Goethite Contributes to Increased N ₂ O Emissions From Autotrophic Nitrification in Paddy Soils

Background Iron (Fe) oxides play a crucial role in biogeochemical processes governing nitrous oxide (N 2 O) emissions. However, the precise impacts of Fe oxides on various N 2 O production pathways remain inadequately understood. Aim To elucidate how goethite influences the relative contributions of both principal biotic pathways, specifically autotrophic nitrification, heterotrophic nitrification, and denitrification, as well as abiotic processes, to N 2 O production. Methods Sterilization and inhibition experiments were carried out in acidic (pH 5.5) and alkaline paddy (pH 7.9) soils with/without goethite addition under N‐fertilizer and non‐N‐fertilizer conditions. Low‐concentration acetylene and high‐pressure O 2 were used to distinguish biotic nitrification and denitrification pathways, whereas high‐pressure steam sterilization differentiated biotic and abiotic N 2 O production. Results On the basis of the comparison of sterilized and unsterilized setups, we found that under the condition of 60% water‐holding capacity (WHC), N 2 O emissions from the acidic and alkaline paddy soils were mainly from biological processes (>82%), whereas abiotic reactions made a minimal contribution. Nitrification (including autotrophic nitrification and heterotrophic nitrification) produced 14.2–17.3 µg N kg −1 in the acidic soils and 71.4–79.7 µg N kg −1 in the alkaline soils, accounting for 48%–55% and 79%–84% of total emissions, respectively. Moreover, autotrophic nitrification contributed 78%–83% to N 2 O production in the alkaline soil, which was significantly higher than the 38%–47% in the acidic paddy soil. Denitrification also played a substantial role in the acidic paddy soil, contributing 29%–49% to N 2 O production. Goethite addition altered the contributions of these pathways. In the untreated soils, the contribution of non‐denitrification pathways (such as autotrophic and heterotrophic nitrification) to N 2 O production was 38% and 78% in the acidic and alkaline paddy soils, respectively. After supplementing with goethite, these contributions increased to 47% and 83%. Conversely, the contributions of denitrification to N 2 O production decreased from 49% to 20% in the untreated the acidic and alkaline paddy soils to 42% and 15% in the goethite‐supplemented soils. Conclusions Goethite addition under 60% WHC primarily enhances N 2 O production by promoting autotrophic nitrification, particularly in alkaline paddy soils, while reducing denitrification's contribution in acidic soils. These findings advance our understanding of the role of Fe oxides in soil nitrogen cycling and N 2 O release, providing insights for mitigating greenhouse gas emissions in agricultural ecosystems.