Extreme isotopic depletion of nitrogen in New Zealand lithophytes and epiphytes; the result of diffusive uptake of atmospheric ammonia?

W. C. Tozer, D. Hackell, D. B. Miers, W. B. Silvester*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

28 Citations (Scopus)

Abstract

Several lichens and the terrestrial alga Trentepohlia were found to have extremely depleted 15N signatures at two sites near the Rotorua geothermal area, New Zealand. Values, typically -20‰, with several extreme cases of -24‰, are more isotopically depleted than any previously quoted δ15N signature for vegetation growing in natural environments. For Trentepohlia, distance from a geothermal source did not affect isotopic signature. A 100-km transect showed that the phenomenon is widespread and the discrimination is not related to substrate N, or to elevation. Rainfall NHx and atmospheric gaseous NH3 (NH3(g)) were shown to be isotopically depleted in the range -1‰ to -8‰ and could not, of themselves, be responsible for the plant values obtained. A simulation of Trentepohlia thallus was created using an acidified fiberglass mat and was allowed to absorb NH3(g) from the atmosphere. Mats exposed at the geothermal sites and on farmland showed a significant further depletion of 15N to -17‰. We hypothesize that the extreme isotopic depletion is due to dual fractionation: firstly by the volatilization of NH 3(g) from aqueous sources into the atmosphere; secondly by the diffusive assimilation of that NH3(g) into vegetation. We further hypothesize that lithophytes, epiphytes, and higher plants, growing on strongly N-limited substrates, will show this phenomenon more or less, depending on the proportion of diffusively assimilated NH3(g) utilized as a N source. Many of the isotopically depleted δ15N signatures in vegetation, previously reported in the literature, especially epiphytes, may be due to this form of uptake depending on the concentration of atmospheric NH 3(g), and the degree of reliance on that form of N.

Original languageEnglish
Pages (from-to)628-635
Number of pages8
JournalOecologia
Volume144
Issue number4
DOIs
Publication statusPublished - Aug 2005
Externally publishedYes

Keywords

  • δN
  • Ammonia diffusion
  • Isotopic fractionation
  • Lichens
  • Stable isotopes
  • Trentepohlia

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