Stable isotope natural abundance of nitrous oxide emitted from Antarctic tundra soils: effects of sea animal excrement depositions

<jats:title>Abstract</jats:title><jats:p>Nitrous oxide (N<jats:sub>2</jats:sub>O), a greenhouse gas, is mainly emitted from soils during the nitrification and denitrification processes. N<jats:sub>2</jats:sub>O stable isotope investigations can help to characterize the N<jats:sub>2</jats:sub>O sources and N<jats:sub>2</jats:sub>O production mechanisms. N<jats:sub>2</jats:sub>O isotope measurements have been conducted for different types of global terrestrial ecosystems. However, no isotopic data of N<jats:sub>2</jats:sub>O emitted from Antarctic tundra ecosystems have been reported although the coastal ice‐free tundra around Antarctic continent is the largest sea animal colony on the global scale. Here, we report for the first time stable isotope composition of N<jats:sub>2</jats:sub>O emitted from Antarctic sea animal colonies (including penguin, seal and skua colonies) and normal tundra soils using <jats:italic>in</jats:italic> <jats:italic>situ</jats:italic> field observations and laboratory incubations, and we have analyzed the effects of sea animal excrement depositions on stable isotope natural abundance of N<jats:sub>2</jats:sub>O. For all the field sites, the soil‐emitted N<jats:sub>2</jats:sub>O was <jats:sup>15</jats:sup>N‐ and <jats:sup>18</jats:sup>O‐depleted compared with N<jats:sub>2</jats:sub>O in local ambient air. The mean <jats:italic>δ</jats:italic> values of the soil‐emitted N<jats:sub>2</jats:sub>O were <jats:italic>δ</jats:italic><jats:sup>15</jats:sup>N = −13.5 ± 3.2‰ and <jats:italic>δ</jats:italic><jats:sup>18</jats:sup>O = 26.2 ± 1.4‰ for the penguin colony, <jats:italic>δ</jats:italic><jats:sup>15</jats:sup>N = −11.5 ± 5.1‰ and <jats:italic>δ</jats:italic><jats:sup>18</jats:sup>O = 26.4 ± 3.5‰ for the skua colony and <jats:italic>δ</jats:italic><jats:sup>15</jats:sup>N = −18.9 ± 0.7‰ and <jats:italic>δ</jats:italic><jats:sup>18</jats:sup>O = 28.8 ± 1.3‰ for the seal colony. In the soil incubations, the isotopic composition of N<jats:sub>2</jats:sub>O was measured under N<jats:sub>2</jats:sub> and under ambient air conditions. The soils incubated under the ambient air emitted very little N<jats:sub>2</jats:sub>O (2.93 µg N<jats:sub>2</jats:sub>ON kg<jats:sup>−1</jats:sup>). Under N<jats:sub>2</jats:sub> conditions, much more N<jats:sub>2</jats:sub>O was formed (9.74 µg N<jats:sub>2</jats:sub>ON kg<jats:sup>−1</jats:sup>), and the mean <jats:italic>δ</jats:italic><jats:sup>15</jats:sup>N and <jats:italic>δ</jats:italic><jats:sup>18</jats:sup>O values of N<jats:sub>2</jats:sub>O were −19.1 ± 8.0‰ and 21.3 ± 4.3‰, respectively, from penguin colony soils, and −17.0 ± 4.2‰ and 20.6 ± 3.5‰, respectively, from seal colony soils. The data from <jats:italic>in situ</jats:italic> field observations and laboratory experiments point to denitrification as the predominant N<jats:sub>2</jats:sub>O source from Antarctic sea animal colonies. Copyright © 2008 John Wiley & Sons, Ltd.</jats:p>