Exchange of important greenhouse gases (GHGs) methane (CH4) and nitrous oxide (N2O) in forest ecosystems has traditionally focused on gas flux measurements between the soil and the atmosphere only. Soils act as substantial sources and sinks of both gases. However, the processes underlying the production and consumption of these gases are still not fully known and their understanding is a pre-supposition for improving the estimations of the gas fluxes within the soil-plant-atmosphere system. Over the last years, it has become evident that trees may play an important, and until recently overlooked, role in the net exchange of these GHGs in forests. Trees can contribute to ecosystem exchange by uptake and transport of soil-produced CH4 and N2O to the atmosphere, in-situ production (and perhaps consumption?) of both gases in plant tissues, and alternation of carbon- and nitrogen-turn-over in adjacent soil. However, the contribution of these individual processes to the net ecosystem GHGs exchange is still unclear and seems to depend on tree species, forest ecosystem type, environmental parameters and seasonal dynamics. Wetland tree species may be important CH4 sources, whereas some upland tree species are even known to be sinks for CH4. High N2O emissions have been particularly detected from trees grown under increased N2O concentrations in soils. The question thus remains whether mature trees exchange N2O with the atmosphere under low soil N2O concentration. First studies detected even N2O uptake by upland trees.
This session seeks to bring together scientists working on the exchange of CH4 and N2O in forest ecosystems at any relevant scale, and from the full climatic and hydrological forest range. We therefore welcome contributions on microbial processes in soils, plant tissues and microtopographic forms; measurements of soil gases and modelling of gas transport, incl. innovative approaches for soil gas sampling; gas transport processes in soils and trees incl. methodological aspects (application of stable/radioactive isotopes); flux measurements on the forest floor/soil, on cryptogams, on tree stems and at the leaf and canopy level; micrometeorological measurements using flux towers, and satellite, inverse and numerical modelling studies that seek to integrate our understanding of CH4 and N2O exchange in soils, trees and forest ecosystems. To understand the complexity of gas turn-over and transport processes in soils and trees in its entirety, related studies on other important gases as carbon dioxide (CO2), and biogenic volatile organic compounds (BVOC) and nitrous acid (HONO), which are important precursors of atmospheric chemistry, will be also included in the session.

Key-note speaker: Prof. Dr. Ülo Mander, University of Tartu, Estonia


The following sessions were merged into this session:
BG2.8 Forests and the CH4 and N2O cycles
BG2.51 Transport processes of trace gases in soils: measurements, modelling and ecological implications