δ15N of nitric oxide produced under aerobic or anaerobic conditions from seven soils and their associated N isotope fractionations

Measuring the nitrogen isotope compositions (δ15N) of nitric oxide (NO) from different sources helps to quantify the relative contributions of atmospheric NOx. Soil is one of the most important sources of atmospheric NOx, but only limited measurements on the δ15N of soil emitted NO exist, hampering our ability to partition sources to air pollution. Here we conducted soil incubations to measure the δ15N-NO under defined aerobic or anaerobic conditions, favoring either nitrification or denitrification. Soils were collected from seven sites spanning three ecosystems in northern China (two agricultural, two forest, and three grassland sites). We found that the δ15N-NO and their associated N isotope fractionations were significant different between anaerobic and aerobic conditions in seven soils. Under aerobic condition, the δ15N-NO ranged from -62‰ to -50‰ (averaged -56 ± 4‰), being significantly more negative (by 23‰) than those under anaerobic condition (-45‰ to -23‰, averaged -33 ± 7‰). ...