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A variety of pathways for N 2 O production are known, both biotic (autotrophic nitrification, heterotrophic nitrification, nitrifier-denitrification, denitrification, nitrate ammonification, aerobic denitrification) and abiotic (chemodenitrification) (Wrage et al., 2005). According to Baggs (2008), N 2 O production in soils is predominantly biological and can be mediated by ammonia oxidizers either during nitrification and/or during nitrifier-denitrification (Wrage et al., 2004a), or via nitrate reduction by denitrifiers (e.g., Master et al., 2004). Nitrification and nitrifier-denitrification are both performed by autotrophic ammonia-oxidizing bacteria. As a by-product of ammonia oxidation to NO 2 − , N 2 O can be produced in aerobic zones of soils. Nitrifier-denitrification is thought to occur when ammonia oxidizers are subject to oxygen deficiency and thus reduce the formed NO 2 − to N 2 O via NO. Denitrification occurs usually under anaerobic conditions through the sequential reduction of NO 3 − to NO 2 − , NO, N 2 O, and fi-