Tuesday, November 6, 2007 - 2:45 PM
189-2

Nitrifier Denitrification: What We Know, Don't Know and Thought We Knew.

Nicole Wrage1, Dorien M. Kool2, Oene Oenema2, and Jan Willem Van Groenigen2. (1) Georg-August-University of Göttingen, Department of Crop Sciences, von-Siebold -Strasse 8, 37075, Göttingen, Germany, (2) Alterra, Wageningen University and Research Centre, PO Box 47, Wageningen, 6700AA, Netherlands

Nitrifier denitrification is a pathway of autotrophic ammonia oxidizers known since 1972 (Ritchie and Nicholas, 1972). The organisms oxidize NH3 to NO2-, which they consequently reduce via NO and N2O to N2 (Wrage et al., 2001). The greenhouse gas N2O can also be the end product of the reaction. Nitrifier denitrification might be a universal pathway of ammonia oxidizers. The genes and enzymes involved are similar to those of denitrifiers, suggesting lateral gene transfer. Nevertheless, genes and thus optimal conditions for nitrifier denitrification are diverse and amounts of N2O produced vary between strains of ammonia oxidizers as well as between environmental conditions. So far, two methods have been suggested for measuring N2O production by nitrifier denitrification in soils. One is based on the use of the inhibitors O2 and C2H2 (Webster and Hopkins, 1996), the other is a dual-isotope labelling method using single and double 15N-labelled NH4NO3 and 18O-labelled H2O (Wrage et al., 2005). Both methods have indicated nitrifier denitrification as a potentially prominent source of N2O in soils. However, both methods also have shortcomings, which will be discussed in the presentation. An overview of ongoing research and research needs will be given.

References

Ritchie, G.A.F., and D.J.D. Nicholas. 1972. Identification of the sources of nitrous oxide produced by oxidative and reductive processes in Nitrosomonas europaea. Biochemical Journal 126:1181-1191.

Webster, E.A., and D.W. Hopkins. 1996. Contributions from different microbial processes to N2O emission from soil under different moisture regimes. Biology and Fertility of Soils 22:331-335.

Wrage, N., G.L. Velthof, M.L. van Beusichem, and O. Oenema. 2001. Role of nitrifier denitrification in the production of nitrous oxide. Soil Biology and Biochemistry 33:1723-1732.

Wrage, N., J.W. van Groenigen, O. Oenema, and E.M. Baggs. 2005. A novel dual-isotope labelling method for distinguishing between soil sources of N2O. Rapid Communications in Mass Spectrometry 19:3298-3306.


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