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To explore the long-term impact of different fertilization regimes on microbial communities, we targeted total bacteria and the genus Pseudomonas at a field site established in 1979, in the Loess Plateau of China. Soils were sampled thrice during the growing period of winter wheat in 2008, with treatments: N (inorganic N), NP (inorganic N and P), MNP (farmyard manure, inorganic N and P), M (farmyard manure), SNP (straw, inorganic N and P), and CK (no fertilized control). Soil samples were analyzed by PCR-DGGE (16S rRNA gene fragments), cloning and sequencing techniques. The recovered bacteria sequences were grouped into five major taxa: Bacteroidetes, Proteobacteria,Firmicutes, Gemmatimonadetes, and Actinobacteria. Most of Pseudomonas phylotypes were similar to species Pseudomonas sp., Pseudomonas fluorescens, andPseudomonas putida. The community structures microbes we detected were influenced diversely by the different fertilization regimes and plots amended with NP (NP, MNP and SNP) fostered more bacterial taxa as compared to N, M, or CK treatments, but application of organic fertilizers (MNP, M and SNP) enhanced the richness of Pseudomonascompared to mineral fertilizers treated alone (N and NP), or unfertilized control. Furthermore, application of fertilizers, was beneficial to the accumulation of soil organic carbon and microbial taxon with respect to the unfertilized control. Meanwhile, a reduction in bacterial taxon richness throughout the growing season was also manifested. Factors of sampling time, edaphic characteristics, such as soil moisture, organic carbon, and pH contributed much to the shifts of community structures. Balanced-fertilization should be encouraged for the maintaining of soil quality and agricultural sustainability in such a typical rain-fed agroecosystem. Key words: Bacteria, polymerase chain reaction - denaturing gradient gel electrophoresis, Pseudomonas, soil chemical characteristics, canonical correspondence analysis, Loess Plateau. |
