Application of δN to trace the impact of penguin guano on terrestrial and aquatic nitrogen cycles in Victoria Land, Ross Sea region, Antarctica.

Penguin colonies in Antarctica offer an ideal "natural laboratory" to investigate ecosystem function and the nitrogen (N) cycle. This study assessed the spatial distribution of penguin-derived N from guano and quantitatively assessed its impact on plant N utilization strategies in Victoria Land, Ross Sea region, Antarctica. Soil, moss, and aquatic microbial mats were collected inside and outside an active Adélie penguin (Pygoscelis adeliae) colony and analyzed for δN of total and inorganic nitrogen (NH-N and NO-N). The soil total nitrogen (TN), NH-N, and NO-N concentrations, as well as their δN values were significantly higher in guano-impacted areas than those in guano-free areas, verifying that guano is an important N source at and near penguin colonies. However, even far from the penguin colonies, soil δN values resembled those in penguin colonies, suggesting strong spatial impacts of penguin-derived N. The moss impacted by guano was more enriched in δN than in guano-free areas. The δN values of NH-N and NO-N in soils covered with moss revealed that the moss might prefer inorganic N in the absence of guano, while the dissolved organic N would become an important source for moss growing on ornithogenic soils. Aquatic microbial mat samples near penguin colonies were N-enriched, but N-depleted at upland sites.