title: How does elevated ozone reduce methane emissions from peatlands?
abstract: The effects of increased tropospheric ozone (O3) pollution levels on methane (CH4) emissions from peatlands, and their underlying mechanisms, remain unclear. In this study, we exposed peatland mesocosms from a temperate wet heath dominated by the sedge Schoenus nigricans and Sphagnum papillosum to four O3treatments in open-top chambers for 2.5years, to investigate the O3impacts on CH4emissions and the processes that underpin these responses. Summer CH4emissions, were significantly reduced, by 27% over the experiment, due to summer daytime (8hday-1) O3exposure to non-filtered air (NFA) plus 35ppb O3, but were not significantly affected by year-round, 24hday-1, exposure to NFA plus 10ppb or NFA plus 25ppb O3. There was no evidence that the reduced CH4emissions in response to elevated summer O3exposure were caused by reduced plant-derived carbon availability below-ground, because we found no significant effect of high summer O3exposure on root biomass, pore water dissolved organic carbon concentrations or the contribution of recent photosynthate to CH4emissions. Our CH4production potential and CH4oxidation potential measurements in the different O3treatments could also not explain the observed CH4emission responses to O3. However, pore water ammonium concentrations at 20cm depth were consistently reduced during the experiment by elevated summer O3exposure, and strong positive correlations were observed between CH4emission and pore water ammonium concentration at three peat depths over the 2.5-year study. Our results therefore imply that elevated regional O3exposures in summer, but not the small increases in northern hemisphere annual mean background O3concentrations predicted over this century, may lead to reduced CH4emissions from temperate peatlands as a consequence of reductions in soil inorganic nitrogen affecting methanogenic and/or methanotrophic activity.
authors.affiliation: Environment Department, University of York, York YO10 5NG, UK. Electronic address: sylvia.toet@york.ac.uk.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Toet
authors.affiliation: Environment Department, University of York, York YO10 5NG, UK.
authors.forename: Viktoria
authors.initials: V
authors.lastname: Oliver
authors.affiliation: Department of Biology, University of York, York YO10 5DD, UK.
authors.forename: Phil
authors.initials: P
authors.lastname: Ineson
authors.affiliation: Environment Department, University of York, York YO10 5NG, UK.
authors.forename: Sophie
authors.initials: S
authors.lastname: McLoughlin
authors.affiliation: Department of Biology, University of York, York YO10 5DD, UK.
authors.forename: Thorunn
authors.initials: T
authors.lastname: Helgason
authors.affiliation: School of Biology, Newcastle University, Newcastle upon Tyne NE1 7RU, UK.
authors.forename: Simon
authors.initials: S
authors.lastname: Peacock
authors.affiliation: Natural Environment Research Council Life Sciences Mass Spectrometry Facility, Centre for Ecology and Hydrology, Lancaster LA1 4AP, UK.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Stott
authors.affiliation: School of Biology, Newcastle University, Newcastle upon Tyne NE1 7RU, UK.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Barnes
authors.affiliation: Stockholm Environment Institute, University of York, York YO10 5NG, UK.
authors.forename: Mike
authors.initials: M
authors.lastname: Ashmore
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D029785:Cyperaceae; D017753:Ecosystem; D004784:Environmental Monitoring; D008697:Methane / Q000032:analysis*; D010126:Ozone / Q000032:analysis*; D044003:Sphagnopsida
chemical_list: D000393:Air Pollutants; D010126:Ozone; D008697:Methane
keywords: (13)C; CH(4); Mires; Nitrogen; Sedge; Sphagnum papillosum