The source of N
2O in terrestrial ecosyste
ms has long been debated. Both nitrification and denitrification produce N
2O but their relative i
mportance re
mains uncertain. Here we apply site preference, SP (the difference in δ
15N between the central and outer N ato
m in N
2O), to esti
mate the relative i
mportance of bacterial denitrification (including nitrifier denitrification) to total N
2O production fro
m soil. We
measured SP over a diurnal cycle following the third year of tillage of a previously uncultivated grassland soil at the Kellogg Biological Station (KBS) in southwestern Michigan. Fluxes of N
2O in our study ranged between 7.8 and 12.1 g N
2O–N ha
−1 d
−1 and were approxi
mately 3 and 10 ti
mes greater than fluxes observed in
managed agricultural and successional fields, respectively, at KBS. Consequently, our study captured a period of high flux resulting fro
m the cultivation of a historically never-tilled soil. Concentration weighted SP values decreased fro
m 12.9‰ in the
morning to a
mini
mu
m value of −0.1‰ in the afternoon.
Based on SP values reported for bacterial denitrification (−5 to 0‰; Toyoda et al., 2005; Sutka et al., 2006), hydroxylamine oxidation (nitrification) and fungal denitrification (33–37‰; Sutka et al., 2006) we found that production attributable to bacterial denitrification increased from between 52.9 and 60.9 % in the morning to between 87.5 and 100 % in the afternoon. Further, we observed diurnal variation in flux and SP that is consistent with increased production from bacterial denitrification associated with temperature-driven increases in respiration.