A mesocosm study of the role of the sedge Eriophorum angustifolium in the efflux of methane-including that due to episodic ebullition-from peatlands

Vascular plants may reduce episodic ebullition losses of methane (CH4) from peatlands. They transport CH4 to the atmosphere, which may lead to a reduction in pore-water [CH4], bubble formation and release. This effect may be compounded by rhizospheric oxidation and associated methanotrophy. However, any reduction in pore-water [CH4] may be countered by root exudation (substrate for methanogens). The aim of this study was to determine how the presence of sedges affects CH4 emissions from peatlands. Five pairs of peat cores were collected from a raised bog. One of each pair contained Sphagnum cuspidatum and Eriophorum angustifolium ('sedge' cores); the other was dominated by S. cuspidatum ('no-sedge'). From these the total CH4 efflux-including that due to episodic ebullition-were measured. A partial-shading treatment helped isolate the potential effect of root exudation. Sedge samples had significantly higher CH4 fluxes than no-sedge samples, but episodic-ebullition fluxes were not significantly different. Between full-light and partially-shaded conditions, there was a significant increase in the difference in CH4 fluxes between the sedge and no-sedge cores. The higher rates of CH4 flux from the sedge cores cannot be explained simply by higher rates of CH4 production due to rapid utilisation of exudates.