Fig. S1. Regression plot of nosZ copy numbers estimated by Kloos and colleagues (2001) and Henry and colleagues (2006) primers.

Fig. S2. Geographic location of three experimental sites in circumpolar arctic region: Truelove Lowland (75°40′N, 84°35′W), Simpson Lake (68°35′N, 91°57′W) and Ross Point (68°31′N, 111°10′W). Adapted from the Toolik-Arctic Geobotanical Atlas (; Alaska Geobotany Center).

Table S1. Soil properties at three sites (from Banerjee et al., 2011a). Mean values (n = 93) of different variables for three sites. Standard errors are shown in parentheses.

Table S2. The rate of N2O production (rN2O) and Spearman Rank correlations between rN2O and other variables at three arctic ecosystems. The rN2O was calculated as the ratio of N2Of to DEA (i.e. rN2O = N2Of/DEA) (Rich and Myrold, 2004; Ma et al., 2008).

Table S3. Spearman Rank correlation coefficients among denitrifier abundance, denitrifier potential activities and soil properties.

Table S4. Primers and thermal cycling conditions used for the quantification of denitrifier functional genes.

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