, Volume 119, Issue 1–3, pp 293–306 | Cite as

Stable nitrogen isotope patterns of trees and soils altered by long-term nitrogen and phosphorus addition to a lowland tropical rainforest

  • Jordan R. MayorEmail author
  • S. Joseph Wright
  • Edward A. G. Schuur
  • Mollie E. Brooks
  • Benjamin L. Turner


Foliar nitrogen (N) isotope ratios (δ15N) are used as a proxy for N-cycling processes, including the “openness” of the N cycle and the use of distinct N sources, but there is little experimental support for such proxies in lowland tropical forest. To address this, we examined the δ15N values of soluble soil N and canopy foliage of four tree species after 13 years of factorial N and P addition to a mature lowland rainforest. We hypothesized that N addition would lead to 15N-enriched soil N forms due to fractionating losses, whereas P addition would reduce N losses as the plants and microbes adjusted their stoichiometric demands. Chronic N addition increased the concentration and δ15N value of soil nitrate and δ15N in live and senesced leaves in two of four tree species, but did not affect ammonium or dissolved organic N. Phosphorus addition significantly increased foliar δ15N in one tree species and elicited significant N × P interactions in two others due to a reduction in foliar δ15N enrichment under N and P co-addition. Isotope mixing models indicated that three of four tree species increased their use of nitrate relative to ammonium following N addition, supporting the expectation that tropical trees use the most available form of mineral N. Previous observations that anthropogenic N deposition in this tropical region have led to increasing foliar δ15N values over decadal time-scales is now mechanistically linked to greater usage of 15N-enriched nitrate.


Ecosystem ecology Gigante Fertilization Experiment Mass balance mixing models Panama Stoichiometry 



Support for J.M. was provided by the National Science Foundation’s International Research Fellowship Program (OISE-1012703) and in-kind support from the Smithsonian Tropical Research Institute’s Fellowship Program. We thank Julio Rodriquez, Dayana Agudo, Helene Mueller-Landau, Luis Ramos, Rueben Hernandez, Sarah Dale, and Tania Romero for their contributions, and the Republic of Panama for providing access to their natural resources for scientific research. We thank Grace Crummer, Jason Curtis, and Kathy Curtis for their contributions at the University of Florida. JM, BT, and JW designed the experiment and wrote the manuscript; TS contributed analytical ideas and logistical support, MB contributed a statistical method. The manuscript was improved due to the untiring efforts of three anonymous reviewers.

Supplementary material

10533_2014_9966_MOESM1_ESM.pdf (491 kb)
Supplementary material 1 (PDF 491 kb)
10533_2014_9966_MOESM2_ESM.csv (4 kb)
Supplementary material 2 (CSV 4 kb)


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Copyright information

© Springer International Publishing Switzerland 2014

Authors and Affiliations

  • Jordan R. Mayor
    • 1
    • 2
    Email author
  • S. Joseph Wright
    • 1
  • Edward A. G. Schuur
    • 3
  • Mollie E. Brooks
    • 3
    • 4
  • Benjamin L. Turner
    • 1
  1. 1.Smithsonian Tropical Research InstituteBalboa, AnconRepublic of Panama
  2. 2.Department of Forest Ecology & ManagementSwedish University of Agricultural SciencesUmeåSweden
  3. 3.Department of BiologyUniversity of FloridaGainesvilleUSA
  4. 4.Institute of Evolutionary Biology and Environmental StudiesUniversity of ZurichZurichSwitzerland

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