Biological-chemical comprehensive effects of goethite addition on nitrous oxide emissions in paddy soils

Purpose Iron (Fe) oxides play an important role in regulating nitrification and N2O emissions, but there is very little study on the biological-chemical comprehensive effects of Fe oxides on nitrification and N2O emissions. Materials and methods A laboratory incubation experiment was performed to evaluate the effect of goethite addition on nitrification and N2O emissions from acidic and alkaline paddy soils. Results and discussion The cumulative N2O emissions from alkaline paddy soil were significantly higher than those from acidic paddy soil, no matter whether goethite had been added or not. Adding goethite decreased the average net rate of soil nitrification in acidic paddy soil by 33.2% in comparison with the treatment without adding goethite; however, adding goethite scarcely decreased the average net rate in alkaline paddy soil. Adding goethite increased the maximal N2O emissions by 85.6% in alkaline paddy soil, but had no obvious effect in acidic paddy soil. Adding goethite significantly increased the abundance of ammonia-oxidizing archaea (AOA) and bacteria (AOB)amoAgenes in both alkaline and acidic paddy soils. High-throughput pyrosequencing of 16S rRNA gene showed that adding goethite significantly increased the relative abundance ofNitrosomonadaceaein alkaline paddy soil and that the dominant species of AOB and AOA wereNitrosomonadaceaeandNitrososphaeraceae, respectively. Conclusions N2O emissions in alkaline paddy soil were higher than those in acidic paddy soil. The enhancement of N2O emissions by goethite was more significant in alkaline paddy soil than in acidic paddy soil. Goethite stimulated the abundance ofamoAgene (both of AOB and AOA) and participated in nitrification process via chemical reaction with intermediates.