A recently published study, completed by researchers from the University of Helsinki together with Dr Katerina Machacova, a visiting scholar, demonstrates that boreal forests of the Northern Hemisphere are sources of the greenhouse gas nitrous oxide (N2O).
The study provides new information on the significance of trees as sinks and sources of greenhouse gases, proving that forests have relevance not only in the absorption of carbon, but also as a source of other greenhouse gases.
The research group observed that the greenhouse gas nitrous oxide is released into the atmosphere not only by the forest soil, but also by pine, birch and spruce, the trees of the northern boreal zone. The group has previously demonstrated (Machacova et al., 2016; Scientific Reports) that the stems and canopies of pine trees in the northern boreal zone are sources of N2O. This recent study indicated that also birches and spruces release the gas into the atmosphere.
“Trees may have an impact more significant than previously thought on the nitrous oxide balance of forests, as well as on the global N2O balance,” says Associate Professor Mari Pihlatie from the Faculty of Agriculture and Forestry, University of Helsinki.
The most important discovery in the study was that the N2O emissions of tree stems clearly vary by season, corresponding with the physiological activity of the trees. During the growing season, trees release nitrous oxide from their stems, while during dormancy in the winter, they can become consumers of the gas. Even though the consumption of N2O over the winter reduces annual emissions, trees remain annual N2O sources. Seasonal variation in N2O emissions corresponded with the carbon dioxide emissions of tree stems. Both types of emissions peaked in the summer.
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