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.