Periodic Reporting for period 3 - MEMETRE (From processes to modelling of methane emissions from trees)
Berichtszeitraum: 2021-02-01 bis 2022-07-31
Contribution of trees to the CH4 budget of forest ecosystems has long been overlooked due to the perception that trees do not play a role in the CH4 dynamics. Recent evidence shows that whole forest ecosystems may act as sources of CH4 despite the soils being sinks, and more specifically that CH4 emissions from tree stems may substantially contribute to the net CH4 exchange. Despite the growing evidence of the capacity of trees to emit CH4 in different climatic zones, the process-level understanding is incomplete. MEMETRE project fills the gap and provides state-of-the-art laboratory and field measurements to identify the mechanisms of tree CH4 exchange, their drivers and spatio-temporal variability. Furthermore, the process understanding will be used to construct a soil-tree-atmosphere process model of CH4 cycling in forest ecosystems, which allows to evaluate the role of trees to the CH4 budget at forest and global scales.
The project has a strong experimental base necessary to obtain the process level information for the modelling. We use novel enclosure methods in specifically designed laboratory setups and in the field to investigate gas exchange of tree seedlings and mature trees. We utilize existing research infrastructure sites in Europe (e.g. ICOS) to guarantee state-of-the-art facilities and supporting tree-physiological and environmental data for our CH4 flux measurements. Simultaneously, we work towards a process-based model that includes CH4 production and consumption processes in the soil, gas transport processes in tree, and in-situ CH4 production processes in trees.
The project has a strong experimental base necessary to obtain the process level information for the modelling. We use novel enclosure methods in specifically designed laboratory setups and in the field to investigate gas exchange of tree seedlings and mature trees. We utilize existing research infrastructure sites in Europe (e.g. ICOS) to guarantee state-of-the-art facilities and supporting tree-physiological and environmental data for our CH4 flux measurements. Simultaneously, we work towards a process-based model that includes CH4 production and consumption processes in the soil, gas transport processes in tree, and in-situ CH4 production processes in trees.
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. With the setup we have conducted four measurement campaigns: Two campaigns focusing on the diurnal cycle of CH4 emissions, with and without added UV-light, from the conifers species Scots pine, Norway spruce and Siberian larch saplings (WP1, Task 1.2); The third aiming to assess CH4-emitting processes in Betula species (B. nana, B. pubescens, B. pendula) (WP1, Task 1.2 1.3); and the fourth investigating the transfer of soil-produced methane via tissues of the B. nana and Carex sp. growing on peat. For Betula species, B. nana showed strong conductivity of CH4 from the soil to the atmosphere via leaves. The results suggest that Betula species differ in the capacity to transport soil-derived CH4.
In addition, we developed an automated multi-chamber shoot enclosure system for field measurements, to be utilized in WP2. A prototype of this system was built at the Viikki greenhouse facility in 2020, and tested with Scots pine saplings (Kohl et al. in review). During the spring of 2020 this system was also tested with Scots pine saplings that were exposed to additional UV-radiation. This experiment confirmed that Scots pine shoots emitted CH4 from their shoots when exposed to UV-radiation. With the setup we conducted three measurement campaigns: one focusing on diurnal cycles of CH4 emissions from Scots pine saplings (WP1), the second to test for a pulse-chase method on 13-CO2 labelled pine shoots, and thirdly, in an on-going experiment, to see if drought effects shoot-level CH4 emissions. Related to WP1 (task 1.4) 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 yet in the field (flux measurements continue during the next growing seasons). 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., in preparation). 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 press, New Phytologist).
In WP3 progress has been made towards regional landscape estimation of the CH4 exchange of boreal forests (WP3, Task 3.4). 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., 2021. Biogeosciences). In 2021 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 has been started. The first task was to parametrize the gas transport model (Hölttä et al., 2009) to include CH4 transport in boreal trees (Anttila et al., in review). In the second task, the water and gas transport processes were implemented in an existing ecosystem model, which will further be developed to include canopy CH4 processes (Tikkanen et al., in preparation).
In addition, we developed an automated multi-chamber shoot enclosure system for field measurements, to be utilized in WP2. A prototype of this system was built at the Viikki greenhouse facility in 2020, and tested with Scots pine saplings (Kohl et al. in review). During the spring of 2020 this system was also tested with Scots pine saplings that were exposed to additional UV-radiation. This experiment confirmed that Scots pine shoots emitted CH4 from their shoots when exposed to UV-radiation. With the setup we conducted three measurement campaigns: one focusing on diurnal cycles of CH4 emissions from Scots pine saplings (WP1), the second to test for a pulse-chase method on 13-CO2 labelled pine shoots, and thirdly, in an on-going experiment, to see if drought effects shoot-level CH4 emissions. Related to WP1 (task 1.4) 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 yet in the field (flux measurements continue during the next growing seasons). 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., in preparation). 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 press, New Phytologist).
In WP3 progress has been made towards regional landscape estimation of the CH4 exchange of boreal forests (WP3, Task 3.4). 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., 2021. Biogeosciences). In 2021 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 has been started. The first task was to parametrize the gas transport model (Hölttä et al., 2009) to include CH4 transport in boreal trees (Anttila et al., in review). In the second task, the water and gas transport processes were implemented in an existing ecosystem model, which will further be developed to include canopy CH4 processes (Tikkanen et al., in preparation).
Building of the growth chamber setup allows for the first time to assess the diurnal variability of leaf-level CH4 exchange of small trees under fully controlled light, temperature, humidity and CO2 conditions. Automatically controlled and programmed conditions, online measurements of CH4 and CO2 fluxes, including stable C-isotopes (13C-CH4, 13C-CO2) allowing to follow a tracer in the soil-plant system (Pihlatie et al., 2019, Geophysical Abstracts; Kohl et al. 2019, Kohl et al., 2021 in review), and several manuscripts in preparation.
Viewpoint paper in New Phytologist "New insight to the role of microbes in the methane exchange in trees – evidence from metagenomic sequencing" opened a new field of research with the first efforts in combing CH4 flux measurements from tree canopies and DNA-based sequencing of the microbiome of tree and their connection to the CH4 exchange (Putkinen et al., 2021, in press).
Our field measurements of stem and shoot CH4 emissions at Skogaryd (southern Sweden) and Kenttärova (northern Finland) add critically needed field data from boreal forests. To our understanding, such comprehensive CH4 flux measurements from tree canopies are only conducted within our group, and available data exist currently only from the campaigns mentioned above and from our earlier measurements.
Viewpoint paper in New Phytologist "New insight to the role of microbes in the methane exchange in trees – evidence from metagenomic sequencing" opened a new field of research with the first efforts in combing CH4 flux measurements from tree canopies and DNA-based sequencing of the microbiome of tree and their connection to the CH4 exchange (Putkinen et al., 2021, in press).
Our field measurements of stem and shoot CH4 emissions at Skogaryd (southern Sweden) and Kenttärova (northern Finland) add critically needed field data from boreal forests. To our understanding, such comprehensive CH4 flux measurements from tree canopies are only conducted within our group, and available data exist currently only from the campaigns mentioned above and from our earlier measurements.