『Abstract
The biological and physical controls on microbial processes that
produce and consume N2O in soils are highly
complex. Isotopomer ratios of N2O, with abundance
of 14N15N16O, 15N14N16O,
and 14N14N18O relative to 14N14N16O,
are promising for elucidation of N2O biogeochemistry
in an intact ecosystem. site preference, the nitrogen isotope
ratio of the central nitrogen atom minus that of the terminal
nitrogen atom, is useful to distinguish between N2O
via hydroxylamine oxidation and N2O via nitrite
reduction.
We applied this isotopomer analysis to a groundwater system in
a temperate coniferous-forested ecosystem. Results of a previous
study at this location showed that the N2O
concentration in groundwater varied greatly according to groundwater
chemistry, i.e. NO3-, DOC, and
DO, although apportionment of N2O production
to nitrification or denitrification was ambiguous. Our isotopic
analysis (δ15N and δ18O) of NO3-
and N2O implies that denitrification is the
dominant production process of N2O, but definitive
information is not derived from δ15N and δ18O
analysis because of large variations in isotopic fractionations
during production and consumption of N2O.
However, the N2O site preference and the
difference in δ15N between NO3-
and N2O indicate that nitrification contributes
to total N2O production and that most measured
N2O has been subjected to further N2O reduction to N2. The implications
of N2O biogeochemistry derived from isotope
and isotopomer data differ entirely from those derived from conventional
concentration data of DO, NO3-,
and N2O. That difference underscores the
need to reconsider our understanding of the N cycle in the oxic-anoxic
interface.』
1. Introduction
2. Materials and methods
2.1. Study area
2.2. Chemical analysis
2.3. Statistical analysis
2.4. Interpretation of isotopic signature of N2O
dynamics
3. Results and discussion
3.1. Spatial variations in DO, NO3-,
DOC, and N2O concentrations
3.2. Spatial variations in NO3-
isotope ratios
3.3. Isotope data of N2O
3.4. Site preference of N2O
3.5. A δ15N-δ18O map of N2O
and NO3- in groundwater
3.6. SP and Δδ15N of N2O
4. Conclusion
Acknowledgements
Appendix A. Interpretation of the isotopic signature of N2O dynamics
Appendix B. Calculation of the minimum contribution of nitrification
to total N2O production from Fig.2a
References