Nitrification gene ratio and free ammonia explain nitrite and nitrous oxide production in urea-amended soils. (August 2017)

• Record Type: Journal Article
• Authors: Breuillin-Sessoms, Florence; Venterea, Rodney T.; Sadowsky, Michael J.; Coulter, Jeffrey A.; Clough, Tim J.; Wang, Pang
• Is Part Of: Soil biology and biochemistry. Volume 111(2017)
• Page Start: 143
• Page End: 153
• Publication Date: 2017-08
• Subjects: Soil biochemistry -- Periodicals; Soil biology -- Periodicals; Sols -- Biochimie -- Périodiques; Sols -- Biologie -- Périodiques; Sols -- Microbiologie -- Périodiques; Bodembiologie; Biochemie; 631.46
• DOI: 10.1016/j.soilbio.2017.04.007
• Languages: English
• ISSNs: 0038-0717

Abstract

Abstract: The atmospheric concentration of nitrous oxide (N2 O), a potent greenhouse gas and ozone-depleting chemical, continues to increase, due largely to the application of nitrogen (N) fertilizers. While nitrite (NO2 − ) is a central regulator of N2 O production in soil, NO2 − and N2 O responses to fertilizer addition rates cannot be readily predicted. Our objective was to determine if quantification of multiple chemical variables and structural genes associated with ammonia (NH3 )- (AOB, encoded by amo A) and NO2 − -oxidizing bacteria (NOB, encoded by nxr A and nxr B) could explain the contrasting responses of eight agricultural soils to five rates of urea addition in aerobic microcosms. Significant differences in NO2 − accumulation and N2 O production by soil type could not be explained by initial soil properties. Biologically-coherent statistical models, however, accounted for 70–89% of the total variance in NO2 − and N2 O. Free NH3 concentration accounted for 50–85% of the variance in NO2 − which, in turn, explained 62–82% of the variance in N2 O. By itself, the time-integrated nxr A: amo A gene ratio explained 78 and 79% of the variance in cumulative NO2 − and N2 O, respectively. In all soils, nxr A abundances declined above critical urea addition rates, indicating a consistent pattern of suppression of Nitrobacter -associated NOB due to NH3 toxicity. In contrast, Nitrospira -associated nxr B abundances exhibited a broader range of responses, and showed that long-term management practices (e.g., tillage) can induce a shift in dominant NOB populations which subsequently impacts NO2 − accumulation and N2 O production. These results highlight the challenges of predicting NO2 − and N2 O responses based solely on static soil properties, and suggest that models that account for dynamic processes following N addition are ultimately needed. The relationships found here provide a basis for incorporating the relevant biological and chemical processes into N cycling and N2 O emissions models. Highlights: NO2 − and N2 O responses to N fertilizer inputs still cannot be readily predicted. Chemical substrates and nitrification genes were measured in eight urea-amended soils. Differences in NO2 − and N2 O by soil type could not be explained by initial soil properties. Biologically-coherent models explained ≥87% of the variance in NO2 − and N2 O. By itself, the nxr A: amo A gene ratio explained ≥78% of the variance.