Contrasting delta super(15)N Values of Atmospheric Deposition and Sphagnum Peat Bogs: N Fixation as a Possible Cause

Nitrogen (N) isotope systematics were investigated at two high-elevation ombrotrophic peat bogs polluted by farming and heavy industry. Our objective was to identify N sources and sinks for isotope mass balance considerations. For the first time, we present a time-series of delta super(15)I values o...

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Bibliographic Details
Published in:Ecosystems (New York) 2016-09, Vol.19 (6), p.1037-1050
Main Authors: Novak, Martin, Jackova, Ivana, Curik, Jan, Stepanova, Marketa, Veselovsky, Frantisek, Buzek, Frantisek, Vile, Melanie A, Bufkova, Ivana, Valkova, Ivana, Adamova, Marie, Bohdalkova, Leona, Komarek, Arnost
Format: Article
Language:English
Subjects:
Sphagnum
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Summary:Nitrogen (N) isotope systematics were investigated at two high-elevation ombrotrophic peat bogs polluted by farming and heavy industry. Our objective was to identify N sources and sinks for isotope mass balance considerations. For the first time, we present a time-series of delta super(15)I values of atmospheric input at the same locations as delta super(15)I values of living Sphagnum and peat. The mean delta super(15)I values systematically increased in the order: input NH sub(4) super(+) (-10.0ppt) < input NO sub(3) super(-) (-7.9ppt) < peat porewater (-5.6ppt) < Sphagnum (-5.0ppt) < shallow peat (-4.2ppt) < deep peat (-2.2ppt) < runoff (-1.4ppt) < porewater N sub(2)O (1.4ppt). Surprisingly, N of Sphagnum was isotopically heavier than N of the atmospheric input (P < 0.001). If partial incorporation of reactive N from the atmosphere into Sphagnum was isotopically selective, the residual N would have to be isotopically extremely light. Such N, however, was not identified anywhere in the ecosystem. Alternatively, Sphagnum may have contained an admixture of isotopically heavier N. Ambient air contains such N in the form of N sub(2) ( delta super(15)I sub(N2) = 0ppt). Because high energy is required to break the triple bond, microbial N fixation is likely to proceed only under limited availability of pollutant N. Also for the first time, a delta super(15)I comparison is presented between anoxic deeper peat and porewater N sub(2)O. Isotopically light N is removed from anoxic substrate by denitrification, whose final product, N sub(2), escapes into the atmosphere. Porewater N sub(2)O is an isotopically heavy residuum following partial N sub(2)O reduction to N sub(2).
ISSN:1432-9840
1435-0629
DOI:10.1007/s10021-016-9985-y