External nutrient inputs into terrestrial ecosystems of the Falkland Islands and the Maritime Antarctic region

Polar Biology, Sep 2007

Antarctic terrestrial ecosystems are nutrient-poor 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°76′S), and the Maritime Antarctic Signy (60°71′S) and Anchorage Islands (67°61′S). 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 (δ15N) 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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External nutrient inputs into terrestrial ecosystems of the Falkland Islands and the Maritime Antarctic region

S. Bokhorst 0 1 2 A. Huiskes 0 1 2 P. Convey 0 1 2 R. Aerts 0 1 2 0 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 2 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. - 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)


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S. Bokhorst, A. Huiskes, P. Convey, R. Aerts. External nutrient inputs into terrestrial ecosystems of the Falkland Islands and the Maritime Antarctic region, Polar Biology, 2007, pp. 1315-1321, Volume 30, Issue 10, DOI: 10.1007/s00300-007-0292-0