Feammox in the Yellow River Delta wetlands is weak

Context Anaerobic ammonium oxidation coupled with iron (III) reduction (feammox) is an important nitrogen loss pathway in natural ecosystems. This is the first research to investigate the feammox process in the Yellow River Delta wetlands. Aims To reveal the nitrogen (N) loss caused by feammox in the Yellow River Delta wetland. Methods Slurry incubation, N isotope tracer technology, and metagenomic sequencing were used to study the feammox process and nitrogen-cycling functional microorganisms and genes. Key results Feammox was not detected in the Phragmites australis-covered (Phragmites) and mudflat (Mudflat) sites, and the feammox rate in the willow-covered site (Willow) was 0.02 mg N kg−1 d−1, accounting for 0.2% of the total N loss, which was lower than in other types of wetlands. The contributions of anammox to N loss were 32% (Phragmites), 17% (Mudflat), and 31% (Willow). Denitrification gene abundance was the highest, accounting for more than 40%, and anammox genes were not detected. The dominant genus of feammox functional microorganisms at Willow site was Anaeromyxobacter with an abundance of 62%, and the dominant genus at Phragmites and Mudflat sites was Pseudomonas, with abundances of 79% and 82%, respectively. Conclusions Feammox in the Yellow River Delta Wetland was weak, and denitrification was the main N removal pathway. Implications Further research is required to study why feammox rate is low in the Yellow River Delta wetlands.