The fate of <sup>15</sup>N-nitrate in mesocosms from five European peatlands differing in long-term nitrogen deposition rate
Elevated nitrogen (N) deposition changes the retention, transformation, and fluxes of N in ombrotrophic peatlands. To evaluate such effects we applied a <sup>15</sup>N tracer (NH<sub>4</sub> <sup>15</sup>NO<sub>3</sub>) at a rate of 2.3 g N m<sup>...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-02-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/13/707/2016/bg-13-707-2016.pdf |
| Summary: | Elevated nitrogen (N) deposition changes the retention, transformation, and
fluxes of N in ombrotrophic peatlands. To evaluate such effects we applied a
<sup>15</sup>N tracer (NH<sub>4</sub> <sup>15</sup>NO<sub>3</sub>) at a rate of
2.3 g N m<sup>−2</sup> yr<sup>−1</sup> to mesocosms of five European peatlands with
differing long-term N deposition rates for a period of 76 days of dry and 90
days of wet conditions. We determined background N content and moss length
growth, and recovered the <sup>15</sup>N tracer from the mosses, graminoids,
shrubs, the peat, and dissolved N. Background N contents in <i>Sphagnum</i>
mosses increased from 5.5 (Degerö Stormyr, deposition < 0.2 g N m<sup>−2</sup> yr<sup>−1</sup>) up to 12.2 mg g<sup>−1</sup> (Frölichshaier
Sattelmoor, 4.7–6.0 g N m<sup>−2</sup> yr<sup>−1</sup>). In peat from Degerö,
nitrate and ammonium concentrations were below 3 mg L<sup>−1</sup>, whereas up to
30 (nitrate) and 11 mg L<sup>−1</sup> (ammonium) was found in peat from
Frölichshaier Sattelmoor. <i>Sphagnum</i> mosses (down to 5 cm below
surface) generally intercepted large amounts of <sup>15</sup>N (0.2–0.35
mg g<sup>−1</sup>) and retained the tracer most effectively relative to their
biomass. Similar quantities of the <sup>15</sup>N were recovered from the peat,
followed by shrubs, graminoids, and the dissolved pool. At the most polluted
sites we recovered more <sup>15</sup>N from shrubs (up to 12.4 %) and from
nitrate and ammonium (up to 0.7 %). However, no impact of N deposition on
<sup>15</sup>N retention by <i>Sphagnum</i> could be identified and their length
growth was highest under high N background deposition. Our experiment
suggests that the decline in N retention at levels above ca.
1.5 g m<sup>−2</sup> yr<sup>−1</sup>, as expressed by elevated near-surface peat N
content and increased dissolved N concentrations, is likely more modest than
previously thought. This conclusion is related to the finding that
<i>Sphagnum</i> species can apparently thrive at elevated long-term N
deposition rates in European peatlands. |
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| ISSN: | 1726-4170 1726-4189 |