Effects of Long-term Fertilization on Diversity and Composition of Ammonia-oxidizing Bacterium Communities in Weibei Dry-land

Ammonia-oxidizing microbes play an important role in the biogeochemical cycle of N element and it is also the limited rate of ni-trification.The diversity and composition of soil ammonia-oxidizing bacteria were analyzed through constructing its amoA gene(amoA en-codes ammonia monooxygenase)clone library and by PCR-based Restriction Fragment Length Polymorphism analysis(RFLP).The soil sim-ple which had received 23 years continuous fertilization treatments,include fallow(LD),control without fertilizers(CK)、nitrogen inpu(tN)、 phosphorus inpu(tP)and combination of fertilizer nitrogen and phosphorus(NP).They derived from Changwu Agro-ecological Eexperimen-tal Station on the Loess Plateau,Chinese Academy of Sciences.About 150 positive clones from five different ammonia-oxidizing bacteria li-braries were digested by Rsa I and Hha I,respectively.According to the statistics of diversity index,Shannon-Wiene(rH′)and Margale(fdM)a in the N treatment were the highest,followed by CK,NP and P treatments,and the lowest appeared in the CK.These results demonstrated that the diversity and abundance of soil ammonium-oxidizing bacteria were improved after long-term fertilizers N,but after fertilizers P and com-binations of fertilizer N and P,the diversity and abundance of soil ammonium-oxidizing bacteria were both reduced.Phylogenetic tree based on analysis of amoA gene sequences showed that the sequences of soil ammonia-oxidizing bacteria affiliated with Nitrosospira or Nitrosospi-ra-like,and grouped with Nitrosospira cluster 3.The proportion of the distribution of sequence types affiliated with amoA clusters in the clone libraries were different,which indicated that the composition of soil ammonia-oxidizing bacteria were affected by treatments became changed.Our results also indicated the sequences related to Nitrosomonas were predominant in these of five treatments,as well as P was important ef-fects of ammonia-oxidizing bacteria diversity and community.These findings could be fundamental to improve our understanding of the im-portance of ammonia-oxidizing bacteria in the cycling of nitrogen and other nutrients in terrestrial ecosystems.