[B-BC02] Methane in terrestrial and aquatic ecosystems: from microbes to the atmosphere

[BBC02-02] Shoot-level methane emissions from Scots pine trees: New insights and technical advances

*Salla A. M. Tenhovirta^1,2, Lukas Kohl^1,2,3, Markku Koskinen^1,2, Tatu Polvinen^1,2, Mari Pihlatie^1,2,4 (1.Environmental Soil Science, Department of Agricultural Sciences, University of Helsinki, Finland, 2.Institute for Atmospheric and Earth System Research / Forest Sciences, University of Helsinki, Finland, 3.Department of Environmental and Biological Sciences, University of Eastern Finland, Kuopio, Finland, 4.Viikki Plant Science Centre (ViPS), University of Helsinki, Finland)

Keywords:boreal forests, Pinus sylvestris, shoot-level emissions, aerobic methane production

Recent evidence shows that shoots of Scots pine trees are a source of methane (CH₄) emissions, but it remains unclear if these emissions significantly reduce the CH₄ sink strength of boreal mineral soil forests. Progress in the shoot CH₄ flux research has been hindered by technical challenges in shoot-level trace-gas flux measurements which require closed-loop, non-steady-state chamber systems, as well as by the difficulties in producing sufficient measurement data from hard-to-reach canopies in remote field sites. The absence of such CH₄ flux data, together with a lack of process-level understanding of the CH₄ sources within plants, prevents making comprehensive estimates on the significance of boreal forest canopies in the global CH₄ cycles.

In this contribution we show how we have overcome some of the technical issues in manual and automated chamber systems, under which environmental conditions Scots pine shoots have been observed to emit CH₄ and discuss what our findings reveal about the possible source of shoot-level CH₄ emissions.

Extended measurement campaigns in ambient conditions were made possible by conducting the measurements on tree saplings instead of mature trees, resulting in the finding that CH₄ emissions from Scots pine shoots increase with solar radiation and are enhanced by temperature (Tenhovirta et al., 2022). Our automated chamber measurement system in the greenhouse (Kohl, Koskinen et al., 2021) has enabled continuous measurements and control/treatment experiments, revealing that the CH₄ emissions from Scots pine shoots follow diel cycles (Kohl, Tenhovirta, et al., in prep.), and rule out transport of soil-produced CH₄ or photosynthesis as a source for these emissions (Tenhovirta et al., in prep). In addition, developing this system has provided solutions to common issues associated to chamber measurements, including excessive heating, water vapour accumulation and leakage.

References

Kohl L, Koskinen M, Polvinen T, Tenhovirta SAM, Rissanen K, Patama M, Zanetti A, Pihlatie M. 2021. An automated system for trace gas flux measurements from plant foliage and other plant compartments. Atmospheric Measurement Techniques 14: 4445–4460.
Tenhovirta SAM, Kohl L, Koskinen M, Patama M, Lintunen A, Zanetti A, Lilja R, Pihlatie M. 2022. Solar radiation drives methane emissions from the shoots of Scots pine. New Phytologist 235: 66–77.