B065-0002
Trees and their Role in Seasonal Dynamics of Forest Nitrous Oxide (N2O) and Methane (CH4) Exchange

Friday, 11 December 2020
Poster
Katerina Machacova, Global Change Research Institute CAS, Department of Ecosystem Trace Gas Exchange, Brno, Czech Republic, Elisa Vainio, Environmental Soil Science, Department of Agricultural Sciences, University of Helsinki, Helsinki, Finland, Otmar Urban, Global Change Research Institute CAS, Brno, Czech Republic and Mari Pihlatie, University of Helsinki, Institute for Atmospheric and Earth System Research / Physics, Faculty of Science, Helsinki, Finland
Abstract:
Recent research has revealed that not only soils and herbaceous plants but also woody plants can be significant sources of nitrous oxide (N2O) and methane (CH4). The capacity of trees to exchange trace gases and their contribution to whole ecosystem exchange vary considerably among tree individuals and species, forest ecosystems, and climatic zones, and depend on soil and climatic conditions, tree size, age and vitality, and seasonal dynamics. Wetland trees seem to be stronger CH4 emitters than upland trees. High N2O emissions were detected mostly in trees under (artificially) increased soil N2O concentrations, while exceptional studies under natural field conditions revealed only low N2O emissions or even N2O uptake.

We will present a brief overview of how trees contribute to forest N2O and CH4 exchange and will further focus on seasonal dynamics of N2O and CH4 fluxes in dominant tree species of nitrogen-limited boreal forests (Finland): Scots pine, Norway spruce, and downy/silver birch.

All species studied were identified as net annual sources of N2O and CH4. Spruce was the strongest emitter of N2O, whereas birch grown under the conditions of high soil water content was the strongest CH4 source. The tree fluxes of N2O and CH4 showed clear seasonality, which in the case of N2O followed the physiological activity of trees. Stem N2O emissions peaked during vegetation season and remained low, but detectable during winter. Trees growing on dry soils even turned to consume N2O from the atmosphere during dormancy. The tree species emitted CH4 mainly during the vegetation season with considerable emissions detected already from February onwards. Our results indicate the necessity to include seasonality of tree N2O and CH4 exchange into process models to determine comprehensive total flux estimates of forest ecosystems.

Acknowledgement

This research was supported by Czech Science Foundation (17-18112Y), National Programme for Sustainability I (LO1415), EU FP7 project ExpeER (262060), Academy of Finland Research Fellow projects (292699, 263858, 288494), Academy of Finland Centre of Excellence (1118615, 272041), ICOS-Finland (281255), and European Research Council (757695). We thank M. Jakubík, M. Pavelka, J. Dušek, S. Stellner, J. Mikula and U. Großmann for their support.

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