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| Titel |
Indications of nitrogen-limited methane uptake in tropical forest soils |
| VerfasserIn |
E. Veldkamp, B. Koehler, M. D. Corre |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 8 ; Nr. 10, no. 8 (2013-08-09), S.5367-5379 |
| Datensatznummer |
250085290
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| Publikation (Nr.) |
 copernicus.org/bg-10-5367-2013.pdf |
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| Zusammenfassung |
| It is estimated that tropical forest soils contribute 6.2 Tg yr−1
(28%) to global methane (CH4) uptake, which is large enough to
alter CH4 accumulation in the atmosphere if significant changes would
occur to this sink. Elevated deposition of inorganic nitrogen (N) to
temperate forest ecosystems has been shown to reduce CH4 uptake in
forest soils, but almost no information exists from tropical forest soils
even though projections show that N deposition will increase substantially in
tropical regions. Here we report the results from two long-term,
ecosystem-scale experiments in which we assessed the impact of chronic N
addition on soil CH4 fluxes from two old-growth forests in Panama: (1) a
lowland, moist (2.7 m yr−1 rainfall) forest on clayey Cambisol and
Nitisol soils with controls and N-addition plots for 9–12 yr, and (2) a
montane, wet (5.5 m yr−1 rainfall) forest on a sandy loam Andosol soil
with controls and N-addition plots for 1–4 yr. We measured soil CH4
fluxes for 4 yr (2006–2009) in four replicate plots (40 m × 40 m
each) per treatment using vented static chambers (four chambers per plot).
CH4 fluxes from the lowland control plots and the montane control plots
did not differ from their respective N-addition plots. In the lowland forest,
chronic N addition did not lead to inhibition of CH4 uptake; instead, a
negative correlation of CH4 fluxes with nitrate (NO3–)
concentrations in the mineral soil suggests that increased NO3–
levels in N-addition plots had stimulated CH4 consumption and/or reduced
CH4 production. In the montane forest, chronic N addition also showed
negative correlation of CH4 fluxes with ammonium concentrations in the
organic layer, which suggests that CH4 consumption was N limited. We
propose the following reasons why such N-stimulated CH4 consumption did
not lead to statistically significant CH4 uptake: (1) for the lowland
forest, this was caused by limitation of CH4 diffusion from the
atmosphere into the clayey soils, particularly during the wet season, as
indicated by the strong positive correlations between CH4 fluxes and
water-filled pore space (WFPS); (2) for the montane forest, this was caused
by the high WFPS in the mineral soil throughout the year, which may not only
limit CH4 diffusion from the atmosphere into the soil but also favour
CH4 production; and (3) both forest soils showed large spatial and
temporal variations of CH4 fluxes. We conclude that in these extremely
different tropical forest ecosystems there were indications of N limitation
on CH4 uptake. Based on these findings, it is unlikely that elevated N
deposition on tropical forest soils will lead to a rapid reduction of
CH4 uptake. |
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