Laboratory Investigations of Methane Buildup in, and Release from, Shallow Peats

Abstract

Peatlands are significant sources of the important greenhouse gas methane (CH4). Here we explore the design and uses of experimental systems developed for the determination of continuous fluxes of CO2 and CH4 in closed ecosystem monoliths including the capture of 14CO2 and 14CH4 following radiolabeling. In this chapter, we detail the experimental design developed in our laboratory that may be used to study a range of different processes controlling formation, oxidation, and emission of methane in shallow peat soils under controlled conditions. These include methanogenic production versus methanotrophic oxidation; relative contribution of different methanogenic pathways; the importance of rhizospheric processes including root exudation for methanogenic substrate provision; the time lag between photosynthetic carbon assimilation and CH4 emission; and finally the relative proportion of different emission pathways: plant mediated transport, diffusion, and ebullition. The results that may be produced using the range of experimental measurement systems presented have implications for better understanding wetland ecosystem/atmosphere interactions, including possible feedback effects on climate change. Much attention has been devoted to field-based ecosystem-atmosphere flux measurement campaigns investigating the relationship between peatland net ecosystem productivity and CH4 emission. The experimental laboratory-based systems presented here represent useful compliments to these field studies. Under controlled conditions, the complex relationship between plant composition, productivity, and CH4 emission may be studied. Here we show examples of how this complex relationship may change considerably in nature depending on plant species composition as this varies both within and between ecosystems.