Atmospheric nitrogen deposition and precipitation as an important phenomenon of global climate change have a great impact on grassland ecosystems. However, little is known about how the soil ammonia-oxidizing microorganisms respond to the both changes. Ammonia oxidization is a crucial step in the soil nitrification and greatly influenced by soil nitrogen availability. We used PCR and DGGE (denaturing gradient gel electrophoresis) approaches to investigate the responses of AOB (ammonia-oxidizing bacteria) 16S rRNA and AOA (ammoniaoxidizing archaea) amoA genes to nitrogen and water input in Stipa baicalensis steppe, Inner Mongolia, northern China. After two years of nitrogen and water addition treatment, it was found that PNA (potential nitrification activity) was greatly enhanced by lower N fertilization treatment under water addition and higher N fertilization under nowater addition, while it decreased markedly in higher N fertilization under water addition. The community structure of AOB responded more sensitively to N fertilization and water input than AOA, resulting in the significantly decreased diversity in the AOB community along with a higher N fertilizer rate, but an obvious increase in the AOA community, demonstrating the active growth of AOA in higher N fertilization soils. Phylogenetic analysis showed that AOB communities were dominated by Nitrosospira clusters3, 4 and Nitrososmonas clusters 6 under water addition and Nitrosospira culsters 1, 3 and 4 and under no-water addition, while AOA communities were grouped into Crenarchaeote clusters 1, 2 and 5 under no-water addition and Crenarchaeote clusters 1, 2 and water lineage under water addition. The differences between the two water addition regimes strongly suggest that water input acts as an important role in shifting AOA and AOB communities. Moreover, in contrast to the AOA, the diversity of AOB was negatively correlated with total N, NH4 , NO3- and pH under water addition, implying a significant N fertilization and water effect on shaping AOA and AOB communities. In conclusion, our studies suggested that N fertilization and water addition and their composite effects had significantly changed AOB and AOA communities, meanwhile, AOB and AOA communities could develop a desirable complementary mechanism in response to external changes.
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Vol. 6 • No. 1