Campus Units

Ecology, Evolution and Organismal Biology

Document Type

Article

Publication Version

Submitted Manuscript

Publication Date

8-2012

Journal or Book Title

Oecologia

Volume

181

Issue

4

First Page

1221

Last Page

1231

DOI

10.1007/s00442-016-3626-1

Abstract

Natural abundance nitrate (NO3−) isotopes represent a powerful tool for assessing denitrification, yet the scale and context dependence of relationships between isotopes and denitrification have received little attention, especially in surface soils. We measured the NO3−isotope compositions in soil extractions and lysimeter water from a semi-arid meadow and lawn during snowmelt, along with the denitrification potential, bulk O2, and a proxy for anaerobic microsites. Denitrification potential varied by three orders of magnitude and the slope of δ18O/δ15N in soil-extracted NO3− from all samples measured 1.04 ± 0.12 (R2 = 0.64, p < 0.0001), consistent with fractionation from denitrification. However, δ15N of extracted NO3− was often lower than bulk soil δ15N (by up to 24 ‰), indicative of fractionation during nitrification that was partially overprinted by denitrification. Mean NO3− isotopes in lysimeter water differed from soil extractions by up to 19 ‰ in δ18O and 12 ‰ in δ15N, indicating distinct biogeochemical processing in relatively mobile water versus soil microsites. This implies that NO3− isotopes in streams, which are predominantly fed by mobile water, do not fully reflect terrestrial soil N cycling. Relationships between potential denitrification and δ15N of extracted NO3− showed a strong threshold effect culminating in a null relationship at high denitrification rates. Our observations of (1) competing fractionation from nitrification and denitrification in redox-heterogeneous surface soils, (2) large NO3− isotopic differences between relatively immobile and mobile water pools, (3) and the spatial dependence of δ18O/δ15N relationships suggest caution in using NO3− isotopes to infer site or watershed-scale patterns in denitrification.

Comments

This is a manuscript of an article from Oecologia 1881 (2016): 1221, doi: 10.1007/s00442-016-3626-1. Posted with permission.

Copyright Owner

Springer-Verlag Berlin Heidelberg

Language

en

File Format

application/pdf

Published Version

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