Bruhn, Dan1; Albert, Kristian Rost1; Mikkelsen, Teis Nørgaard3; Ambus, Per1
1 Department of Chemical and Biochemical Engineering, Technical University of Denmark2 Ecosystems Programme, Department of Chemical and Biochemical Engineering, Technical University of Denmark3 Department of Environmental Engineering, Technical University of Denmark
Nitrous oxide (N 2 O) is an important long-lived greenhouse gas and precursor of stratospheric ozone- depleting mono-nitrogen oxides. The atmospheric concentration of N 2 O is persistently increasing; however, large uncertainties are associated with the distinct source strengths. Here we investigate for the fi rst time N 2 O emission from terrestrial vegetation in response to natural solar ultra violet radiation. We conducted fi eld site measurements to investigate N 2 O atmosphere exchange from grass vegetation exposed to solar irradiance with and without UV-screening. Further laboratory tests were conducted with a range of species to study the controls and possible loci of UV-induced N 2 O emission from plants. Plants released N 2 O in response to natural sunlight at rates of c. 20 e 50 nmol m 2 h 1 , mostly due to the UV component. The emission response to UV-A is of the same magnitude as that to UV-B. Therefore, UV-A is more important than UV-B given the natural UV-spectrum at Earth's surface. Plants also emitted N 2 O in darkness, although at reduced rates. The emission rate is temperature dependent with a rather high activation energy indicative for an abiotic process. The prevailing zone for the N 2 O formation ap- pears to be at the very surface of leaves. However, only c. 26% of the UV-induced N 2 O appears to originate from plant-N. Further, the process is dependent on atmospheric oxygen concentration. Our work dem- onstrates that ecosystem emission of the important greenhouse gas, N 2 O, may be up to c. 30% higher than hitherto assumed.