External nutrient inputs into terrestrial ecosystems of the Falkland Islands and the Maritime Antarctic region
S. Bokhorst
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A. Huiskes
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P. Convey
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R. Aerts
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R. Aerts Institute of Ecological Science, Department of Systems Ecology, Vrije Universiteit
, De Boelelaan 1085, 1081 HV Amsterdam,
The Netherlands
1
P. Convey British Antarctic Survey,
Natural Environmental Research Council
, High Cross, Madingley Road, CB3 0ET Cambridge,
UK
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S. Bokhorst (&) A. Huiskes Netherlands Institute of Ecology, Centre for Estuarine and Marine Ecology
, Korringaweg 7, 4401 NT Yerseke,
The Netherlands
Antarctic terrestrial ecosystems are nutrientpoor and depend for their functioning in part on external nutrients. However, little is known about the relative importance of various sources. We measured external mineral nutrient sources (wind blown material, precipitation and guano) at three locations, the cold temperate oceanic Falkland Islands (51 76S), and the Maritime Antarctic Signy (60 71S) and Anchorage Islands (67 61S). These islands differ in the level of vegetation development through different environmental constraints and historical factors. Total mineral nitrogen input differed considerably between the islands. During the 3 month summer period it amounted to 18 mg N m-2 on the Falkland Islands and 6 and 102 mg N m-2 at Signy and Anchorage Islands, respectively. The high value for Anchorage was a result of guano deposition. By measuring stable isotopic composition (d15N) of the different nitrogen sources and the dominant plant species, we investigated the relative utilisation of each source by the vegetation at each island. We conclude that external mineral nitrogen inputs to Antarctic terrestrial ecosystems show great spatial variability, with the local presence of bird (or other vertebrate) colonies being particularly significant.
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Antarctic terrestrial ecosystems have amongst the least
developed soils in the world and are generally nutrient poor
(Beyer and Bolter 2000). Nitrogen limitation of plant
growth appears to be one of the main factors restricting
vegetation development at some locations (Davey and
Rothery 1992; Arnold et al. 2003; Wasley et al. 2006).
Therefore it is expected that external nitrogen sources may
play a major role in the nutrient budget of these ecosystems
(Greenfield 1992a). However, only a few studies have
investigated the utilisation of these external sources by
vegetation in Antarctic terrestrial ecosystems (Greenfield
1992b; Erskine et al. 1998). Large but spatially localised
and mostly coastal bird and seal colonies are known to
influence vegetation in their vicinity through extra nitrogen
deposition (Lindeboom 1984; Staley and Herwig 1993;
Crittenden 1998). Penguin colonies, in particular, are
associated with large guano deposits. When such colonies
become unoccupied or move to other sites the abandoned
rookeries form a nutrient rich area for plants and mosses
(Tatur et al. 1997).
Not all Antarctic locations experience a large direct
influence from penguin or other vertebrate colonies,
because many areas are inaccessible for such animals. These
areas are often vegetated, but are thought to receive lower
nitrogen input than vegetation closer to such colonies.
These remote ecosystems are thought to be dependent for
their nitrogen on precipitation, wind blown material, such as
sea spray, and occasional guano from passing birds
(Holdgate 1967; Smith 1985; Ryan and Watkins 1989; Cocks
et al. 1998). In order to understand and quantify the major
sources and pathways of nitrogen flow in Antarctic
terrestrial ecosystems it is, therefore, imperative to develop a
better description of the main external sources of nutrients.
Nitrogen use in ecosystems can be tracked by
investigating the concentrations of the stable isotope, 15N. Plants
that take up nitrogen from sources with a certain 15N
signature will normally obtain a signature that closely
resembles that of the source (Robinson 2001; Dawson et al.
2002). However, plants can take up nitrogen from different
sources, and the consequential mixing of these different
signatures may lead to uncertainty in the identity of the
source. Fractionation during uptake and transport may
further obscure the signal. However, if the 15N signal of a
major source is distinct, it still is possible to determine this
distinct nitrogen source in the plants (Erskine et al. 1998).
Precipitation, wind blown material, soils and guano
potentially have distinct stable isotope signatures. Large
differences in stable isotope composition are already
known to exist between mosses and lichens from the
Antarctic (Galimov 2000; Huiskes et al. 2006). These
differences partly result from the utilisation of different
nitrogen sources by these cryptogams (Crittenden 1998;
Wainright et al. 1998). Analyses of the different potential
sources of nitrogen for their 15N content should, therefore,
provide clarification of the origin of external nitrogen into
these ecosystems.
This study aims to provide a better description and
understanding of external nitrogen sources that a (...truncated)