Environmental Factors, More Than Spatial Distance, Explain Community Structure of Soil Ammonia-Oxidizers in Wetlands on the Qinghai-Tibetan Plateau.

In wetland ecosystems, ammonia oxidation highly depends on the activity of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), which are, therefore, important for studying nitrogen cycling. However, the ammonia-oxidizer communities in the typical high-elevation wetlands are poorly understood. Here, we examined ammonia-oxidizer communities in soils from three wetland types and 31 wetland sites across the Qinghai-Tibetan Plateau. The amoA gene of AOA and AOB was widespread across all wetland types. Nitrososphaera clade (Group I.1b) overwhelmingly dominated in AOA community (90.36%), while Nitrosospira was the principal AOB type (64.96%). The average abundances of AOA and AOB were 2.63 × 104 copies g-1 and 9.73 × 103 copies g-1. The abundance of AOA amoA gene was higher in riverine and lacustrine wetlands, while AOB amoA gene dominated in palustrine wetlands. The environmental conditions, but not spatial distance, have a dominant role in shaping the pattern of ammonia-oxidizer communities. The AOA community composition was influenced by mean annual temperature (MAT) and mean annual precipitation (MAP), while MAT, conductivity and plant richness, pH, and TN influenced the AOB community composition. The net nitrification rate had a significant correlation to AOB, but not AOA abundance. Our results suggest a dominant role for climate factors (MAT and MAP) in shaping community composition across a wide variety of wetland sites and conditions.