Forest canopy mitigates soil N2O emission during hot moments
Ülo Mander, Alisa Krasnova, Jordi Escuer-Gatius, Mikk Espenberg, Thomas Schindler, Kateřina Macháčová, Jaan Pärn, Martin Maddison, J. Patrick Megonigal, Mari Pihlatie, Kuno Kasak, Ülo Niinemets, Heikki Junninen, Kaido Soosaar
Abstract
Abstract 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 N 2 O from a typical riparian forest in Europe. Hot moments (extreme events of N 2 O emission) lasted a quarter of the study period but contributed more than half of soil fluxes. We demonstrate that high soil emissions of N 2 O 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 N 2 O. We propose photochemical reactions and dissolution in canopy-space water as reduction mechanisms.