Nitrogen isotope fractionation explains the 15N enrichment of Antarctic cryptogams by volatilized ammonia from penguin and seal colonies

• Published in: Polar Research
• Main Authors: Bokhorst, Stef, van Logtestijn, Richard, Convey, Peter, Aerts, Rien
• Format: Article in Journal/Newspaper
• Language: English
• Published: Norwegian Polar Institute 2019
• Subjects: lichen; Moss; nitrogen pathway; nutrient transfer; ocean-land interaction; Antarctic; Guano; Antarc*; Antarctica; Elephant Seal; Polar Research
• Online Access: https://polarresearch.net/index.php/polar/article/view/3355; https://doi.org/10.33265/polar.v38.3355

Vegetation near bird and seal rookeries typically has high δ15N signatures and these high values are linked to the enriched δ15N values of rookery soils. However, Antarctic cryptogams are mostly dependent on atmospheric ammonia (NH3) and volatized NH3from rookeries is severely depleted in δ15N-NH3. So there is an apparent discrepancy between the isotopically depleted source (NH3) and δ15N-enriched vegetation. In this article, we aim to resolve this discrepancy to better understand the mechanisms and processes involved in isotopic changes during nitrogen transfer between Antarctic marine and terrestrial ecosystems. Under laboratory conditions, we quantified whether volatized NH3affects the isotopic signature of cryptogams. NH3volatilizing from penguin guano and elephant seal dung was depleted (44–49‰) in δ15N when captured on acidified filters, compared to the source itself. Cryptogams exposed to the volatized NH3were enriched (18.8–23.9‰) in δ15N. The mossAndreaea regularisgained more nitrogen (0.9%) than the lichenUsnea antarctica(0.4%) from volatilized NH3, indicating a potential difference in atmospheric NH3acquisition that is consistent with existing field differences in nitrogen concentrations and δ15N between mosses and lichens in general. This study clarifies the δ15N enrichment of cryptogams resulting from one of the most important nitrogen pathways for Antarctic vegetation.