The global budget for nitrous oxide (N 2 O), an important greenhouse gas and probably dominant ozone-depleting substance emitted in the 21 st century, is far from being fully understood. Cycling of N 2 O in terrestrial ecosystems has traditionally exclusively focused on gas exchange between the soil surface (nitrification-denitrification processes) and the atmosphere. Terrestrial vegetation has not been considered in the global budget so far, even though plants are known to release N 2 O.Here, we report the N 2 O emission rates of 32 plant species from 22 different families measured under controlled laboratory conditions. Furthermore, the first isotopocule values (d 15 N, d 18 O and d 15 N sp ) of N 2 O emitted from plants were determined. A robust relationship established between N 2 O emission and CO 2 respiration rates, which did not alter significantly over a broad range of changing environmental conditions, was used to quantify plant-derived emissions on an ecosystem scale. Stable isotope measurements (d 15 N, d 18 O and d 15 N sp ) of N 2 O emitted by plants clearly show that the dual isotopocule fingerprint of plant-derived N 2 O differs from that of currently known microbial or chemical processes.Our work suggests that vegetation is a natural source of N 2 O in the environment with a large fraction released by a hitherto unrecognized process.