Periodic Reporting for period 4 - MEMETRE (From processes to modelling of methane emissions from trees)
Période du rapport: 2022-08-01 au 2024-01-31
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 resulted in several significant breakthroughs that advance the research field significantly. We designed and built an automated trace gas flux measurement system which allowed us to conduct completely new types of experiment which revealed that tree canopy CH4 emissions follow a diurnal cycle, the emissions are dependent on radiation and temperature, and that the CH4 emitted is not produced by photosynthesis related processes nor, at least to significant degree, by microbes. These results and process understanding will enormously progress the research and when implemented in models, they allow to estimate regional and global CH4 emissions from forest ecosystems. Furthermore, our interdisciplinary work resulted in new insights to plant metagenome and the role of methane producing and oxidizing microbes in trees, shrubs and herbaceous plants. The understanding and data from experimental work was used to construct the first ever CH4 transport model for trees. This model enables partitioning of physical transport phenomena from biological CH4 production processes within tree stems. As a result, the model reveals the contribution of simultaneously occurring processes within tree stems, bringing new insight and progressing the research field enormously. Overall, the project enabled making a leap in our understanding of tree CH4 exchange processes in forest ecosystems.
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 resulted in several significant breakthroughs that advance the research field significantly. We designed and built an automated trace gas flux measurement system which allowed us to conduct completely new types of experiment which revealed that tree canopy CH4 emissions follow a diurnal cycle, the emissions are dependent on radiation and temperature, and that the CH4 emitted is not produced by photosynthesis related processes nor, at least to significant degree, by microbes. These results and process understanding will enormously progress the research and when implemented in models, they allow to estimate regional and global CH4 emissions from forest ecosystems. Furthermore, our interdisciplinary work resulted in new insights to plant metagenome and the role of methane producing and oxidizing microbes in trees, shrubs and herbaceous plants. The understanding and data from experimental work was used to construct the first ever CH4 transport model for trees. This model enables partitioning of physical transport phenomena from biological CH4 production processes within tree stems. As a result, the model reveals the contribution of simultaneously occurring processes within tree stems, bringing new insight and progressing the research field enormously. Overall, the project enabled making a leap in our understanding of tree CH4 exchange processes in forest ecosystems.
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).
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).
Developing and building of the automated trace gas flux measurement system, and material and instrument testing related to it allowed measuring CH4 exchange rates that are very small in magnitude, but still significant to the CH4 budget of forest ecosystems. The system revealed the diurnal variability of leaf-level CH4 exchange, and that the leaf-level CH4 production is independent of photosynthesis-related processes and is not produced by microbes living in the leaves. Each of these findings is a breakthrough in the field.
Overall, our field and laboratory measurements of stem and shoot CH4 emissions have enabled to identify drivers and processes behind tree stem and canopy CH4 emissions. To our understanding, such comprehensive measurements that integrate CH4 flux measurements from the soil, tree stems and tree canopies combined with plant metagenomic analysis are only conducted within our group. This makes us the pioneers in this field and underlines the urgent need for such measurements across the globe from different climatic zones.
Model of methane transport within trees is a significant and important output of MEMETRE project. This model is the first of its kind that enables to separate physical and biological processes within tree stems and differentiate their role in the stem CH4 emissions. The model is an open access tool that is currently being used in multiple collaborative projects.
Overall, our field and laboratory measurements of stem and shoot CH4 emissions have enabled to identify drivers and processes behind tree stem and canopy CH4 emissions. To our understanding, such comprehensive measurements that integrate CH4 flux measurements from the soil, tree stems and tree canopies combined with plant metagenomic analysis are only conducted within our group. This makes us the pioneers in this field and underlines the urgent need for such measurements across the globe from different climatic zones.
Model of methane transport within trees is a significant and important output of MEMETRE project. This model is the first of its kind that enables to separate physical and biological processes within tree stems and differentiate their role in the stem CH4 emissions. The model is an open access tool that is currently being used in multiple collaborative projects.