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Title: Shifts in the composition and activities of denititrifiers dominate CO2-stimulation of N2O emissions

Author
item QIU, YUNPENG - Nanjing Agricultural University
item JIANG, YU - Nanjing Agricultural University
item GUO, LINJIN - Hainan University
item ZHANG, LIN - Nanjing Agricultural University
item Burkey, Kent
item ZOBEL, RICHARD - North Carolina State University
item REBERG-HORTON, CHRIS - North Carolina State University
item SHEW, DAVID - North Carolina State University
item HU, SHUIJIN - North Carolina State University

Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2019
Publication Date: 8/29/2019
Citation: Qiu, Y., Jiang, Y., Guo, L., Zhang, L., Burkey, K.O., Zobel, R., Reberg-Horton, C., Shew, D., Hu, S. 2019. Shifts in the composition and activities of denititrifiers dominate CO2-stimulation of N2O emissions. Environmental Science and Technology. 53:11204-11213.

Interpretive Summary: Nitrous oxide is a potent greenhouse gas with a global warming potential 300 times greater than that of carbon dioxide, and is a factor in the depletion of the stratospheric ozone that shields the earth from ultraviolet light. Globally, agricultural soils are a major source of nitrous oxide from microbial processes associated with the use of chemical fertilizers. A team of scientists from Nanjing Agricultural University and Hainan University in China, North Carolina State University, and USDA-ARS at Raleigh showed that elevated carbon dioxide interacts with oxidized nitrogen fertilizer (nitrate) to produce nitrous oxide. In a greenhouse study with wheat, the combination of elevated carbon dioxide and nitrate fertilizer stimulated nitrous oxide emission and the soil microbes associated with nitrous oxide production. In contrast, very little nitrous oxide was produced when plants were supplied with reduced nitrogen in the form of ammonium. Together, these findings suggest that effective management of nitrogen resources may help harness the positive effects of elevated carbon dioxide on crop production, while reducing nitrous oxide emissions from agricultural fields.

Technical Abstract: Elevated atmospheric CO2 (eCO2) often increases soil N2O emissions but the underlying mechanisms remain largely unknown. One hypothesis suggests that high N2O emissions may stem from increased denitrification induced by CO2-enhancement of C allocation belowground. However, direct evidence illustrating linkages among N2O emissions, plant C allocation and denitrifying microbes under eCO2 are still lacking. We examined the impact of eCO2 on C allocation to plant roots and their associated arbuscular mycorrhizal fungi (AMF) and its subsequent effects on N2O emissions and denitrifying microbes in the presence of two distinct N sources, ammonium nitrogen (NH4+ -N) and nitrate nitrogen (NO3- -N). Our results showed that the form of the N inputs dominated the effects of eCO2 on N2O emissions: eCO2 significantly increased N2O emissions with NO3- -N inputs but had no effect with NH4+ -N inputs. Also, eCO2-enhancement of plant biomass N was more profound with NH4+ than NO3- inputs, likely reducing microbial access to available N when NH4+ was the primary N source. While eCO2 enhanced root and mycorrhizal N uptake, it also increased N2O emissions under NO3- inputs. eCO2-enhancement of N2O emissions under NO3- inputs concurred with a shift in the soil denitrifier community composition in favor of N2O-producing (nirK- and nirS-type) over N2O consuming (nosZ-type) denitrifiers. Together, these findings provide new insights into the interactive effects of eCO2 and N sources on soil denitrifiers and their activities, highlighting the challenges and potential of managing the denitrifying microbes via N sources for mitigation of N2O emissions under the future CO2 scenarios.