Effects of the addition of nitrogen and phosphorus on anaerobic ammonium oxidation coupled with iron reduction (Feammox) in the farmland soils.

Anaerobic ammonium oxidation coupled with iron reduction is termed as Feammox, and is a new nitrogen removal process. However, there is a paucity of studies on the response of nutrient additions on Feammox process in farmland ecosystems. In this study, we investigated the shifts of Feammox and iron-reducers under nitrogen (N) and phosphorus (P) applications via isotopic tracing and high-throughput sequencing technology. In the isotopic tracing experiment, Feammox rates was significantly greater in the N and/or P applications soil (0.184-0.239 μg N g-1 day-1) than in the no fertilizer soil (0.172 μg N g-1 day-1). The results indicated that N and P applications could favor the Feammox reaction. Molecular analysis showed that five predominant iron-reducing bacteria, including Geobacter, Anaeromyxobacter, Pseudomonas, Thiobacillus and Bacillus, were detected. Their abundance in the soil with no fertilizer, N, P and N combined with P was 0.93%, 1.11%-1.71%, 0.99%, and 1.40%-1.75%, respectively. This implied that iron-reducing bacteria can be stimulated under N and P applications. Overall, the results of this study demonstrated that N and/or P applications could alter the activity of Feammox, and modulate the potential of IRB in the farmland soils.