Insight into the Mechanism of Feammox in the Surface Soils of 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 the Feammox process in riparian zones. In this study, evidence of Feammox in the riparian zone soil layers (0-20 cm) was demonstrated using the isotope tracing technique and a high-throughput sequencing technology. The results showed that Feammox occurred in the riparian zones in four different soil layers (A:0-5 cm, B:5-10 cm, C:10-15 cm, D:15-20 cm) and the Feammox rates ranged from 0.25 mg·(kg·d)-1 to 0.29 mg·(kg·d)-1. In the B soil sample, the Feammox rate was significantly higher than in the other soil samples (P<0.05). In addition, iron reducing bacteria played an essential role in the Feammox process, and Anaeromyxobacter and Geobacter were detected in all the soil samples. In the B soil sample, the abundance of iron reducing bacteria was significantly higher than in the other soil samples (P<0.05). 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.