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.

Automated summary

Riparian forests are considered hotspots of nitrogen cycling, with climate warming accelerating the process. High soil emissions of N2O in riparian forests are mainly processed in the canopy, with rapid water content changes and freeze-thaw periods being major factors contributing to elevated soil emissions. Eddy covariance measurements suggest that riparian forests are a moderate source of N2O, with photochemical reactions and dissolution in canopy-space water proposed as reduction mechanisms.