Evidence for the predominance of denitrification as a source of N₂O in temperate agricultural soils based on isotopologue measurements

Abstract

Isotopologue values were used to quantify the contribution of denitrification to nitrous oxide (N 2 O) flux in agricultural and early successional fields in southwest Michigan. Nitrous oxide‐ δ 15 N and δ 18 O values were poor estimators of microbial origins compared to site preference (SP) (difference in δ 15 N between the outer and central N atoms of N 2 O). Site preference was used to evaluate the importance of denitrification (including nitrifier denitrification) in N 2 O production. Average flux‐weighted SP values for each field ranged between 2.9 and 14.6‰ and, on the basis of SP values for N 2 O production from denitrification (0‰) and collectively for nitrification and fungal denitrification (37‰), these values indicate that between 61 and 92% of N 2 O originated from denitrification. Reduction of N 2 O ranged from undetectable to as much as 50% of production; and because reduction increases SP, our results underestimate the percentage of N 2 O from bacterial denitrification. The SP values in our study clearly indicate that denitrification is the predominant source of soil‐derived N 2 O.