Journal
SOIL BIOLOGY & BIOCHEMISTRY
Volume 43, Issue 6, Pages 1180-1185Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.soilbio.2011.02.006
Keywords
Oxygen exchange; Nitrate source determination; Oxygen stable isotopes; Nitrogen stable isotopes
Categories
Funding
- European Commission
- Netherlands Organization of Scientific Research/Earth and Life Sciences (NWO-ALW)
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Combined oxygen (O) and nitrogen (N) stable isotope analyses are commonly used in the source determination of nitrate (NO3-). The source and fate of NO3- are studied based on distinct O and N isotopic signatures (delta O-18 and delta N-15) of various sources and isotopic effects during NO3- transformation processes, which differ between sources like fertilizer, atmospheric deposition, and microbial production (nitrification). Isotopic fractionation during production and consumption of NO3- further affects the delta O-18 and delta N-15 signal. Regarding the delta O-18 in particular, biochemical O exchange between O from NO3- and H2O is implicitly assumed not to affect the 8180 signature of NO3-. This study aimed to test this assumption in soil-based systems. In a short (24 h) incubation experiment, soils were treated with artificially O-18 and N-15 enriched NO3-. Production of NO3- from nitrification during the incubation would affect both the O-18 and the N-15 enrichment. Oxygen exchange could therefore be studied by examining the change in O-18 relative to the N-15. In two out of the three soils, we found that the imposed O-18 enrichment of the NO3- declined relatively more than the imposed N-15-NO3- enrichment. This implies that O exchange indeed affected the O isotopic signature of NOT, which has important implications for NO3- source determination studies. We suggest that O exchange between NO3- and H2O should be taken into consideration when interpreting the O isotopic signature to study the origin and fate of NO3- in ecosystems. (C) 2011 Elsevier Ltd. All rights reserved.
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