Herbivore damage increases methane emission from emergent aquatic macrophytes.

Wetlands are the largest natural methane (CH 4 ) source and the vegetated littoral areas are the major contributors for CH 4 release from sediment to the atmosphere. Although the effects of herbivores on biomass removal, growth and reproduction of emergent macrophytes have been well documented, their effect on plant-mediated CH 4 fluxes, especially by insects, remains unknown. We performed a mesocosm experiment in which we simulated the damage caused by herbivorous insects and manipulated the density of damaged culms of Eleocharis equisetoides (4 levels — 0, 20, 50 and 100%) measuring the corresponding CH 4 emission, concentration and potential production in the sediment. We hypothesized that an increased percentage of culms with simulated herbivory would be associated with increased CH 4 fluxes from sediment toward the atmosphere. Simulated herbivory positively affected CH 4 emissions, but only under high herbivory pressure. The average CH 4 flux from mesocosms with 50% and 100% damaged culms was 3.5 higher than those with intact or low levels of damage. These results indicate that physical damage on macrophytes affects gas transport within the plants. A field survey in our studied system revealed that plant biomass consumed by herbivores is relatively low. This result highlight that insects may have a disproportional effect on CH 4 emissions, i.e., a very small damage (low biomass removal), when performed in many culms (50% and 100% of damaged culms treatments), may substantially increase CH 4 fluxes. In summary, our findings bring a new perspective to the influence of herbivory on CH 4 and carbon cycling, especially regarding the role insects might play. [ABSTRACT FROM AUTHOR]