Upland forests offset soil methane sinks by 1-6% through stem emissions.
Upland forest soils remove methane from the atmosphere and are represented in global budgets as net methane sinks. However, we demonstrate that upland trees can also emit methane.
Studies of methane fluxes in upland forests have focused on exchanges between the atmosphere and soils, but we conclude that methane fluxes across tree surfaces are also potentially important for upland forest methane budgets.
Upland forests remove methane from the atmosphere and are represented in global budgets as net methane sinks. However, this view is based almost entirely on measurements of methane exchange across forest soil surfaces, with little attention to the exchange of methane across plant surfaces. Here we report that methane is emitted from the stems of dominant tree species in a temperate upland forest. The source of the methane emitted from these trees is uncertain but may include transport in the transpiration stream from anoxic groundwater, or methane produced inside the tree itself. High-frequency measurements revealed diurnal patterns in the rate of tree-stem methane emissions that support a groundwater source. A simple scaling exercise suggested that tree emissions offset 1-6% of the growing season soil methane sink, and the forest may have briefly changed to a net source of methane to the atmosphere due to tree methane emissions.
Contacts (BER PM)
Smithsonian Environmental Research Center
This study was supported primarily by the DOE Terrestrial Ecosystem Science program (grant DE-SC0008165). The components of an automated flux system was developed with funds from NSF-ERC MIRTHE (EEC-0540832).
S.A. Pitz and J.P. Megonigal, “Temperate Forest Methane Sink Diminished by Tree Emissions”. New Phytologist (2017). [DOI: 10.1111/nph.14559]. (Reference link)
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