Methane (CH_{4}) fluxes in trees of temperate and boreal zones. What have we learned?
Abstract
The increase in atmospheric methane (CH4) concentration affects global radiative forcing consequently leading to changes in the Earth's climate. Plants are known to be able to emit CH4 under certain conditions; however, the role of trees, especially upland tree species, in the CH4 exchange of forest ecosystems is still not well understood. We have particularly investigated (1) whether trees exchange CH4 with the atmosphere, (2) to which extent trees contribute to net ecosystem CH4exchange, (3) how soil water content affects the tree fluxes and (4) whether these fluxes show seasonal dynamics. To answer these questions, we have measured, since 2009, stem CH4 fluxes in a wide spectrum of tree species under different environmental conditions in the Czech Republic, Germany, and Finland, including seasonality of these fluxes. The fluxes were studied in common broad-leaf and coniferous tree species of boreal and temperate zones: Scots pine (Pinus sylvestris, including shoot fluxes), Norway spruce (Picea abies), European beech (Fagus sylvatica), bay and crack willow (Salix pentandra, S. fragilis), black alder (Alnus glutinosa), downy and silver birch (Betula pubescens, B. pendula), and poplar hybrids (Populus sp.). Stem and also forest floor fluxes were measured using static chamber systems followed by gas chromatographic and/or laser analyses of CH4 concentration changes. Such a broad data set enables now to make some general conclusions about the role of trees in the forest ecosystem CH4 exchange. Our research revealed that stems of all tree species studied mostly emitted CH4 into the atmosphere, even though the studied soils, except wetlands, were predominant sinks for CH4. The CH4 emissions decreased with increasing stem height and being highest close to the soil surface. The stem CH4 emissions showed high spatial heterogeneity likely related to variability in soil water content (larger scale) and variability in subsoil CH4 production (small scale). Different seasonal courses in CH4 and CO2 emissions were observed. While high CH4 emissions were detected in stems of pine, spruce, birch, and willow trees during the winter and/or spring time; CO2 respiratory efflux, an indicator of a physiological activity, was substantialy reduced. Since shoot CH4 emissions in pine trees were substantially higher than emissions from stems, shoots might be the primary tree surface emitting CH4 into the atmosphere. Therefore, the up to now rarely investigated shoot fluxes have to be incorporated in the future experiments. All tree species studied contributed to the CH4 exchange between forest ecosystems and the atmosphere, indicating that these fluxes need to be included in the forest CH4 emission inventories. Acknowledgement This research was supported by Czech Science Foundation (17-18112Y), Czech Academy of Sciences and German Academic Exchange Service (DAAD-15-03), National Programme for Sustainability I (LO1415), CzeCOS (LM2015061), DFG (MA 5826/2-1), DAAD (PhD scholarship), EU FP7 project ExpeER (262060) and Academy of Finland projects (288494, 294088, 1118615, 272041). We thank M. Jakubík, J. Mikula, S. Paulus, E. Halaburt, S. Haddad and U. Großmann for their support.
- Publication:
-
EGU General Assembly Conference Abstracts
- Pub Date:
- April 2018
- Bibcode:
- 2018EGUGA..20.7299M