| The loess plateau was an ancient rain-fed agricultural area in China, and the cultivated land area was 18 million hectares which account for 19% in China, so the further study of the loess plateau was significant. Due to erosion and drought, food production in the loess plateau was generally less than 2.0 t/hm2, which was lower than the national level. Although using chemical fertilizer was a necessary measure to increase crop yields, it could cause a large number of nitrate zone of invalid accumulation in the soil. Studies showed that there was a clear phenomenon of nitrate accumulation in soil by using a large number of nitrogen fertilizer in loess area. It not only caused high level of nitrogen waste and soil nitrogen fertility reduction, but also leads to the pollution for groundwater. Ammonia oxidation was the first reaction step of nitrification, rate-limiting step and the central link in the global nitrogen cycle. Therefore, the study of ammonia-oxidizing microorganisms (bacteria and archaea) had an important environmental significance. Study of soil ammonia-oxidizing bacteria and ammonia-oxidizing archaea community's structure and diversity could provide the necessary theoretical basis to understand the characteristics of soil nitrification.The long-term field experiment was located in the Changwu State Key Experimental Station for Agriculture, Shannxi province, northwest China. The fertilization experiment included five treatments for each treatment in a randomized plot design. The five treatments were control without fertilizer (CK); those with combinations of fertilizer nitrogen, phosphorus and and organic manure:M, NM, PM, NPM. Fertilizers N, P and M were applied in the form of urea (120 kg N ha-1 per year), super phosphate (60 kg P ha-1 per year) and dairy manure (7500 kg ha-1 per year). Total DNA of five samples were extracted directly. Constructed amoA gene and Arch-amoA clone libraries, and the influence of CK, M, NM, PM and NPM fertilizer treatments on soil AOB diversity and community structure were analyzed by restriction fragment length polymorphism (PCR-RFLP). The main results were as follows:1. The soil ammonia-oxidizing bacteria amoA gene libraries were generated from the five treatments, the diversity and phylogenetic analysis showed that:(1) Total RFLP patterns of five treatments were 59(CK),56(M),83(NM),71(PM) and 42(NPM), respectively. The coverage (C value) of the clone libraries were 80.67%,80.67%, 60.00%,66.67% and 84.56%, respectively. Dominant ammonia-oxidizing bacteria existed in each treatment.(2) a-measurement indices analysis illuminated that there was differentia among five fertilizer treatments. The diversity was highest in NM treatment and lowest in NPM treatment. The Shannon-Wiener index and Species Evenness index represented an identical order NM>PM>CK>M>NPM, the Simpson index represented NM>CK>PM>NPM>M, and the Margalef index represented PM>NM>CK>M>NPM. The Sorenson index was 0.61 between M and NPM (M-NPM), which indicated there was a high community similarity. The lowest level of community similarity was existed in NM-CK and PM-CK, whose Sorenson indices were both 0.15. Sorenson indices of other treatments were from 0.23 to 0.38. The results indicated that long term fertilization resulted in change of AOB community.(3) Phylogenetic analysis of amoA gene amino acid sequences showed that Nitrosospira cluster 3 sequences was dominant in all treatments, but the proportion of clones in each treatment belonging to Nitrosospira cluster 3a or 3b was different, and some clones were affiliated with the Nitrosospira cluster 4. Different fertilizer environment could lead to the significant species variation of soil AOB.2. The soil ammonia-oxidizing archaea amoA gene libraries were generated from the five treatments, the diversity and phylogenetic analysis of ammonia-oxidizing archaea showed that:(1) Total RFLP patterns of CK treatment was 25, and the coverage (C value) of the clone library was 92.00%. Total RFLP patterns of NPM treatment was 29, and the coverage (C value) of the clone library was 92.31%.(2) a-measurement indices analysis illuminated that in terms of index value, CK |
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