Effects of copper on nitrous oxide (N2O) reduction in denitrifiers and N2O emissions from agricultural soils
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Biochemical reduction of nitrous oxide (N2O) to dinitrogen (N2) by N2O reductase (N2OR) is the only known sink to consume N2O. Copper (Cu) and pH are two key factors determining the activity of the enzyme N2OR. We hypothesized that changes in the Cu level could enhance the reduction of N2O to N2 in denitrifier strains and decrease the N2O emissions from agricultural soils. To test this hypothesis, Cu-modified culture medium was applied to denitrifier strains, and Cu-modified organic fertilizer was applied to both soil microcosms and fields. Of 46 denitrifier strains, 25 showed higher denitrifying activities and 30N2/(46N2O + 30N2) after the addition of Cu under pure culture conditions. Among 10 genera, Azospirillum and Herbaspirillum were the most responsive to the Cu level changes. The N2O flux was significantly reduced 4 or 8 days onwards after the application of 130 mM CuSO4-modified organic fertilizer (vol:wt = 1:1) into Andosol or Fluvisol, respectively, under soil microcosm conditions. In addition, the cumulative N2O emissions were significantly reduced after the application of 130 mM CuSO4-modified organic fertilizer. They were moderately reduced after the application of 130 mM CuSO4-modified organic fertilizer (vol:wt = 1:1) into a Fluvisol field. They were significantly lower in Azospirillum sp. UNPF1-inoculated soils after the application of 130 mM CuSO4-modified organic fertilizer when compared with that in dual non-inoculated and unmodified soils. Soils inoculated with Herbaspirillum sp. UKPF54 showed results similar to non-inoculated Fluvisol fields. These results suggest that Cu may enhance N2O conversion to N2 in denitrifiers and that Cu-modified organic fertilizer may enhance N2O consumption or decrease N2O emissions in agricultural soils.
KeywordsCopper Denitrifier Greenhouse gas Nitrous oxide (N2O) emission N2O reductase N2O reduction to dinitrogen
We thank Shigeto Otsuka for his helpful discussion and Chie Hayakawa for her help with gas sampling in the fields. We also thank the technical staffs from the Niigata Agricultural Research Institute and Institute for Sustainable Agro-ecosystem Services, The University of Tokyo for their assistance with fieldwork.
This study was supported by grants from the National Natural Science Foundation of China (41771291, 31972503), Japan Society for the Promotion of Science through a Postdoctoral Fellowship (14F04390), JSPS KAKENHI (JP15KT0024), and Science and Technology Research Promotion Program for Agriculture, Forestry, Fisheries and Food Industry (26037B and 27004C), Japan.
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