HR: 1340h
AN: B53A-0935    [Abstracts]
TI: Exploring the Relationship Between Wetland Methane Emissions and Net Ecosystem Productivity Using Experimental Shading and Labile Carbon Additions.
AU: * Owens, S
EM: sowens@lamar.colostate.edu
AF: Graduate Degree Program in Ecology and Department of Biology, Colorado State University, Fort Collins, CO 80523,
AU: von Fischer, J C
EM: jcvf@lamar.colostate.edu
AF: Graduate Degree Program in Ecology and Department of Biology, Colorado State University, Fort Collins, CO 80523,
AB: Methane (CH₄) emissions from wetlands are positively correlated with net ecosystem productivity (NEP); however the relative importance of proposed controlling mechanisms remains poorly understood. The carbon supply hypothesis suggests that recent photosynthesis contributes labile carbon substrate to methanogenic habitats, resulting in higher CH₄ emissions with increases in NEP. Plant gas transport is also hypothesized to be important for conducting gases between the soil and the atmosphere. High CH₄ production rates often occur in saturated wetland soils where gas diffusion is extremely slow. The aerenchymous tissues of vascular wetland plants can serve as the primary pathway for CH₄ emissions from the soil to the atmosphere, while also allowing CH₄ to bypass more aerobic soil regions where CH₄ oxidation could occur. Using a hypothesis-driven experimental approach, we established shading treatments in a Juncus- dominated wetland in the northern Colorado Front Range, and measured CH₄ and CO₂ fluxes with a static chamber technique. In the summer of 2007, the shading manipulations (45% and 65% shade) significantly reduced net ecosystem exchange (NEE; an approximation of NEP) and mean CH₄ fluxes compared to control plots (p=0.02 and p=0.01, respectively). To test the carbon supply hypothesis, we injected a solution containing acetate (a primary methanogenic carbon source) to a depth of 20cm below the soil surface. Acetate additions stimulated CH₄ emission rates across all plots by an average of 29.3% (p=0.01). However the strength of the CH₄ emission response was not significantly related to plot treatment or NEE, indicating that reduced carbon supply could not explain the response to shading. We hypothesize that reduced plant gas transport was more important than labile carbon supply for driving the lower CH₄ emission rates in shaded plots. The dry weight of above-ground biomass was lower in shaded plots (p=0.04), suggesting a possible link between plant gas transport capacity and the quantity of above-ground tissues. More work is necessary to understand the role of wetland vegetation communities and their gas transport properties as a mechanism to control patterns of CH₄ emissions from wetlands.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0497 Wetlands (1890)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting