Jökull - 01.12.2006, Side 29

Reviewed research article
The stable isotopic (C and N) composition of modern plants
and lichens from northern Iceland:
with ecological and paleoenvironmental implications
Yiming Wang1,2 and Matthew J. Wooller1,3
1 Alaska Stable Isotope Facility, Water and Environmental Research Center,
University of Alaska Fairbanks, Fairbanks, Alaska 99775
2 Department of Geology & Geophysics, University of Alaska Fairbanks, Fairbanks, Alaska 99775
3 School of Fisheries and Ocean Sciences and Institute of Marine Science,
University of Alaska Fairbanks, Fairbanks, Alaska, 99775
email: ftyw@uaf.edu
Abstract – The stable carbon and nitrogen isotopic composition (δ13C and δ15N) of plants and lichens can
indicate a considerable amount of information about the physiology and ecology of an environment. To our
knowledge no stable isotope (C and N) data have been generated for plants and lichens from Iceland. These
data could subsequently provide a unique perspective of nitrogen and carbon cycling in Iceland and aid in
interpretation of data generated from stable isotope analyses of organic matter preserved in lake sediments. We
analyzed plants and lichens around four lakes (Litla-Viðarvatn, Torfadalsvatn, Stífluvatn, Arnarvatn stóra) in
northern and interior Iceland. The δ13C values for plants from the sites ranged from –30.9‰ to –23.3‰ that
are typical of plants using C3 photosynthesis. Aquatic plant samples (e.g. Potamogeton sp.) analyzed from the
sites had δ13C values (mean=–13.0‰) that were considerably less negative than the terrestrial plants and are
typical for submerged freshwater aquatic macrophytes. The δ15N values from the analyses of plants and lichens
showed a surprisingly large range (∼ –12.4‰ to +5.5‰), and many of the specimens had δ15N values lower
than –6.0‰. A number of competing and testable causal mechanisms for the low δ15N values are proposed and
discussed, including plant uptake of atmospheric ammonia and phosphorus limitation.
INTRODUCTION
Measurements of the stable carbon and nitrogen iso-
topic composition (δ13C and δ15N, respectively) of
lake sediments can be used to infer past and present
environmental conditions (e.g., Kendell 1998; Her-
czeg et al., 2001; Hodell and Schelske, 1998; Lucke
et al., 2003; Meyers et al., 1998; Schelske and Hodell,
1991; Wooller et al., 2005). The δ13C values of Total
Organic Carbon (TOC) can provide an integrated per-
spective of carbon cycling processes and information
about the proportion of different sources of carbon
(e.g. terrestrial vs. aquatic) (e.g. Lucke et al., 2003).
The δ13C values of potential carbon sources into lake
sediments can vary considerably. For example, the
δ13C values of plants have proven to be useful in de-
termining the photosynthetic pathway of plants (C3
vs. C4) in a lake catchment (e.g. Wooller et al., 2005)
due to the differences in isotopic discrimination dur-
ing photosynthesis (Ehleringer, 1991). Some plants
(mostly tropical grasses and some forbs) that are prin-
cipally adapted to hot and dry environments are char-
acterized by the C4 pathway of photosynthesis (Ward
et al., 1999). Terrestrial plants in Iceland today are
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