Methane emissions through water hyacinth are controlled by plant traits and environmental conditions

Abstract

Wetlands are large sources of methane (CH4), and plant-mediated fluxes can contribute considerably to their total CH4 emissions. However, plant-mediated fluxes vary considerably even within species, and the factors explaining this variation are not fully understood. This study focuses on the role of plant traits and environmental conditions in regulating plant-mediated CH4 emissions in water hyacinths (Eichhornia crassipes). We investigate the role of: (1) plant traits on water hyacinth-mediated CH4 emission using laboratory incubations; and (2) key environmental factors mediating CH4 emission through water hyacinths in the laboratory and in the field (Amazon/Pantanal). CH4 emission intensities increased proportionally with total plant biomass. The laboratory assays furthermore showed a clear positive relation between CH4 emission and leaf and bulb surface area and volume. In addition, both in the Amazon/Pantanal field data and in the laboratory we found a strong positive relationship between the CH4 concentration in the water surrounding the plant roots and the plant-mediated CH4 emission. CH4 emission intensity was not related to light intensity, suggesting that stomatal conductance of water hyacinths is playing a minor role in mediating CH4 emission. Temperature, in contrast, played an important role, where an 8 °C temperature rise from 22 to 30 °C induced, on average, 58 % (SD = 33 %) higher CH4 emission from water hyacinths. Mimicked herbivory in water hyacinths also affected CH4 emission. Intact water hyacinths emitted approximately 25 % (SD = 13 %) more CH4 than water hyacinths that were experimentally perforated. This study clearly shows that intra-species trait variation can strongly govern ecosystem CH4 emissions. To accurately predict CH4 emissions from macrophytes these traits should be taken into account.