 |
| Titel |
The role of forest floor and trees to the ecosystem scale methane budget of
boreal forests |
| VerfasserIn |
Mari Pihlatie, Elisa Halmeenmäki, Olli Peltola, Iikka Haikarainen, Jussi Heinonsalo, Minna Santalahti, Anuliina Putkinen, Hannu Fritze, Otmar Urban, Katerina Machacova |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250134696
|
| Publikation (Nr.) |
 EGU/EGU2016-15443.pdf |
|
|
|
|
|
| Zusammenfassung |
| Boreal forests are considered as a sink of atmospheric methane (CH4) due to the activity of
CH4 oxidizing bacteria (methanotrophs) in the soil. This soil CH4 sink is especially strong
for upland forest soils, whereas forests growing on organic soils may act as small sources due
to the domination of CH4 production by methanogens in the anaerobic parts of the soil. The
role of trees to the ecosystem-scale CH4 fluxes has until recently been neglected
due to the perception that trees do not contribute to the CH4 exchange, and also
due to difficulties in measuring the CH4 exchange from trees. Findings of aerobic
CH4 formation in plants and emissions from tree-stems in temperate and tropical
forests during the past decade demonstrate that our understanding of CH4 cycling
in forest ecosystems is not complete. Especially the role of forest canopies still
remain unresolved, and very little is known of CH4 fluxes from trees in boreal
region.
We measured the CH4 exchange of tree-stems and tree-canopies from pine (Pinus
sylvestris), spruce (Picea abies) and birch (Betula pubescens, Betula pendula) trees growing
in Southern Finland (SMEAR II station) on varying soil conditions, from upland mineral soils
to paludified soil. We compared the CH4 fluxes from trees to forest-floor CH4 exchange,
both measured by static chambers, and to CH4 fluxes measured above the forest
canopy by a flux gradient technique. We link the CH4 fluxes from trees and forest
floor to physiological activity of the trees, such as transpiration, sap-flow, CO2 net
ecosystem exchange (NEE), soil properties such as temperature and moisture, and to the
presence of CH4 producing methanogens and CH4 oxidizing methanotrophs in trees or
soil.
The above canopy CH4 flux measurements show that the whole forest ecosystem was a
small source of CH4 over extended periods in the spring and summer 2012, 2014 and 2015.
Throughout the 2013-2014 measurements, the forest floor was in total a net sink of CH4, with
variation between high CH4 uptake in the dominating dry upland areas and high emissions
from the few wet spots of the forest. All the studied tree species emitted small amounts of
CH4 from the stems and shoots, with emission rates depending on the season, tree species
and soil conditions. Especially, CH4 emissions from birch canopies were high and can
therefore contribute significantly to the ecosystem-scale CH4 fluxes. Processes behind the
canopy and stem CH4emission remain unresolved, however, ongoing analysis of the
methanogens and methanotrophs within the plant-soil systems will reveal whether CH4
production or consumption is of microbial origin. Also, comparison of the CH4 fluxes from
trees and forest floor to sap-flow, transpiration, and NEE as well as soil parameters will
help to explain the seasonality and mechanisms involved in the CH4 emissions. |
|
|
|
|
|
|