Factors driving the distribution and role of AOA and AOB in Phragmites communis rhizosphere in riparian zone.

Ammonia oxidation, mainly driven by ammonia-oxidizing archaea (AOA) and bacteria (AOB), plays an important role in determining the rate of nitrification in riparian zones. However, the underlying factors driving the distribution and activity of AOA and AOB in riparian zones, especially in the rhizosphere of Phragmites communis remain unknown. This study revealed the dominance of AOA in ammonium oxidization with higher abundance and activity in both rhizosphere and bulk soil in summer and winter over AOB in riparian zones, based on molecular methods and double-inhibitors method. Phylogenetic analysis showed that 54d9 cluster and Nitrososphaera dominated the AOA community and Nitrosospira dominated the AOB, respectively. For the distribution of AOA and AOB, it was the spatial heterogeneity of physicochemical properties that had the most significant effect. Specifically, TOM & TC were the main physicochemical variables accounting for the difference in abundance and community composition of AOA, and TN had an important influence on AOB in the sediment/soil in riparian zones. For abundance and activity, seasonal heterogeneity and P. communis rhizosphere had a significant impact on the archaeal activity and abundance, respectively, but did not show significant influencing on AOB. These findings suggest that the small-scale environmental heterogeneities in riparian zones are important in shaping the community composition and abundance of AOA and AOB.