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| Titel |
Seasonal courses revealed that boreal trees emit methane even during winter
time |
| VerfasserIn |
Katerina Machacova, Elisa Halmeenmäki, Mari Pihlatie, Otmar Urban |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250127548
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| Publikation (Nr.) |
 EGU/EGU2016-7440.pdf |
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| Zusammenfassung |
| Boreal forests are considered to be a significant natural sink of methane (CH4) due to
predominant soil deposition of CH4 from the atmosphere. However, plants are known to
contribute to the CH4 exchange with the atmosphere. Fluxes of CH4 have been mostly
studied on herbaceous plants, whereas investigations on trees, particularly boreal tree species,
are sporadic.
Therefore we determined CH4 fluxes from common boreal tree species: Scots pine (Pinus
sylvestris), Norway spruce (Picea abies) and silver birch (Betula pendula). The objectives
were to investigate whether these tree species contribute to CH4 exchange with the
atmosphere, particularly in winter, how soil water content affects these fluxes, and how trees
contribute to overall forest CH4 fluxes.
The measurements were performed on mature trees in the boreal forest surrounding the
SMEAR II station in Finland. Fluxes of CH4 at stem and forest floor level were
simultaneously measured over the whole year (from June 2014 until May 2015) using static
chamber systems and quantified by gas chromatographic analyses.
Our results show that the trees mostly emitted CH4 in the summer. Birch was the
strongest emitter of CH4(9.5 μg CH4 m−2stem area h−1, medians) among the tree species
studied, particularly under high soil volumetric water content (0.92 ± 0.01 m3 m−3).
Similarly, the forest floor released CH4 into the atmosphere (37 μg CH4 m−2 soil area h−1).
Under low soil water content (0.37 ± 0.02 m3 m−3), the flux rates from stems of birch and
pine decreased but remained mostly positive (i.e. emissions), whereas forest floor reversed to
sink for CH4 (-44 μg CH4 m−2 h−1). In contrast, spruce CH4 emissions increased with
decreasing soil water content up to 0.55 μg CH4 m−2 h−1. In general, the emission
rates of all the tree species decreased from September/October onwards. In the
winter, the tree fluxes remained low, but slightly positive, and increased again in the
spring. The CH4 fluxes were modulated by soil water content also during the winter
period.
Summarised, boreal tree species and their CH4 emissions play an important role in the
ecosystem CH4 exchange, thus reducing the sink strength of boreal forest soils. Therefore, it
is necessary to incorporate tree CH4 fluxes and their seasonal variations in the estimation of
CH4 balance of boreal forests.
Acknowledgement
This research was supported by the project ENVIMET (CZ.1.07/2.3.00/20.0246) and the
National Programme for Sustainability I (LO1415), EU FP7 project ExpeER (Grant
Agreement 262060), Emil Aaltonen Foundation, The Academy of Finland Centre of
Excellence (projects 1118615 and 272041), and Helsinki University Centre for Environment,
HENVI. We thank Marian Pavelka, Jiří Dušek, Stanislav Stellner, Jiří Mikula and Marek
Jakubík for technical support. |
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