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Partioning Tree Methane Emissions

Periodic Reporting for period 1 - PaTreME (Partioning Tree Methane Emissions)

Reporting period: 2020-01-01 to 2021-12-31

The scientific aim of the project PaTreME was to quantify the contribution of different source processes to methane emissions from plant surfaces. Other aims of the project were to facilitate my return and integration into the European Research area after working in Canada for over six years, bi-directional knowledge exchange with my Finnish host institution (stable isotope analysis, trace gas flux measurements), and my development towards academic independence. As described below, both the scientific and non-scientific work plan had to be adapted due to the CoViD pandemic and technical set-backs during the project. Nevertheless, I am confident that PaTreME made improtant contribution to the scientific field as well as to its other goals.

The overall goals of PaTreME was to (a) develop a method to partitioning of plant methane emissions from different source processes (aerobic methane production (AMP), soil methane export (SM), and endophytic microbial methane production (MMP)) using stable isotope, radiocarbon, and chemical tracer techniques, and (b) apply this method to partition the methane fluxes at the SMEAR II boreal forest station.
The scientific work in PaTreME was to be organized in four work packages with the following objectives:
1. Develop an enclosure chamber system for isotope analysis of plant methane emissions;
2. Identify characteristic isotope and methane:methanol values of methane source processes;
3. Measure isotope and methane:methanol values of methane emitted by boreal trees at the SMEAR II research forest;
4. Develop and apply an isotope partitioning model to quantify methane emissions from AMP, SM, and MMP.
In addition, a fifth WP was dedicated to training, career development, and research communication activities.
PaTreME was based upon a shoot chamber system developed as part of the ERC StG MEMETRE (PaTreME supervisor M. Pihlatie). The development of this system was delayed and it was not yet operational at the start of PaTreME. I therefore re-focused my activity on completing the development of this initial system, which is now operational; a description of the system has been published (Kohl et al., 2021, AMT). Furthermore, I successfully modified to measure of the chamber system to measure stable carbon isotope values of methane emissions and concurrent methanol fluxes. Attempts to measure hydrogen or radiocarbon of methane emissions were not successful, and initial measurements revealed that in practice methane fluxes were to small for meaningful carbon isotope analyses. We therefore refocused the project on quantifying the size of methane emissions from plants rather than their origin. In addition, I have re-focused my efforts of using isotope values to constrain the methane cycle to peatlands, where methane concentrations and fluxes are significantly higher than at plant surfaces. Planned field measurements at SMEAR II have not been possible due to the CoViD pandemic and technical issues,but I conducted conducted three field campaigns at the Lompolojänkkä research fen in 2021. Partitioning methane source processes of methane emissions from plant shoots based on stable isotope values was not be possible as planned because these methane fluxes are too small for stable isotope measurements. I have therefore re-focused WP4 to study methane cycling in peatlands, where both concentrations and fluxes are higher. As a first step, I have adapted the peatland methane model HIMMELI (Raivonen et al. 2017, GMD) to simulate carbon and hydrogen isotope values. This model will be used together with the measurements conducted in WP3 to quantify the fraction of methane produced in peatlands that is re-oxidized before it reaches the peat surface, an analysis similar to the one originally planned in PaTreME for plant derived methane.

Secondments: Due to the CoViD, only one physical visit to Heidelberg University was possible. Exchange with the secondment host has, however, been close and resulted in the developed two grant proposals (to the Academy of Finland).

Furthermore, I have advanced my career by taking 20 cr of university pedagogy, 30 cr of Finish language training, and grant coaching for applications to the Academy of Finland and ERC StG applications. I gained mentoring and leadership experience by (co)supervising 2 PhD students (1 ongoing, 1 withdrawn) and 2 completed MSc thesis, and submitted my application for docentship at the University of Helsinki in Jan 2022. Unfortunately, my opportunities for research communication to a wider audience were somewhat limited during the PaTreME period due to the ongoing CoViD pandemic. Unlike planned, it was therefore not possible to conduct a workshop at the Researchers Night. I have, however, produced two short videos explaining the PaTreME (and MEMETRE) research together with my PhD supervisees. Knowledge transfer was highly successful. I have become an expert in trace gas flux measurements due to training provided by the host group, seen e.g. in our technical letter (Kohl el al., 2022, New Phyt.) on this issue. Knowledge transfer from me to the host group was conducted through the joint supervision of two PhD students instead of the originally planned workshop.
Scientific impact. Together with the larger MEMETRE project of my host, PaTreME has allowed me to develop two unique measurement systems that quantify methane fluxes at tree shoots. These systems have lead to the first real-time measurements of methane fluxes at plant surfaces, which is a significant breakthrough for understanding the role of plants in the global methane cycle. We have published a first paper describing this new system (Kohl et al., 2021, AMT) and have at least two more publications in preparation. We are now in the process of further exploiting this new system by deploying it at the Hyytiälä field station in fall 2022.

Career development. PaTreME has allowed me to re-integrate into the European research community and put me on a course to forming my own research group. I have been able to established myself as an recognized expert in stable isotope analysis with a unique position in the Finnish research landscape, and I am in the process of establishing an internationally recognized research program that bridges the gap between chemical and isotopic measurements and biogeochemical model development. Overall, I have been able to advance from a junior postdoc to independent researcher during my time in Helsinki, and I am now well qualified for and in the process of submitting proposals for group founding fellowships (Academy of Finland Reserach Fellow, ERC StG). Starting in Fall 2022, I will take over the coordination of the stable isotope laboratory at the University of Eastern Finland for two years (sabbatical replacement). These advancements were to a significant part facilitated by PaTreME funding.

Dissemination of project results. So far, my work in PaTreME has resulted in five publications (some co-authored), with at least two manuscripts in preparation based on data produced during the project. Unfortunately, CoViD has limited my ability to present the project results at international conferences, however, I was still able to attend and present PaTreME results multiple remote meetings (European Geosciences Union 2020, Nordic ICOS meeting 2021, Finnish Ecoysstem research meeting 2021) and an invited presentation at a workshop on the methane balance of tropical peatlands.