Emergent wetland plants as conduits for methane

Posted on December 13, 2016

Wetlands release more methane to the atmosphere than other any other type of ecosystem and wetland plants, especially those in the shallow fringing zones, play an important role in methane dynamics. However, aquatic plants can be damaged by the grazing activities of herbivorous animals. To examine the impacts of grazing damage on the release of methane, Brazilian scientists used 24 plastic, 45 cm-deep mesocosms filled with lagoon water. Prior to filling, a bottom layer of sand and organic sediment was placed into the mesocosms, and shoots of spike-rush (Eleocharis equisetoides) were transplanted into the sediment. A razor blade was used to simulate damage caused by grasshoppers (Stenacris spp.) to the upper parts of the hollow plant stems. There were four treatments, with different levels of damage (0, 20, 50 and 100% of stems). Two weeks later, an acrylic chamber was sealed over each mesocosm. Gas samples were taken from the chamber and methane concentrations were measured using chromatography. The methane flux from mesocosms with 50% and 100% damaged stems was over three times greater than that from the 0% and 20% treatments. Although grasshoppers damage individual stems only slightly, the accumulated damage to many stems can have a significant impact on methane flux. It seems that damaged parts of the plant serve as extra pathways along which the methane that’s produced in the sediment can leak to the atmosphere. Methane emissions from damaged wetland plants are likely to be greatest when, as here, the damage is permanent, and when grazing occurs above the water surface, since that eliminates the possibility of methane oxidization in the water column.

Reference: Petruzzella, A. et al. 2015. Herbivore damage increases methane emission from emergent aquatic macrophytes, Aquatic Botany 127, 6–11. http://ccbs.sites.ufms.br/files/2015/09/Herbivore-damage-increase-methane-emissions-from-emergent-aquatic-macrophytes.pdf