Subantarctic Macquarie Island - a model ecosystem for studying animal-derived nitrogen sources using 15 N natural abundance

Abstract

Plants collected from diverse sites on subantarctic Macquarie Island varied by up to 30‰ in their leaf δN values. N natural abundance of plants, soils, animal excrement and atmospheric ammonia suggest that the majority of nitrogen utilised by plants growing in the vicinity of animal colonies or burrows is animal-derived. Plants growing near scavengers and animal higher in the food chain had highly enriched δN values (mean = 12.9‰), reflecting the highly enriched signature of these animals' excrement, while plants growing near nesting penguins and albatross, which have an intermediate food chain position, had less enriched δN values (>6‰). Vegetation in areas affected by rabbits had lower δN values (mean = 1.2‰), while the highly depleted δN values (below -5‰) of plants at upland plateau sites inland of penguin colonies, suggested that a portion of their nitrogen is derived from ammonia (mean N =-10‰) lost during the degradation of penguin guano. Vegetation in a remote area had δN values near -2‰. These results contrast with arctic and subarctic studies that attribute large variations in plant N values to nitrogen partitioning in nitrogen-limited environments. Here, plantN reflects the N of the likely nitrogen sources utilised by plants.

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

“…However, Anchorage Island received a much greater total input through guano deposition by skuas. This finding gives an explicit demonstration that the presence of vertebrates such as skuas can have a major impact on the nutrient balance of Antarctic ecosystems, as also proposed by various other studies (Lindeboom 1984;Erskine et al 1998). Parallel findings are also reported in ecosystems at lower latitudes (Mizutani and Wada 1988;Polis and Hurd 1996;Post et al 1998).…”

“…However, fractionation during uptake should act to reduce 15 N levels, thereby leading to lower signature values in the plant than that of the source. In cases where an important nitrogen source has a distinct and high 15 N signature compared to other sources, a relatively high 15 N signature would still be expected in the vegetation (see Erskine et al 1998 andPearson et al 2000).…”

“…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).…”

“…Fractionation during uptake and transport may further obscure the signal. However, if the 15 N 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.…”

Influence of allochtonous nutrients delivered by colonial seabirds on soil collembolan communities on Spitsbergen

“…They feed at sea and breed on land, often in very large colonies. During the summer reproductive season, seabirds deposit considerable amounts of guano, along with feathers, egg shells and carcasses, which locally provide the main sources of nutrients for tundra plants (Lindeboom 1984;Erskine et al 1998;Ellis 2005;Stempniewicz 2005). For example, during one breeding season in Hornsund, south-west Spitsbergen, little auks (Alle alle) deliver *60 tonnes of guano dry mass km -2 of colony area (Stempniewicz 1990(Stempniewicz , 1992.…”