|Guo-Wei Zhou, Xiao-Ru Yang*, Hu Li, Christopher W. Marshall, Bang-Xiao Zheng, Yu Yan, Jian-Qiang Su,and Yong-Guan Zhu |
Anaerobic ammonium oxidation coupled to iron(III) reduction, termed Feammox, is a newly discovered nitrogen cycling process. However, little is known about the roles of electron shuttles in the Feammox reactions. In this study, two forms of Fe(III) (oxyhydr)oxide ferrihydrite (ex situ ferrihydrite and in situ ferrihydrite) were used in the dissimilatory Fe(III) reduction (DIR) enrichments from paddy soil. Evidence for Feammox in DIR enrichments was demonstrated using 15N-isotope tracing technique. The extent and rate of both the 30N2/29N2 and Fe(II) formation were enhanced when amended with electron shuttles (either 9,10-anthraquinone-2,6-disulfonate (AQDS) or biochar), and further simulated when combining these two shuttling compounds. Although the Feammox-associated Fe(III) reduction was accounted for only a minor proportion of total Fe(II) formation compared to DIR, it was estimated that the potentially Feammox-mediated N loss (0.13-0.48 mg N L-1 d-1) was increased by 17-340% in the enrichments by addition of electron shuttles. The addition of electron shuttles led to increase the abundance of unclassified Pelobacteraceae, Desulfovibrio and denitrifiers but decrease the Geobacter. Overall, we demonstrated a stimulatory effect of electron shuttles on Feammox that led to higher N loss, suggesting that electron shuttles might play a crucial role in Feammox-mediated N loss from soils.