Foliar N 2 O emissions constitute a significant source to atmosphere.

Nitrous oxide (N 2 O) is a potent greenhouse gas and causes stratospheric ozone depletion. While the emissions of N 2 O from soil are widely recognized, recent research has shown that terrestrial plants may also emit N 2 O from their leaves under controlled laboratory conditions. However, it is unclear whether foliar N 2 O emissions are universal across varying plant taxa, what the global significance of foliar N 2 O emissions is, and how the foliage produces N 2 O in situ. Here we investigated the abilities of 25 common plant taxa, including trees, shrubs and herbs, to emit N 2 O under in situ conditions. Using 15 N isotopic labeling, we demonstrated that the foliage-emitted N 2 O 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 N 2 O emissions were driven by endophytic bacteria. The seasonal N 2 O emission rates ranged from 3.2 to 9.2 ng N 2 O-N g -1 dried foliage h -1 . Extrapolating these emission rates to global foliar biomass and plant N uptake, we estimated global foliar N 2 O emission to be 1.21 and 1.01 Tg N 2 O-N year -1 , respectively. These estimates account for 6%-7% of the current global annual N 2 O emission of 17 Tg N 2 O-N year -1 , indicating that in situ foliar N 2 O emission is a universal process for terrestrial plants and contributes significantly to the global N 2 O inventory. This finding highlights the importance of measuring foliar N 2 O emissions in future studies to enable the accurate assigning of mechanisms and the development of effective mitigation.