Methane concentration and emission as affected by methane transport capacity of plants in freshwater marsh

Abstract

To elucidate effect of the CH4 transport capacity of plants on CH4 production and CH4 emission, we measured CH4 emission and the CH4 transport capacity of plants as well as CH4 and dissolved organic carbon (DOC) concentrations in porewater and redox potential in the freshwater marsh vegetated with Carex lasiocarpa, Carex meyeriana and Deyeuxia angustifolia. Although only 31% of CH4 emitted was released via Deyeuxia angustifolia into the atmosphere compared to 72–86% via Carex plants and the CH4 transport capacity of per stem of Deyeuxia angustifolia was only 8.0 μg CH4 stem−1 h−1 being equal to half for Carex plants, the flux of CH4 emission from the Deyeuxia angustifolia marsh was just lower by 17–28% than those from the Carex marshes as the standing water depth decreased significantly from 15–20 to 5 cm, indicating that despite the poor CH4 transport capability of Deyeuxia angustifolia partly reduced CH4 emission via plants, however CH4 emission was not greatly reduced as expected. This is because although the poor gas transport capability of Deyeuxia angustifolia lowered CH4 emission to some extent, however it also decreased the input of O2 into the rhizosphere via plants; the latter not only reduced CH4 oxidation in the rhizosphere and/or rhizome but also lowered redox potential in the vertical profile resulting in an increase in CH4 production potential and CH4 concentration especially at 5 cm depth, which in turn facilitated CH4 emission through diffusion in the Deyeuxia angustifolia marsh. This study suggests that the sharp decrease in the CH4 transport capacity of plants did not necessary result in an expected lowering of CH4 emission in the freshwater marsh.