title: Temperate forest methane sink diminished by tree emissions.
abstract: Global budgets ascribe 4-10% of atmospheric methane (CH4) sinks to upland soils and have assumed until recently that soils are the sole surface for CH4exchange in upland forests. Here we report that CH4is emitted from the stems of dominant tree species in a temperate upland forest, measured using both the traditional static-chamber method and a new high-frequency, automated system. Tree emissions averaged across 68 observations on 17 trees from May to September were 1.59 ± 0.88 μmol CH4m-2stem h-1(mean ± 95% confidence interval), while soils adjacent to the trees consumed atmospheric CH4at a rate of -4.52 ± 0.64 μmol CH4m-2soil h-1(P < 0.0001). High-frequency measurements revealed diurnal patterns in the rate of tree-stem CH4emissions. A simple scaling exercise suggested that tree emissions offset 1-6% of the growing season soil CH4sink and may have briefly changed the forest to a net CH4source.
authors.affiliation: Department of Earth and Planetary Sciences, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD, 21218, USA.|Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, MD, 21037, USA.
authors.forename: Scott
authors.initials: S
authors.lastname: Pitz
authors.affiliation: Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, MD, 21037, USA.
authors.forename: J Patrick
authors.initials: JP
authors.lastname: Megonigal
mesh_terms: D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods; D065928:Forests; D008396:Maryland; D008697:Methane / Q000032:analysis* / Q000378:metabolism; D018547:Plant Stems / Q000737:chemistry / Q000378:metabolism; D012987:Soil / Q000737:chemistry; D014197:Trees / Q000378:metabolism*
chemical_list: D012987:Soil; D008697:Methane
keywords: carbon; diurnal; freely drained soil; methane (CH4); temperate forests; tree stems; upland forests