Fertilization On Diversity And Composition Of Ammonia-Oxidizing Bacterium Communities In Weibei Dry-Land

Ammonia-oxidizing bacteria (ammonia-oxidizing bacteria, AOB) are a type of bacteria which can oxidize ammonia to nitrite, and they are widely distributed in almost all soil, freshwater and marine environments. The process that ammonia-oxidizing bacteria catalyzed nitrosation is rate-limiting step of nitrification, and it plays an important role in natural geochemical cycling of nitrogen. Therefore in microbial ecology, AOB has been proposed as a model organism. In recent years, the agricultural soil study of the Loess Plateau is mainly focused on long-term fertilization effects on soil moisture, soil fertility, and crop yield. AOB'S number and types play an important role in nitrogen transformation. The study materials are on long-term fertilized soil samples from Changwu County, Shaanxi. The purpose is to explore the effects of long-term fertilization on the diversity of ammonia oxidizing bacteria and community structure composition and in order to reveal the characteristic of AOB'diversity and community structure in long-term fertilized agricultural soil in Loess Plateau, finally, provide a theoretical basis for reasonable fertilization.The test samples are collected from Changwu Agricultural Ecological Station, Chinese Academy of long-term fertilization base. The experiment using a completely random design method with 5 treatments: LD (bare land); CK (cultivation without fertilization); P(superphosphate); N(urea); NP(superphosphate+urea). Fertilizer amount in each treatment is: N fertilizer (urea) 120 kg/hm2, P fertilizer (superphosphate) 60 kg/hm².The total DNA of soil microorganisms was directly extracted from soil samples. Primers which were designed according to the functional gene, ammonia monooxygenase gene (amoA) were used to establish five clone libraries of ammonia-oxidizing bacteria. The clone libraries was analyzed by PCR-RFLP with cleavaging of Rsa I and Hha I, two four-base restriction enzymes, respectively.Through construction of amoA gene library ammonia-oxidizing bacteria from five treatment soil samples and phylogenetic analysis of community diversity, it showed that:(1) Different RFLP types by enzyme digestion were obtained from five kinds of fertilized soils. They are 38/154(LD), 48/150(CK), 65/152(N), 45/152(P) and 46/152(NP), respectively. Storage capacity values were 86.36%, 80.67%, 73.68%, 84.87% and 81.57% , respectively. In all treatments, there is a clear advantage flora.(2)αdiversity index showed that the diversity of different treated soils was various. In N treatment soil, Shannon-Wiener (H') and Margalef (d_Ma) index of ammonia-oxidizing bacteria was the highest, then followed by CK, NP, P treatment, and the lowest was the LD treatment. These indicated that after long-term N fertilizer's treatment, the diversity and richness of ammonia oxidizing bacteria had been increased. At the same time, long-term cultivation of crops can also increase ammonia oxidizing bacterial diversity and richness. However, in single P and N and N, P mixed treated soil, the diversity and richness were reduced. These indicated that long-term fertilization changed the diversity and richness of ammonia-oxidizing bacteria.(3) Phylogenetic tree based on amoA gene showed that the dominant ammonia oxidizing bacteria in all treated solids, belongs to Nitrosospira and Nitrosospira-like, and most of dominant bacteria are grouped with Nitrosospira cluster 3. But the dominant strain's proportion in clone library was different, indicating that in the soils under different fertilization treatments, the structure of ammonia oxidizing bacterial community had been changed.