Abstract: We examined the effects of nitrate (NO₃^--N) and ammonium (NH₄⁺-N) input at different concentrations (0, 1, 5 and 25 mg·kg^-1) on N₂O production rate from the surface sediment (0-5 cm) of Luoshijiang Wetland, located upstream from Lake Erhai. The contribution of nitrification, denitrification, nitrifier denitrification, and other factors to the N₂O production rate in sediments was studied by the inhibitor method. The relationships between N₂O production and the activities of hydroxylamine (HyR), nitrate (NAR), nitric oxide (NOR), and nitrous oxide (NOS) reductases in sediments were analyzed. We found that NO₃^--N input significantly increased total N₂O production rate (1.51-11.35 nmol·kg^-1·h^-1), which led to N₂O release, whereas NH₄⁺-N input decreased that (-0.80 to -0.54 nmol·kg^-1·h^-1), causing N₂O absorption. NO₃^--N input did not change the dominant roles of nitrification and nitrifier denitrification in N₂O production in sediments, but increased the contributions of these two factors to 69.5% and 56.5%, respectively. The NH₄⁺-N input significantly changed N₂O gene-ration process, and the nitrification and nitrifier denitrification changed from N₂O release to uptake. There was a positive correlation between total N₂O production rate and NO₃^--N input. NO₃^--N input significantly increased NOR activity and decreased NOS activity, thereby promoting N₂O production. The total N₂O production rate in sediments was negatively correlated with NH₄⁺-N input. NH₄⁺-N input significantly increased the activities of HyR and NOR, decreased NAR activity, and inhibited N₂O production. Nitrogen inputs with different forms and concentrations changed the degree of contribution and mode of N₂O production by affecting enzyme activities in sediments. NO₃^--N input significantly promoted N₂O production, acting as a source of N₂O, while NH₄⁺-N input inhibited N₂O production, resulting in an N₂O sink.

Key words: N₂O, nitrogen input, enzyme activity, wetland sediment