Carbon‐iron coupling reduced N2O emissions via promoting the conversion to N2 in paddy soils

Abstract The influence of redox reactions involving carbon‐iron coupling (organic carbon and iron oxides) on nitrous oxide (N 2 O) production in paddy soils remains poorly understood. In this study, two microcosm experiments were conducted to investigate the effects of carbon‐iron coupling on N 2 O emissions, and the underlying mechanisms were verified using quantitative denitrification functional genes ( nirS , nirK , nosZ I and nosZ II) and high‐throughput sequencing. The results showed that ferrihydrite (iron) significantly promoted N 2 O‐N emissions ( p < 0.05) after adding ammonium nitrogen, while glucose (carbon) significantly inhibited N 2 O‐N emissions ( p < 0.05). Carbon‐iron coupling significantly decreased N 2 O‐N emissions ( p < 0.05) but did not affect soil total nitrogen loss and increased nitrogen (N 2 ) emissions. After adding high concentrations of acetylene (10% C 2 H 2 ), the N 2 O‐N emissions from carbon‐iron coupling treatment increased significantly from 6.4 to 11.9 mg N kg −1 ( p < 0.05), which confirmed that the carbon‐iron coupling reduced the N 2 O emissions by promoting the conversion of N 2 O to N 2 . The mechanisms behind carbon‐iron coupling promoting complete denitrification and reducing N 2 O emissions were attributed to glucose promoting iron reduction and carbon‐iron coupling enhancing the abundance of nosZ I (42.7%) and nosZ II (16.6%).