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

摘要

Nitrous oxide (N2O), a greenhouse gas, is mainly emitted from soils during the nitrification and denitrification processes. N2O stable isotope investigations can help to characterize the N2O sources and N2O production mechanisms. N2O isotope measurements have been conducted for different types of global terrestrial ecosystems. However, no isotopic data of N2O 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 N2O emitted from Antarctic sea animal colonies (including penguin, seal and skua colonies) and normal tundra soils using in situ field observations and laboratory incubations, and we have analyzed the effects of sea animal excrement depositions on stable isotope natural abundance of N2O. For all the field sites, the soil-emitted N2O was N-15- and O-18-depleted compared with N2O in local ambient air. The mean delta values of the soil-emitted N2O were delta N-15 -13.5 +/- 3.2 parts per thousand and delta O-18 = 26.2 +/- 1.4 parts per thousand for the penguin colony, delta N-15 = -11.5 +/- 5.1 parts per thousand and delta O-18 = 26.4 +/- 3.5 parts per thousand for the skua colony and delta N-15 = -18.9 +/- 0.7 parts per thousand and delta O-18 = 28.8 +/- 1.3 parts per thousand for the seal colony. In the soil incubations, the isotopic composition of N2O was measured under N-2 and under ambient air conditions. The soils incubated under the ambient air emitted very little N2O (2.93 mu g N2O-N kg(-1)). Under N-2 conditions, much more N2O was formed (9.74 mu g N2O-N kg(-1)), and the mean delta N-15 and delta O-18 values of N2O were -19.1 +/- 8.0 parts per thousand and 21.3 +/- 4.3 parts per thousand, respectively, from penguin colony soils, and -17.0 +/- 4.2 parts per thousand and 20.6 +/- 3.5 parts per thousand, respectively, from seal colony soils. The data from in situ field observations and laboratory experiments point to denitrification as the predominant N2O source from Antarctic sea animal colonies. Copyright (c) 2008 John Wiley & Sons, Ltd.