为探明大豆-玉米轮作对土壤固氮细菌的影响，以玉米连作为对照(MMM)，以nif-H基因为指示，采用高通量测序技术，分析大豆-玉米2年轮作周期(MSM)和大豆-玉米-玉米3年轮作周期(SMM)下土壤固氮细菌群落结构及多样性。结果表明：大豆-玉米轮作下0~20、20~40 cm土层土壤有机质、全氮、碱解氮、铵态氮和硝态氮均显著增加。固氮细菌的Chao1指数和ACE指数在0~20、20~40 cm土层均为轮作高于对照，轮作下MSM显著高于SMM；Shannon指数和Simpson指数在0~20 cm土层轮作显著高于MMM；20~40 cm土层MSM显著高于MMM。在门水平上，MSM和SMM的0~20、20~40 cm土层变形菌门的相对丰度均高于MMM。在属水平上，2个轮作类型0~20 cm土层的慢生根瘤菌属、弗兰克氏菌属和纤毛菌属相对丰度显著较高；20~40 cm土层慢生根瘤菌属、伪食酸菌属、地杆菌属和固氮弧菌属相对丰度显著较高；MSM 0~20、20~40 cm土层慢生根瘤菌属、甲基孢囊菌属和固氮弧菌属较SMM均提高。方差分析表明，固氮细菌丰度指数（Chao1和ACE指数）与有机质、碱解氮和硝态氮的含量均呈显著正相关关系，慢生根瘤菌属的丰度与有机质、全氮和铵态氮的含量呈极显著正相关。综上，大豆-玉米轮作土壤养分较高是提高土壤固氮菌丰度和改变群落结构的重要因素，其中大豆-玉米2年周期下的固氮细菌丰度较高；大豆-玉米轮作可以增加土壤中具有高固氮效率和多功能的有益微生物类群。

To study the effects of soybean-maize rotation on soil nitrogen-fixing bacteria, using maize continuous cropping as control (MMM) and nif-H gene as indicator, we adopted high-throughput sequencing technology to analyze the community structure and diversity of soil nitrogen-fixing bacteria under two-year soybean-maize rotation cycle (MSM) and three-year soybean-maize-maize rotation cycle (SMM). The results showed that soil organic matter, total nitrogen, alkali-hydrolyzed nitrogen, ammonium nitrogen and nitrate nitrogen in 0-20 and 20-40 cm soil layers increased significantly under soybean-maize rotation. Chao1 index and ACE index of nitrogen-fixing bacteria in 0-20 and 20-40 cm soil layers under rotation were higher than those under control, and the indexes under MSM were significantly higher than those under SMM. Shannon index and Simpson index under rotation in 0-20 cm soil layer were significantly higher than those under control (MMM); and the indexes under MSM in 20-40 cm soil layer were significantly higher than those under MMM. At the phylum level, the relative abundance of Proteobacteria in 0-20 cm and 20-40 cm soil layers under MSM and SMM were higher than that under MMM. At the genus level, the relative abundance of Bradyrhizobium, Frankia and Leptotrichia in 0-20 cm soil layer under the two rotation types were significantly higher. The relative abundance of Bradyrhizobium, Pseudoacidibacter, Geobacillus and Nitrogen-fixing Vibrio in 20-40 cm soil layer were significantly higher. In 0-20 cm and 20-40 cm soil layers, Bradyrhizobium, Methylocystis and Nitrogen-fixing Vibrio under MSM were higher than those under SMM. Variance analysis showed that the abundance indexes of nitrogen-fixing bacteria (Chao1 index and ACE index) were significantly and positively correlated with the content of organic matter, alkali-hydrolyzed nitrogen and nitrate nitrogen, and the abundance of Rhizobium was extremely significantly and positively correlated with the content of organic matter, total nitrogen and ammonium nitrogen. In summary, higher soil nutrients in soybean-maize rotation were important factors for increasing the abundance of soil nitrogen-fixing bacteria and changing community structure, and the abundance of nitrogen-fixing bacteria in soybean-maize two-year cycle was relatively high. Soybean-maize rotation can increase the beneficial microbial groups with high nitrogen-fixing efficiency and multi-functions in soil.