Since the start of the project, we have built a novel system to measure the shoot and soil gas exchange of tree saplings within a controlled-environment chamber (WP1). This unique system allows us to study the response of CH4 emissions and transport to environmental variables. In addition, we developed an automated multi-chamber shoot enclosure system to be used in field measurements. A prototype of this system was built at the Viikki greenhouse facility. The experiments in the greenhouse facility confirmed that Scots pine shoots emitted CH4 from their shoots, the emissions have a distinct diurnal cycle, and the emissions are independent of photosynthesis-related processes. Fungal CH4 production potential was tested both with a field setup in Hyytiälä, Southern Finland (logs/disks infected with three saprotrophic fungi) and in laboratory incubations. Methane production was detected in the laboratory, but not in the field (unpublished work). In WP2 we finalized the field measurements of stem fluxes in Pallas, northern Finland. In addition, to reveal if soil CH4 cycling is related to the tree fluxes, CH4 potential production and oxidation were analysed from the Pallas soil layers, followed by soil chemical and microbial analyses (in progress). To see if the shoots of Scots pine and Norway spruce are a source of CH4 in the spring, we conducted greenhouse gas measurements in the garden on potted saplings. The initial results show that both Scots pine and Norway spruce emit CH4 from their shoots, and the emissions correlate positively with photosynthetically active radiation (PAR), (Tenhovirta et al.,2021). To reveal the potential CH4 cycling microbes within trees (WP2, task 2.3) samples were collected from spruces and pines in connection to different field/greenhouse/laboratory setups. Methane related functional genes are sequenced using a novel probe-targeted method. First results combined with the current understanding on the role of microbes in tree CH4 fluxes are presented as a viewpoint paper (Putkinen et al., 2021).
In WP3 we constructed a regional landscape estimation of the CH4 exchange of boreal forests. Forest floor CH4 flux data and soil moisture were combined with airborne laser scanning and imaging to construct a topography-based modelled CH4 flux map of the forest (Vainio et al., 2022). This map will further be complemented with CH4 fluxes from trees to eventually provide a landscape level map of the whole-forest CH4 exchange (Kohl et al., in preparation). In WP3, work towards a process model for aerobic CH4 emissions from trees was started but did not progress due to lack of process understanding during the project. The first task was to parametrize the gas transport model (Hölttä et al., 2009) to include CH4 transport in boreal trees (Anttila et al., 2023). In the follow-up project, the water and gas transport processes will be implemented in an existing ecosystem model, which will further be developed to include canopy CH4 processes (Tikkanen et al., in preparation).
