In situ 15N-N2O site preference and O2 concentration dynamics disclose the complexity of N2O production processes in agricultural soil

Authors: WEI, HUANHUAN - China Agricultural University; SONG, XIAOTONG - China Agricultural University; LIU, YAN - Chinese Academy Of Sciences; WANG, RUI - Chinese Academy Of Sciences; ZHENG, XUNHUA - Chinese Academy Of Sciences; BUTERBACH-BAHL, KLAUS - Karlsruhe Institute Of Technology; Venterea, Rodney - Rod; WU, DI - China Agricultural University; JU, XIAOTANG - China Agricultural University

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2023
Publication Date: 5/15/2023
Citation: Wei, H., Song, X., Liu, Y., Wang, R., Zheng, X., Buterbach-Bahl, K., Venterea, R.T., Wu, D., Ju, X. 2023. In situ 15N-N2O site preference and O2 concentration dynamics disclose the complexity of N2O production processes in agricultural soil. Global Change Biology. 29(17):4910-4923. https://doi.org/10.1111/gcb.16753.
DOI: https://doi.org/10.1111/gcb.16753

Interpretive Summary: Nitrous oxide is a potent ozone-depleting and greenhouse gas that is emitted from agricultural soils to the atmosphere following application of nitrogen fertilizers. Identifying the main processes responsible for nitrous oxide production is important because it can help to guide the development of technologies to reduce those emissions. However, because nitrous oxide can be produced by a variety of different microbial and chemical processes in soil, it is difficult to identify the main sources of N2O under any given set of conditions. In this study, we used a combination of advanced measurement methods that help to identify the specific processes responsible for nitrous oxide production during both summer and winter growing seasons in the North China Plain, which is one of China’s most important agricultural regions, producing wheat, maize, sorghum, millet, and a variety of other crops. The techniques utilized included high-frequency measurements of soil matrix oxygen and nitrous oxide gas concentrations, standard isotope labeling, and more specialized site preference isotope detection. The methods indicated that oxygen availability was the main determining factor that regulated nitrous oxide emissions from the soil. The results also showed that the main source for nitrous oxide emissions during the hot-wet summer was a specific microbial process, bacterial denitrification, while other processes, nitrification or fungal denitrification, contributed about half of the total nitrous oxide emissions during the cold-dry winter. These results will be helpful to scientists, land managers, and policy makes in developing targeted practices to reduced nitrous oxide emissions and also to improve models that estimate emissions at the farm to global scale.

Technical Abstract: Arable soil continues to be the dominant anthropogenic source of nitrous oxide (N2O) emissions owing to application of nitrogen (N) fertilizers and manures across the world. Using laboratory and in-situ studies to elucidate the key factors controlling soil N2O emissions remains challenging due to the potential importance of multiple complex processes. We examined soil surface N2O fluxes in an arable soil, combined with in-situ high-frequency measurements of soil matrix oxygen (O2) and N2O concentrations, in situ 15N labeling, and N2O 15N site preference (SP). The in situ O2 concentration and further microcosm visualized spatiotemporal distribution of O2 both suggested that O2 dynamics were the proximal determining factor to matrix N2O concentration and fluxes due to quick O2 depletion after N fertilization. Further SP analysis and in situ 15N labeling experiment revealed that the main source for N2O emissions was bacterial denitrification during the hot-wet summer, while nitrification or fungal denitrification contributed about 50% to total emissions during the cold-dry winter. The robust positive correlation between O2 concentration and SP values underpinned that the O2 dynamics were the key factor to differentiate the composite processes of N2O production in in situ structured soil. Our findings deciphered the complexity of N2O production processes in real field conditions, and suggest that O2 dynamics rather than stimulation of functional gene abundances play a key role in controlling soil N2O production processes in undisturbed structure soils. Our results help to develop targeted N2O mitigation measures and to improve process models for constraining global N2O budget.