The effect of clipping on methane emissions from Carex

The purpose of this study was to estimate theresistance to methane release of the above-groundportion of Carex, a wetland sedge, and todetermine the locus of methane release from the plant. Measurements conducted on plants clipped to differentheights above the water level revealed that themethane flux from clipped plants was on the order of97% to 111% of control (unclipped) values. Thegreatest increase was observed in the initial fluxmeasurement after the plants had been clipped to aheight of 10 cm. Subsequent measurements on the 10 cmhigh stubble were similar to control values. When theends of plants which had been clipped to 10 cm weresealed, the methane flux was reduced to 65% ofcontrol values. However, sealing had no effect on theflux from plants which were clipped at 15 cm andhigher, indicating that virtually all methane wasreleased on the lower 15 cm of the plants as theyemerged from the water. The results indicate that theabove-ground portions of Carex at our studysite offered only slight resistance to the passage ofmethane, and that the main sites limiting methaneemission are below-ground, at either theporewater-root or root-shoot boundary. We hypothesizethat the transitory increase in flux associated withclipping was due to the episodic release of methaneheld within the plant lacunae. The buildup ofCH₄ partial pressure within lacunal spacesovercomes the resistance to gas transport offered byaboveground parts.