Community Structure Of Ammonia-Oxidizing Bacteria During Long-term Fertilizer Application In The Loess Plateau

At present, long-term fertilization in agricultural ecosystem changed the soil characteristics artificially as well as the characteristics of soil microbes. As one of the model species for microbial ecology studying, ammonia oxidiser have received wide attention. Microbial ammonia oxidation is the first and rate-limiting step of nitrification, a central process in the global nitrogen cycle that sustains life on Earth. The effects of mineral fertilizer and organic manure on the community structure of soil ammonia oxidizing bacteria (AOB) were investigated in a 29-year fertilizer experiment site in the Loess Plateau of northwestern China using PCR-DGGE. The trial included the following six treatments:control without fertilization (CK), inorganic nitrogen (N), inorganic nitrogen and phosphorus (NP), farmyard manure (M), farmyard manure plus inorganic NP (MNP), straw plus inorganic NP (SNP). The AOB community structure was analyzed by amplification of the amoA gene, which encodes the a-subunit of ammonia monooxygenase, followed by denaturing gradient gel electrophoresis (DGGE) analysis of the amplified products. DGGE profiles showed that the AOB community was more diverse in the balanced fertilizer treatments (MNP and SNP). Moreover, N application was found to increase the diversity of AOB in mature stages when compared with treatments that did not receive N. Our results also indicated that stages of wheat growth and the soil depth significantly influenced the AOB community structure. The filling stage (in May) was found to have a higher Shannon index than the jointing (in April) and maturity (in June) stages (P<0.05), especially in the MNP treatment. As the soil depth increased, the diversity of the AOB community decreased. Phylogenetic analysis showed that Nitrosospira cluster 3 dominated the different treatments, and that Nitrosomonas sequences were also present. These results suggest that a long-term fertilization regime can differentially affect the composition of AOB in agricultural soils of the Loess Plateau, and the composition of AOB was diverse under different crop growing stages in different soil profiles.