秸秆覆盖免耕对土壤氮素转化细菌区系的影响

不同耕作方法影响土壤N素转化细菌的组成和数量。多年连续秸秆覆盖免耕试验结果表明，好氧固氮菌和厌氧固氮菌数量在铁茬处理土壤中较少，而在免耕与翻耕土壤中较多，免耕厌氧固氮菌数量明显地高于翻耕和铁茬，而铁茬最低，这种趋势特别在0～0．1m和0．1～0．2m土层中表现明显。土壤反硝化细菌的数量在表层土壤中较少，三种耕作方法相差较小，但在0．1～0．2m，0．2～0．3m土层中，翻耕反硝化细菌数量比免耕和铁茬多，而铁茬最少。不同耕作方法间氨氧化细菌数量相差不明显，免耕土壤中氨氧化细菌数量较高，动态变化趋势不规则。0～0．1m土层中免耕亚硝酸氧化细菌数量高于翻耕和铁茬，0．1～0．2m土层免耕与翻耕亚硝酸氧化菌数较多，而铁茬较少。

Effects of straw mulch no-tillage on community composition of soil nitrogen transferous bacteria

Long-term continuous two-crop winter wheat and summer corn rotation with no-tillage,direct drilling and conventional tillage affected the structure and numbers of the microbial flora for nitrogen transferous bacteria in soils.In the layers of 0~0.1m and 0.1 ~0.2m soils,the numbers of anaerobic dinitrogen fixed bacteria in no-tillage were increased remarkably,and aerobic dinitrogen fixed bacteria in no-tillage and conventional tillage were also increased compared to other tillage treatment.The numbers of denitrifying bacteria were decreased and differed insignificantly in the surface soil layer for the three tillage methods,but conventional tillage had more and direct drilling less denitrifying bacterial numbers in the 0.1 ~0.2m and 0.2 ~0.3m soil layer.Ammonia oxidizing bacteria fluctuated largely,and no-tillage soil had more numbers.Nitrite oxidizing bacteria were increased in no-tillage soils in 0~ 0.1m soil layer,but in 0.1 ~0.2m soil layer it were more in no-tillage and conventional tillage soils.