Production and diffusion of methane in tree trunks: new insights into forest methane dynamics
|EPRON Daniel (Kyoto University, Graduate School of Agriculture)
|TAKAHASHI Kenshi,（Kyoto University, RISH）
SAKABE Ayaka (Kyoto University, Graduate School of Agriculture)
ASAKAWA Susumu (Nagoya University, Graduate School of Bioagricultural Sciences)
Methane (CH4) is the second most important anthropogenic greenhouse gas and rise of atmospheric CH4 concentration has accelerated these last years. In addition to global warming, CH4 oxidation in the troposphere leads to ozone production, which is harmful to human health and crop yields. Soils in upland forests are the largest biological sink for atmospheric CH4, providing a valuable ecosystem service. However, CH4 emission by trees weaken the sink strength of forests, becoming nowadays a major concern. The biological functions of trees and microbes within trees, in addition to that of the soil, must therefore be considered in the biogeochemical cycling of CH4 in forests, to better apprehend the role of the forest sector in mitigating climate change.
The trunk of several tree species harbours methanogenic archaea which produce CH4 internally and emit it to the atmosphere, but the rate of CH4 emission varies considerably between species and individuals, and within individuals. This depends on the presence of favourable microenvironmental conditions inside the trunk, including high moisture and low oxygen concentration, but also on the variations in radial CH4 diffusion resistance and preferential diffusion pathways. The concomitant measurements of CH4 emission and CH4 concentration within the trunk, with a description of microbial communities in the heartwood and a characterization of radial diffusivity, will greatly improve our understanding of the production and transfer of methane.
The experiment will be conducted in the Ashiu experimental forest (Kyoto University). We will install measuring chambers on 10 dominant species (❶ on the figure above), which will be connected to a laser-based CH4 analyser, and gas samplers (❷) in the trunk of these trees to measure the internal concentrations of CH4.
We will investigate the composition of the microbial community within the trunk of these trees, by extracting DNA from sections of wood cores and using a PCR approach to amplify the gene coding the coenzyme M reductase subunit alpha (mcrA), characteristics of methanogenic archaea. Concomitantly, we will estimate of the potential rate of methane production by incubating these core sections.
We will develop an experimental set-up for measuring gas diffusion through wood section and relate the observed diffusivity to the wood air filled porosity, which will be estimated. Together, all of this data will be used to develop, calibrate and validate a model for trunk CH4 emission, which will relate emission to production and concentration, mechanistically considering microbial production and radial diffusion within the trunk.