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ARS Home » Midwest Area » St. Paul, Minnesota » Soil and Water Management Research » Research » Publications at this Location » Publication #336271
Title: Nitrification gene ratio and free ammonia explain nitrite and nitrous oxide production in urea-amended soils

Author
item BREUILLIN-SESSOMS, FLORENCE - UNIVERSITY OF MINNESOTA
item Venterea, Rodney - Rod
item SADOWSKY, MICHAEL - UNIVERSITY OF MINNESOTA
item COULTER, JEFFREY - UNIVERSITY OF MINNESOTA
item CLOUGH, TIM - LINCOLN UNIVERSITY - PENNSYLVANIA
item WANG, PING - UNIVERSITY OF MINNESOTA

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2017
Publication Date: 8/1/2017
Citation: Breuillin-Sessoms, F., Venterea, R.T., Sadowsky, M., Coulter, J., Clough, T., Wang, P. 2017. Nitrification gene ratio and free ammonia explain nitrite and nitrous oxide production in urea-amended soils. Soil Biology and Biochemistry. 111(1):143-153. doi:10.1016/j.soilbio.2017.04.007.

Interpretive Summary: Nitrous oxide (N2O) is a potent greenhouse gas and important ozone depleting chemical. Substantial efforts have been made to characterize soil N2O emissions following N fertilizer addition. While nitrite (NO2-) is a central regulator of N2O production, NO2- and N2O responses to nitrogen (N) fertilizer amendments still cannot be readily predicted. Our objective was to determine if quantification of multiple chemical substrates and structural genes associated with ammonia (NH3)- (AOB, encoded by amoA) and NO2--oxidizing bacteria (NOB, encoded by nxrA and nxrB) could explain the contrasting responses of eight agricultural soils to urea addition in aerobic microcosms. Significant differences in individual soil responses could not be explained by basic soil properties. Coherent linear models, however, accounted for 70 to 89% of the total variance in NO2- and N2O. Free NH3, quantified using sorption isotherms, accounted for 50 to 85% of the variance in NO2- which, in turn, explained 62 to 82% of the variance in N2O. Abundances of nxrA declined above critical urea addition rates (Uc), indicating suppression of NOB. The nxrA:amoA gene ratio, by itself, explained 78 and 79% of the variance in cumulative NO2- and N2O, respectively. The current results are the first to demonstrate the usefulness of the nxrA:amoA ratio and the Uc concept in understanding NO2- accumulation and N2O production. The results also indicate that NH3 inhibition is more pronounced and consistent in its effects on Nitrobacter (nxrA) relative to Nitrospira (nxrB), and that Nitrobacter exert greater regulatory control over NO2- and N2O. While field N2O emissions will be affected by plant and climatic factors, the robust and biologically-coherent relationships found here provide a basis for better understanding and predicting soil responses to fertilizer N inputs.These results will be useful for developing accurate global change models and developing mitigating practices.

Technical Abstract: Substantial efforts have been made to characterize soil nitrous oxide (N2O) emissions following N fertilizer addition. While nitrite (NO2-) is a central regulator of N2O production, NO2- and N2O responses to nitrogen (N) fertilizer amendments still cannot be readily predicted. Our objective was to determine if quantification of multiple chemical substrates and structural genes associated with ammonia (NH3)- (AOB, encoded by amoA) and NO2--oxidizing bacteria (NOB, encoded by nxrA and nxrB) could explain the contrasting responses of eight agricultural soils to urea addition in aerobic microcosms. Significant differences in individual soil responses could not be explained by basic soil properties. Coherent linear models, however, accounted for 70 to 89% of the total variance in NO2- and N2O. Free NH3, quantified using sorption isotherms, accounted for 50 to 85% of the variance in NO2- which, in turn, explained 62 to 82% of the variance in N2O. Abundances of nxrA declined above critical urea addition rates (Uc), indicating suppression of NOB. The nxrA:amoA gene ratio, by itself, explained 78 and 79% of the variance in cumulative NO2- and N2O, respectively. The current results are the first to demonstrate the usefulness of the nxrA:amoA ratio and the Uc concept in understanding NO2- accumulation and N2O production. The results also indicate that NH3 inhibition is more pronounced and consistent in its effects on Nitrobacter (nxrA) relative to Nitrospira (nxrB), and that Nitrobacter exert greater regulatory control over NO2- and N2O. While field N2O emissions will be affected by plant and climatic factors, the robust and biologically-coherent relationships found here provide a basis for better understanding and predicting soil responses to fertilizer N inputs.