Wetlands are one of the largest natural sources of methane to the atmosphere. In the face of global climate change it is imperative that we gain a better understanding of the factors that control methane emissions from wetlands. We conducted a controlled outdoor mesocosm experiment to assess the effects of plant community composition and functional group richness on methane production and iron reduction potentials. The mesocosms were located at The Ohio State University. Four macrophyte functional groups were arranged in a full factorial design and additional mesocosms were assigned as no-plant controls. Destructive sampling for above and belowground biomass was conducted in September 2008. Soil samples from the top 10 cm were collected in June, August, and November 2008 and shipped to The University of New Hampshire to determine moisture, organic matter, pH, and methane production and iron reduction potentials. Soils were mixed with deionized water or 200 mM formate and incubated anaerobically. Headspace samples were taken four times over an 11 day period and analyzed for methane content. A second set of water-only slurries was analyzed immediately for initial reduced iron content using the Ferrozine reagent. Post-incubation a sub-sample from each slurry was analyzed for final reduced iron content.
Results/Conclusions
In these mesocosms low levels of organic matter combined with an abundance of oxidized iron appear to have inhibited methane production. Both methane production and iron reduction potentials were enhanced in the presence of formate. Sampling month had an effect on both methane production and iron reduction, with methane production highest in June for samples incubated in water, but lowest in June for samples incubated with formate. Iron reduction potentials were highest in August for samples incubated in water and formate. Preliminary results suggest that both plant community composition and functional group richness had an effect on methane production and iron reduction potentials, though mostly in soils incubated with formate. The effect of functional group richness was most obvious between the no-plant controls and all other levels of richness, with the controls generally exhibiting lower methane production and iron reduction potentials. The relationship to plant community composition seems to be mostly due to the presence or absence of specific functional groups, particularly the reeds and tussocks. Methane production and iron reduction potentials were also correlated with the soil properties of moisture, organic matter, and pH and the plant properties of leaf area index, and above and belowground biomass.
