Estimation of isotope variation of N₂O during denitrification by Pseudomonas aureofaciens and Pseudomonas chlororaphis: implications for N₂O source apportionment

Journal Article · Wed Jun 27 00:00:00 EDT 2018 · Biogeosciences (Online)

DOI:https://doi.org/10.5194/bg-15-3873-2018· OSTI ID:1503313

Haslun, Joshua A.  ^[1]; Ostrom, Nathaniel E. ^[1]; Hegg, Eric L. ^[1]; Ostrom, Peggy H. ^[1]

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1. Michigan State Univ., East Lansing, MI (United States)

Soil microbial processes, stimulated by agricultural fertilization, account for 90% of anthropogenic nitrous oxide (N₂O), the leading source of ozone depletion and a potent greenhouse gas. Efforts to reduce N₂O flux commonly focus on reducing fertilization rates. Management of microbial processes responsible for N₂O production may also be used to reduce N₂O emissions, but this requires knowledge of the prevailing process. To this end, stable isotopes of N₂O have been applied to differentiate N₂O produced by nitrification and denitrification. To better understand the factors contributing to isotopic variation during denitrification, we characterized the δ¹⁵N,δ¹⁸O and site preference (SP; the intramolecular distribution of¹⁵N in N₂O) of N₂O produced during ${\mathrm{NO}}_3^{-}$ reduction by Pseudomonas chlororaphis subsp. aureofaciens and P. c. subsp. chlororaphis. The terminal product of denitrification for these two species is N₂O because they lack thegene nitrous oxide reductase, which is responsible for the reduction ofN₂O to N₂. In addition to species, treatments include delectron donor (citrate and succinate) and electron donor concentration(0.01, 0.1, 1 and 10mM) as factors. In contrast to the expectation of a Rayleigh model, all treatments exhibited curvilinear behaviour between δ¹⁵N or δ¹⁸O and the extent of the reaction. The curvilinear behaviour indicates that the fractionation factor changed over the course of the reaction, something that is not unexpected for a multi-step process such as denitrification. Using the derivative of the equation, we estimated that the net isotope effects (η) vary by as much as 100‰ over the course of a single reaction, presenting challenges for using δ¹⁵N and δ¹⁸O as apportionment tools. In contrast, SP for denitrification was not affected by the extent of the reaction, the electron donor source or concentration, although the mean SP of N₂O produced by each species differed. Hence, SP remains a robust indicator of the origin of N₂O. To improve apportionment estimates with SP, future studies could evaluate other factors that contribute to the variation in SP.

• Research Organization: Univ. of Wisconsin, Madison, WI (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: FC02-07ER64494
• OSTI ID: 1503313
• Journal Information: Biogeosciences (Online), Vol. 15, Issue 12; ISSN 1726-4189
• Publisher: European Geosciences Union
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
54 ENVIRONMENTAL SCIENCES