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www.biogeosciences-discuss.net/5/937/2008/
doi:10.5194/bgd-5-937-2008
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Unusually negative nitrogen isotopic compositions (δ15N) of mangroves and lichens in an oligotrophic, microbially-influenced ecosystem
1Carnegie Institution of Washington, Geophysical Laboratory, 5251 Broad Branch Rd., NW., Washington, DC 20015, USA
2Alaska Stable Isotope Facility: Water and Environmental Research Center, Institute of Marine Science and School of Fisheries and Ocean Sciences, University of Alaska, Fairbanks, Alaska
3Department of Plant Biology, University of Illinois, Urbana, Illinois 61801, USA
4Department of Oceanography, Texas A&M, College Station, Texas 77843–3146, USA
5Univ. of Southern California, 3616 Trousdale Parkway, Los Angeles, California, 90089, USA
Abstract. 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, atmospheric ammonia, mangrove leaves, roots, stems, and wood, and lichens, were examined to study the biogeochemical processes important for establishing these unusual N isotopic ratios. Porewater ammonium concentrations had little to no relationship to N isotopic fractionation in mangrove tissues. The δ15N of fine and coarse roots was 9‰ more positive than leaf tissue from the same tree. When P was added to dwarfed mangrove trees without added N, δ15N increased within one year to a &delta:15N closer to the &delta:15N of porewater ammonium (δ15N=+4‰). Isotopically negative ammonia in the atmosphere (δ15N=−18‰) and in rainwater (δ15N=−9‰) were found on Twin Cays and may be sources of available N for isotopically depleted mangrove trees and lichens. In highly stressed, severely P limited trees, uptake of atmospheric N by Rhizophora mangle may be an important adaptive strategy.
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Citation: Fogel, M. L., Wooller, M. J., Cheeseman, J., Smallwood, B. J., Roberts, Q., Romero, I., and Jacobsen Meyers, M.: Unusually negative nitrogen isotopic compositions (δ15N) of mangroves and lichens in an oligotrophic, microbially-influenced ecosystem, Biogeosciences Discuss., 5, 937-969, doi:10.5194/bgd-5-937-2008, 2008. Bibtex EndNote Reference Manager XML
