Nitrogen loss from anaerobic ammonium oxidation coupled to Iron(III) reduction in a riparian zone.

Anaerobic ammonium oxidation coupled to iron(III) reduction (termed Feammox) is a recently discovered pathway of nitrogen cycling. However, little is known about the pathways of N transformation via Feammox process in riparian zones. In this study, evidence for Feammox in riparian zones with or without vegetation cover was demonstrated using isotope tracing technique and high-throughput sequencing technology. The results showed that Feammox could occur in riparian zones, and demonstrated that N2 directly from Feammox was dominant Feammox pathway. The Feammox rates in vegetated soil samples was 0.32-0.37 mg N kg-1 d-1, which is higher than that in un-vegetated soil samples (0.20 mg N kg-1 d-1). Moreover, the growth of vegetation led to a 4.99-6.41% increase in the abundance of iron reducing bacteria (Anaeromyxobacter, Pseudomonas and Geobacter) and iron reducing bacteria play an essential role in Feammox process. An estimated loss of 23.7-43.9 kg N ha-1 year-1 was associated with Feammox in the examined riparian zone. Overall, the co-occurrence of ammonium oxidation and iron reduction suggest that Feammox can play an essential role in the pathway of nitrogen removal in riparian zones.