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| Titel |
Nitrous oxide fluxes from forest floor, tree stems and canopies of boreal
tree species during spring |
| VerfasserIn |
Iikka Haikarainen, Elisa Halmeenmäki, Katerina Machacova, Mari Pihlatie |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250154394
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| Publikation (Nr.) |
 EGU/EGU2017-19482.pdf |
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| Zusammenfassung |
| Boreal forests are considered as small sources of atmospheric nitrous oxide (N2O) due to
microbial N2O production in the soils. Recent evidence shows that trees may play an
important role in N2O exchange of forest ecosystems by offering pathways for soil produced
N2O to the atmosphere. To confirm magnitude, variability and the origin of the tree mediated
N2O emissions more research is needed, especially in boreal forests which have been in a
minority in such investigation.
We measured forest floor, tree stem and shoot N2O exchange of three boreal tree species
at the beginning of the growing season (13.4.–13.6.2015) at SMEAR II station in Hyytiälä,
located in Southern Finland (61˚ 51´N, 24˚ 17´E, 181 a.s.l.). The fluxes were measured
in silver birch (Betula pendula), downy birch (B. pubescens) and Norway spruce
(Picea abies) on two sites with differing soil type and characteristics (paludified
and mineral soil), vegetation cover and forest structure. The aim was to study the
vertical profile of N2O fluxes at stem level and to observe temporal changes in N2O
fluxes over the beginning of the growing season. The N2O exchange was determined
using the static chamber technique and gas chromatographic analyses. Scaffold
towers were used for measurements at multiple stem heights and at the canopy
level.
Overall, the N2O fluxes from the forest floor and trees at both sites were very small and
close to the detection limit. The measured trees mainly emitted N2O from their stems and
shoots, while the forest floor acted as a sink of N2O at the paludified site and as
a small source of N2O at the mineral soil site. Stem emissions from all the trees
at both sites were on average below 0.5 μg N2O m−2 of stem area h−1, and the
shoot emissions varied between 0.2 and 0.5 ng N2O m−2 g−1 dry biomass. When
the N2O fluxes were scaled up to the whole forest ecosystem, based on the tree
biomass and stand density, the N2O emissions from birch and spruce trees at the
paludified site were 1.4 and 2.2 mg N2O ha−1 h−1, respectively, while the forest floor
was a sink of -6.1 mg N2O ha−1 h−1. At the mineral soil site the upscaled N2O
emissions from birch trees and forest floor were 3.6 and 8.9 mg N2O ha−1 h−1,
respectively, indicating that the emissions from trees significantly contribute to the
N2O emissions from boreal forests. The results also indicate that tree canopies
contributed up to 89% of the whole-tree N2O emissions. Our findings demonstrate
that we urgently need more studies focusing on leaf-level N2O exchange in forest
ecosystems.
Acknowledgement
This research was financially supported by the National Programme for Sustainability I
(LO1415), Czech Science Foundation (17-18112Y), ENVIMET (CZ.1.07/2.3.00/20.0246) ,
Emil Aaltonen Foundation, Academy of Finland Research Fellow projects (292699, 263858,
288494), The Academy of Finland Centre of Excellence (projects 1118615, 272041), and
ICOS-Finland (281255). We thank Hyytiälä SMEAR II station staff and Marek Jakubik for
technical support. |
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