HR: 1340h
AN: B53A-0926    [Abstracts]
TI: Effects of Soil Warming and Drying on Methane Cycling in Northern Peatlands
AU: * White, J R
EM: whitej@indiana.edu
AF: Indiana University, Center for Research in Environmental Science SPEA 331, Bloomington, IN 47405, United States
AU: Shannon, R D
EM: rds13@psu.edu
AF: Pennsylvania State University, 233 Ag. Eng. Bldg. Agricultural and Biological Engineering Department, University Park, PA 16802-1909, United States
AU: Bridgham, S D
EM: bridgham@uoregon.edu
AF: University of Oregon, Environmental Studies Program Box 5289, Eugene, OR 97403-5289, United States
AB: Boreal peatlands contain a large portion of the earth's terrestrial organic carbon and may be particularly vulnerable to changes in climate. Temperature conditions in boreal regions are predicted to increase during the twenty-first century which may accelerate changes in soil microbial processes and plant community dynamics. Climate-driven changes in plant community composition might affect the pathways and rates of methanogenesis, the plant-mediated emission of methane and the scavenging of methane by methanotrophic bacteria. Climate change may also affect nutrient availability and cycling that indirectly affect methane cycling. To date, these feedbacks have not been incorporated into the carbon cycling components of climate models. We investigated the effects of soil warming and water-table manipulations on methane cycling in a field mesocosm experiment in northern Minnesota, USA. Large intact soil monoliths removed from a bog and fen received infrared warming treatments crossed with water-table treatments for six years. In years 5 and 6, concentrations, fluxes and isotopic compositions of methane were measured along with acetate, sulfate, ammonium, belowground net primary productivity and changes in N retention. Methane cycling is affected by changes in N availability associated with soil decomposition and through increased root productivity. An expansion of the rhizosphere of woody shrubs in bogs during the initial 4 yrs was associated with greater methane emission rates. We speculate that an increase in labile substrates associated with root exudates and enhanced plant transport may be factors contributing to the increase in methane emissions. Stable isotopic data from porewater support acetate fermentation as the principal pathway of methanogenesis in bog plots (mean ä13CH4 = -39.3 ‰). Under warm, wet conditions, the majority of the methane was isotopically heavy (mean ä13CH4 = -28.1 ‰), suggesting a predominance of methanotrophic activity throughout the soil system. Fen plots had lower porewater concentrations and emissions of methane than bog plots, despite much higher methane production potentials in fen peat. Increases in porewater ammonium may enhance methane oxidation under conditions of low water table. Our results illustrate the need for a more robust understanding of the multiple feedbacks between climate forcing and plant and microbial feedbacks in the response of northern peatlands to climate change.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0490 Trace gases
DE: 0497 Wetlands (1890)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting