半干旱黄绵土区首蓿土壤NO排放通量的环境因素；AOA群落的norank_c_environmental_samples p_Crenarchaeota、和norank p_environmental_samples_k_norank及AOB群落的unclassified k norank d Bacteria影响黄绵土NzO排放通量的主要生物因子。关键字：黄绵土，紫花苜蓿，NO排放通量；氨氧化古菌；氨氧化细菌：SummaryAlfalfa plays an important role in environment construction and industrialstructure adjustment because of its excellent feeding value and ecological function inLoess Plateau.In view of the study on microbiological mechanism of N2O emissionof alfalfa in loessial soil is less,so,this study took the alfalfa with different growthyears in semi-arid rain-fed agricultural area in Loess Plateau as research object,staticchamber-gas chromatographic techniques were used to continuously measure andanalyze the N2O fluxes of alfalfa with different growth year(L2003,L2005,L2012)during 2018 to 2019,quantitative PCR and Illumina MiSeq high-throughputsequencing were applied to investigate abundance,community structure,and diversityof ammonia-oxidizing archaea (AOA)and ammonia-oxidizing bacteria (AOB)inloessial soil with continuous alfalfa growing.Through the study of N2O emissiondynamic and the abundance,diversity,community structure of AOA and AOB ofalfalfa soil with different growth years,to reveal the soil N2O emission of microbialdrive mechanism,in order to provide scientific basis and effective theory reference forlucerne land rational utilization on western Loess Plateau and productivity sustainabledevelopment on rainfed agricultural area.The research main conclusions are asfollows:(1)The Alfalfa soil in the semi-arid rain-fed agricultural area of the LoessPlateau is the N2O emission source,and presents the seasonal variation characteristicsof summer and autumn are higher than spring and winter.The N2O emission fluxshowed an obvious trend of unimodal variation and reached its peak in July,theemission fluxs were 0.1679 mg'm2.h(2018)and 1715 mg'm2.h(2019),With theextension of alfalfa growth years,the cumulative emissions and the warming potentialgradually increased,which was shown as L2003>L2005>L2012.Compare with L2005and L 2012,The cumulative emissions and the warming potential were significantlygreater in L2003 than in L2005 and L2012,high 4.47%and 14.14%.(2)The abundance of AOA and AOB in alfalfa soil were 6.14x 105-12.68 x105copies'g-1 dry soil and 0.27x106-7.7 x10copies'g!dry soil,and both decreasedgradually 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 AOBabundance was L2005>L2003>L2012,and were significantly correlated with soiltotal nitrogen,nitrate nitrogen,organic carbon,microbial biomass carbon,microbial