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

Citation

Su, Chenxia et al. (2020), δ15N of nitric oxide produced under aerobic or anaerobic conditions from seven soils and their associated N isotope fractionations, Dryad, Dataset, https://doi.org/10.5061/dryad.18931zcss

Abstract

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‰). The apparent N isotope fractionation for NO production under aerobic condition (15εaerobic = 61 ± 3‰) was significantly higher (by 26‰) than under anaerobic condition (15εanaerobic = 35 ± 6‰), with a small variability among ecosystem types. Our study demonstrates that the δ15N-NO from different soils are very different from fuel combustions (mainly from 0 to +20‰), supporting that measuring 15N is a useful tool to partition the contributions of soil NO to atmospheric NOx. Our results also imply δ15N-NO produced by nitrification and denitrification distinctly different, as these two processes are dominant processes producing NO under aerobic and anaerobic conditions, respectively.

Methods

We conducted laboratory incubation experiments with three types of soils collected from seven sites, including two temperate forest (QY-LF,QY-MF), two agricultural (SY, JL) and three grassland soils (EG, HB,DL) under anaerobic or aerobic conditions. We set 5 sampling times, on days 0, 1, 3, 5, and 7. For each sampling time, we determined the concentration and isotope compositions of cumulative nitric oxide (NO) produced and the remaining soil KCl-extractable NH4+ and NO3-, we also calculated the isotope fractionations during NO producing.

 

Funding

The National Key Research and Development Program of China, Award: 2017YFC0212704, 2016YFA0600802

The Key Research Program of Frontier Sciences of Chinese Academy of Sciences, Award: QYZDB - SSW - DQC002

The National Natural Science Foundation of China, Award: 41773094

The National Research Program for Key Issues in Air Pollution Control, Award: DQGG0105-02

Hundred Talents Program of Chinese Academy of Sciences, Award: 2019000186

K. C. Wong Education Foundation, Award: GJTD-2018-07

The Chinese Scholarship Council (CSC) Fellowship