Constraining the global permafrost nitrous oxide budget

Nitrous oxide (N2O) which is also known as the laughing gas is, after carbon dioxide and methane, the third most important greenhouse gas responsible for climate warming. It is produced mainly from soils as a result of microbial activity. Usually, high nitrous oxide emissions occur from agricultural soils, where the availability of mineral nitrogen is high because of nitrogen fertilisation and other management practices. Since the nitrogen cycling in cold permafrost soils is slow, they have previously been regarded as unimportant nitrous oxide sources. Based on accumulating evidence during the past years, however, this is not always true: nitrous oxide release has been found to be a common phenomenon in permafrost-affected soils. However, the magnitude of the emissions as well as factors controlling them remain poorly known. The project PERNO will fill this gap by researching deeply into fluxes and factors controlling N2O emission from permafrost soils. Therefore, we will incubate soils from permafrost regions in the laboratory and manipulate temperature and soil moisture to simulate climate change. Permafrost soils will be also thawn in the laboratory to simulate permafrost melting. We will monitor the emissions of N2O and other reactive and non-reactive nitrogen gases, such as NO and N2 over time with modern laser spectroscopic methods. Additionally, we will investigate accompanying changes in the microbial community and in soil parameters from the soils. Importantly, the stable isotope composition of nitrous oxide will be measured continuously in the laboratory to get valuable information on microbial pathways responsible for the N2O emissions. Nitrous oxide is produced in sols during nitrification and denitrification, and each pathways produces a unique stable isotope fingerprint in N2O. This information is important to characterize and better understand the N2O emissions. Stable isotope techniques have become integral parts in modern ecology and contribute to gain detailed insights into the nitrogen cycle. The stable isotope signature of N2O will be also used in the process-based models which are also employing in the project PERNO. We will use an isotope model (IsoTONE) to simulate the N2O fluxes and extrapolate them in space and time. Overall, PERNO aims to fill critical gaps in knowledge on N2O dynamics from permafrost soils and shed light on the importance of these emissions from permafrost soils in present and future climate. We hypothesize that N2O from permafrost soils forms a potentially significant positive feedback to climate change.