Neglecting diurnal variations leads to uncertainties in terrestrial nitrous oxide emissions

Nitrous oxide (N 2 O) is an important greenhouse gas produced in soil and aquatic ecosystems. Its warming potential is 296 times higher than that of CO 2 . Most N 2 O emission measurements made so far are limited in temporal and spatial resolution causing uncertainties in the global N 2 O budget. Recent advances in laser spectroscopic techniques provide an excellent tool for area-integrated, direct and continuous field measurements of N 2 O fluxes using the eddy covariance method. By employing this technique on an agricultural site with four laser-based analysers, we show here that N 2 O exchange exhibits contrasting diurnal behaviour depending upon soil nitrogen availability. When soil N was high due to fertilizer application, N 2 O 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 N 2 O exchange. This study highlights the potential of new technologies in improving estimates of global N 2 O sources.