Foliar N₂O emissions constitute a significant source to atmosphere

Nitrous oxide (N₂O) is a potent greenhouse gas and causes stratospheric ozone depletion. While the emissions of N₂O from soil are widely recognized, recent research has shown that terrestrial plants may also emit N₂O from their leaves under controlled laboratory conditions. However, it is unclear whether foliar N₂O emissions are universal across varying plant taxa, what the global significance of foliar N₂O emissions is, and how the foliage produces N₂O in situ. Here we investigated the abilities of 25 common plant taxa, including trees, shrubs and herbs, to emit N₂O under in situ conditions. Using ¹⁵N isotopic labeling, we demonstrated that the foliage-emitted N₂O was predominantly derived from nitrate. Moreover, by selectively injecting biocide in conjunction with the isolating and back-inoculating of endophytes, we demonstrated that the foliar N₂O emissions were driven by endophytic bacteria. The seasonal N₂O emission rates ranged from 3.2 to 9.2 ng N₂O–N g⁻¹ dried foliage h⁻¹. Extrapolating these emission rates to global foliar biomass and plant N uptake, we estimated global foliar N₂O emission to be 1.21 and 1.01 Tg N₂O–N year⁻¹, respectively. These estimates account for 6%–7% of the current global annual N₂O emission of 17 Tg N₂O–N year⁻¹, indicating that in situ foliar N₂O emission is a universal process for terrestrial plants and contributes significantly to the global N₂O inventory. This finding highlights the importance of measuring foliar N₂O emissions in future studies to enable the accurate assigning of mechanisms and the development of effective mitigation.