A novel mesocosm set-up reveals strong methane emission reduction in submerged peat moss Sphagnum cuspidatum by tightly associated methanotrophs

Wetlands present the largest natural sources of methane (CH 4 ) and their potential CH 4 emissions greatly vary due to the activity of CH 4 -oxidizing bacteria associated with wetland plant species. In this study, the association of CH 4 -oxidizing bacteria with submerged Sphagnum peat mosses was studied, followed by the development of a novel mesocosm set-up. This set-up enabled the precise control of CH 4 input and allowed for monitoring the dissolved CH 4 in a Sphagnum moss layer while mimicking natural conditions. Two mesocosm set-ups were used in parallel: one containing a Sphagnum moss layer in peat water, and a control only containing peat water. Moss-associated CH 4 oxidizers in the field could reduce net CH 4 emission up to 93%, and in the mesocosm set-up up to 31%. Furthermore, CH 4 oxidation was only associated with Sphagnum , and did not occur in peat water. Especially methanotrophs containing a soluble methane monooxygenase enzyme were significantly enriched during the 32 day mesocosm incubations. Together these findings showed the new mesocosm setup is very suited to study CH 4 cycling in submerged Sphagnum moss community under controlled conditions. Furthermore, the tight associated between Sphagnum peat mosses and methanotrophs can significantly reduce CH 4 emissions in submerged peatlands.