Nitrous oxide effluxes from plants as a potentially important source to the atmosphere

The global budget for nitrous oxide (N₂ 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 N₂ 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 N₂ O. Here, we report the N₂ O emission rates of 32 plant species from 22 different families measured under controlled laboratory conditions. Furthermore, the first isotopocule values (δ¹⁵ N, δ¹⁸ O and δ¹⁵ N^sp ) of N₂ O emitted from plants were determined. A robust relationship established between N₂ O emission and CO₂ 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 (δ¹⁵ N, δ¹⁸ O and δ¹⁵ N^sp ) of N₂ O emitted by plants clearly show that the dual isotopocule fingerprint of plant-derived N₂ O differs from that of currently known microbial or chemical processes. Our work suggests that vegetation is a natural source of N₂ O in the environment with a large fraction released by a hitherto unrecognized process.