Rhizosphere Methane Oxidation in Thermokarst Bogs in the Interior of Alaska.

Methane is a potent greenhouse gas, and wetlands represent the largest natural source of methane to the atmosphere. However, much of the methane generated in anoxic wetlands never gets emitted to the atmosphere; between 20 and 90% of generated methane gets oxidized to carbon dioxide. Thus, methane oxidation is an important methane sink and changes in the rate of methane oxidation can affect wetland methane emissions. Most methane is aerobically oxidized at oxic–anoxic interfaces within wetlands, such as in the rhizosphere, where rates of oxidation strongly depend on methane and oxygen concentrations. To improve our understanding of methane oxidation in the rhizospheres of vascular plants, plant-level methane flux measurements were conducted in concert with bulk methane fluxes and optode oxygen measurements. Oxygen concentrations in the soil profile were monitored in two dimensions using four planar oxygen optodes on a rhizotron. Rates of methane oxidation were determined by the difference between methane fluxes conducted under an N₂ atmosphere, and under an ambient atmosphere for both plant-level and bulk flux measurements. Carex aquatilis Wahlenb. was the focus of this study because it was the only vascular plant present that also exhibits aerenchymous root tissue and deep rooting. In order to better understand the factors controlling diffusion of methane and oxygen through Carex, plant physiology measurements were conducted, and included rates of photosynthesis, stomatal conductance, leaf area, and root porosity – in addition to a suite of root morphological traits determined from 7.6 cm diameter soil cores centered on the carex stem. Flux measurements and plant physiology samples were collected at four different times during the 2015 growing season. The data from this study will help identify the controlling factors of rhizosphere methane oxidation, particularly in boreal thermokarst bogs.