1) Biogeochemistry research group, Department of Environmental and Biological Sciences, University of Eastern Finland, Yliopistoranta 1D E, PO Box 1627, Kuopio campus, FI-70211 Finland, 2) Department of Physics, P.O. Box 48, University of Helsinki, 00014 Finland, 3) Department of Food and Environmental Sciences, Division of Microbiology and Biotechnology, P.O. Box 56, University of Helsinki, FI-00014 Finland, 4) Natural Resources Institute Finland, Green technology, Halolantie 31A Maaninka FI-71750, Finland, 5) Aerodyne Research, Inc., 45 Manning Road Billerica, MA 01821-3976, USA, 6) Viikki Plant Science Centre, University of Helsinki, P.O. Box 27, FI-00014 Finland, 7) Department of Forest Sciences, P. O. Box 27, University of Helsinki, 00014 Finland Nature Scientific Reports (2016), V6, 25739, doi: 10.1038/srep25739 Neglecting diurnal variations leads to uncertainties in terrestrial nitrous oxide emissions Narasinha J. Shurpali (1), Üllar Rannik (2), Simo Jokinen (1), Saara Lind (1), Christina Biasi (1), Ivan Mammarella (2), Olli Peltola (2), Mari Pihlatie (2,3), Niina Hyvönen (1), Mari Räty (4), Sami Haapanala (2), Mark Zahniser (5), Perttu Virkajärvi (4), Timo Vesala (2,6,7) and Pertti J. Martikainen (1) Nitrous oxide (N2O) is an important greenhouse gas produced in soil and aquatic ecosystems. Its warming potential is 296 times higher than that of CO2. Most N2O emission measurements made so far are limited in temporal and spatial resolution causing uncertainties in the global N2O budget. Recent advances in laser spectroscopic techniques provide an excellent tool for area-integrated, direct and continuous field measurements of N2O fluxes using the eddy covariance method. By employing this technique on an agricultural site with four laser-based analysers, we show here that N2O exchange exhibits contrasting diurnal behaviour depending upon soil nitrogen availability. When soil N was high due to fertilizer application, N2O emissions were higher during daytime than during the night. However, when soil N became limited, emissions were higher during the night than during the day. These reverse diurnal patterns supported by isotopic analyses may indicate a dominant role of plants on microbial processes associated with N2O exchange. This study highlights the potential of new technologies in improving estimates of global N2O sources.