Forest canopy mitigates soil N2O emission during hot moments.

Riparian forests are known as hot spots of nitrogen cycling in landscapes. Climate warming speeds up the cycle. Here we present results from a multi-annual high temporal-frequency study of soil, stem, and ecosystem (eddy covariance) fluxes of N₂O from a typical riparian forest in Europe. Hot moments (extreme events of N₂O emission) lasted a quarter of the study period but contributed more than half of soil fluxes. We demonstrate that high soil emissions of N₂O do not escape the ecosystem but are processed in the canopy. Rapid water content change across intermediate soil moisture was a major determinant of elevated soil emissions in spring. The freeze-thaw period is another hot moment. However, according to the eddy covariance measurements, the riparian forest is a modest source of N₂O. We propose photochemical reactions and dissolution in canopy-space water as reduction mechanisms. [ABSTRACT FROM AUTHOR]