Foliar N O emissions constitute a significant source to atmosphere.

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