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| Titel |
Unusually negative nitrogen isotopic compositions (δ¹⁵N) of mangroves and lichens in an oligotrophic, microbially-influenced ecosystem |
| VerfasserIn |
M. L. Fogel, M. J. Wooller, J. Cheeseman, B. J. Smallwood, Q. Roberts, I. Romero, M. J. Meyers |
| 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 ; 5, no. 6 ; Nr. 5, no. 6 (2008-12-11), S.1693-1704 |
| Datensatznummer |
250002934
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| Publikation (Nr.) |
 copernicus.org/bg-5-1693-2008.pdf |
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| Zusammenfassung |
| Extremes in δ15N values in mangrove tissues and lichens (range
=+4 to −22‰) were measured from a mangrove forest ecosystem located on
Twin Cays, offshore islands in Belize, Central America. The N isotopic
compositions and concentrations of NH4+/NH3 in porewater,
rainwater, and atmospheric ammonia, and the δ15N of lichens,
mangrove leaves, roots, stems, and wood were examined to study the
biogeochemical processes important for establishing these unusual N isotopic
ratios. Dwarfed Rhizophora mangle trees had the most negative δ15N, whereas
fringing Rhizophora trees, the most positive δ15N values. Porewater
ammonium concentrations had little relationship to N isotopic fractionation
in mangrove tissues. In dwarfed mangroves, the δ15N of fine and
coarse roots were 6–9‰ more positive than leaf tissue from the same tree,
indicating different sources of N for root and leaf tissues. When P was
added to dwarfed mangrove trees without added N, δ15N increased
within one year from −12‰ to −2‰, approaching the δ15N of
porewater ammonium (δ15N=+4‰). Isotopically depleted ammonia
in the atmosphere (δ15N=−19‰) and in rainwater (δ15N=−10‰)
were found on Twin Cays. We propose that foliar uptake of
these atmospheric sources by P-stressed, dwarfed mangrove trees and lichens
can explain their very negative δ15N values. In environments
where P is limiting for growth, uptake of atmospheric N by Rhizophora mangle may be an
important adaptive strategy. |
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